Description:BACKGROUND

FIELD OF THE DISCLOSURE
[0001] Various embodiments of the disclosure relate generally to novel diketopyrrolopyrrole compounds. More specifically, various embodiments of the disclosure relate to semiconductor devices comprising the novel diketopyrrolopyrrole compounds-based self-assembled monolayers (SAMs).
DESCRIPTION OF THE RELATED ART
[0002] Organic semiconductor devices such as organic light-emitting diodes (OLEDs), organic photovoltaics (OPVs), and field-effect transistors (OFETs) have garnered considerable attention due to their lightweight, low-cost production, mechanical flexibility, and availability when compared to inorganic counterparts. However, the widespread commercialization of these devices is impeded by several challenges, including limited stability, low efficiency, and inconsistent performance.
[0003] Self-assembled monolayers (SAMs) have emerged as a promising strategy to address these challenges by modifying the interfaces in organic semiconductor devices. SAMs are molecular assemblies formed spontaneously on surfaces through chemisorption or physisorption, offering control over surface properties such as energy levels, charge transport, and interfacial interactions.
[0004] Existing SAMs, primarily based on fullerenes and carbazoles, have demonstrated improvements in device performance. However, they suffer from several drawbacks that hinder their widespread adoption.
[0005] Fullerene derivatives, such as [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), have been widely used as electron transport layers in organic electronic devices. While effective in enhancing charge extraction and transport, fullerene-based SAMs exhibit limited stability under prolonged device operation. Their susceptibility to environmental factors, such as moisture and oxygen, leads to device degradation over time, compromising long-term performance and reliability.
[0006] Carbazole derivatives have been employed as hole transport layers in organic electronic devices due to their favorable electronic properties. However, carbazole-based SAMs suffer from poor interfacial stability and inefficient charge injection, particularly in high-performance devices. The delocalized π-electron system of carbazole moieties often results in non-uniform surface coverage and weak intermolecular interactions, leading to interface defects and charge recombination.
[0007] Limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of described systems with some aspects of the present disclosure, as set forth in the remainder of the present application and with reference to the drawings.
SUMMARY
[0008] According to embodiments of the present disclosure, a diketopyrrolopyrrole (DPP) compound having a phosphonic acid group of general structure [I] is provided. In general structure [I],

[I]
R1 and R2 comprise at least one phosphonic acid group, and wherein R1 and R2 independent of each other is a hydrogen, a straight or branched alkyl group having 1 to 20 carbon atoms, a phosphonic acid group, or an alkyl phosphonic acid group having 1 to 5 carbon atoms. R3 and R4 of general structure [I] independent of each other is a phenyl, a thiophenyl, a pyridyl, a 2-phenyl thiophenyl, a 2-thienyl pyridine, or a thienothiophenyl functional group.
[0009] In another embodiment, a method of preparing a diketopyrrolopyrrole (DPP) compound having a terminal phosphonic acid group is provided. The method comprises providing a diketopyrrolopyrrole (DPP) compound having a general structure [II] in a first solvent.

[II]
In general structure [II], R3 and R4 independent of each other is a phenyl, a thiophenyl, a pyridyl, a 2-phenyl thiophenyl, a 2-thienyl pyridine, or a thienothiophenyl functional group. R5 and R6 comprise at least one hydrogen, and R5 and R6 independent of each other is a hydrogen, or a straight or branched alkyl group having 1 to 20 carbon atoms. The method further comprises reacting the diketopyrrolopyrrole compound [II] with a bromoalkylphosponate ester in presence of a base at a temperature in a range of 100 °C to 180 °C to form a DPP compound having terminal phosponato ester groups. The method further comprises hydrolyzing the terminal phosponato ester groups by treating with trimethylbromosilane at room temperature in a second solvent to form the diketopyrrolopyrrole compound having a terminal phosphonic acid group of general structure [III]. In general structure [III], R1 and R2 comprise at least one phosphonic acid group, and R1 and R2 independent of each other is a hydrogen, a phosphonic acid group, or an alkyl phosphonic acid group having 1 to 5 carbon atoms.

[III]

[0010] In yet another embodiment, a method of preparing a diketopyrrolopyrrole (DPP) compound having a terminal phosphonic acid group is provided. The method comprises providing a diketopyrrolopyrrole (DPP) compound having a general structure [IV] in a first solvent.

[IV]

In general structure [IV], R3 and R4 independent of each other is a phenyl, a thiophenyl, a pyridyl, a 2-phenyl thiophenyl, a 2-thienyl pyridine, or a thienothiophenyl functional group. The method further comprises reacting the diketopyrrolopyrrole compound [IV] with an alkyl halide, or an aryl halide at room temperature in the first solvent to form an N-alkyl derivative of diketopyrrolopyrrole compound, or an N-aryl derivative of diketopyrrolopyrrole compound, respectively. The method further comprises reacting the N-alkyl derivative of diketopyrrolopyrrole compound, or the N-aryl derivative of diketopyrrolopyrrole compound with a bromoalkylphosponate ester in presence of a base at a temperature in a range of 100 °C to 180 °C to form an N-alkyl diketopyrrolopyrrole compound having a terminal phosphonato ester group, or an N-aryl diketopyrrolopyrrole compound having a terminal phosphonato ester group, respectively. The method further comprises reducing the N-alkyl diketopyrrolopyrrole compound having the terminal phosphonato ester group, or the N-aryl diketopyrrolopyrrole compound having the terminal phosphonato ester group in presence of a hydrogenation catalyst in alcohol at room temperature to obtain a hydrogenated diketopyrrolopyrrole compound having the terminal phosponato ester group. The method further comprises hydrolyzing the terminal phosponato ester group by treating with trimethylbromosilane at room temperature in a second solvent to form the diketopyrrolopyrrole compound having a terminal phosphonic acid group of general structure [V]. In general structure [V], R7 is a phosphonic acid group, or an alkyl phosphonic acid group having 1 to 5 carbon atoms.

[V]

[0011] In yet another embodiment, a semiconductor device comprising an anode, a cathode, an active layer and a self-assembled monolayer comprising a diketopyrrolopyrrole (DPP) compound having a terminal phosphonic acid group of general structure [I] is provided. The self-assembled monolayer is provided on the anode, and is disposed between the anode and the active layer.


[I]

Here, R1 and R2 comprise at least one phosphonic acid group, and R1 and R2 independent of each other is a hydrogen, a straight or branched alkyl group having 1 to 20 carbon atoms, a phosphonic acid group, or an alkyl phosphonic acid group having 1 to 5 carbon atoms. R3 and R4 independent of each other is a phenyl, a thiophenyl, a pyridyl, a 2-phenyl thiophenyl, 2-thienyl pyridine, or a thienothiophenyl functional group.
BRIEF DESCRIPTION OF DRAWINGS

[0012] FIG. 1 is a flow chart that illustrates a method of preparing a diketopyrrolopyrrole (DPP) compound having a terminal phosphonic acid group, in accordance with an exemplary embodiment of the disclosure;
[0013] FIG. 2 is a flow chart that illustrates a method of preparing a diketopyrrolopyrrole (DPP) compound having a terminal phosphonic acid group, in accordance with another exemplary embodiment of the disclosure;
[0014] FIG.3 is a schematic diagram of a device incorporating a self-assembled monolayer comprising diketopyrrolopyrrole (DPP) compound having a terminal phosphonic acid group, in accordance with yet another exemplary embodiment of the disclosure;
[0015] FIG. 4 is a reaction scheme illustrating preparation of DPP compounds of Examples 1 to 8; and
[0016] FIG. 5 is a plot of cyclic voltammogram of DPP compounds.
[0017] Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description of exemplary embodiments is intended for illustration purposes only and is, therefore, not intended to necessarily limit the scope of the present disclosure.
DETAILED DESCRIPTION OF EMBODIMENTS

[0018] The following description illustrates some exemplary embodiments of the disclosed disclosure in detail. Those of skill in the art will recognize that there are numerous variations and modifications of this disclosure that are encompassed by its scope. Accordingly, the description of a certain exemplary embodiment should not be deemed to limit the scope of the present disclosure.
[0019] The term “comprising” as used herein is synonymous with “including,” or “containing,” and is inclusive or open-ended and does not exclude additional, unrecited elements, or process steps.
[0020] All numbers expressing quantities of ingredients, property measurements, and so forth used in the specification are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth herein are approximations that may vary depending upon the desired properties sought to be obtained.
[0021] These and other features and advantages of the present disclosure may be appreciated from a review of the following detailed description of the present disclosure, along with the accompanying figures in which like reference numerals refer to like parts throughout.
[0022] A typical semiconductor device includes an anode, a cathode (the anode and the cathode are collectively termed electrodes), and an active layer disposed between the anode and the cathode. The device may further include one or more of a hole transport layer (positive (p)-type), and an electron transport layer (negative (n)-type) depending on device fabrication and intended application. The active layer of the semiconductor device may also be referred to as an electron/hole generation layer (intrinsic (i)-type), or as an absorber layer in the case of a photovoltaic device. The hole transport layer (HTL) and the electron transport layer (ETL) are in contact with the anode and the cathode, respectively, and the electron/hole generation layer is sandwiched between the hole transport layer and the electron transport layer. An organic semiconductor device is a semiconductor device where the active layer comprises organic molecules or polymers.
[0023] In a photovoltaic device, when incident light falls on a transparent anode and reaches an active layer, an electron/hole pair is generated within the active layer (absorber layer), the hole and the electron are transported to their respective electrodes through the hole transport layer and the electron transport layer, respectively generating a photocurrent. A light emitting diode (LED), works in an opposite way to the photovoltaic device. The electron/hole pair generated in the LED on application of an external current recombines to emit a photon of a specific wavelength.
[0024] In semiconductor devices, interfaces between dissimilar materials, such as an interface between organic molecules comprising the active layer and metal electrodes are key to optimizing electron and/or hole generation, transport, and recombination. A work function, Φ, of the metal electrode is a critical parameter to improve the performance of the device. The term “work function” is defined as the amount of energy required to remove an electron from a metal surface.
[0025] In an organic light emitting diode (OLED), the work function of an anode must be within 0.1 eV of the highest occupied molecular orbital (HOMO) of a hole transport layer (HTL) to transport holes efficiently while a cathode must consist of a low work function material to extract electrons into LUMO (lowest occupied molecular orbital) of an electron transport layer (ETL). Since interfacial electronic properties govern rates of charge injection, transport and/or recombination at organic/electrode interfaces, controlling the work function and energy-level alignment between the various layers (for example, active layer, electron transport layer and/or hole transport layer) and the electrodes is essential to designing superior devices. Further, for enhancing charge transfer at metal/active layer interface a dipole layer formation on electrode surface is required.
[0026] The dipole layer formation or tuning of the work function of the metal electrode has been demonstrated using self-assembled monolayers (SAM). The term “self-assembled monolayer” or “SAM”, as used herein refers to a two-dimensional molecular arrangement that spontaneously forms on a surface of an electrode. SAMs comprise versatile molecules that can be intentionally designed to provide specific functionalities, such as surface passivation, work function tuning, or interface modification, based on the requirement of the device.
[0027] A typical SAM molecule has an anchoring group, a spacer moiety, and a functional group. The anchoring group is involved in the bonding interactions of each SAM molecule to the surface of the electrode. As the attachment (bonding) to the surface is through the anchoring group, SAM molecules are aligned vertically over the surface to form monolayers. The spacer moiety acts as a bridge between the anchoring group and the functional group. The functional group defines the SAM layer and is responsible for all the physical and chemical interactions at an interface between overlying layers of the device and the SAM layer. As used herein, the term “SAM molecule(s)” refers to molecules that form self-assembled monolayers on a surface. The term “SAM layer” as used herein, refers to a layer comprising self-assembled monolayer (SAM) molecule(s).
[0028] Diketopyrrolepyrrole (DPP) compounds are well-known for their physical and chemical properties, such as high charge carrier mobility, and thermal/photostability. The objective of the present disclosure is to provide DPP-based SAM molecules that may overcome some of the drawbacks of prior art SAM molecules. Moreover, newly designed SAM molecules should be easily adaptable for large-scale manufacturing and at the same time cost-effective. Several key parameters are considered to qualify a compound as a SAM molecule namely, HOMO-LUMO energy level matching to work function of electrodes; presence of anchoring groups that can adhere to an electrode surface to form the SAM layer; a spacer moiety that may assist in and promote self-assembly; and presence of functional group(s) that can modify the nature of the SAM layer and trigger possible interactions with overlying layers of the device.
[0029] In the present disclosure, a structured approach has been followed to identify and develop new DPP-based SAM molecules. A series of DPP compounds with extended ring systems and various functional groups are designed. Extensive theoretical calculations are performed to determine HOMO and LUMO energy levels of each new molecule. In one embodiment, density functional theory (DFT) calculation, using the Gaussian 09 program based on Becke’s three-parameter set with Lee-Yang-Parr correlation functional (B3LYP) and the 6-31G(d,p) basis set, are performed on each new molecules. The HOMO and LUMO energy levels of the new molecules are compared to work functions of electrodes intended for use in devices. The new molecules for which the HOMO-LUMO gaps match the work function of the electrodes are short-listed. The short-listed molecules are then synthesized. However, it is not always feasible to synthesize all molecules as synthetic routes have to be evaluated for adaptability for large-scale manufacturing and practical feasibility. For example, phosphonic acid end groups when present in a compound are known for their instability. The ability of the synthesized molecules to form a stable and well-ordered SAM on an electrode surface needs to be tested. Finally, the performance of the SAM in devices needs to be evaluated under relevant conditions so as to confirm molecule's effectiveness and to identify any need for further optimization.
[0030] According to embodiments of the present disclosure, a diketopyrrolopyrrole (DPP) compound having a phosphonic acid group of general structure [I] is provided. In general structure [I]

[I]
R1 and R2 comprise at least one phosphonic acid group, and R1 and R2 independent of each other is a hydrogen, a straight or branched alkyl group having 1 to 20 carbon atoms, a phosphonic acid group, or an alkyl phosphonic acid group having 1 to 5 carbon atoms. R3 and R4 independent of each other is a phenyl, a thiophenyl, a pyridyl, a 2-phenyl thiophenyl, a 2-thienyl pyridine, or a thienothiophenyl functional group.
[0031] In structure [I], R1 and R2 constitute an anchoring group, diketopyrrolopyrrole (DPP) along with the extended ring structure that form part of R3 and R4 constitutes a spacer moiety, and R3 and R4 constitute functional groups corresponding to a SAM molecule. The phosphonic acid group can form mono-, bi-, and tridentate binding modes to an electrode surface through oxygen atoms of the phosphonic acid groups. The presence of more than one binding mode of the inventive DPP compounds may advantageously enhance adhesion to the electrode surface thus forming uniform SAM when compared to compounds having a single binding mode. When R1 and R2 are both phosphonic acid groups, there is maximum chemical bonding between the SAM molecule and the electrode surface when compared to a DPP compound having a single phosphonic acid group. Further, the phosphonic acid group can form hydrogen bonding between SAM molecules of the SAM layer thus providing for a compact packing of the resulting SAM layer. The DPP spacer moiety is a strong electron withdrawing group and when attached to R3 and R4 forms donor-pi-acceptor (D-π-A) molecule that can form a dipole layer when coated over an electrode surface. The DPP spacer moiety along with functional groups contributes to the energy level alignment (HOMO–LUMO) between the SAM and work function of the electrode and may add additional surface dipoles that contribute to tunability of the work function. The presence of the anchoring group and the functional group, with different electron densities and separated by the spacer moiety, in the chemical structure of the inventive SAMs, may result in a monolayer with a specific dipole that may increase and/or decrease the work function of the metal surface containing the SAM.
[0032] In one embodiment, R3 and R4 of diketopyrrolopyrrole compound of general structure [I] is thiophenyl group.
[0033] In some embodiments, the diketopyrrolopyrrole compound has the structure (a). The compound (a) is (2-(1,4-dioxo-3,6-di(thiophen-2-yl)-4,5-dihydropyrrolo[3,4-c]pyrrol-2(1H)-yl)ethyl)phosphonic acid (HDPPPA).

[a]

[0034] In some embodiments, the diketopyrrolopyrrole compound has the structure (b). The compound (b) is (1,4-dioxo-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-2,5(1H,4H)-diyl)bis(methylene))bis(phosphonic acid) (PADPPPA).

[b]

[0035] In some embodiments, the diketopyrrolopyrrole compound has the structure (c). The compound (c) is (2-(5-(2-octyldodecyl)-1,4-dioxo-3,6-di(thiophen-2-yl)-4,5-dihydropyrrolo[3,4-c]pyrrol-2(1H)-yl)ethyl)phosphonic acid (C20DPPPA).

[c]
[0036] FIG. 1 is a flow chart 100 that illustrates a method of preparing a diketopyrrolopyrrole (DPP) compound having a terminal phosphonic acid group through exemplary steps 102 through 106, according to embodiments of the present disclosure. At step 102, a diketopyrrolopyrrole (DPP) compound having a general structure [II] is provided in a first solvent.

[II]
[0037] In general structure [II], R3 and R4 independent of each other is a phenyl, a thiophenyl, a pyridyl, a 2-phenyl thiophenyl, a 2-thienyl pyridine, or a thienothiophenyl functional group. R5 and R6 comprise at least one hydrogen, and R5 and R6 independent of each other is a hydrogen, or a straight or branched alkyl group having 1 to 20 carbon atoms.
[0038] The first solvent comprises dimethyl formamide (DMF). In one embodiment, the DPP compound is dispersed in DMF under nitrogen atmosphere to provide the DPP compound of structure [II].
[0039] At step 104, the diketopyrrolopyrrole compound [II] from step 102 is reacted with a bromoalkylphosponate ester in presence of a base at a temperature in a range of 100°C to 180°C to form a DPP compound having terminal phosponato ester groups. In one embodiment, the base is added to the DPP compound dispersed in DMF and the dispersion is heated to a temperature in the range of 100 °C to 180°C for about 2 hours. A bromoalkylphosponate ester dissolved in DMF is added to the dispersion with heating over a period of time in a range of 10 minutes to 45 minutes. Once the reaction is complete the dispersion is poured into crushed ice to form a precipitate comprising DPP compound having terminal phosponato ester groups. The precipitate is washed and filtered with cold alcohol and dried under vacuum to obtain the DPP compound having terminal phosponato ester groups.
[0040] In one embodiment, the base comprises potassium carbonate, caesium carbonate, sodium carbonate, sodium hydride, or combinations thereof. In one embodiment, the base is potassium carbonate.
[0041] At step 106, the DPP compound having the terminal phosponato ester groups is hydrolyzed by treating with trimethylbromosilane at room temperature in a second solvent to form the diketopyrrolopyrrole compound having a terminal phosphonic acid group of general structure [III]. In general structure [III], R1 and R2 comprise at least one phosphonic acid group, and R1 and R2 independent of each other is a hydrogen, a phosphonic acid group, or an alkyl phosphonic acid group having 1 to 5 carbon atoms.

[III]

[0042] In one embodiment, the DPP compound having the terminal phosponato ester groups from step 104 is dissolved in dichloromethane (DCM) by stirring for a time period in a range of 10 to 50 minutes at room temperature to form a reaction mixture. Trimethylbromosilane is added dropwise to the reaction mixture and stirred for a time period in the range of 6 hours to 18 hours, and quenched with alcohol and stirred vigorously. The solvent is removed from the reaction mixture under reduced pressure and water is added. The step of adding water and reducing under pressure is repeated at least three times to obtain the diketopyrrolopyrrole compound having a terminal phosphonic acid group of general structure [III]. In one embodiment, the alcohol is methanol.
[0043] The second solvent is the same as the first solvent, in one embodiment. In another embodiment, the second solvent is dichloromethane.
[0044] FIG. 2 is a flow chart 200 that illustrates a method of preparing a diketopyrrolopyrrole (DPP) compound having a terminal phosphonic acid group through exemplary steps 202 through 210, according to embodiments of the present disclosure. At step 202, a diketopyrrolopyrrole (DPP) compound of formula [IV] in a first solvent is provided. R3 and R4 independent of each other is a phenyl, a thiophenyl, a pyridyl, a 2-phenyl thiophenyl, a 2-thienyl pyridine, or a thienothiophenyl functional group.
[0045] The first solvent comprises dimethyl formamide (DMF). In one embodiment, the DPP compound is dispersed in DMF under nitrogen atmosphere to provide the DPP compound of structure [IV].

[IV]

[0046] At step 204, the diketopyrrolopyrrole compound of formula [IV] from step 202, is reacted with an alkyl halide, or an aryl halide at room temperature in the first solvent to form an N-alkyl derivative of diketopyrrolopyrrole compound, or an N-aryl derivative of diketopyrrolopyrrole compound, respectively. At step 204, alkylation or arylation proceeds at amide group (-NH) of the diketopyrrolopyrrole molecule. The N-alkyl derivative of diketopyrrolopyrrole compound, or the N-aryl derivative of diketopyrrolopyrrole is separated from reaction mixture, in one instance, using column chromatography.
[0047] At step 206, the N-alkyl derivative of diketopyrrolopyrrole compound, or the N-aryl derivative of diketopyrrolopyrrole compound from step 204 reacts with a bromoalkylphosponate ester in presence of a base at a temperature in a range of 100°C to 180°C to form an N-alkyl diketopyrrolopyrrole compound having a terminal phosphonato ester group, or an N-aryl diketopyrrolopyrrole compound having a terminal phosphonato ester group, respectively. The step 206 is similar to step 104, as discussed with reference to FIG. 1.
[0048] At step 208, the N-alkyl diketopyrrolopyrrole compound having the terminal phosphonato ester group, or the N-aryl diketopyrrolopyrrole compound having the terminal phosphonato ester group is reduced in presence of a hydrogenation catalyst in alcohol at room temperature to obtain a hydrogenated diketopyrrolopyrrole compound having the terminal phosponato ester group.
[0049] In one embodiment, the hydrogenation catalyst comprises palladium on carbon catalyst.
[0050] At step 210, the hydrogenated diketopyrrolopyrrole compound having the terminal phosponato ester group from step 208 is hydrolyzed by treating with trimethylbromosilane at room temperature in a second solvent to form the diketopyrrolopyrrole compound having the terminal phosphonic acid group of general structure [V].

[V]
[0051] Here, R7 is a phosphonic acid group, or an alkyl phosphonic acid group having 1 to 5 carbon atoms. The step 210 is similar to step 108, as discussed with reference to FIG. 1. The second solvent, in one embodiment, is dichloromethane.
[0052] In one embodiment, products formed at the end of each step of the methods as illustrated in FIGs. 1 to 2 are optionally purified and isolated before use in a later step.
[0053] The DPP compounds formed using the methods as illustrated in FIGs. 1 to 2 is a semiconducting material.
[0054] In some embodiments, a self-assembled monolayer comprising the diketopyrrolopyrrole compound is formed over a surface. The anchoring unit, namely the phosphonic acid group may form chemical bonding interactions with the surface. In one embodiment, DPP compounds are adsorbed on a metal oxide surface to form a DPP SAM layer.
[0055] The metal oxide comprises aluminum oxide, tin oxide, tungsten oxide, cesium oxide, titanium oxide, fluorine tin oxide (FTO), copper oxide, nickel oxide, tantalum oxide, hafnium oxide, iron oxide, chromium oxide, niobium oxide, zirconium oxide, indium oxide, indium tin oxide, mixed metal oxide or combinations thereof. In one embodiment, the metal oxide is indium tin oxide (ITO). In some embodiments, the metal oxide is provided over a substrate. Examples of substrates include glass, mica, quartz, silicon, polyethylene terephthalate, polycarbonate, or combinations thereof.
[0056] A SAM layer incorporating the inventive DPP compounds (DPP SAM) may advantageously form a highly functionalized, packed, and ordered unidirectional monolayer, where each part of the SAM molecule (for example, anchoring group, spacer moiety, and the functional group) may provide differing electrostatic properties when formed on the metal electrode surface that may fine-tune the work function of the electrode.
[0057] In one embodiment, the DPP SAM when formed over a metal oxide electrode, and sandwiched between the electrode and an active layer comprising a perovskite may improve a crystal quality of the perovskite layer, thereby reducing the degree of defects. Further, it may protect the perovskite layer by isolating it from the metal oxide electrode, and reduce undesired charge recombination.
[0058] In some embodiments, the SAM is transparent to visible light or exhibits narrow absorption in visible light.
[0059] The SAM may be formed by dissolving the DPP compound in a suitable solvent and casting or coating it on a surface to form the SAM layer.
[0060] Non-limiting examples of solvents include dichloromethance, trichloroethane, chloroform, hexane, heptanes, octane, toluene, ethylbenzene, xylene, ethylbenzoate, methylbenzoate, 1,1,2,2-tetrachloroethane, tetrahydrofuran (THF), dioxane, chlorobenzene, dichlorobenzenes, trichlorobenzene, mesitylene or combinations thereof.
[0061] Example casting or coating methods include, but are not limited to, spin coating, microgravure coating, gravure coating, bar coating, roll coating, wire bar coating, dip coating, spray coating, screen printing, flexo printing, micro-contact printing, inkjet printing, offset printing, blade coating or combinations thereof.
[0062] In some embodiments, the self-assembled monolayer forms part of a semiconductor device. The SAM layer may also be layered onto another layer when forming a multilayered device, or onto an electrode. In some embodiments, the SAM comprising the DPP compound is a hole transport layer or a hole injection layer.
[0063] Examples of semiconductor devices include a diode, a photodiode, a transistor, a light-emitting diode (LED), an organic light-emitting diode (OLED), an organic semiconductor device, a photovoltaic device, an optoelectronic device, a sensor, a detector, or combinations thereof. In one embodiment, the semiconductor device is an organic semiconductor device.
[0064] FIG. 3 is a schematic diagram of a device 300, in one exemplary embodiment of the disclosure. The device 300 includes an anode 302, a self-assembled monolayer 304, an active layer 306, an electron transport layer 308, and a cathode 310.
[0065] The anode 302 of the device comprises a metal oxide. The metal oxide comprises aluminum oxide, tin oxide, tungsten oxide, cesium oxide, titanium oxide, fluorine tin oxide (FTO), copper oxide, nickel oxide, tantalum oxide, hafnium oxide, iron oxide, chromium oxide, niobium oxide, zirconium oxide, indium oxide, indium tin oxide (ITO), mixed metal oxide or combinations thereof. In one embodiment, the metal oxide is indium tin oxide.
[0066] The self-assembled monolayer 304 comprises the DPP compounds of structure [I], as described above. The self-assembled monolayer 304 is formed by dispersing the DPP compound in a suitable solvent and forming a layer or coating over the anode 302. The DPP compound advantageously adsorbs on the anode surface through chemical bonding of the anchoring group to form the self-assembled monolayer 304. The self-assembled monolayer 304 functions as a hole transport layer. The self-assembled monolayer 304 may have a thickness in a range of 1 nanometer (nm) to about 100 nm. In one embodiment, the self-assembled monolayer 304 has a thickness in the range of 1 nm to 10 nm.
[0067] The active layer 306 comprises metal oxide perovskites, metal halide perovskites, organic-inorganic hybrid perovskites, donor-acceptor complexes, fullerene-based donor-acceptor complexes, or combinations thereof.
[0068] In some embodiments, the active layer 306 comprises an organic-inorganic hybrid perovskite compound having the general formula R.M.X3, where R is an organic molecule, M is a metal atom and X is a halogen or a chalcogen atom.
[0069] Non-limiting examples of organic molecules include, methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine, dihexylamine, trimethylamine, triethylamine, tripropylamine, tributylamine, tripentylamine, trihexylamine, ethylmethylamine, methylpropylamine, butylmethylamine, methylpentylamine, hexylmethylamine, ethylpropylamine, ethylbutylamine, imidazole, azole, pyrrole, aziridine, azirine, azetidine, azole, imidazoline, carbazole or combinations thereof. Non-limiting examples of metal atoms include lead, tin, zinc, titanium, antimony, bismuth, nickel, iron, cobalt, silver, copper, gallium, germanium, magnesium, calcium, indium, aluminum, manganese, chromium, molybdenum, europium or combinations thereof. Non-limiting examples of halogen and chalcogen include chlorine, bromine, iodine, sulfur, selenium or combinations thereof. The organic/inorganic perovskite compound is preferably a crystalline semiconductor.
[0070] In some embodiments, the active layer 306 comprises a triple cation perovskite containing a mixture of formamidinium (FA), methylammonium (MA) monovalent cations along with inorganic alkali metal and a metal halide. In one embodiment, the active layer 306 comprises Cs0.05[(FA)5/6(MA)1/6]0.95Pb(I0.9Br0.1)3.
[0071] In some embodiments, the active layer 306 comprises a donor-acceptor complex. Non-limiting examples of donor molecules of the donor-acceptor complex include phthalocyanines, functionalized squaraines, functionalized polyacenes, oligothiophenes, merocyanine dyes, modified perylenes (for e.g. DIP or DBP), conducting polymers, low-bandgap polymers, or combinations thereof. In one embodiment, the donor molecule is a copolymer of benzodithiophene (BDT) and dithienobenzothiadiazole (DTBT) (D18).
[0072] Non-limiting examples of acceptor molecules of the donor-acceptor complex include fullerenes, C60 or C70, modified polyacenes such as naphthalenetetracarboxylic dianhydride (NTCDA), perylenetetracarboxylic dianhydride (PTCDA), perylenetetracarboxylic bisbenzimidazole (PTCBI), perylenetetracarboxylic diimide (PTCDI) or combinations thereof. In one embodiment, the acceptor molecule is composed of a fused thienothienopyrrolo-thienothienoindole (TTP-TTI) core base and 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (2FIC) end units (Y6).
[0073] The active layer 306 may comprise a single layer or more than one layer. For example, the donor molecules may form one layer over which an acceptor layer may be formed to complete the active layer 306.
[0074] The electron transport layer 308 comprises an n-type conductive polymer, an n-type low molecular organic semiconductor, an n-type metal oxide, an n-type metal sulfide, an alkali metal halide, an alkali metal, or combinations thereof. Non-limiting examples include cyano group-containing polyphenylenevinylene, boron-containing polymer, bathocuproin, bathophenanthrene, hydroxyquinolinatoaluminum, oxadiazole compound, benzimidazole compound, naphthalene tetracarboxylic acid compounds, perylene derivatives, phosphine oxide compounds, phosphine sulfide compounds, fluoro group-containing phthalocyanine, titanium oxide, zinc oxide, indium oxide, tin oxide, gallium oxide, tin sulfide, indium sulfide, or combinations thereof. In one embodiment, the electron transport layer 308 comprises phenyl-C61-butyric acid methyl ester (PCBM) doped with bathocuproine (BCP). In another embodiment, the electron transport layer 308 comprises (Poly[[2,7-bis(2-ethylhexyl)-1,2,3,6,7,8-hexahydro-1,3,6,8-tetraoxobenzo[lmn][3,8]phenanthroline-4,9-diyl]-2,5-thiophenediyl[9,9-bis[3’((N,N-dimethyl)-N-ethylammonium)]-propyl]-9H-fluorene-2,7-diyl]-2,5-thiophenediyl] (PNDIT-F3NBr).
[0075] The electron transport layer 308 may comprise a single layer or more than one layer. For example, when the electron transport layer 308 comprises PCBM and BCP, a PCBM layer may be formed over the active layer 306, and BCP layer is formed over the PCBM layer to complete the electron transport layer 308.
[0076] The cathode 310 comprises a low work function metal or metal alloy. Non-limiting examples of cathode 310 material include barium, calcium, magnesium, indium, aluminum, titanium, tungsten, gold, ytterbium, silver, a calcium-silver alloy, an aluminum-lithium alloy, or a magnesium-silver alloy.
[0077] Both the cathode 310 and the anode 302 may be of a single material or of a compound structure. The cathode 310 and the anode 302 may be reflective, transparent, semi-transparent or translucent. In certain embodiments, one or more of the anode 302 and the cathode 310 may be deposited on a support (not shown). The support may be rigid, for example, made of quartz or glass, or maybe a flexible polymeric substrate. Examples of polymeric substrates include, but are not limited to, polyimides, polytetrafluoroethylenes, polyethylene terephthalates, polyolefins such as polypropylene and polyethylene, polyamides, polyacrylonitrile, polymethacrylonitrile, polystyrenes, polyvinyl chloride, and fluorinated polymers such as polytetrafluoroethylene.
[0078] The device 300 may be fabricated by laying layers on top of one another. The layers may be prepared by methods known in the art, including solution coating techniques as described previously. The coating steps may be carried out in an inert atmosphere, for example, under nitrogen gas. Alternatively, some layers may be prepared by thermal evaporation or by vacuum deposition. Metallic layers may be prepared by known techniques, such as, for example, thermal or electron-beam evaporation, chemical-vapour deposition or sputtering, or printing conductive metal particle inks.
[0079] In a particular embodiment, device 300 comprises the following layers glass/ITO/SAM/triple cation PSK/ PCBM/BCP/Ag. The SAM layer comprises the inventive DPP SAMs and functions as the hole transport layer.
[0080] In another embodiment, the device 300 has the configuration ITO/SAM/D18:Y6/PNDIT-F3NBr/Ag. The SAM layer comprises the inventive DPP SAMs and functions as the hole transport layer.
EXAMPLES
[0081] The present disclosure will now be described in greater detail by the
following non-limiting examples. It is understood that one skill in the art will envision additional embodiments consistent with the disclosure provided herein.
EXAMPLE 1
Preparation of tetraethyl ((1,4-dioxo-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-2,5(1H,4H)-diyl)bis(methylene))bis(phosphonate) PEDPPPE:
[0082] To an oven dried Schlenk flask, thiophene diketopyrrolopyrrole (TDPP) (2.45 g, 8.15 mmol) was added and dispersed in dry DMF (20 mL) under nitrogen (N2) atmosphere. Potassium carbonate (K2CO3) (3.94 g, 28.53 mmol) was added to the flask, and the reaction mixture was heated at 100 ℃ for 2 hours. After that, a dilute solution of diethyl (2-bromoethyl)phosphonate (6.1 g, 24.4 mmol) in dimethylformamide (DMF) was added dropwise to the reaction mixture for 30 minutes. The reaction temperature rises to 120 ℃ and is continued for 12 hours under N2. The reaction mixture was quenched with a few drops of methanol and poured into crushed ice. The red color product was filtered and washed with cold methanol several times. The compound was dried overnight under high vacuum. The compound was used without further purification.
EXAMPLE 2
Preparation of ((1,4-dioxo-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-2,5(1H,4H)-diyl)bis(methylene))bis(phosphonic acid) (PADPPPA):
[0083] To a double-necked round bottom flask, tetraethyl((1,4-dioxo-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-2,5(1H,4H)-diyl)bis(methylene))bis(phosphonate) (1.5 gm, 2.49 mmol) from Example 1 was added and dissolved in dry DCM and stirred at 25 ℃ for 30 minutes. Into this trimethylbromosilane (2.90 mL, 22 mmol) was added dropwise over 10 minutes. The reaction mixture was stirred for 12 hours before being quenched with methanol (MeOH) and stirred vigorously. After a further 2 hours of stirring, the solvent was removed under reduced pressure, and water (20 mL) was added. The mixture was then concentrated under reduced pressure. This step was repeated three times to give((1,4-dioxo-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-2,5(1H,4H)-diyl)bis(methylene))bis(phosphonic acid) as dark red solid. The solid was recrystallized from hot ethanol to give the pure compound (840 mg) at a yield of 78.5 %. Proton nuclear magnetic resonance (1H NMR) spectra, phosphorus nuclear magnetic resonance (31P NMR) spectra along with Infrared (IR) spectra confirmed the formation and purity of the compound.
1H NMR (CDCl3, 400 MHz),  (ppm) 7.95 (d, 2H), 7.84 (d, 2H), 7.30 (t, 2H), 3.24 (t, 2H), 2.01-1.94 (m, 2H)
31P{1H} NMR (CDCl3, 135 MHz),  (ppm) 26.91. IR (KBr, cm1): 1059 (P-OH), 1235 (P=O).
[0084] FIG. 4 is a reaction scheme 400 illustrating preparation of PADPPPA through reaction scheme 402.
EXAMPLE 3
Preparation of diethyl (2-(1,4-dioxo-3,6-di(thiophen-2-yl)-4,5-dihydropyrrolo[3,4-c]pyrrol-2(1H)-yl)ethyl)phosphonate (HDPPPE):
[0085] To an oven dried Schlenk flask, TDPP (thiophene diketopyrrolopyrrole) (2.5 g, 8.31 mmol) was added and dispersed in dry DMF (40 mL) under N2 atmosphere. K2CO3 (1.85 g, 12.47 mmol) was added to the flask, and the reaction mixture was heated at 100 ℃ for 2 hours. After that, a dilute solution of diethyl (2-bromoethyl)phosphonate (3.64 g, 14.9 mmol) in DMF was added dropwise to the reaction mixture for 30 minutes. The reaction temperature rises to 120 ℃ and is continued for 12 hours under N2. The reaction mixture was quenched with a few drops of methanol and poured into crushed ice. The red color product was filtered and washed with cold methanol several times. The compound was dried overnight under high vacuum. The compound was used as such without further purification.
EXAMPLE 4
Preparation of (2-(1,4-dioxo-3,6-di(thiophen-2-yl)-4,5-dihydropyrrolo[3,4-c]pyrrol-2(1H)-yl)ethyl)phosphonic acid (HDPPPA):
[0086] To a two-neck round bottom flask, diethyl (2-(1,4-dioxo-3,6-di(thiophene-2-yl)-4,5-dihydropyrrolo[3,4-c]pyrrol-2(1H)-yl)ethyl)phosphonate (1.2 gm, 2.58 mmol) from Example 3 was added and dissolved in dry DCM followed by stirring at 25 ℃ for 30 minutes. Trimethylbromosilane (2.2 mL, 7.74 mmol) was added dropwise for over 10 minutes. The reaction mixture was stirred for 12 hours before being quenched with MeOH and stirred vigorously. After a further 2 hours of stirring, the solvent was removed under reduced pressure, and water (20 mL) was added. The mixture was then concentrated under reduced pressure. This step was repeated three times to give 2-(1,4-dioxo-3,6-di(thiophene-2-yl)-4,5-dihydropyrrolo[3,4-c]pyrrol-2(1H)-yl)ethyl)phosphonic acid as a dark red solid. The solid was recrystallized with hot ethanol twice to obtain the pure compound at a yield of 78.5% (840 mg). Proton nuclear magnetic resonance (1H NMR) spectra, phosphorus nuclear magnetic resonance (31P NMR) spectra along with Infrared (IR) spectra confirmed the formation and purity of the compound.
1H NMR (CDCl3, 400 MHz),  (ppm) 7.95 (d, 2H), 7.84 (d, 2H), 7.30 (t, 2H), 3.24 (t, 2H), 2.01-1.94 (m, 2H).
31P{1H} NMR (CDCl3, 135 MHz),  (ppm) 25.85. IR (KBr, cm1): 1059 (P-O-H), 1234 (P=O).
[0087] FIG. 4 illustrates preparation of HDPPPA through reaction scheme 404.
EXAMPLE 5
Preparation of 2-(2-octyldodecyl)-3,6-di(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (C20DPPH):
[0088] To an oven dried two neck flask, TDPP (thiophene diketopyrrolopyrrole) (2.2 g,7.32 mmol) was added and dispersed in 30 mL dry DMF under N2. K2CO3 (1.85 g, 12.47 mmol) was added to the flask and the reaction mixture was heated at 100 ℃ for 1 hour. A dilute solution of 9-(iodomethyl) nonadecane (5.9 g, 14.6 mmol) in DMF was added dropwise to the reaction mixture for 30 minutes. The reaction temperature rises to 120 ℃ and is continued for 12 hours under N2. The reaction mixture was quenched with a few drops of methanol, and DMF was distilled off. The compound was extracted with chloroform and washed with cold water several times. The crude product was purified through column chromatography using DCM: hexane mixture to afford the red color solid. The compound was further purified through recrystallization from methanol. The compound was dried overnight under high vacuum. Proton nuclear magnetic resonance (1H NMR) spectra confirmed the formation and purity of the compound.
1H NMR (CDCl3, 400 MHz),  (ppm) 7.95 (d, 2H, J = 8.0 Hz), 7.84 (d, 2H, J = 12 Hz), 7.30 (t, 2H, J = 8.0 Hz), 3.24 (t, 2H), 2.01-1.94 (m, 2H).
EXAMPLE 6
Preparation of diethyl (2-(5-(2-octyldodecyl)-1,4-dioxo-3,6-di(thiophen-2-yl)-4,5-dihydropyrrolo[3,4-c]pyrrol-2(1H)-yl)ethyl)phosphonate (C20DPPPE):
[0089] To an oven-dried Schlenk flask, 2-(2-octyldodecyl)-3,6-di(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione) (2.2 g, 3.78 mmol) from Example 5 was added and dispersed in 20 mL dry DMF under N2. Sodium hydride (NaH) (230 mg, 9.46 mmol) was added to the flask, and the reaction mixture was heated at 100 ℃ for 30 minutes. A dilute solution of diethyl (2-bromoethyl)phosphonate (2.03 g, 8.31 mmol) in DMF was added dropwise to the reaction mixture for 10 minutes. The reaction temperature rises to 120 ℃ and is continued for 12 hours under N2. The reaction mixture was quenched with a few drops of methanol and poured into crushed ice. The red color product was filtered and washed with cold methanol several times. The compound was dried overnight under high vacuum. The compound was used without further purification.
EXAMPLE 7
Preparation of (2-(5-(2-octyldodecyl)-1,4-dioxo-3,6-di(thiophen-2-yl)-4,5-dihydropyrrolo[3,4-c]pyrrol-2(1H)-yl)ethyl)phosphonic acid (C20DPPPA):
[0090] To a two-neck round bottom flask, diethyl (2-(5-(2-octyldodecyl)-1,4-dioxo-3,6-di(thiophen-2-yl)-4,5-dihydropyrrolo[3,4-c]pyrrol-2(1H)-yl)ethyl)phosphonate (1.6 gm, 3.58 mmol) from Example 6 was added and dissolved in dry DCM followed by stirring at 25 ℃ for 40 minutes. After that, trimethylbromosilane (2.5 mL, 10.2 mmol) was added dropwise for over 10 minutes. The reaction mixture was stirred for 12 hours before being quenched with MeOH and stirred vigorously. After a further 2 hours of stirring, the solvent was removed under reduced pressure, and water (20 mL) was added. The mixture was then concentrated under reduced pressure. This step was repeated three times to give ((2-(5-(2-octyldodecyl)-1,4-dioxo-3,6-di(thiophen-2-yl)-4,5-dihydropyrrolo[3,4-c]pyrrol-2(1H)-yl)ethyl)phosphonic acid as a dark red solid. The solid was recrystallized with hot ethanol two times to yield the pure compound (1.1 gm) at a yield of 88.5 %. Proton nuclear magnetic resonance (1H NMR) spectra, phosphorus nuclear magnetic resonance (31P NMR) spectra along with Infrared (IR) spectra confirmed the formation and purity of the compound.
1H NMR (CDCl3, 400 MHz),  (ppm) 7.95 (d, 2H), 7.84 (d, 2H), 7.30 (t, 2H), 3.24 (t, 2H), 2.01-1.94 (m, 2H) .
31P {1H} NMR (CDCl3, 135 MHz),  (ppm) 26.92. IR (KBr, cm1): 1042 (P-OH), 1229 (P=O).
[0091] FIG. 4 illustrates preparation of C20DPPA through reaction scheme 406.
UV-Vis Spectra
[0092] The steady-state UV-visible absorption spectra of compounds C20DPPPA (corresponding to Example 7), PADPPPA (corresponding to Example 2) and HDPPPA (corresponding to Example 4) (collectively termed DPP compounds) were recorded in solution and thin films. Solutions of the compounds were prepared in chloroform at a concentration of 10 micromoles and thin films were formed by casting the solution using spin casting. The DPP compounds exhibited two bands, as shown in Table 1, one at high energy (~506-515 nm region), which is attributed to the pi-pi*(-*) transition. In contrast, the other band that appeared at lower energy (~538-547 nm) arises from the interaction between the electron-rich donor and the electron-deficient DPP lactam ring. Due to their similar electronic backbone, there is no significant shift in the absorption band from compound PADPPPA to HDPPPA to C20DPPPA.
Compound labs.(nm) labs.(nm)

C20DPPPA Solution 547 515
Thin film 553 -

PADPPPA Solution 540 509
Thin film 560 519

HDPPPA Solution 538 506
Thin film 558 519
Table 1

Electrochemical studies
[0093] The electrochemical properties of the DPP compounds namely, PADPPPA (Example 2) and HDPPPA (Example 4) were investigated by cyclic voltammetry. The PADPPPA and HDPPPA were dissolved in acetonitrile at a concentration of 10 µM. 0.1 M Tetrabutylammonium hexafluorophosphate (TBAPF6) in dry dichloromethane was used as the supporting electrolyte and the voltammograms were recorded at a scan rate of 50 milliVolts per second (mV/s). FIG. 5 is a plot 500 of cyclic voltammogram of PADPPA 502 (darker line) and HDPPA 504 (lighter line).
[0094] The HOMO and LUMO energy levels were calculated from the onset of oxidation and reduction potentials, respectively. The HOMO energy levels were calculated from the onset of oxidation wave using the equation EHOMO (eV) = -[Eoxonset - Eox(ferrocene)]. The LUMO energy levels were calculated from the onset of reduction wave using the equation, ELUMO (eV) = -[Eredonset – Ered(ferrocene)]. The electrochemical band gap was calculated from equation Eg(cv)(eV) = ELUMO (eV) – EHOMO (eV) as tabulated in Table 2. The DPP compounds show reversible oxidation and reduction peaks.
Compound EHOMO (eV) ELUMO (eV) Eg(CV) (eV)
C20DPPPA -5.39 -3.42 1.97
PADPPPA -5.63 -3.63 2.00
HDPPPA -5.65 -3.65 2.00

Table 2
EXAMPLE 8
Fabrication of a perovskite-based solar device:
[0095] Devices were fabricated in a positive-intrinsic-negative (p-i-n) structure on a glass substrate of patterned indium tin oxide (ITO). The glass substrates were cleaned with hot soap solution, deionized (DI) water, acetone, isopropanol, and DI water for 15 minutes in an ultrasonic bath. DPP compounds (Example, 2, 4 and 7) were dissolved in a mixture of chloroform (CHCl3) and ethanol and statically spin coated on ozonated ITO and annealed at 100 °C for 10 minutes to form SAM layers. The spin coated ITO substrates were rotated at a higher rpm to remove any non-bonded SAM, and absolute ethanol was poured dynamically. In this Example, SAM layer functions as the hole transport layer (HTL), corresponding to p type of the p-i-n structure. Triple A-site cation perovskite precursor solution (Cs0.05[(FA)5/6(MA)1/6]0.95Pb(I0.9Br0.1)3) (1.2 M) was prepared in a mixture of DMF and dimethyl sulfoxide (DMSO). The perovskite solutions were then spin-coated onto SAM-coated ITO substrates under one-step coating conditions and annealed at 100 °C for 30 minutes to form triple cation perovskite layer (absorber layer corresponding to intrinsic type of the p-i-n) over SAM. An antisolvent such as chlorobenzene may be dropped over the perovskite layer to remove the solvent. Examples of other antisolvents include toluene, anisole, and diethyl ether. PCBM/BCP layer was formed over the triple cation perovskite layer, where the PCBM/BCP layer functions as the electron transport layer corresponding to n type of the p-i-n structure. A silver cathode was patterned over the electron transport layer to complete the device. The devices had the configuration ITO/SAM/triple cation PSK/ PCBM/BCP/Ag, and correspond to FIG. 3.
[0096] Table. 3 shows the current-voltage (IV) characteristics of SAM-based perovskite solar devices. The performance of the solar devices can be characterized in terms of open circuit voltage (Voc), which is the maximum voltage obtainable from a solar device at zero current, current density (Jsc), which is the maximum current that flows through a solar device when the voltage across it is zero, and fill factor (FF) that corresponds to maximum power value divided by the product of Voc and Jsc. The devices including HDPPPA SAM exhibited the highest performance with Voc of 0.984, Jsc of 18.45, and FF of 72.49 % with 13.18% efficiency. The term “efficiency’ can be defined as the percentage of solar energy converted into usable electric current. The efficiency as reported in Table 3 may further be enhanced by optimizing device parameters, for example, layer thickness, coating conditions, varying other layers of the device, and the like.

SAM Absorber Voc (V) Jsc (mA/cm2) Fill Factor Efficiency
C20DPPPA CsFAMAPbI1-XBrX 0.79 3.38 52.67 1.86
PADPPPA CsFAMAPbI1-XBrX 0.977 19.35 67.77 12.82
HDPPPA CsFAMAPbI1-XBrX 0.984 18.45 72.49 13.18

Table 3
EXAMPLE 9
Fabrication of a non-fullerene donor-acceptor-based solar device
[0097] PADPPA and C20DPPPA SAMs were incorporated with a non-fullerene donor-acceptor (D-A) organic solar device. Unlike the previous example (Example 8), the donor-acceptor-based device of the present Example is lead-free and is purely organic molecule-based. The devices had the configuration ITO/SAM/D18:Y6/PNDIT-F3NBr/Ag. The DPP SAM layers were formed over ITO as described in Example 8. A solution of D18:Y6 in chloroform (CHCl3) was prepared. The D18:Y6 solution was then spin-coated onto an ITO substrate coated with SAM under one-step coating conditions and subjected to solvent vapor annealing. This was followed by the deposition of the electron transport layer consisting of PNDIT-F3NBr and thermal evaporation of Ag as the metal contact.
SAM Absorber Voc (V) Jsc (mA/cm2) Fill Factor Efficiency
C20DPPPA D18:Y6 0.465 24.7 38.11 4.39
PADPPPA D18:Y6 0.50 24.77 44.11 5.46

Table 4

[0098] The efficiency of the devices of Example 9 was lower than that of the devices of Example 8. This demonstrates that though SAM can fine-tune the work function of the electrode surface, the overall performance of the device depends on the overlying layers of the device as well, such as the absorber layers. For successful incorporation of SAM in semiconductor devices, the interaction of SAM layers with the overlying layers needs to be considered from real-time performance testing of the devices based on which further optimization of SAM layers may be performed.
[0099] It is to be understood that the above description is intended to be illustrative, and not restrictive. Furthermore, many other embodiments will be apparent to those of skill in the art upon reading and understanding the above description. Although the present disclosure has been described with reference to specific exemplary embodiments, it will be recognized that the disclosure is not limited to the embodiments described, but can be practiced with modification and alteration within the scope of the appended claims.
 
, Claims:CLAIMS
We claim,

1. A diketopyrrolopyrrole (DPP) compound having a terminal phosphonic acid group of general structure [I]:

[I]
wherein
R1 and R2 comprise at least one phosphonic acid group, and wherein R1 and R2 independent of each other is a hydrogen, a straight or branched alkyl group having 1 to 20 carbon atoms, a phosphonic acid group, or an alkyl phosphonic acid group having 1 to 5 carbon atoms; and
R3 and R4 independent of each other is a phenyl, a thiophenyl, a pyridyl, a 2-phenyl thiophenyl, 2-thienyl pyridine, or a thienothiophenyl functional group.

2. The diketopyrrolopyrrole compound as claimed in claim 1, wherein R3 and R4 are thiophenyl group.

3. The diketopyrrolopyrrole compound as claimed in claim 1, wherein the compound has structure [a].

[a]

4. The diketopyrrolopyrrole compound as claimed in claim 1, wherein the compound has structure [b].

[b]

5. The diketopyrrolopyrrole compound as claimed in claim 1, wherein the compound has structure [c].

[c]

6. The diketopyrrolopyrrole compound as claimed in claim 1, wherein the compound is a semiconducting material.

7. A self-assembled monolayer (SAM) comprising the diketopyrrolopyrrole compound as claimed in claim 1, adsorbed on a metal oxide surface.

8. The self-assembled monolayer as claimed in claim 7, wherein the metal oxide comprises aluminum oxide, tin oxide, fluorine tin oxide (FTO), tungsten oxide, cesium oxide, titanium oxide, copper oxide, nickel oxide, tantalum oxide, hafnium oxide, iron oxide, chromium oxide, niobium oxide, zirconium oxide, indium oxide, indium tin oxide (ITO), mixed metal oxide or combinations thereof.

9. The self-assembled monolayer as claimed in claim 7, wherein the self-assembled monolayer forms part of a semiconductor device.

10. A semiconductor device comprising the diketopyrrolopyrrole compound as claimed in claim 1, wherein the semiconductor device is a diode, a photodiode, a transistor, an organic semiconductor device, a light-emitting diode (LED), a photovoltaic device, an optoelectronic device, a sensor, a detector, or combinations thereof.

11. A method (100) of preparing a diketopyrrolopyrrole (DPP) compound having a terminal phosphonic acid group, the method comprising steps of:
providing a diketopyrrolopyrrole (DPP) compound of general structure [II] (102) in a first solvent, wherein R3 and R4 independent of each other is a phenyl, a thiophenyl, a pyridyl, a 2-phenyl thiophenyl, a 2-thienyl pyridine, or a thienothiophenyl functional group, wherein R5 and R6 comprise at least one hydrogen, and wherein R5 and R6 independent of each other is a hydrogen, or a straight or branched alkyl group having 1 to 20 carbon atoms;

[II]

reacting the diketopyrrolopyrrole compound of general structure [II] with a bromoalkylphosponate ester (104) in presence of a base at a temperature in a range of 100°C to 180°C to form a diketopyrrolopyrrole compound having terminal phosponato ester groups; and
hydrolyzing the terminal phosponato ester groups by treating with trimethylbromosilane (106) at room temperature in a second solvent to form the diketopyrrolopyrrole compound having the terminal phosphonic acid group of general structure [III], wherein

[III]
R1 and R2 comprise at least one phosphonic acid group, and wherein R1 and R2 independent of each other is a hydrogen, a straight or branched alkyl group having 1 to 20 carbon atoms, a phosphonic acid group, or an alkyl phosphonic acid group having 1 to 5 carbon atoms.

12. A method (200) of preparing a diketopyrrolopyrrole (DPP) compound having a terminal phosphonic acid group, the method comprising steps of:
providing a diketopyrrolopyrrole (DPP) compound of general structure [IV] (202) in a first solvent, wherein R3 and R4 independent of each other is a phenyl, a thiophenyl, a pyridyl, a 2-phenyl thiophenyl, a 2-thienyl pyridine, or a thienothiophenyl functional group;

[IV]

reacting the diketopyrrolopyrrole compound of general structure [IV] with an alkyl halide, or an aryl halide (204) at room temperature in the first solvent to form an N-alkyl derivative of diketopyrrolopyrrole compound, or an N-aryl derivative of diketopyrrolopyrrole compound, respectively;

reacting the N-alkyl derivative of the diketopyrrolopyrrole compound, or the N-aryl derivative of diketopyrrolopyrrole compound with a bromoalkylphosponate ester (206) in presence of a base at a temperature in a range of 100°C to 180°C to form an N-alkyl diketopyrrolopyrrole compound having a terminal phosphonato ester group, or an N-aryl diketopyrrolopyrrole compound having a terminal phosphonato ester group, respectively;

reducing the N-alkyl diketopyrrolopyrrole compound having the terminal phosphonato ester group, or the N-aryl diketopyrrolopyrrole compound having the terminal phosphonato ester group (208) in presence of a hydrogenation catalyst in alcohol at room temperature to obtain a hydrogenated diketopyrrolopyrrole compound having the terminal phosponato ester group; and

hydrolyzing the terminal phosponato ester group by treating with trimethylbromosilane (210) at room temperature in a second solvent to form the diketopyrrolopyrrole compound having the terminal phosphonic acid group of general structure [V], wherein

[V]
R7 is a phosphonic acid group, or an alkyl phosphonic acid group having 1 to 5 carbon atoms.

13. The method (100, 200) as claimed in claims 11 or 12, wherein the first solvent comprises, dimethyl formamide (DMF), and wherein the second solvent comprises dichloromethane (DCM).

14. The method (200) as claimed in claim 12, wherein the hydrogenation catalyst comprises palladium on carbon catalyst.

15. The method (100, 200) as claimed in claims 11 or 12, wherein a product formed from a step is optionally purified and isolated before use in a later step.

16. The method (100, 200) as claimed in claims 11 or 12, wherein the base comprises potassium carbonate, caesium carbonate, sodium carbonate, sodium hydride, or combinations thereof.

17. A semiconductor device (300) comprising:
an anode (302);
a cathode (310);
an active layer (306); and
a self-assembled monolayer (304) comprising a diketopyrrolopyrrole (DPP) compound having a terminal phosphonic acid group of general structure [I], wherein the self-assembled monolayer (304) is provided on the anode (302), and is disposed between the anode (302) and the active layer (306), wherein


[I]

R1 and R2 comprise at least one phosphonic acid group, and wherein R1 and R2 independent of each other is a hydrogen, a straight or branched alkyl group having 1 to 20 carbon atoms, a phosphonic acid group, or an alkyl phosphonic acid group having 1 to 5 carbon atoms; and
R3 and R4 independent of each other is a phenyl, a thiophenyl, a pyridyl, a 2-phenyl thiophenyl, a 2-thienyl pyridine, or a thienothiophenyl functional group.

18. The semiconductor device (300) as claimed in claim 17, wherein the anode (302) comprises a metal oxide, and wherein the metal oxide comprises aluminum oxide, tin oxide, fluorine tin oxide (FTO), tungsten oxide, cesium oxide, titanium oxide, copper oxide, nickel oxide, tantalum oxide, hafnium oxide, iron oxide, chromium oxide, niobium oxide, zirconium oxide, indium oxide, indium tin oxide (ITO), mixed metal oxide or combinations thereof.

19. The semiconductor device (300) as claimed in claim 18, wherein the metal oxide is indium tin oxide.

20. The semiconductor device (300) as claimed in claim 17, wherein the cathode (310) comprises barium, calcium, magnesium, indium, aluminum, titanium, silver, tungsten, gold, ytterbium, a calcium-silver alloy, an aluminum-lithium alloy, a magnesium-silver alloy, or combinations thereof.

21. The semiconductor device (300) as claimed in claim 17, wherein the active layer (306) comprises metal oxide perovskites, metal halide perovskites, organic-inorganic hybrid perovskites, donor-acceptor complexes, fullerene-based donor-acceptor complexes, or combinations thereof.

22. The semiconductor device (300) as claimed in claim 17, wherein the self-assembled monolayer (304) has a thickness in a range of 1 nanometer (nm) to 10 nm.

23. The semiconductor device (300) as claimed in claim 17, wherein the self-assembled monolayer (304) is a hole transport layer of the semiconductor device (300).

24. The semiconductor device (300) as claimed in claim 17, wherein the device is a diode, a photodiode, a transistor, an organic semiconductor device, a light-emitting diode, a photovoltaic device, an optoelectronic device, a sensor, a detector, or combinations thereof.