FIELD OF INVENTION
The current invention relates to the fabrication o~: organic solar cells using solution
processed hole transport material. More specifically, the process involves use of
solution processed, cost effective, easily available and robust hole transport layer
material which can be used for efficient and low cost large area organic solar cell
fabrication with simplest device architect under ambient conditions. The aim of the
invention is to fabricate efficient and cost effective large area. organic solar cells by
using hole transport layer which is economic and gives better efficiency as compared to
conventional hole transport layer.
KEY WORDS AND ABBREIATIONS USED
It may be noted that the abbreviations are not necessarily used commonly. For the
•
facilitation of drafting, several abbreviations may be formulated strictly for this
specification describing the present invention.
OPV: Organic Photo Voltaic
OSC(s): Organic Solar Cell(s)
OPVD(s): ·Organic Photo Voltaic Device(s)
BHJ: Bulk Hetero Junction
OLEO: Organic Light Emitting Device(s)
HTL(s): Hole Transport Layer(s)
ETL(s): Electron Transport Layer(s)
ITO: Indium Tin Oxide
IFL(s): Interface Layer(s)
PEDOT: Poly (3,4-EthyleneDiOxyThiophene)
PSS: Poly (Styrene Sulfonate)
Co304: Cobalt Oxide
r.i? -11- ·:>r.t1 "l 1- 7 . ? ;;: nctl..lT -- --- ----"' -. ~ -· -· "" ,.,._ r.· l ~ ......
I
' ! . '
'
I~
Ill
' ·Cl
'~
i .!
I :!:::::
' 1-
·~ ; N
''u0-E..
•
:Io~
en
I")
....0.. ... .....
: "'f"""
'0
s:::!.
CIO
0
I") en
!..e... .... 0.
~
> 1 ·O
'Z
N'
0
T-·C .n....
BACKGROU~D OF INVENTION
. The Organic photovoltaic (OPV) devices have drawn great scientific attention over the.
last few years, due to its potential to produce flexible, light weight, low cost solar cells
using organic materials. However, the power conversion efficiency achieved for these
systems is low for extensive implementation of the technology. Among the various
photoyoltaic technologies, organic/ polymer photovoltaics based on solution processed
bulk-heterojunction (BHJ) concept gained significant attention due to the use of
inexpensive light-weight materials, exhibiting high mechanical flexibility and
compatibility with low temperature roll-to-roll manufacturing techniques. In OPVs,
especially in bulk heterojunction organic solar cells consist of many components such
as electrodes (anode/ cathode), interface layers (IFLs) and active materials (donor/
acceptor). Interface layers play a very important role in collection and extraction of the
charge carriers, these layers are inserted between electrodes (anode/cathode) and
active layer interface. To moderate the charge carrier recombination at the electrodes,
various interface layer (IFL) materials have been developed to selectively allow desired
charge carriers to pass through and block undesired carriers. Therefore, charge carrier
recombination at electrodes can be substantially suppressed and PCEs can be
significantly improved for the cells with engineered IFLs. Hole transport layer (HTLs)
and electron transport layer (ETLs) are part of Interface layers.
In the field of organic solar cells (OSCs), conventional as well as inverted. structures,
Poly (3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), is a most
successfully used solution processed HTL but due to its hygroscopic, aci.dic and
protonation nature of PSS influences the device stability and degradation due to these
limitations hole transport layer PEDOT:PSS replaced by the several inorganic materials
and organic materials. In inorganic materials, Transition. metal oxides were also used,
these materials have air stability and high optical transparency but due to insolubility in
most of the common solvents, these materials are usually deposited by vacuum
deposition technique, which is incompatible with the concept of low-cost OSCs
fabrication. To overcome the problem of vacuum deposition of inorganic materials the
preference comes to solution processable approach. Several solution processable
-1. .7 "')'Z "--
i
!
'
. I''
~
Cll
C)
o"'. .·
-Cll !:..
N
E
0 -u.. ·N
,L~ oen
' (I)
<')
..0.. .... ,.._ ....
0
~
co
0 :"B'
j:;: .... ·o
-~
0 z.
N'
0
.. . •
methods were reported by using different inorganic precursors,, nanoparticles, colloidal
• • !' .
particles etc. In recent years, moreand more solution processable metal oxides have
been used for stable OSCs. Out of these copper based materials like copper iodide .
(Cui) and copper thiocyanate (CuSCN) have recently emerged as other effective and
robust inorganic hole transport materials for OSCs. Cui and CuSCN are highly
transparent and efficient HTL for organic solar cells but· these materials required
. I .
selective solvents to dissolve which is very expensive and bad smelly because of these
reasons we required inexpensive, easily soluble in common solvents and stable hole
transport material for low cost and efficient OSCs fabrication.
Although significant efforts have been devoted for solution processed HTL for
fabrication of large area, stable and cost effective solar cells, it is unexpected that very
few materials have been reported.
Following are the works done so far in the field of solution processed hole transport
layer materials for organic solar cells.
US 8963132 82: Solution processable doped triarylamine hole injection materials.
This invention relates to the organic light emitting devices (OLEOs). More especially on
device fabrication methods, device containing an organic layer which is a combination
of an organic electron donor material and an organic electron acceptor material that
forms a layer insoluble in a non-polar solvent, and devices containing the organic layer.
In Opto-electronic devices there are several reasons using organic materials such as
these materials are relatively inexpensive so these devices are cost effective than
inorganic devices. In addition, the important property of organic materials such as
deposited on flexible substrates so these materials well suited for large area roll to roll
fabrication. Examples of organic opto-electronic devices included light emitting devices
(OLEOs), organic phototransistors, organic photovoltaic devices and organic photo
detectors. In OLEOs, the organic materials may have performance advantages over
conventional materials. For example, the wavelength at which an organic emissive layer
emits light may generally be readily tuned with appropriate dopants. Methods for
n__e_ t 1-tT ,_~-8-
-? ....... ,..,_.7 -1•1 --. - 1- t -· .J' D•l I --""" -·-- ~
-1 7 '
.. ,. .· ..
~
Cl>
CJ
Cll
II..
.-.!!! -1-" N
.E. 0 -u.. N en
0 .e.n,
..0.. .. ....... 0
!:::! co
.0. ,
~... 0
NT On
I --a" --
~ z
N'
0
fabricating a solution-processed OLEO are provided. The methods include depositing
an organic layer comprising mixtute of an organic electron acceptor and an organic
electron donor to form a layer that is insoluble to a non-polar solvent. Devices
containing the organic layer may demonstrate improved lifetime and have a lower
operating voltage while maintaining good luminous efficiency.
WO 2013123605 A1: Solution-processable tungsten oxide buffer layers and electronics
comprising same.
The present invention related to the field of organic electronic devices like organic
photovoltaic devices (OPVs) and organic light emitting devices (OLEOs). It provides
intermediates and materials suitable for organic electronics manufacturing to specific
manufacturing method as well as uses. In the field of organic electronics such as OLEO
s and OPVs, buffer layers are used to improve the device efficiencies. The typically
thickness of these layers less than 1 OOnm to retain optical transparency and low series
resistance. These buffer layers may consist of W03 or Mo03 , which have deep lying
electronic states and are strongly n-doped by oxygen vacancies. Meyer et al. (Adv.
Mater . 2008 , 20, 3839-3843 ) reported the efficient hole-injection into organic
materials with deep-lying HOMO levels from an ITO electrode covered with a Mo03 or
W03 hole transport layer (HTL) or hole injection layer (HIL). The simplest device
structures consist of one or two organic layers. The hole injection layers Mo03 and W03
are typically deposited by thermal evaporation method under high vacuum, which is
major drawback for cost effective and large area fabrication.
US 9543537 82: Solution processed metal oxide thin film hole transport layers for high
performance organic solar cells.
The present work relates to the organic solar cells and similar optoelectronic devices.
Solar energy is most important renewable energy sources to develop cost effective and
efficient photovoltaic devices. Organic photovoltaics (OPVs) devices are an important
and attractive technology to solve energy prob!em. In OPVs, Bulk heterojunction (BHJ)
.-~.-.-.--.·..-...- ...•..·....
~-·""""
i-'-7-1":-}--11---?-·n-#t7' 17"?'2:
-1- ~--
..... :
-1- N
E o·
-u.. N en
0 .e.n,
..0.. .... ........
0
~ co
.0. ,
~....
0 NT·cn
-~-·-~··-
z
N'
0
solar cells have several advantages such as low cost, light weight, flexible and high
throughput manufacturing like as roll-to-roll and other similar techniques. The BHJ solar
cells have shown power conversion efficiencies (PCEs) around 4 to 7%.The PCEs of
organic solar cells increases around 2.5% to 7.7% in between the years of 2001 to
2010. A benchmark for OPV researchers is to achieve PCE around 10%, which would
help to make OPV competitive with other photovoltaic technologies. To achieve the high
efficiency and performance of the devices interfaces play a very important role. A
method of solution processable metal ·oxide hole transport layers used in organic
photovoltaic devices described. The metal oxide may be resulting from a metal-organic
precursor enabling solution processing from p-type metal oxide. A solution processable
metal oxide thin film as a hole transport layer used in organic photovoltaic devices.
CN101673806B: Solution processable material for electronic and electro-optic
applications. '
This invention discloses a solution processed material for electronic and electro-optic
applications. In electro-optic device, this has a first electrode separated from a second
electrode, an active layer deposited between the first and second electrode and an
interfacial layer in contact with the active layer. The interfacial layer consists of a metal
oxide and a second material that at least. one material reduces a work function or
increases an electrical conductivity of the interfacial layer according to the work. It is
necessary a composition for electro-optic devices is a combination of at least one metal
oxide and at least one salt in a ratio, by volume, of at least 1 :0.1 and less than 1: 1.2.
US 8980677 82: Transparent contacts organic solar panel by spray.
This invention described the fabrication technique of organic solar panels with
transparent contacts. In this method layer-by-layer spray technique is used for anode
layer deposition. This method includes placing the substrate, using photoresist on to the
substrate using photolithography, substrate etching, substrate cleaning, spin coating a
tuning layer on substrate, active layer combination P3HT/PCBM deposited by spin
!"'"!!--· 1t 1t 11 ~ 111--Jt. ...... ~
-----~~~ .... -r.'i ") - 't 1 - ·;;. r.'i 1 7 _. -· --- ---·-· .,_
.-.
Q)
Cl m
0..
--Q) 1-- N
E
0 -u.. N
a>
0
a>
I')
..0.. .. ........ 0
~ co
0
I')
a>
!...:..e... 0
~· TOI"'
> -- .. - -- 0 z
N'
0
coating method, the modified PEDOT solution was deposited by spray coating on the
substrate and then annealed the substrate.
WO 2013142850 A1: Inert solution-processable molecular chromophores for organic
electronic devices.
In the field of organic photovoltaic (OPV), small molecule based bulk hetrojunction (SM
BHJ) solar cells have become a competitive alternative. Intense investigation into the
design and utility of conjugated polymers for light harvesting has provided great· insight
into the design and implementation of organic semiconductors for OPV technology, to
the point where power conversion efficiencies (PCEs) up to 8.4 % have been achieved.
However, polymer systems inherently suffer from batch-to-batch variations and limited
options for purification of the polymeric materials. Small-molecule semiconductors avoid
the drawbacks inherent to polymeric semiconductors, as they are monodisperse in
nature and due to having a higher solubility than polymeric analogs, can be purified and
characterized using standard organic chemistry protocols. Additionally, modifications to
fine-tune properties can be made to small molecules more readily and with fewer
complications. Recently, it has been demonstrated that small molecule-based solar cells
can achieve efficiencies comparable to that of polymer-based solf!r cells. A small
molecule system with a central electron-rich core, flanked by relatively electron-poor
units, and terminated with a rr-conjugated end-cap has been previously described
(Welch et al, J. Materials Chemistry 21(34): 12700-12709 (2011), U.S. Provisional
Patent Appl. No. 61/416,251, International Patent Appl. No. PCT/US2011/061963. The
success of this system is in large part due to the inclusion of pyridal[2,1,3] thiadiazole
(PT) as an acceptor unit. The PT-based compounds have led to fabrication of a SM BHJ
solar cell with a PCE of 6.7% (see Sun et al., Nature Materials, 11:44-48 (2011).0ne
drawback to using PT-based materials in fabrication of small molecule solar cells is that
the cells must employ molybdenum oxide as a hole-transport layer (HTL) for maximum
efficiency. Molybdenum oxide is thermally evaporated onto devices, which prevents the
use of inexpensive solution deposition during roll-to-roll manufacture. It would be
preferable to use a solution-processable HTL material, such as poly(3,4-
-11:7 'c?-%-
1""""-------------~---~------,-------------------------
~
Cll
Cl
('!I
0..
--Cll ,·I_-
N
IE.. . u0.
IN
en
0 en
,. oI') , ....... .. .........
0
!:::! co
0
I') en
l..e... ....
0
:~·> .T.....·. cn ~-
·0
'Z
I' N' [o
I
l
'
ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS), or other doped
conjugated polymers. Due to hygroscopic, acidic and protonation nature of PSS
influences the device stability and degradation. This is a major cause of device
degradation, so there are several alternatives were used such as Graphene, Carbon
nanotubes (CNTs}, Polyaniline: poly (styrene sulfonate) and small molecules. For high
efficiency there is a need of high efficiency small molecule materials, which do not limit
manufacturing options, and which do not have sites that react with materials like
PEDOT:PSS, other acidic materials. The present invention seeks to address the need
for improved light harvesting molecules for bulk hetrojunction devices by using new and
efficient materials for organic solar cells.
US 20130263916 A1: All spray see-through organic solar array with encapsulation.
This invention described the fabrication of an inverted organic solar photovoltaic cell
onto grid or flexible substrates using spray-on technology for various layers deposition.
A thin layer of cesium carbonate deposited on Indium tin oxide used as a cathode
electrode for inverted cells. A combination of Poly-3(hexylthiophene) and [6,6]-phenyl
Cwbutyric acid methyl ester having a thickness around 200nm to 600nm used as a
active layer combination, facilitates a high level of light transmittal through the cell. A
modified PEDOT:PSS layer made by the doping of conductive polymer with
dimethylsulfoxide (DMSO) used as an anode electrode. A fabrication method of inverted
organic solar cell is described by using gas-propelled spraying for thin layers deposition.
After layers deposition the cell is sealed by using vacuum and temperature based
annealing and encapsulated with UV-core epoxy.
US 20130284242 A 1: Partially-sprayed layer organic solar photovoltaic cell using a selfassembled
monolayer and method of manufacture.
This invention describes the fabrication and characterization of large scale inverted
organic solar array by all-spray process. The solar illumination has been demonstrated
to improve transparent solar photovoltaic devices. The technology using SAM has a
(:1'")-l1-?r."i17 --- --- ____ ,
Q) -!::.
N
I§
·'u-.. N en
0 en
1S
, ......
.".". 0 N. -· co
.0. ,
en
CD
.j:.;.: 0
...
potential to revolute the silicon based photovoltaic technology by providing a. complete
solution processed manufacturing process. The solar module used for windows and
windshields applications due to its semi transparent property. The inventive solar
modules are more efficient as compare to the silicon solar cells in artificial light
environments; which significantly expand their use in indoor applications. Additionally,
these modules can be incorporated into soft fabric substances like tents, military backpacks
or uniforms, providing a highly portable renewable power supply for deployed
military forces. In recent years, the energy consumption has drastically increased due to
increased industrial development throughout the world. Due to increased energy
consumption we required natural resources, such as fossil fuels, as well as global
capacity to handle the byproducts of consuming these resources. In future demands for
energy are expected in greatly increase due to increase in population so we required
the development of new and clean energy sources which is efficient, cost effective and
have minimal impact on the global environment. Photovoltaic technology has been used
since 1970s as an alternative to traditional energy sources. Because the photovoltaic
cells use existing energy from sunlight, the environmental impact from photovoltaic
energy generation is significantly less than traditional energy generation. Most of
commercialized photovoltaic cells are inorganic or silicon based like single crystal,
polycrystalline and amorphous silicon. Mainly, solar modules fabricated by silicon for
different applications like rooftops of buildings. But due to high cost of silicon as well as
complicated fabrication process limits its large area commercialization. Silicon wafer
based cells are brittle, opaque substance they limit their use such as on window
technology where transparency is most important issue. To re.s olve the problems or
drawbacks of· inorganic photovoltaic technology organic materials have been
investigated for efficient, cost effective and large area flexible solar cells. There are
several organic materials are used like organic polymers, small molecules, carbon
nanotubes and self assemble monolayers so in this work self assembled monolayers
are used.
-(:-"l'}--ll--'")-t·:-'l-"-l7 "'-·•
~> T_..,·-cn ni=·t. u·T :'b!"· --- It • ~
0 z
N'
0
~
Cl)
C)
01 a.
Cl) -!:..
N
E
-u0.. N en
0 en
M
..0.. ..
."."." 0
~ co
0
Men .
CD
.j:.;.: 0
~ TOn
> --·· - 0 z
N'
0
OBJECTIVE OF THE INVENTION:
The principal object of the present invention is to fabricate efficient, cost effective,
solution processed large area organic solar cells.
Another object of the present invention is to produce solar cells using inexpensive,
effective, stable, easily soluble hole transport material.
Yet another object of the present invention is to disclose a hole transport material with
appropriate effectiveness without inflicting any uncomfort to human being.
SUMMARY OF THE INVENTION:
The present invention describes an organic solar cell, OSCs consist of an Indium Tin
Oxide (ITO) coated glass substrate as anode electrode, Cobalt Oxide (Co304) in 10
mg/ ml optimum concentration as hole transport layer (HTL) soluble in common organic
solvent such as dimethylformamide (DMF), a low band gap material used as active
layer(combinations of electron donor material and electron acceptor material) wherein
said active layer consists of electron donor Poly[N-9"-hepta-decanyl-2,7-carbazole-alt-
5,5- (4', 7'-di-2-thienyl-2', 1 ',3'- benzothiadiazole) (PCDTBT): electron acceptor [6,6]phenyl
C71-butyric acid methyl ester (PC71 BM) (PCDTBT:PC11 BM) in 1 :4 w/w and an
aluminium (AI) cathode wherein said cathode and anode is sandwiching said active
layers and HTL.
The present invention further describes a process of preparation of an organic solar cell
comprising of Indium Tin Oxide (ITO) coated glass as a outer substrate for light incident,
Indium. Tin Oxide (ITO) coated glass substrate was patterned with the help of laser
ablation system, cleaned with soap solution followed by cleaning with deionised water
after that boiled in different solvents like acetone, methanol and isopropanoi.Co304 as
HTL, wherein said Co304 is dissolved in DMF solvent 10 mg/ ml as the optimal
concentration active layer comprising of electron donor and electron recipient duo
wherein electron donor material PCDTBT and electron acceptor material PC71BM were
weighed (1 :4 w/w) and dissolved in mixed solvents of chlorobenzene (CB) and 1 ,2-
dichlorobenzene (DCB), wherein further active layer solution was stirred for 12 hrs at
• i'
~
.Cil
C)
01
D..
Cl) -!:..
N
E
-u0.. . Nen
·o
en
<')
..0.. .... ,.._ ....
0
~
00
0
<')
::B
.j:.;.:. .
0
•
room temperature, and Aluminium (AI) as cathode electrode deposited by thermal
evaporation.
BREIF DESCRIPTION OF ACCOMPANYING DRAWINGS
In the drawings accompanying this specification:
Fig. 1: Schematic diagram of Organic Solar cell with Co304 as a hole transport layer,
wherein 1 is sunlight, 2 is Substrate (glass), 3 is Anode (ITO coated glass), 4 is
Co304 used as HTL, 5 is Active Layer PCDTBT: PC71 BM, and 6 is AI as Cathode.
Fig. 2: Schematic representation of solar cell fabrication process by using Co30 4 as a
HTL, wherein 1: ITO electrode, 1 ': Spin Coated HTL (Co30 4), 2: Hole Transport
Layer (HTL), 2': Active layer deposition, 3: Active layer(s), 3': Cathode (AI)
electrode Deposition, 4: Cathode/ AI electrode, and 4': Device active area.
Fig.3: J-V Characteristics of reference devices with PCDTBT: PC71BM combination
under dark and illumination conditions.
Fig. 4: J-V Characteristics with PCDTBT:PC718tl(l combination using Co30 4 as a HTL.
Fig. 5: Atomic Force Micrographs (AFM) of Co304 in DMF solvent.
~ -rcn nr=t l-.!·7 -> --- •· :'ld" ----.-a ~ - 0 z
N'
0
-1- N
E
0 -u.. N
c:r>
'O
.c:.r>,
..0.. .. ........ 0
~ co
.0. ,
~... 0
'}I Ten
. > -· -- 0 z·
N'
0
Catt10de (AI)
D D D Sunlight
Fig.1: Schematic Organic Solar cell devices with Co30 4 as a Hole Transport Layer.
Glass substrate
evice Active area
Cathode electrode
Deposition
AI electrode
Hole Transport Layer
Active layer
deposition
Active layer
Fig. 2: Schematic representation of solar cell fabrication process by using
Co304 as a HTL.
-n-~-tI tL.J-T 17""><1; -, . --
'
---"ni c
I!!
~ u"
4.0JC10 ..
3.0x10.,.
::i
.;
:::=- 2.0x10 ..
c
~
0" ' 1.0x10. .
0.0
8.0x10"'
6.0x10 ...
4.0x10 ...
2.0x10 ..
D.O
.
-1.0
-1.0
ITO/PEDOT:PSSIPCDTBT:PC71BM/AI l
.
.... 0.0
Voltage(V)
• I • I • I ••' •,' • •' ' ~ • oi •• • /"
o.s 1.0
ITO/PEDOT:PSS/PCDTBT:PC71 BM/AI l
• •' •' ~ • oi
oi ••• ••• •• L
.... 0.0 1.0
Voltage(V)
IITO/PEDOT:PSS/PCDTBT:PC,BM/AI l
Jsc=7.04 mA/cm2 ·:
0.0
Voc•0.57V :
f
FF=36.3% I ;· PCE•1.47%
... / -
1.Dx10.o ...- ; a 5.0x104
-E ~
-.I".i.i ~ -5.0..:10
4
u"
-1.0:1110" ~-
-1.0 .... 0.0 o.s
Voltage(V)
IITO/PEDOT:PSS/PCDTBT:PC71BM/AI l
1.2x10~
Jsc•4.3~ rnA/em' ,.•
Voc•0.49V I 1.0x1o·~ - N 8.0x10~ E
u
:CC 8.0x10-a
E
- 4.0x1o<~
~
-~ 2.0x104
'"g' 0.0 -c
! ·Z.Ox104
~ 0" -4.0x10o~
-8.0x104
FF=48.6%
PCE•1.06%
• •• •••
-1.0 ....
I
I
I
/
./
0.0 o.s 1.0
Voltage(V)
Cll
Fig. 3: J-V Characteristics of reference devices with PCDTBT:PC71BM
combination under dark and illumination conditions.
1-.
~
N
.E....
0 -u... N en
Q .e.n,
Q ......
........... ......
Q
~ ·. 00
·.c.,
~ ......
Q
N> ··-=nT-1!-e· n· ~--
0 z
N'
Q
n__;:_:_: _t __u , ..,..,.. -ll--?re...-J--t·7 ... -1-- .·-.,. • a ''), ~- ,. --
..
. !
!'
~
.,
I
I,
I
-!:::..
N
E
-u0. N en
0 en
I")
..0.. .... ......... . o
·N- ·~
I")
~-m
,, j::: ....
0
~
~ z • N
0
----- -1-· -·.. .... l I ~
..
,I, .•
IITOICo,OjPCDTBT:PC,BMIAI I
1.8x10.3 .
1.6x10~
1.4x10~
1.21t10~ -:i 1.0x104 .,;
~
• I • I • I • I • I ••
~104
- 2.0x104'
N
E
1.6x104
~
E 1.0l104
~ 2:'
'
Jsc=11.9 mA/cm2 • •' •' v~.68V ,;
,;
,;
FF=41.1o/o ,;
,; - • c: &Ox1a'
l!!
~ ........ ·o"
4.0x1D~
........
I • I • I • •' •' j
'icii: &.Ox'I0-3
.Q.,l - 0.0 c:
~ -5.0x104 .. :::J u
·1.0x1D.:z
• PCE=3.21o/o .•••
_/
0.0
-1.6x104
·1.0 45 0.0 0.5 1.0 -2.0x10~
VollageM ·1.0 .... 0.0 1.0
VollageM
IITOICo,OjPCDTBT:PC,BMIAI r
2.5J:tlt
•
t.Bxto""
2.0x104 Jscr11.0 rnA/em' • I • I • I • I • I • I • I . • I • •' •' ,; . • ~·
1.4xt04
t.zxto" - 1.0x104
:i
.,;
~- a.oxto"' c:
l!! s.o~eto• ~ 0"
4,0xto•
2.0x10 ..
0.0
- N
E
1.5x104 ~"
E 1.0xt
0
a>
M
..0.. .... .........
0
!:::!
CIO
0
M
a>
~
·~
lI.'.tN> -T- Ifc -n
!,0 :z
N'
0
Fig. 5: AFM images showing morphology of Co304 in DMF solvent.
Table 1. Comparison of different operating parameters of OSCs based on the
PEDOT:PSS and Co304 as HTLs.
Different HTLs
PEDOT:PSS
Co304
-n -.-._I t. ..~.~.- ·1-~!!--
Active Layer
PCDTBT/PC71 BM
PCDTBT/PC71BM
PCDTBT/PC71BM
PCDTBT/PC71 BM
2
J (rnA/em) sc:
7.04
4.39
11.9
11.0
V '(V)
oc: FF(%) PCE (%)
0.57 36.3 1.47
0.49 48.6 1.06
0.68 41.1 3.21
0.74 37.4 3.07
I
•
-1-- N
E
0 -u.. N
a>
0
a>
.M
..0.. .... . ..........
§
co
0
M
a>
!..!.:.!. ....
0
-·
DETAILED DESCRIPTION OF THE INVENTION
This invention describes an organic solar cell, which consist of an Indium Tin Oxide
(ITO) coated glass substrate as anode electrode for light incident, a hole transport layer
(HTL) soluble in common organic solvent such as dimethylformamide (DMF), a active
layer combination of electron donor material and electron acceptor material duo. The
'
active layer may consist of electron donor Poly[N-9"-hepta-decanyl-2,7-carbazole-alt-
5,5- (4', 7'-di-2-thienyl-2',1 ',3'- benzothiadiazole) · (PCDTBT): electron acceptor [6,6]phenyl
C71-butyric acid methyl ester (PC71BM) (PCDTBT:PC71BM), and an aluminium
(AI) cathode electrode deposited by thermal evaporation. wherein said cathode and
anode is sandwiching said active layer and HTL.
The present invention further describes a process of preparation of an organic solar cell
comprising of an ITO coated glass substrate wherein the ITO coated glass substrate
was patterned with the help of laser ablation system, cleaned with soap solution
followed by cleaning with deionised water and boiled in different solvents such as
acetone, methanol and isoprpanoi,Co30 4 as HTL, wherein said Co30 4 is dissolved in
DMF as the optimal con active layer comprising of electron donor and electron recipient
duo wherein electron donor material PCDTBT and electron acceptor material PC71BM
were weighed and dissolved in mixed solvents of chlorobenzene (CB) and 1,2-
dichlorobenzene (DCB), wherein further active layer solution was stirred for 12 hrs at
room temperature, and Aluminium (AI) cathode.
Embodiments:
In one embodiment of the invention, the hole transport material chosen for study is
Cobalt Oxide (Co304).
In another embodiment of the invention, the material taken as HTL is selected because
of low cost, easily soluble in common organic solvents, stable, efficient and the like .
N T 0 n . n C f .w, T ;':) ")I - 1. 1 - ·J> t:'i 1 7· 1 7 • ·J> ~
·"~>I -·•. - - -- ._ •- ~ --·· - -· - - --- _. " -" - - -
·, 0 z
''N ' ·o
•,''
'I-- 'N
:-~E
0 -u.. N en
0 .e.n,
..0.. .... ........
0
-N · CIO
.0. ,
~
;..:.:.
0
.-
'>}I T_ 'O... -rli ~-
,0 z
'
:·~:s
In another embodiment of the invention, the process of organic solar fabrication is cost
effective.
In another embodiment of the invention, the HTL material used is easily soluble in DMF
which is used in device fabrication.
In further embodiment of the invention, the quantity of HTL material required ranges
from 5mg/ml to 15 mg/ml.
In another embodiment of the invention, the HTL material spin coated on clean
patterned ITO coated glass substrates with 3000rpm and annealed at 1 00°C.
In another embodiment of the invention, the solvents for another active layer
combination PCDTBT:PC11BM was chlorobenzene and dichlorobenzene.
In one embodiment of the invention, after HTL active layer combination was spin coated
on it.
In another embodiment of the invention, the active layer film was annealed at 70°C
(PCDTBT:PC11 BM).
In another embodiment of the invention, after annealing cathode electrode (AI) were
deposited by thermal evaporation method with base pressure 1 a-s torr.
In another embodiment of the invention, J-V characteristics of the fabricated devices
were characterized by using Keithley source meter having with power intensity
100mW/cm2
.
In another embodiment of the invention, the HTL coated (Co30 4) samples were tested
by AFM for their surface morphological study.
Below table disclose the operating parameters of OSCs based on the Co30 4as a HTL
and comparison with different operating parameters of OSCs based on the
PEDOT:PSS.
Table 1: Comparison of different operating parameters of OSCs based on the
PEDOT:PSS and Coa04as HTLs with active layer combination.
.::
' '
'
. .
. J
~
Ill
Cl
Ill
D.
--Ill 1-
·~
...,. N
'J1E
:~
';f:il
., ,eon ,~ r')
..0.. .. ........ 0
~
CIO
.0. ,
en
·..·.(.-..Q.... ·
. No,
.-
TOn
''*"> --~- -- 0 z
N'
0
Different HTLs Active Layer J (rnA/em2) V oc (V) FF (%) PCE (%) sc
PEDOT:PSS PCDTBT/PC71BM 7.04 0.57 36.3 1.47
PCDTBT/PC71BM 4.39 0.49 48.6 1.06
Co304 PCDTBT/PC71BM 11.9 0.68 41.1 3.21
PCDTBT/PC71BM 11.0 0.74 37.4 3.07
The following examples are given to illustrate the process of the present invention and
should not be construed to limit the scope of the present invention:
Example 1:
Reference photovoltaic devices using solution processed PEDOT: PSS as a hole
Transport Layer:
In this example, a well known and widely used solution processed HTL layer material
poly (3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS), is used in the
fabrication of reference device. These devices were fabricated under same
environmental conditions which are used in making devices using Co30 4 as hole
transport layer. These reference devices were fabricated for comparing the results with
the novel hole transport layer which is used in fabricating devices.
Device fabrication procedure-
The reference devices were fabricated with simplest device geometry
ITO/PEDOT:PSS/active layer/AI. Prior to use, ITO coated glass (used as anode
electrode) substrates were patterned with the help of la$er ablation systern after that
n -,· ••T A?- 1. l-? 1711.7
:--=-r':~ -·- -- --·-·· ,. ,. • ') 'Z
--~-----
cleaned with soap solution followed by deionized water. After that these substrates were
boile~ in different solvents like acetone, trichloroethylene and isopropanol respectively.
For drying the substrates put inside the heating oven after drying the substrates a thin
film of PEDOT: PSS was spin coated at 1500 rpm for 60seconds.The resulting PEDOT:
PSS films were annealed at 120°C for 20 minutes. Active layer combination (donoracceptor
combination) PCDTBT:PC71BM were weighed (1:4 w/w) and dissolved in
mixed solvents of chlorobenzene (CB) and 1 ,2-dichlorobenzene (DCB). The active layer
solution was stirred for 12 hrs at room temperature. After annealing the active layer
solution (PCDTBT:PC71BM) were spin coated at 1000rpm for 90 seconds and the
resulting substrates were further annealed at 70°C.Finally devices were completed by
the deposition of AI as a cathode electrode at a base pressure 10.s torr.
Device characterization-
All device measurements were performed in ambient conditions. The current-voltage (JV)
characteristics were measured using computer controlled keithley 2400 source
meter. The devices were illuminated from the transparent ITO anode electrode side
using a solar simulator with AM 1.5G and incident power is 100 mW/cm2.From J-V
measurements, we found that the resulting reference devices show PCE with
PCDTBT:PC71BM combination PCE is 1.47 %, Voc 0.57 v; Jsc 7.04 mA/cm2 and FF
36.3%, respectively (shown in figure 3 and Table 1 ).
Example 2:
Solution preparation of Hole Transport Material (Co30 4) and Active Layer
(PCDTBT: PC11BM):
For this study, Co304 was used as a solution processable hole transport layer. Different
inorganic materials such as transition metal oxide, Copper based materials are used as
a solution proceesed hole transport layer but due to solubility issue, required selective
solvents to dissolve, which is very expensive and bad smell. Due to these reasons we
have selected Co304 material as a solution processable hole transport layer for efficient
n ;::;; ~ T n ·""'J - 1 1 - ? n 1'· 7
- - - • a """" - ,.,.. -- -- 1!!-· -· -- "'
·---------------------------------
.·.
organic solar cells, which is inexpensive, stable, environment friendly, good film quality
and easily soluble in common solvents like DMF. Firstly, Co304 dissolve in a DMF
solvent in different weight ratios and the optimized concentration of Co304 is 1 Omg/ml.
For active layer solution, a well studied active layer combination was used for device
fabrication. Electron donor material PCDTBT and electron acceptor material PC11BM
were weighed (1 :4 w/w) and dissolved in mixed solvents of chlorobenzene (CB) and
1 ,2-dichlorobenzene (DCB). The active layer solution was stirred for 12 hrs at room
temperature. The optimized concentration of Co304 was weighed out and dissolved in
DMF solvent.
Example 3:
Process of device fabrication:
All devices were fabricated on ITO coated glass substrates. ITO coated substrates were
patterned using laser ablation technique. The patterned ITO coated substrates were
cleaned in sequential with acetone, methanol and isopropanol, followed by drying for 20
min. After that the Co304 HTL solution in DMF solvent was spin coated on cleaned ITO
substrates at 3000 rpm, followed by baking on a hot plate at 1 oo•c for 20 minutes and
then drying for 1 hour at room temperature. The active layer solution was spin-coated
onto the HTL layer (Co30 41ayer) with spin speed of 1000 rpm and annealed for 10 min
at 1o•c on a hot plate. Finally, the devices were completed by thermally deposited AI as
cathode electrode at base pressure of 10"6Torr. The completed devices were then
transferred for the characterization.
Example 4:
Thin film and device characterization:
The surface morphology of Co304 film in DMF solvent on ITO substrates was acquired
by using atomic force microscopy (AFM) NT-MDT Solver Pro. To study the surface
morphology of Co304 HTL layer because smoother surface allow the formation of a
•
Q) -!::..
N
E
-u0.. N en
0 .e.n.,
0 ......
........... ......
0
!:::! co
.0. .,
'
better contact between the HTL and active layer and improve device performance. To
examine the effectiveness of Co30 4 as a solution processable HTL material for OSCs,
we have fabricated devices by using simplest device structure ITO/HTUactive.layer/AI.
A most studied low band gap donor polymer PCDTBT blended with PC11BM was used
as active layer for device fabrication. The current density-voltage (J-V) characteristics
of fabricated devices were measured using a computer controlled Keithley 2400 source
meter under dark and illumination conditions. The devices were illuminated from the
transparent ITO anode electrode side using a solar simulator with AM 1.5G. and incident
power is 100 mW/cm2
. From J-V characteristics we have calculated the device
parameters summarized in table 1 and the power conversion efficiency of fabricated
devices with PCDTBT: PC71BM combination the device efficiencies are 3.21% and 3.07
% in DMF solvent (shown in figure 4 and table 1 )

.
CLAIMS
We Claim:
1. An organic solar cell, said cell in series comprising of:
2.
a) an ITO coated glass substrate used as an anode electrode
for light incident.
b) a solution processed hole transport layer (HTL) soluble in common
organic solvent such as dimethylformamide (DMF),
c) an active layer combination of electron · donor material and electron
acceptor material, and
d) a cathode wherein said cathode and anode is sandwiching said active
layers and HTL.
The organic solar cell as claimed in claim 1, wherein said outer substrate is
glass. .
·~
·:1N·> -T: ·0· :n-- -n -r::-: I- .1: .1·• -T- r-.l -?- - -1. -1· -· -":> -r.'i -1 7 1 7 - ? -;::· ~ -eo-~ ~- - -· 'o •z
' N'
0
''
'
,;t
, ' ',, '·
j
..:• -...
'
'
.I
'·
3.
'·
, ,
The organic solar cell as claimed in claim 1, wherein said anode is Indium Tin
Oxide (ITO) coated glass substrate.
4. The organic. cell as claimed in claim 1, wherein said HTL is Cobalt Oxide (Co304)
in 10 mg/ ml optimum concentration.
5.
6.
7 .
8.
The organic cell as claimed in claim 1, wherein said active layer consists of
electron donor Poly [N-9"-hepta-decanyl-2, 7 -carbazole-alt-5,5 (4', 7'-di-2-thienyl-
2', 1 ',3'- benzothiadiazole) (PCDTBT): electron acceptor [6,6]-phenyl C71-butyric
acid methyl ester (PC11BM) (PCDTBT:PC11BM) in 1:4 w/w ..
The organic cell as claimed in claim 1, wherein said cathode is Aluminium (AI).
A process of preparation of an organic solar cell comprising arranging in a series
the glass substrate, Indium Tin Oxide (ITO) coated glass as anode, Co304 as
HTL, active layer consisting of electron donor and electron recipient pairs, and
Aluminium (AI) cathode electrode .
The process as claimed in claim 7, wherein ITO coated glass substrate was
patterned with the help of laser ablation system, cleaned with soap solution
followed by cleaning with deionised water after that boiled in acetone,methanol
and isopropanol respectively.
9. The process as claimed in claim 7, wherein electron donor material PCDTBT and
electron acceptor material PC11BM were weighed (1:4 w/w) and dissolved in
mixed solvents of chlorobenzene (CB) and 1 ,2-dichlorobenzene (DCB), wherein
further active layer solution was stirred for 12 hrs at room temperature.
10. The process as claimed in claim 1, wherein the Co30 4 as a solution processed
HTL material was weighed out and dissolved in common solvent DMF 10 mg/ ml
as the optimal concentration.