Description:FORM 2
THE PATENT ACT, 1970
(39 of 1970)
COMPLETE SPECIFICATION
(See section 10, rule 13)

TITLE: IONOVOLTAIC POWER GENERATION BASED ON LEAD-FREE LAYERED Cs3Bi2Br9 PEROVSKITE NANOSHEETS

INVENTORS
PRAMOD, Ashna - Indian Citizen
Department of Sciences, Amrita School of Physical Sciences, Coimbatore, Amrita Vishwa Vidyapeetham, India

BATABYAL, Sudip - Indian Citizen
Department of Sciences, Amrita School of Physical Sciences, Coimbatore, Amrita Vishwa Vidyapeetham, India

APPLICANT
Amrita Vishwa Vidyapeetham
Coimbatore Campus
Coimbatore, Tamil Nadu- 641112, India

THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED

IONOVOLTAIC POWER GENERATION BASED ON LEAD-FREE LAYERED Cs3Bi2Br9 PEROVSKITE NANOSHEETS

CROSS-REFERENCES TO RELATED APPLICATIONS
None.
FIELD OF THE INVENTION
The present invention generally relates to electricitygenerating devicesand more particularly relates to moisture induced electricity generationdevices and methods thereof.
BACKGROUND OF THE RELATED ART
The decreasing availability of fossil fuels highlights the importance of solar energy as a partial alternative. Finding sustainable energy sources is crucial due to the depletion of most fossil fuel reserves. Exploring eco-friendly options is vital to tackling global environmental issues and the energy crisis. Solar energy and moisture are plentiful on Earth, offering a vast potential energy source that has attracted considerable interest. The recent development of moisture-driven electricity represents a significant advancement in harnessing environmental energy. In these devices, materials with hydrophilic and functional groups serve as ion or carrier generators by absorbing water molecules. Subsequently, the ion or carrier gradient facilitates directional current flow or electric potential between the electrodes.
Saline water, comprising 97% of the Earth's water, presents an opportunity to develop electricity generators. Water, a highly polar liquid, can stabilize charged species like salts, acids, and bases. When solvated cations and anions separate, they create electric fields. An electromotive force can be generated by achieving a macroscopic asymmetric ion distribution. This force can produce a voltage between two electrodes in a device, driving a current through an external circuit. Various processes can create asymmetric ion distributions, such as achieving different mobilities of anions and cations. Another approach involves systems with non-mobile charges, such as having the cation or anion attached to a stationary phase. In such systems, water movement can selectively transport the mobile counterion, creating an electric field.This process can be appropriately termed an "ionovoltaic" process. Furthermore, the unique nature of perovskite materials allows for the easy release of halide ions when exposed to moisture due to the weak bonding between the different cations and inorganic octahedral. This release occurs through the interaction between water molecules and perovskites, creating an ion gradient and an electric output.
Ionovoltaics represents an innovative approach to energy conversion, utilizing water motion and ion dynamics to generate electrical energy. Ma et al. demonstrated the ionovoltaics effect of 2D halide perovskite, which can generate electricity by absorbing moisture. They utilized the hydrophilic and ionic nature of 2D perovskite EOA2PbI4 (EOA-ethanolammonium), achieving a power density of 30mW/cm3. Similarly, Sharma et al. reported that IEG can generate an open-circuit voltage of up to ~0.5 V and a short-circuit current density of ~0.1 mA cm–2, sufficient to power small electronic devices. Interactions between ions and solids and solid-liquid interfacial potentials determine the output voltage resulting from macroscopic water motion. This process primarily relies on the reversible hydration and dehydration of materials.
Though the existing art providesperovskite materials to generate ionovoltaic cells, commercializing the cells are bottlenecked by the toxicity issues caused by lead in the perovskite. Therefore, there is a need to fabricate lead free perovskite ionovoltaic devices.
SUMMARY OF THE INVENTION
In various embodiments an ionovoltaic device (100) for moisture induced electricity generation is disclosed. The device (100) includes an FTO layer (102) fabricated on a glass substrate (101) having a top end and a bottom end. The FTO layer (102) is etched in a middle portion, thereby forming a top electrode (102a) and a bottom electrode (102b) at both ends of the substrate (101), the electrodes (102a,102b) forming an active region (103) therebetween. In various embodiments, a lead-free perovskite nanocrystal (104) coated on the active region(103), wherein the perovskite nanocrystal (104) is configured to absorb moisture(105) and form an electric double layer at the perovskite-moisture interface, thereby generating a voltage and current flow between the electrodes (102a,102b).
In various embodiments, the perovskite nanocrystal (104) is of general formula A3B2X9 wherein A is cesium, B is one of bismuth or antimony and X is selected from chlorine, bromine or iodine.
In various embodiments, the perovskite nanocrystal is Cs3Bi2Br9 having intense XRD peaks at 31.600 along (022) plane, at 26oalong (003) plane and at 46o along (220) plane.
In various embodiments, the device (100) generates voltage is in the range 0.2 to 0.3 V.
In various embodiments, the device (100) generates current of 25 µA/ sq. cm or more.
In various embodiments, the distance between the top and bottom electrode ranges from 1 to 5 mm.
In various embodiments, a method (200) of synthesis of Cs3Bi2Br9 is disclosed. The method includes mixing (201) powders of CsBr and BiBr3 in a stoichiometric ratio with DMF to obtain a yellow-green solution, stirring (202) the obtained solution at 70o C for 1 hour to form Cs3Bi2Br9 precipitate, placing (203) the precipitate for centrifugation at 8000rpm for 10 minutes to form Cs3Bi2Br9 powder and drying (204) the obtained Cs3Bi2Br9 powder in a vacuum oven at 80oC for 12 hours.
In various embodiments, the stoichiometric ratio of CsBr and BiBr3 is 3:2.
In various embodiments, a method (300) for moisture induced ionovoltaic power generation is disclosed. The method comprising the steps of providing (301) FTO coated (102) glass substrate (101) having a top end and a bottom end, etching (303) the substrate (101) in a middle portion to an optimal distance thereby forming a top electrode (102a) and a bottom electrode (102b) at both the ends and an active region (103) in the middle portion thereof, drop casting (304) a lead free perovskite nanocrystal (104) on the active region (103) of the substrate (101) to form an ionovoltaic device(100), sealing (305) the ionovoltaic device in a beaker comprising a salt solution;exposing (306) the device to varying relative humidity causes absorption of water molecules to the perovskite nanocrystal surface (104); andforming (307) an electric double layer at perovskite-moisture interfaces, thereby generating voltage and causing flow of current across the electrodes of the device (100).
In various embodiments, etching the middle portion substrate to the optimal distance is ranging from 1to 5mm.
In various embodiments, drop casting the nanocrystal comprises a unique crystal structure Cs3Bi2Br9.

BRIEF DESCRIPTION OF THE DRAWINGS
The invention has other advantages and features which will be more readily apparent from the following detailed description of the invention and the appended claims, when taken in conjunction with the accompanying drawings, in which:
FIG.1A: a schematic representation of an ionovoltaic device.
FIG. 1B: a flow diagram of a solution processing method of synthesizing Cs2Bi3Br9.
FIG. 1C: a flow diagram of a method of fabricating Cs2Bi3Br9 perovskite based ionovoltaic device to generate voltage and current.
FIG. 2A: image showing XRD patterns of Cs3Bi2Br9.
FIG. 2B: image showing Raman spectrum of Cs3Bi2Br9 halideperovskite.
FIG. 3A: shows UV-Vis DRS reflectance spectra.
FIG. 3B:shows bandgap of Cs3Bi2Br9 calculated from Kubelka – Munk plot.
FIG. 4: shows survey scan XPS spectra of 2D bismuth halide perovskite Cs3Bi2Br9
FIG.5: image showing SEM image of Cs3Bi2Br9perovskite.
FIG.6: image showingEDS spectrum of Cs3Bi2Br9.
FIG. 7:image showing the I-V characteristics of the Cs3Bi2Br9.
FIG. 8: image showing voltage and current obtained with different RH.
FIG. 9: image showing periodically changed relative humidity from 11% to 85 % with corresponding open circuit voltage.
FIG.10A: shows Nyquist plot at 11% & 85% RH.
FIG. 10B: shows11 % RH Nyquist plot with equivalent circuit.
FIG. 10C: shows 85 % RH Nyquist plot with equivalent circuit.
FIG. 10D: shows ionic conductivity in different RH.
FIG. 11: shows stability analysis of the fabricated ionovoltaic device.
DETAILED DESCRIPTION OF THE EMBODIMENTS
While the invention has been disclosed with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt to a particular situation or material to the teachings of the invention without departing from its scope.
Throughout the specification and claims, the following terms take the meanings explicitly associated herein unless the context clearly dictates otherwise. The meaning of "a", "an", and "the" include plural references. The meaning of "in" includes "in" and "on." Referring to the drawings, like numbers indicate like parts throughout the views. Additionally, a reference to the singular includes a reference to the plural unless otherwise stated or inconsistent with the disclosure herein.
Although the detailed description contains many specifics, these should not be construed as limiting the scope of the invention but merely as illustrating different examples and aspects of the invention. It should be appreciated that the scope of the invention includes other embodiments not discussed herein. Various other modifications, changes and variations which will be apparent to those skilled in the art may be made in the arrangement, operation and details of the system and method of the present invention disclosed herein without departing from the scope of the invention as described here and as set forth in the claims attached herewith.
The present subject matter discloses a lead free perovskite based ionovoltaicdevice which generate electricity through moisture absorption, as further disclosed with reference to the drawings. In various embodiments, synthesis of a lead free perovskite nanosheets using solution processing method is disclosed. In various embodiments, a method of fabricating a lead free perovskite based ionovoltaic device to generate voltage and current is disclosed.
A schematic representation of lead free perovskite based ionovoltaic device is illustrated in FIG. 1A, according to one embodiment of the present subject matter. The lead free perovskite based ionovoltaic device 100 includes a glass substrate 101, an FTO layer 102, and an active region 103. In various embodiments, the FTO layer 102 is etched in a middle portion and coated with a lead free perovskite nanosheets102.
In various embodiments, the lead free perovskite based ionovoltaic device 100 includes the glass substrate 101 having a top end and a bottom end. In various embodiments, the substrate 101 surface is coated with the FTO layer 102. In one embodiment, the FTO layer 102 is etched in the middle portion to form a top electrode 102a and a bottom electrode 102b at both the ends ofthe substrate 101. In various embodiments, the space between the electrodes102a, 102b forms an active region 103 on the substrate 101.
In one embodiment, the perovskite nanocrystal 104 is drop casted on the active region 103 of the substrate 101. The perovskite nanocrystal 104 is configured to absorb moisture 105 from the surrounding environment.
In various embodiments, the device 100on exposure to moisture produces high voltage and high current between the electrodes 102a, 102b, without any external energy such as light, heat or wind being applied.In various embodiments, interaction between theperovskite nanocrystal 104and the moisture 105 creates an electric double layer at theperovskite nanocrystal -moisture interface to generate electricity thereby.
In various embodiments, the perovskite nanocrystal 104coated in the active region 103 is having general formula A3B2X9 wherein A is cesium, B is one of bismuth or antimony and X is selected from chlorine, bromine or iodine.In various embodiments, the perovskite nanocrystal 104 is Cs3Bi2Br9 and the XRD pattern of the perovskite nanocrystal 104 is revealed. The perovskite nanocrystal 104 have main peak along the (022) plane was observed at 31.600.
In various embodiments, interaction of Cs3Bi2Br9 crystalswith moisture,generates free Cs+ and Br- ions. The mobility of these ions influences their speed in reaching the grain boundary, with one of the ions arriving faster due to its higher mobility. To maintain charge balance, opposite ions from adjacent grains migrate towards the other side of the grain boundary. This process forms an electrical double layer on the grain boundary with positive charges on one grain and negative charges on the other. The current persists until ions move sufficiently to establish an electrical double-layer around the grain boundaries. The presence of water molecules derived from moisture reduces the energy barrier associated with ion transport, enhancing ionic mobility, and contributing to the overall efficiency of the device100.
In one embodiment, the device 100 is configured to produce voltages in the range of 0.2V to 0.3V. In various embodiments, the device 100 is configured to generate currents in 25µA or more from single device 100 without applying any voltage.
In various embodiments, the distance between the top and bottom electrode 102a,102b ranges from 1 to 5 mm.
In various embodiment, a solution processing method 200 for the synthesis of Cs3Bi2Br9crystals are disclosed. A flow diagram of a method of synthesis of Cs3Bi2Br9is illustrated in FIG. 1B, according to one embodiment of the present subject matter. The method in step 201 includes mixing powders of CsBr and BiBr3 in a stoichiometric ratio of 3:1with DMF to obtain a yellow-green solution. Step 202 includesstirring the obtained solution in step 201 at 70o C for 1 hour to form Cs3Bi2Br9 precipitate. In various embodiment, step 203 includesplacing the Cs3Bi2Br9precipitate for centrifugation at 8000rpm for 10 minutes to form Cs3Bi2Br9 powder. This is followed by step 204of drying the obtained Cs3Bi2Br9 powder in a vacuum oven at 80oC for 12 hours to form Cs3Bi2Br9crystals.
In another embodiment, a method 300 for moisture induced power generation usinglead free perovskite based ionovoltaic device 100is disclosed. A flow diagram of a method of fabricating the lead free perovskite based ionovoltaic device 100to generate voltage and current is illustrated in FIG. 1C, according to one embodiment of the present subject matter. The method in step 301 includes providing FTO coated 102 glass substrate 101 having a top end and a bottom end pre-treated. Step 302 includes cleaning the substrate101 with a soap solution followed by rinsing with double distilled water, ethanol, acetone, methanol and isopropyl alcohol. In various embodiments, step 303 includes etching the substrate 101 in a middle portion to an optimal distance thereby forming a top electrode102a and a bottom electrode 102b at both the ends and an active region 103in the middle portion thereof. In step 304, a perovskite nanocrystal 104 is drop casted on the active region 103 of the substrate 101 to form an ionovoltaic device100. In step 305, the device 100 is sealedin a beaker containing a salt solution for moisture induced power generation. In step 306, the device is exposed to varying relative humidity which causes absorption of water molecules to the perovskite nanocrystal surface104. Finally, the method includes step 307 of forming anelectric double layer at perovskite-moisture interfaces, thereby generating voltage and causing flow of current across the electrodes of the device 100.
In various embodiment, the etching the middle portion substrate to the optimal distance is ranging from 1to 5mm.
In various embodiments, drop casting the nanocrystal 104 comprises a unique crystal structure Cs2Bi3Br9.
The ionovoltaic device 100 may generate power in a simple, efficient way withoutany external energy support. The method 300 has been experimentally validated and has demonstrated production of an extremely low cost ionovoltaic device. The interaction between the lead free perovskite and water are believed to be responsible for this performance.Thus the device of the present invention is configured to be lightweight and cost efficient.Moreover, the ionovoltaic device of the present invention is an eco-friendly alternative to conventional perovskite which contain toxic lead and thus may have higher environmental impact. Furthermore, the abundant availability of moisture in the environment, coupled with the easy processability of perovskite materials, makes the device to harvesting ambient energy.

EXAMPLES:
EXAMPLE 1: FABRICATION OF LEAD FREE PERVOSKITE BASED IONOVOLTAIC (PIV) DEVICE:
A two-dimensional perovskite microcrystal based ionovoltaic device as shown in FIG.1A was fabricated to converthumidity into electricity.
Chemicals:Cesium bromide (99%, Sigma Aldrich), bismuth (III) bromide (> 98%, Sigma Aldrich), DMF (N, N-dimethylformamide (99%, Finar), fluorine–doped tin oxide (FTO, 7 O/sq to15 O/sq, Sigma Aldrich), lithium chloride anhydrous (98% LobaChemie), magnesium chloride (98% AR, Avra), sodium chloride (98% LobaChemie) and potassium chloride 98% AR, Avra).
Synthesis of layered bismuth Cs3Bi2Br9-based perovskite material:The step wise synthesis procedure is shown in FIG. 1B. In a beaker, 1.5 mmol of CsBr (159.6 mg) and 1 mmol of BiBr3 (224.34 mg) were combined in a 3:2 stoichiometric ratio, and 6 mL of DMF was added. The solution turned yellow-green and was stirred at 70°C for 1 hour, forming Cs3Bi2Br9 precipitate. After centrifugation at 8000 rpm for 10 minutes, the powders were obtained by drying at 80°C for 12 hours.
Ionovoltaic Cs3Bi2Br9 device fabrication:The step wise fabrication procedure is shown in FIG. 1C. FTO-coated glass substrates were subjected to a 10-minute sonication in water, followed by cleaning with a soap solution and rinsing with double distilled water (DDI), ethanol, acetone, methanol, and isopropyl alcohol (IPA). For the ionovoltaic device fabrication, a 0.2cm gap was etched in the middle of the lateral device on the FTO. The solution was drop-cast on the active area (0.2cm×1.5cm=0.3cm²) of the device, which was defined by the distance between the two electrodes, i.e., the etched region in the middle. The device was sealed in a beaker containing a salt solution and exposed to various humidities using saturated solutions of 11% lithium chloride (LiCl2), 33% magnesium chloride (MgCl2), 75% sodium chloride (NaCl), and 85% potassium chloride (KCl).
EXAMPLE 2:ELEMENTAL ANALYSIS OF SYNTHESIZED Cs3Bi2Br9-BASED PEROVSKITE MATERIAL
A) X-ray diffraction (XRD) analysis:
The Cs3Bi2Br9-based perovskite material was analyzed using various techniques. X-ray diffraction (XRD) analysis was conducted using Japan's RigakuUltima 4 model, with a Cu Ka rotating anode and a wavelength of 0.15406 nm. The solution processing method was employed to synthesize the lead-free perovskite material Cs3Bi2Br9. XRD measurements shown in Fig. 2A confirms the purity and structure, align with the hexagonal perovskite structure (ICSD No.01-070-0493) in space group P-3m1 (space group number 164). The confirmation of hexagonal Cs3Bi2Br9 formation was supported by lattice constants a = 7.97Å, b=7.97 Å, and c= 9.86Å, which agreed well with a previous report. This material adopts a unique 2D layered [BiBr6]3-structure. Within the unit cell, each Cs+ group is surrounded by six halides in an octahedral structure. The main peak along the (022) plane was observed at 31.600. The crystal structure of Cs3Bi2Br9 perovskite significantly influences ion migration within ionovoltaic devices. The activation energy (EA) dictates the ease of ion movement within a solid material, and the migration rate (rm) is influenced by EA, which in turn is responsive to the crystal structure, ionic radius, ion-jumping distance, and the charge of ions. Generally, ions exhibit faster migration in crystals with more and larger available interstitial sites, smaller and less charged ions, and a smaller jumping distance11. In Cs3Bi2Br9 perovskites, Br- ions are likely the mobile ions.
B)Spectral analysis
Raman spectroscopy:
To understand the M-X vibrational mode, confocal Raman spectroscopy was performed using a 532 nm laser (WiTec alpha 300, Germany). FIG.2B shows the Raman spectroscopy of the synthesized Cs3Bi2Br9.As shown in FIG. 2B, three characteristic peaks at 85 (F2g) cm-1,133(Eg) cm-1 and 165 (A1g) cm-1 were observed. The high-intensity peak at 165 cm-1 is due to a stretching vibration of Bi-Br bonds in BiBr6 octahedral. Cs3Bi2Br9 consists of BiBr6octahedra that share corners to form layers with a corrugated structure. It is important to note that the original compound, BiBr3, shows oscillations (with a maintained mode at around 85 cm–1) despite being heavily damped. Each Raman spectrum displays dual sets of bands: a high-frequency group (? > 160 cm-1) and a low-frequency group (? < 110 cm-1). These bands are attributed to the distinctive vibrations of Bi-Br bonds within BiBr6octahedra. Regarding hexagonal Cs2Bi3Br9 with space group P-3m1, theoretical calculations by Kentsch et al. and Valakh et al. confirm the presence of nine fundamental Raman active modes (four A1g and five Eg). The molecular-like structure of BiBroctahedra suggests an intramolecular vibrational spectrum featuring five bands: 2A1g + 3Eg. Based on symmetry group analysis, it's crucial to note that only two vibrations involve Bi atoms (1A1g + 1Eg), while the remaining vibrations (1A1g + 2Eg) linked to BiBroctahedra stem solely from the movement of Br (2’) atoms, excluding Bi participation. Among these, one (1Eg) corresponds to octahedral vibrations around the x and y axes, while the other two may result from deformational vibrations of the octahedra.
UV-visible Diffuse Reflectance Spectroscopy (UVDRS)
To assess the optical properties diffuse reflectance spectroscopy (DRS) were performed using a Jasco V-750 instrument to determine the band gap of perovskite powder. FIG. 3A shows the reflectance spectra.The band gap of Cs3Bi2Br9 microcrystals was calculated using the Kubelka-Munkequation. The equation is expressed as follows,
F(R)=(1-R)^n/2R 1
Here, R represents the reflectance data. In the KM plot relation, (1-R)2 corresponds to the absorption coefficient, 2R denotes the scattering coefficient, and takes a n value of 2 or ½ for permitted direct and indirect transitions, respectively. The direct band gap of the Cs3Bi2Br9 microcrystals is determined to be 2.58Ev as shown in FIG. 3B.
XPS analysis
To confirm Cs3Bi2Br9 the presence of Cs, Bi, and Br elementsin perovskite powder X-ray photoelectron spectroscopy (XPS) measurements were conducted using a K-Alpha instrument from the PHI5000 Version probe III model, equipped with an AlKa X-ray source. A charging correction was applied, and the binding energy (BE) of the C1s core level was determined to be 284.6 eV.
XPS survey spectra of 2D bismuth halide Cs3Bi2Br9 perovskite powder confirm the presence of Cs, Bi, and Br elements, as shown in FIG.4.The chemical bonding states of Cs3Bi2Br9, specifically Cs 3d, Bi 4f, and Br 3d were studied. The core level scan of Cs 3d states reveals two binding energy peaks at 738.7 eV and 724.6 eV, corresponding to Cs 3d3/2 and Cs 3d5/2. The binding energy difference between Cs 3d peaks was 14.1 eV, consistent with the reported binding energy for Cs element. The core level scan of Bi 4f shows two prominent spin–orbit coupled peaks at 164.5 eV and ~159.1 eV, corresponding to Bi 4f5/2 and Bi 4f7/2 electronic states, respectively. The binding energy difference of 5.4 eV between these two peaks is observed. Additionally, the Br 3d5/2 at 68.53 eV and 3d3/2 at 69.3 eV,depicts an energy separation of 1.04 eV, which alignswith previously documented results. A comprehensive comparison of the Cs3Bi2Br9 data is presented in Table 1.
Table 1: XPS data of Cs3Bi2Br9 Perovskite material
Sample
Cs 3d3/2 eV
Cs 3d5/2 eV
Bi 4f7/2 eV
Bi 4f5/2 eV
Br 3d5/2 eV
Br 3d3/2 eV
Atomic %
Spin-orbit split
eV

Cs3Bi2Br9
738.8 724.8 159.2 164.5 68.5 69.6 Br3d- 73.0
Cs3d- 15.8
Bi4f- 11.2
Cs -14
Bi - 5.3
Br -1.1

EXAMPLE 3:MORPHOLOGICAL ANALYSIS OF SYNTHESIZED Cs3Bi2Br9-BASED PEROVSKITE MATERIAL
FESEM and HRTEM analyses were conducted to characterize the morphology of the Cs3Bi2Br9 bismuth-based perovskite powders. As shown in FIG.5, the synthesized Cs3Bi2Br9 exhibits a hexagonal morphology with a particle size of 3-6 µm. The elemental composition of the prepared Cs3Bi2Br9 material was determined through EDS analysis and shown in FIG. 6. As the Cs3Bi2Br9 phase has fully formed, the elemental compositions exhibit a homogeneous distribution in a stoichiometric ratio, with no observed impurity elements in the EDS measurements. Additionally, the elemental mapping images revealed a uniform distribution of Cs, Bi, and Br elements, demonstrating a homogeneous and consistent coverage over the entire area of the bismuth halide perovskite.Based on TEM images, it is evident that the product exhibits a sheet-like morphology. Prior research suggests that this specific morphology boasts numerous active sites and a short diffusion length for charge carriers. The TEM data validate that the sheet-like structure of the bismuth-based perovskite plays a crucial role in enhancing ionovoltaic power generation. TEM analysis of Cs3Bi2Br9. The HRTEM analysis revealed lattice fringes with an interplanar distance value of 0.20nm for the (220) plane. The Inverse Fast Fourier-transformed (IFFT) results and the inset power spectrum showcasedSAED patterns corresponding to the zone axis [11-1] for the Br analog.
EXAMPLE 4:IONOVOLTAIC CHARACTERIZATION OF FABRICATED DEVICE
The fabricated device demonstrates a peak open-circuit voltage (Voc) of 0.257V and a short-circuit current (Isc) of 25 µA under 85% environmental relative humidity (RH) as shown in FIG. 7A. FIG. 7A, shows the current-voltage (I-V) characteristics of a lateral device utilizing Cs3Bi2Br9 under 11% and 85% relative humidity conditions in the dark. The inset zooms into the I-V curve at 11% RH, revealing a diode behavior indicative of a metal-insulator junction within the lateral device architecture. FIG. 7B shows the Isc is reliably maintained at around 25 µA when exposed to 85% RH for nearly 2 hours, even after more prolonged exposure to humidity, there were no issues related to the stability of the materials. FIG. 7C illustrates the variation in the VOC with changing humidity from 11% RH to 85% RH. The humidity-induced voltage remains stable at approximately 257 mV throughout the test duration. When the relative humidity is at 11%, Vocis around 60 mV. It's worth mentioning that the open-circuit potential between the electrodes is observed without any external electric field or mechanical energy being applied. FIG. 7D illustrates the variations in short circuit current and open circuit voltage as the humidity transitions from 11-85 % RH. The supporting information areshown FIG.8A, which presents the Vocand Isc(FIG.8B) data for2000s.

FIG.9, presents the measured voltage when subjecting the device to periodic humidity changes from 11% to 85% RH. The sustained increase in current over 30s is ascribed to the dynamic water adsorption process, reaching equilibrium with desorption. As shown in FIG. 9, exposure to 85% RH yields an immediate voltage of 0.25V, while removal from this humidity level results in a relatively gradual voltage reduction.
Comparison of other Ionovoltaic and hydrovoltaic devices with PIV(this work):Though there is no previously reported work on moisture induced power generation using lead free perovskite,here some comparisons were tabulated with previously reported power generating devices.The comparison data is shown in Table 2.
Table 2: Comparison ofExisting art With This Work
Material used Mechanism References Obtained voltage/current
MA4PbBr6 Ionovoltaic electricity generation Moisture-Induced Ionovoltaic Electricity Generation by Manipulating Organic–Inorganic Hybrid Halide (https://doi.org/10.1021/acsenergylett.3c00023) 0.5 V
EOA2PbI4 Ionovoltaic electricity generation Moisturized 2-Dimensional Halide Perovskite (https://doi.org/10.1039/D3EE01765F) 0.7V
Cs0.91Rb0.09PbBr3 A Photovoltaic–Hydrovoltaic-Coupled Carbon-Based, All-Inorganic CsPbBr 3 Perovskite Solar Cell
(https://doi.org/10.1039/D3CC00431G) 0.39V/1.40 µA
Filter paper into a gold nanoparticle Gold Nanoparticle-Attached Perovskite Cs3Bi2Br9QDs/BiOBr Heterostructures for PhotoelectrochemicalBiosensing
https((https://doi.org/10.1021/acsanm.1c04493) 0.423 V/5.42 µA
Milk protein nanofibers Moisture-Enabled Hydrovoltaic Power Generation with Milk Protein Nanofibrils (https://doi.org/10.1016/j.nanoen.2022.107709) 0.65V/2.9 µA
Present work -- 0.25V/25 µA

Example- 4: PERFORMANCE ASSESSMENT OF DEVICE UNDER VARIOUS CONDITIONS
Electrical Impedance
Device impedance analysis was performed using an Origalys electrochemical workstation instrument Ionic conductivity was calculated using the Origalys instrument and electrochemical impedance spectroscopy (EIS). An impedance study was carried out in the frequency range of 1 Hz to 1000000 Hz, with a 10mV alternative signal applied in the 11 % RH and 85% RH conditions. EIS software was used to assess and measure the EIS Nyquist plot in terms of relevant equivalent circuits. Ionic conductivity (s) was computed using the formula,
s=I/RA 1
R denotes the resistance computed from Nyquist plots, I denotes the thickness of the film, and A is the area of the perovskite film.
Nyquist plots of 11 and 85 % relative humidity, measured and fitted, are depicted in FIG.10A-10C, illustrating the ionic conductivity. These plots are based on the electrochemical impedance spectroscopy (EIS). The link between ionic conductivity and relative humidity levels is depicted in this graph. The analogous circuit is displayed in the inset of FIG.10C and represents the related mechanism. The analogous circuits associated with resistor and capacitor values are in Table 3.

Table 3: Resistance and capacitance value at 11& 85 % relative humidity
RH (%) Resistance-1
(O) Capacitance-1 Resistance-2
(O) Resistance-3
(O) Capacitance-2
11% 1×106 6.03×10-10 1×106 99428 4.582×108
85% 2370 5.13×10-9

There aren’t many intrinsic dipoles of Cs3Bi2Br9 in an AC electric field, as indicated by the nearly linear Nyquist plot observed at lower relative humidity. Proton migration is restricted to a hopping mechanism by the uneven distribution of the few water molecules adsorbed onto the Cs3Bi2Br9 surface. As the relative humidity increases to 85%, it denotes the start of physisorption. Water molecules form the liquid network through hydrogen bonding, facilitating the transfer of hydrated protons between near H2O molecules to enhance conductivity further. In addition to bulk water, the device's conductivity might be influenced by the potentially dissociated free Cs+ and Br- ions. When no water molecules are present on the film surface, conductivity arises from carriers within the p-type material, possibly due to Br vacancies.Ion migration results from the ionic nature of the perovskites; the Nyquist plot shows that as humidity increases, the semicircle radius progressively shrinks, indicating a significant decrease in reactance and resistance. Ionic conductivity gradually increases with increasing RH.
STABILITY ANALYSIS
To emphasize the stability of Cs3Bi2Br9 perovskite materials stability studies were carried out and depicted in FIG. 11A-11D. Remarkably, despite exposure to high humidity, the XRD diffraction peaks of Cs3Bi2Br9 did not exhibit accelerated degradation through halide ion emission as in FIG.11A. The reduction in crystallinity suggests interactions with water molecules. However, after exposure to moisture, the intensity of the 2D peak recovered, indicating an adsorption and desorption process. To further understand the vibrational modes of the material before and after humidity exposure, we analyzed the Raman spectrum, as shown in FIG.11B. The 85 cm-1, 133 cm-1, and 165 cm-1 vibrational modes correspond well with Cs3Bi2Br9's characteristic vibrations. Notably, the surface of the Cs3Bi2Br9 perovskite-based ionovoltaic device remained unchanged after humidity cycles, as evidenced by the consistent Raman peaks of Cs3Bi2Br9 perovskites. To analyse the ionovoltaic property of the two-dimensional lead-free Cs3Bi2Br9 device by keeping the device in a vacuum desiccator for six months. The test was carried out after six months later. The resulting I-t and V-t data for this period are depicted in FIG. 11C and 11D. The figures indicate that the device continues to exhibit voltage and current even after six months. The humidity-induced voltage remains stable at approximately 70 mV throughout the test duration at 85% RH. The short-circuit current was reliably maintained at around 30 nA at 85% RH. Furthermore, the device demonstrates a long lifetime.

, Claims:We claim:
1. An ionovoltaic device (100) for moisture inducedelectricity generation, comprising:
an FTO layer (102) fabricated on a glass substrate (101) having a top end and a bottom end, the layer (102) etched in a middle portion, thereby forming a top electrode (102a) and a bottom electrode (102b) at both ends of the substrate (101),the electrodes (102a,102b) forming an active region (103) therebetween;
a lead free perovskite nanocrystal (104) coated on the active region(103) , wherein the perovskite nanocrystal (104) is configured to absorb moisture(105)and form an electric double layer at the perovskite-moisture interface, thereby generating a voltage and current flow between theelectrodes (102a,102b).

2. The ionovoltaic device (100) as claimed in claim 1, wherein the perovskite nanocrystal(104) is of general formula A3B2X9 wherein A is cesium,B is one of bismuth or antimony and X is selected from chlorine, bromine or iodine.

3. The ionovoltaic device (100) as claimed in claim 1, wherein the perovskite nanocrystal is Cs3Bi2Br9 having intense XRD peaks using Cu Karadiation at 31.600 along (022) plane, at 26oalong (003) plane and at 46oalong (220) plane.

4. The ionovoltaic device (100) as claimed in claim 1, wherein the generated voltage is in the range 0.2 to 0.3 V.

5. The ionovoltaic device (100) as claimed in claim 1, wherein the device (100) generates current of 25 µA/ sq. cm or more.

6. The ionovoltaic device (100) as claimed in claim 1, wherein the distance between the top and bottom electrode ranges from 1 to 5 mm.

7. A method (200) of synthesis of Cs3Bi2Br9, the method comprising:
mixing (201) powders of CsBr and BiBr3in a stoichiometric ratio with DMF to obtain a yellow-green solution;
stirring(202) the obtained solution at 70oC for1 hour to form Cs3Bi2Br9 precipitate;
placing(203) the precipitate for centrifugation at 8000rpm for 10 minutes to form Cs3Bi2Br9 powder.
drying (204) the obtained Cs3Bi2Br9powder in a vacuum oven at 80oC for 12 hours.

8. The method (200) as claimed in claim 7, wherein the stoichiometric ratio of CsBr and BiBr3 is 3:2.

9. A method (300) for moisture induced ionovoltaic power generation, the method comprising the steps of:
providing (301)FTO coated (102) glass substrate (101) having a top end and a bottom end;
etching(303) the substrate (101) in a middle portion to an optimal distance thereby forming a top electrode (102a) and a bottom electrode (102b) at both the ends and an active region (103) in the middle portion thereof;
drop casting(304) a Cs3Bi2Br9perovskitenanocrystal (104) on the active region (103) of the substrate(101) to form an ionovoltaic device(100);
sealing(305) the ionovoltaic device in a beaker comprising a salt solution;
exposing(306) the device to varying relative humidity causes absorption of water molecules to the perovskite nanocrystalsurface (104); and
forming (307) an electric double layer at perovskite-moisture interfaces, thereby generating voltage and causing flow of current across the electrodes of the device (100).

10. The method as claimed in claim 9, wherein the optimal distance ranges from 1 to 5mm.

Dr V. SHANKAR
IN/PA-1733
For and on behalf of the Applicants