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Point defect engineering in Cu2ZnSnSe4 (CZTSe) thin films is the main issue to improve its device performance. This study reveals the correlation between the reaction pathway and the point defects in the CZTSe film. The reaction pathway from a metallic precursor (Mo/Zn/Sn/Cu) to a kesterite CZTSe film is varied by changing the annealing process. The synthesized CZTSe films under different reaction pathways induce different device performances with different defect energy levels, although all CZTSe films have similar structural and optical properties (Eg ∼ 1.0 eV). The admittance spectroscopy demonstrates the correlations between point defect types (VZn, ZnSn, ZnCu, CuZn, and VCu) and the reaction pathways for the formation of CZTSe films. The different growth rates of binary selenides, such as ZnSe and/or Sn-Se phases, during the annealing process are especially strongly related to the formation of point defects, leading to the different open-circuit voltages (396-451 mV) and fill factors (51-65%). The results of this study suggest that controlling the reaction pathway is an effective approach to adjust the formation of defects in the kesterite CZTSe film as well as to fabricate high-performance solar cell devices.

Kesterite surface properties and band alignment behavior at an absorber/buffer interface are key issues for highly efficient kesterite solar cell devices. Herein, we report new insights into surface and interface engineering and favorable band alignment of Cu2ZnSnSe4 (CZTSe)/CdS buffer in solar cells via in situ formed ZnSe nanoparticles (NPs) on the CZTSe surface. The device characteristics and junction qualities of the CZTSe solar cells with in situ formed ZnSe NPs are improved even though they have similar bulk properties to CZTSe thin films. X-ray photoelectron spectroscopy (XPS) characterization revealed a favorable conduction band offset (CBO, +0.26 eV) for CZTSe/ZnSe NPs/CdS compared to that for CZTSe/CdS (+0.01 eV) and CZTSe/ZnSe layer/CdS (+0.976 eV), respectively. In this regard, we also postulated a formation mechanism for in situ formed ZnSe NPs on the CZTSe surface via annealing of metallic precursors with different stacking orders. This work offers a simple and source-free interface engineering strategy using in situ formed ZnSe NPs (secondary phase) on the CZTSe surface to further improve the performance of kesterite solar cell devices.

Polyaniline (PANI) nanofibers have been synthesized by in-&!blank;situ chemical oxidative polymerization of aniline monomer. The synthesized nanofibrous PANI was deposited as a thin film on a glass substrate by using dip-coating technique. The deposited thin films of PANI were characterized for their structural, morphological, and compositional studies using x-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), and x-ray photoelectron spectroscopy (XPS). The XRD patterns reveal the amorphous nature of deposited PANI thin films. FE-SEM micrographs exhibited the interconnected nanofibrous network of the PANI. TEM micrographs show the detailed structure of nanofibrous PANI having an average diameter of 45 nm and the selected-area electron diffraction (SAED) pattern reveals the amorphous nature. The prepared PANI thin films were investigated for ammonia (NH3) gas sensing performance. The possibility of PANI thin films being used as sensors was verified in terms of sensitivity, response-recovery time, selectivity, and stability by varying the NH3 gas concentration. The optimized PANI thin-film gas sensor showed a highest sensitivity of 29.30% at room temperature with stable response even after 45 days with 87% retention of stability. The gas-sensing results suggested the PANI nanofibrous sensor possess an excellent response for NH3 gas even at low concentrations of 10 ppm.

The WO3 thin films have been synthesized on to the glass substrates by a simple and easy spin coating method at different deposition cycles and their sensor responses towards various concentrations of NO2 gas were investigated. The WO3 films were spin coated at a spinning rate of 2500–3000 rpm for 5, 10 and 15 deposition cycles, respectively. Then the films were annealed at 400 °C for 1 h in a furnace. The structural, morphological, optical and electrical properties of WO3 films were studied by different characterization techniques such as X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), FT-RAMAN Spectroscopy and electrical resistivity measurements by laboratory made two probe method respectively. It reveals a spherical grain – like morphology with a pure monoclinic phase of WO3. The FT-RAMAN spectra also confirm the pure monoclinic phase of WO3. The WO3-10 film sensor exhibits maximum gas sensitivity 21.93 and 102.4% to 5 and 100 ppm NO2 at 200 °C, respectively. The WO3-10 thin film sensors is highly sensitive and selective to NO2 over other gases.

s In0.024Cd0.976O thin films were inserted between two layers of Ga0.04Zn0.96O films, in an effort to improve the electrical properties of the oxide film. The multilayer structure with an optimum InCdO layer thickness of ∼30 nm showed significantly improved electrical properties without seriously deteriorating the optical properties, with an average optical transmittance of ∼90% over the visible and the NIR range and a resistivity of 7.5 × 10−5 Ω cm. It was also observed that efficiency of the CuInGaSe solar cell devices using the Ga0.04Zn0.96O (50 nm)/In0.024Cd0.976O (30 nm)/Ga0.04Zn0.96O (50 nm) structure as the front electrode shows much higher efficiency (8.5%) than that (4.7%) of the devices with 100 nm Ga0.04Zn0.96O front electrode. This result indicates that the proposed multilayer structure would be a strong candidate for the transparent conducting electrode for the high performance optoelectronic devices.

ZnO is of great interest for large-area optoelectronic devices, e.g., flat panel displays, light-emitting diodes, transparent semiconductors, and transparent conductive oxides (TCOs) etc., owing to its good optical properties. In the present study, quaternary ZnO thin films are deposited on a soda lime glass substrate using Mg and group III elements, such as Al, Ga, and In, to enhance the optical and electrical properties. The structural, optical, and electrical properties of quaternary ZnO TCO materials are investigated for improved thin film solar cell performance. All of the films show a uniform microstructure without any void and crack and have a transmittance over 75% in the visible region. They possess comparable band gap differences. Especially, as for the optical properties, a Mg and Ga co-doped ZnO, MgGaZnO (MGZO) thin film shows a high optical band gap of 3.87 eV with a transmittance of about 90% in the visible region. In addition, the MGZO thin film shows improved electrical properties with the lowest resistivity of 3.97 × 10−4 Ωcm, higher carrier concentration of 1.11 × 1021cm−3, high mobility of 14.07 cm2V−1s−1 and lower sheet resistance of 7.39Ω/sq. Moreover, a wide band gap of 3.87 eV is obtained for MGZO thin films, and the performance of a Cu2ZnSn(S, Se)4 (CZTSSe) photovoltaic device fabricated with a MGZO TCO layer is improved owing to higher band gap and outstanding electronic properties. The improved short circuit current results in a device with a MGZO thin film with a power conversion efficiency of 8.79%.

In this work, copper indium gallium selenide (Cu(In,Ga)Se2; CIGS) absorbers were grown on polyimide (PI)/molybdenum substrates by a three-stage co-evaporation process at various temperatures, film formation was systemically studied using various advanced characterization methods such as transmission electron microscopy, micro-Raman spectroscopy, Kelvin probe force microscopy, and atom probe tomography. The CIGS films on PI were found to exhibit considerable physical and electrical variations with respect to the process temperature of three-stage co-evaporation. In particular, when the process temperature reached 400 °C, the CIGS absorber on PI began to exhibit controlled microstructure and intergrain properties. By adjusting the microstructure and intergrain properties of the absorber films by means of the process temperature of three-stage co-evaporation, flexible CIGS solar cells on PI with an efficiency of 16.7% (with anti-refection coating) were achieved.

A copper phosphide (Cu3P) thin film is synthesized on a Ni foam using a one-step electrodeposition method at room temperature and annealed at 300 °C in Ar atmosphere. The Cu3P film is amorphous and has a flat morphology with surface voids. It works as an electrocatalyst for water oxidation in an alkaline 1 M KOH electrolyte. It exhibits excellent catalytic oxygen evolution reaction with an overpotential of 310 mV, Tafel slope of 88 mV/dec, and good stability over 20 h of operation at 10 mA/cm2. The excellent OER performance is due to its large electrochemically active surface area and low charge transfer resistance at the catalyst-electrolyte interface after the annealing.

We have demonstrated that the use of a one-step sputtering process allowed for the fabrication of copper indium gallium diselenide (CIGS) thin films by RF magnetron sputtering without an additional selenization process. The CIGS thin films deposited at different substrate temperatures were synthesized on soda-lime glass (SLG) substrates using a single quaternary CIGS target. The film composition ratios of ([Cu]/[In]+[Ga]), ([Ga]/[In]+[Ga]), and ([Se]/[Cu]+[In]+[Ga]) were almost consistent with those of the sputtering target. X-ray diffraction (XRD) and Raman results showed that the crystallinity of the CIGS thin films was gradually improved as substrate temperatures increased. Transmission electron microscopy (TEM) showed that the films grown at 600 °C have a columnar structure with the grain size of ~100 nm. In addition, for the CIGS films grown at 600 °C, TEM-EDX analysis revealed that the synchronized fluctuation of the Cu and Se signals was observed in the direction of the film depth, while the In and Ga signals were constant. As a result, the CIGS solar cell made using the film showed a degraded cell efficiency of 2.5%, which might be have been caused by not only Cu-rich and Se-poor compositions but the locally unstable composition in the CIGS films fabricated by one-step sputtering.

In the field of energy conversion and storage, the cost-effective and highly active oxygen evolution reaction (OER) catalysts are in much demand. Herein, morphology dependant OER activity of Co3S4 thin film electrodes fabricated using simple and cost effective successive ionic layer adsorption and reaction (SILAR) method is demonstrated for the first time. The morphology of Co3S4 has been influenced by varying number of deposition cycles. The effect of change in morphology on the electrocatalytic properties of Co3S4 thin film electrode is studied. The OER performance of Co3S4 thin film is related to the morphology. The OER activity with an overpotential of 275 mV @10 mA cm−2 and Tafel slope of 53 mV dec−1 in 1 M KOH electrolyte is due to increased electrochemical active surface area, super-hydrophilic nature, and low electron transfer resistance of Co3S4 thin film electrode.

Atomic layer deposition (ALD) has been used to synthesize earth-abundant and non-toxic ZnSnO thin films as potential replacements for CdS buffer layers in thin-film solar cells. In this study, ALD ZnSnO films with various Zn/(Zn+Sn) ratios ranging from 0.66 to 0.96 were synthesized and their application as buffer layers in CZTSSe solar cells was investigated. The solar cells fabricated with ZnSnO buffer layers exhibit a significant improvement in short-circuit current density (Jsc) compared to the CdS-buffered reference device, primarily due to the wide band gap and high transparency of ZnSnO films. The CZTSSe/ZnSnO solar cell results also demonstrated that the device parameters, particularly the open-circuit voltage (Voc) and fill factor (FF), were significantly affected by the Zn/(Zn+Sn) ratio. A cell efficiency of 8.54% with a Voc of 0.436 V, Jsc of 32.98 mA cm−2, and FF of 0.59 was obtained with ALD ZnSnO buffer layer with an optimal Zn/(Zn+Sn) ratio of 0.76. Increasing or decreasing the Zn/(Zn+Sn) ratio leads to a gradual decrease in the FF and Voc values, which eventually deteriorates device performance. Additionally, the uniform and conformal ALD process results in superior cell-to-cell uniformity for ZnSnO-buffered devices compared to chemical-bath-deposited CdS buffer layers.

Ge-doped Cu2SnS3 (CTGS) thin films are promising photovoltaic materials for developing low-cost second-generation solar cells. The present work reported a soft-annealing process (annealing the as-deposited precursor without chalcogenide source) for fabricating CTGS solar cells, which is an efficient method to enhance the quality of CTGS thin films and show significant reforming on both as-deposited precursor and sulfurized film. The enlarged grain size and compact microstructure provide obvious evidence of improved efficiency. Further, the reduced defect density is attributed to using a 200 °C soft-annealed precursor. A clear increase in each performance parameter such as open-circuit voltage (Voc), short-circuit current density (Jsc) and fill factor (FF) is observed as the soft-annealing temperature increased from 0 °C to 200 °C, whereas a limited enhancement was found at 300 °C. The CTGS solar cell prepared using the soft-annealing process showed an efficiency of 2.66%. In comparison, an efficiency of 1.93% has been achieved in cells fabricated without this process. The improved device performance indicates that further improvement in the CTGS solar cells could be achieved by adopting the soft-annealing precursor in an environmentally friendly manner.

In this work, for the first time, we report the direct coating of ternary chalcogenide-based nanostructured Cu4SnS4 (CTS) thin film electrodes for the energy storage application. The phase purity, composition, microstructure, optical and electrical properties of the synthesized electrode are validated through comprehensive characterization techniques. In the supercapacitive application, the CTS electrode delivers an excellent performance with the maximum specific capacitance of 704 F/g, an energy density of 27.77 Wh/kg and a power density of 7.14 kW/kg in 1 M NaOH electrolyte solution. The intrinsic electrode properties such as the electronic conductivity, crystal structure and film hydrophilicity are found to be influential parameters for the obtained high performance and are studied in detail. Furthermore, the solid-state supercapacitive device fabricated using CTS electrodes and polymer gel electrolyte (PVA/NaOH) in a symmetric configuration, demonstrated the highest specific capacitance of 34.9 F/g with an energy density of 2.4 Wh/kg, a power density of 0.291 kW/kg and more than 89.9% capacitive retention. The presented work reports a simple, cost-effective, scalable and replicable approach for electrode application in supercapacitor industry.

The earth-abundant Cu based multinary chalcogenides have great interest in the field of environmentally benign thin film solar cells. Recently, Cu2FeSnS4 (CFTS), one of the important Cu based chalcogenide has drawn prime attention in research and development due to their nontoxic and earth abundant constituent elements. The optical properties of CFTS make it a suitable candidate for thin film solar cells (TFSCs). This paper provides a review on the physical and chemical synthesis of CFTS nanoparticles and thin films and focuses the current status of CFTS based TFSCs. This article begins with a description of the crystal structure of CFTS, and then discussion on various solution and vacuum based techniques used to grow nanostructures and deposit compact thin films. Further, the review will summarize photovoltaic behavior of CFTS thin films. Finally, we discussed the challenges and scope and the perspectives for further developments in the existing research on CFTS based solar cells.

Tin monosulfide (SnS) thin film is one of the most promising absorbers layer for high efficiency solar cells using low cost earth-abundant materials. To fabricate high quality SnS thin films, a simple nanoparticle based approach was employed in this work for phase pure material preparation using non-toxic solvents. Uniform SnS thin films were fabricated via a spin-coating process using phase pure SnS-ORT nanoparticle precursor solutions based on a methanol solvent, followed by post-annealing for grain growth. SnS thin film solar cells were then fabricated and their photovoltaic performance was characterized. The best SnS solar cell fabricated with the as-prepared SnS films with a band gap energy of ~1.25 eV showed a conversion efficiency of 0.12%.

Herein, we report a facile process, i.e., controlling the initial chamber pressure during the postdeposition annealing, to effectively lower the band tail states in the synthesized CZTSSe thin films. Through detailed analysis of the external quantum efficiency derivative (dEQE/dλ) and low-temperature photoluminescence (LTPL) data, we find that the band tail states are significantly influenced by the initial annealing pressure. After carefully optimizing the deposition processes and device design, we are able to synthesize kesterite CZTSSe thin films with energy differences between inflection of d(EQE)/dλ and LTPL as small as 10 meV. These kesterite CZTSSe thin films enable the fabrication of solar cells with a champion efficiency of 11.8% with a low Voc deficit of 582 mV. The results suggest that controlling the annealing process is an effective approach to reduce the band tail in kesterite CZTSSe thin films.

Recently, metal oxide semiconductor based gas sensors have been used to monitor and maintain amount of toxic gases in environment. Use of In2O3 nano/microstructures have been increased as a heterogeneous catalyst for gas sensing due to its high response, good selectivity, short response and recovery time. In the present work, synthesis of In2O3 bricks was carried by a hydrothermal method using biomolecule as green product. The effect of precursor concentrations of In2O3 thin film was studied in this particular work. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Photoluminescence (PL), scanning electron microscope (SEM), Field emission scanning electron microscope (FE-SEM) and Brunauer–Emmett–Teller (BET) analyses were used for structural, optical, morphological and surface analysis characterizations. The In2O3 thin film displays high sensitivity and selectivity due to its active sites present on sensing layer. The results assures that optimized In2O3 thin films exhibit a high response with very low response and recovery time about 600 for NO2 gas.

In this work, SnS films were obtained by the SILAR method at 25 and 50 cycles. These films were used by the first time in the photocatalysis process to produce H2 under simulated sunlight. Additionally, AuPd was deposited by physical vapor deposition method on SnS films, which served as co-catalyst to increase the photocatalytic activity of the films. Characterization was done by X-ray diffraction (XRD), where it was found that SnS crystallizes in an orthorhombic crystal structure. By scanning electron microscopy (SEM) it was appreciated a homogeneous distribution in SnS 25 cycles film, while SnS 50 cycles film showed a greater density of particles deposited on the substrate. Band gap energy (UV-vis) for SnS 25 cycles and SnS 50 cycles films were close to 2.0 and 1.25 eV, respectively. Photoluminescence (PL) analysis showed that the emission spectra intensity of films decreases due to the presence of co-catalyst because of the lower electron-hole pair recombination. Both, SnS 25 cycles and SnS 50 cycles films, were able to produce H2 under solar light simulation (91 and 32 μmol/m2 after 3-h irradiation). This activity was increased when AuPd was deposited as co-catalyst on SnS films; around 8 and 6 times, for SnS-AuPd 25 cycles and SnS-AuPd 50 cycles films, respectively (728 and 175 μmol/m2 after 3-h irradiation). Therefore, it can be assumed that AuPd co-catalyst favors the transfer charge and decrease the electron-hole pair recombination to promote and enhance the photocatalytic H2 production.

In present work, the vertically aligned NiS nano-flakes composed thin film is prepared by anionic exchange process in which hydrothermally prepared Ni(OH)2 is used as a parent thin film and Na2S as a sulfide ion source. This synthesis process produced fully transformed and shape-controlled nano-flakes of NiS from nano-flowers of Ni(OH)2. The electrochemical supercapacitor properties of NiS electrode are studied with cyclic voltammetry (CV), galvonostatic charge discharge (GCD) and electrochemical impedance spectroscopy (EIS) techniques. Highly porous surface area (85 m2/g) of NiS nano-flakes makes large material contribution in electrochemical reaction stretching specific capacitance (Cs) of 880 F/g at scan rate of 5 mV/s and 90% electrochemical stability up to 4000 CV cycles in 2 M KOH electrolyte. Further, the flexible solid-state symmetric supercapacitor device (NiS/PVA–LiClO4/NiS) has been fabricated using NiS electrodes with polyvinyl alcohol (PVA)–lithium perchlorate (LiClO4) gel electrolyte. The NiS/PVA–LiClO4/NiS device exhibits specific capacitance of 56 F/g with specific energy of 14.98 Wh/kg and excellent cycling stability after 2000 cycles. In addition, the NiS/PVA–LiClO4/NiS device demonstrates illumination of red light emitting diode (LED) for 60 s, which confirms the practical applicability of NiS/PVA–LiClO4/NiS device in energy storage.

In this study, the pulsed laser deposition technique was applied for the preparation and characterization of Cu2(ZnxMg1-x)SnS4 (CZMTS) thin films for solar cell applications. The effects of various zinc/magnesium compositional ratios on the properties of the CZMTS thin films were investigated. The field emission scanning electron microscopy studies revealed that the CZMTS thin films exhibited dense, uniform and smooth surfaces. The X-ray diffraction studies on the as-deposited and annealed CZMTS thin films showed the prominent peak from the (112) plane for kesterite phase Cu2ZnSnS4. The Raman studies on the CZMTS thin films further confirmed formation of kesterite phase and beneficial MoS2 layer. Further, the Hall measurement studies on CZMTS thin films confirmed p-type electrical conductivity behavior. The conductivity increased from 2.31 S/cm to 7.98 S/cm with increased Mg concentration. The X-ray energy dispersive spectroscopy studies revealed formation of stoichiometric thin films. The direct optical band gap for the CZMTS thin films were found to be in the range of 1.3–1.5 eV, suggesting their potential application as a low cost and earth abundant thin film solar cell absorber material.

Ge alloyed Cu 2 SnS 3 (CTGS) thin films were prepared by annealing the sputtered deposited Cu-Ge-Sn precursor films under sulfur atmosphere at different annealing temperatures. The influence of different annealing temperatures on morphological, compositional, crystal structure of CTGS thin films were investigated. It was found that the annealing temperature of 550 °C provides a favorable sulfurization environment to promote grain growth leading to a compact thin film formation. Improved performance is ascribed to high Ge contents as evidenced from X-ray fluorescence (XRF) studies. Well incorporated Ge atoms into CTS thin film can be confirmed by X-ray diffraction (XRD). X-ray photoelectron spectroscopy (XPS) study provides an evidence of existence of Ge atoms where its binding energy located at 25.78 and 26.78 eV, respectively. However, the decreased performance was found at unsuitable annealing temperatures such as 500 °C, 520 °C, 580 °C and 600 °C. Finally, with annealing temperatures of 550 °C, the best power conversion efficiency (PCE) of 2.14% was attained with an open circuit voltage ( V oc ) of 220 mV, a short circuit current density ( J sc ) of 23.74 mA/cm 2 and a fill factor ( FF ) of 41%.

Advancing the properties of selective and sensitive metal oxide based gas sensors is a challenging research topic for the detection of toxic, and pollutant gases. In the present research, we successfully deposited a three dimensional (3D) mesoporous ZnO nanostructure on a glass substrate by using a hydrothermal method, and tested the material for its gas sensing performance. These 3D mesoporous ZnO nanostructures were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and photoluminescence techniques. Gas sensing performance analysis was carried out for nitrogen dioxide (NO2) gas at different temperatures and concentrations. The 3D mesoporous ZnO nanostructure revealed excellent gas sensing performance for NO2 gas because of its large surface area. The larger surface area led to an increase in the gas sensitivity. In addition, the sensor based on the 3D mesoporous ZnO nanostructure could be used at a low operating temperature of 150 °C. This work suggests that the 3D mesoporous ZnO nanostructure is a versatile material for NO2 gas sensing applications.

Cu2SnS3 (CTS) thin film has been successfully deposited on the cost effective stainless steel substrate by simple and inexpensive chemical bath deposition method. The film is studied in term of their structural, morphological, optical and photoelectrochemical properties. The XRD study shows that CTS films consists a nanocrystalline structure with triclinic phase Raman analysis confirms the formation of CTS compound thin film. The SEM images show small crystallite grains of CTS material. The optical absorption study shows that the films have direct transitions with band gap energies of 1.35 eV. Moreover, the photoconversion efficiency of CTS thin film-based photoelectrochemical cell (PEC) is studied and found 0.12% efficiency.

The window layer is an important layer that transmits sunlight and generates electric current as the carriers move. Aluminum (Al) -doped zinc oxide (AZO) has been widely applied as the window layer in thin-film solar cells (TFSCs) owing to its favorable optoelectronic properties, as its properties can be controlled and further improved with suitable dopants. In this study, we strategically co-dope Al and fluorine (F) in ZnO thin films (FAZO) to improve the transmittance with controlled carrier concentration. To study the influence of F dopant on the structural, optical, and electrical properties of FAZO thin films, the F doping concentration is varied (0–1.5%) while keeping the Al content fixed (2%). With increasing F doping concentration, the carrier concentration, transmittance, and bandgap values increase, whereas, the sheet resistance and resistivity of the single-layer FAZO thin films decrease, compared to the reference AZO film. The addition of a small amount of F alters the surface roughness with increasing concentration. The properties of the single-layer FAZO thin films show deteriorated properties at the highest doping concentration (1.5%). Under the optimum condition of 1% F, FAZO thin films exhibit the lowest sheet resistance of 5.84 Ω/sq, in addition to the highest transmittance of 89.3% in the visible light region. Furthermore, the FAZO thin films applied in Cu2ZnSn(S,Se)4 (CZTSSe) device shows significant enhancements in the short-circuit current density (Jsc) and fill factor (FF), resulting in improved device performance from ~8 to 9.57%.

We report facile solution processing of mesoporous hematite (α-Fe2O3) thin films for high efficiency solar-driven water splitting. Fe2O3 thin films were prepared on fluorine doped tin oxide(FTO) conducting substrates by spin coating of a precursor solution followed by annealing at 550 oC for 30 min. in air ambient. Specifically, the precursor solution was prepared by dissolving non-toxic FeCl3 as an Fe source in highly versatile dimethyl sulfoxide(DMSO) as a solvent. The as-deposited and annealed thin films were characterized for their morphological, structural and optical properties using field-emission scanning electron microscopy(FE-SEM), X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS) and UV-Vis absorption spectroscopy. The photoelectrochemical performance of the precursor (α-FeOOH) and annealed (α-Fe2O3) films were characterized and it was found that the α-Fe2O3 film exhibited an increased photocurrent density of ~0.78 mA/cm2 at 1.23 V vs. RHE, which is about 3.4 times higher than that of the α-FeOOH films (0.23 mA/cm2 at 1.23 V vs. RHE). The improved performance can be attributed to the improved crystallinity and porosity of α-Fe2O3 thin films after annealing treatment at higher temperatures. Detailed electrical characterization was further carried out to elucidate the enhanced PEC performance of α-Fe2O3 thin films.

La2O3 thin films are synthesized successfully by simple microwave assisted chemical method and characterized with structural and morphological characterisation techniques. CO2 gas sensing properties of La2O3 thin films are enhanced significantly by palladium (Pd) sensitization. La2O3 thin film shows maximum sensitivity of 25% at temperature of 723 K and concentration of 400 ppm CO2 gas, which enhanced to 64% at temperature of 523 K after Pd sensitization.

We report the effects of precursor uniformity on the efficiency of Cu 2 ZnSnS x Se 4 − x (CZTSSe) solar cells using sputtered precursors. The reduction of Sn cluster agglomeration in the Cu/Sn/Zn stacked precursor created synthesis of more uniformly distributed CZTSSe absorbers during the annealing process. The secondary phase difference between the 80 W and 40 W sputtered CZTSSe absorbers was confirmed with Raman analysis at 178 cm − 1 and 259 cm − 1 . The 40 W sputtered CZTSSe cell produced blue region enhancement of external quantum efficiency results due to improvement of the pn-junction properties. The CZTSSe 40 W cells achieved a maximum power conversion efficiency of 5.7% and short-circuit current of 32.4 mA/cm 2 .

Nanostructured iron oxyhydroxide (FeOOH) thin films have been synthesized using an electrodeposition method on a nickel foam (NF) substrate and effect of air annealing temperature on the catalytic performance is studied. The as-deposited and annealed thin films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM) and linear sweep voltammetry (LSV) to determine their structural, morphological, compositional and electrochemical properties, respectively. The as-deposited nanostructured amorphous FeOOH thin film is converted into a polycrystalline Fe2O3 with hematite crystal structure at a high temperature. The FeOOH thin film acts as an efficient electrocatalyst for the oxygen evolution reaction (OER) in an alkaline 1 M KOH electrolyte. The film annealed at 200 °C shows high catalytic activity with an onset overpotential of 240 mV with a smaller Tafel slope of 48 mV/dec. Additionally, it needs an overpotential of 290 mV to the drive the current density of 10 mA/cm2 and shows good stability in the 1 M KOH electrolyte solution.

Cadmium selenide (CdSe) thin films were grown by electrochemical technique on fluorine-doped tin oxide (FTO)-coated conducting glass substrates in the presence of organic surfactants. The influence of organic surfactants like polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP) on different physico-chemical properties and its subsequent impact on photoelectrochemical (PEC) performance of CdSe thin films have been investigated. It has observed that the organic surfactants play an important role in modifying the surface morphology of CdSe thin films. The compact grain like morphology of pure CdSe is tuned to interconnected nanofibrous network on addition of PEG and to sprouting nanorods like morphology on addition of PVP. Among these nanostructures, CdSe sprouting nanorods exhibits improved power conversion efficiency of 0.55% as compared to nanofibrous (0.24%) and granular CdSe (0.16%) nanostructures. It reveals the fourfold enhancement in the PEC performance on PVP-mediated growth which can be attributed to conversion of compact dense nanostructure to porous and relatively high surface area nanostructure. This work exemplifies the ability of organic surfactant to modulate the surface morphology of the electrodeposits and pinpoints the organic surfactant that gives rise to the suitable morphology for PEC solar cell application.

Carbon dioxide gas (CO2) sensing properties of La2O3 thin films synthesized by spray pyrolysis method are reported. La2O3 thin films deposited at different substrate temperatures (573–623 K) are characterized for their structural, surface morphology, optical and electrical properties and used for CO2 gas response measurements. SEM analyses indicate porous surface morphology. The deposited La2O3 films are crystalline with pronounced orientation along (110) plane, uniform and adhere to the glass substrate. From optical absorbance studies, the optical band gap is found to be 4.2 eV. With porous surface morphology, the maximum response of 18% at 623 K substrate temperature is recorded on exposure of 350 ppm of CO2 gas.

Herein, we are exploring hydroxy functionalized ionic liquids (HFILs) as electrolytes in electrochemical studies of Fe2O3 thin films in aqueous medium. The thin films are deposited by simple and cost effective successive ionic layer adsorption and reaction (SILAR) method at room temperature. Four HFILs, [HEMIM][Cl], [TEHEA][Cl], [(EtOH)NH3][Ac] and [(EtOH)3NH][Ac] are synthesized and their aqueous solutions have been studied as electrolytes. Syntheses of ILs are confirmed by NMR spectra whereas the structural and surface properties of Fe2O3 thin film is determined by X-ray diffraction pattern (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDAX) and Brunauer–Emmett–Teller (BET) analysis. XRD pattern confirms the rhombohedral phase of α-Fe2O3 (hematite). Electrochemical performance of Fe2O3 electrode in 0.1 M HFILs is investigated with cyclic voltammetry (CV), galavanostatic charge/discharge (GCD) analysis and electrochemical impedance spectroscopy (EIS). Fe2O3 electrode exhibited good capacitive nature in all HFILs, however, [HEMIM][Cl] conferred highest specific capacitance of 124 Fg−1 at 4.0 mA cm−2 current density amongst the studied HFILs. Good cycle stability and up to 91% retention of capacitance over 1000 cycles is availed with [HEMIM][Cl]. Such promising results are strongly emphasizing the possible utilization of HFILs as environmental benign media in supercapacitor application.

In this work, the WO3 thin films were synthesized onto glass substrates at 673 K by simple and cost-effective spray pyrolysis technique for the NO2 gas sensing. Moreover, the WO3 thin film was synthesized as a function of different spray solution concentration. The structural and morphological results reveal the polycrystalline nature of WO3 thin films with pure monoclinic phase having porous fibrous reticulate morphology. The optical band gaps of WO3 thin films were observed ∼2.73 eV. Moreover, the activation energy in our WO3 sample (0.368 eV) is maximum than the theoretical value of activation energy (0.031 eV). Due to the outstanding morphology and grater activation energy, the WO3 thin films were used for NO2 gas sensing. The gas sensing properties of the thin film sensor based on WO3 thin films were studied in the range of 1–100 ppm of the NO2 at an operating temperature of 423 K (or 150 °C). The sensor exhibits better gas response around 5.75 for 5 ppm of NO2 gas as well as 84.75 for 100 ppm NO2 gas with better selectivity.

La 2 O 3 thin films are synthesized by spray pyrolysis method and decorated with palladium nanoparticles using successive ionic layer adsorption and reaction method. The structural and morphological properties of La 2 O 3 and Pd-La 2 O 3 are studied by X-ray diffraction, scanning electron microscopy, X-ray photo-electron spectroscopy and energy dispersive X-ray spectroscopy techniques. CO 2 gas sensing properties of La 2 O 3 and Pd-La 2 O 3 are investigated at different operating temperatures and CO 2 concentrations. La 2 O 3 exhibited maximum response of 13% at 523 K upon exposure of CO 2 gas (500 ppm) which is improved up to 28% after Pd decoration. Pd-La 2 O 3 film shows more selectivity towards CO 2 gas. Additionally, stability of Pd-La 2 O 3 film has been studied.

The influence of thickness on the properties of cadmium oxide thin films deposited using simple and cost-effective chemical spray pyrolysis technique is studied. The maximum film of thickness 2752 nm is achieved by tuning spraying parameters. The thickness dependent structural, morphological, and optoelectronic properties of CdO thin films have been investigated in detail. The microstructure of CdO thin films significantly changed from rough to smooth and further to rougher surface with increase in film thickness. This behavior has been further confirmed from water contact angle measurement. The optical studies show that the direct band gap energy values ranging between 2.23 and 2.46 eV. The Hall effect measurement indicates that all the films exhibit n-type semiconducting behavior with their electrical resistivity lies in the range of 12.8 × 10 − 4 to 3.7 × 10 − 4 Ω·cm. The CdO film with thickness of 1371 nm exhibited the best optoelectronics properties (transmittance of 74%, figure of merit of 18.23 × 10 − 3 (Ω) − 1 , carrier concentration of 7.30 × 10 20 /cm 3 and mobility of 23.11 cm 2 /Vs) among all the films.

Cu 2 SnS 3 (CTS) thin film solar cell with power conversion efficiency (PCE) of 2.39% is fabricated using sputtered metallic Cu/Sn stacked precursors subjected to sulfurization. The crystal structure, phase purity, atomic composition, oxidation state, external quantum efficiency, optical and electrical properties of the thin films are characterized in detail using X-ray diffraction (XRD), Raman spectroscopy, X-ray fluorescence (XRF) spectroscopy, X-ray photoelectron spectroscopy (XPS), a quantum efficiency study, UV–visible and a hall measurement system, respectively. The influence of various Cu deposition time on the structural, compositional and microstructural properties as well as on the device performance of CTS thin films are evaluated. It is found that the properties of CTS thin films are strongly dependent on the Cu deposition time during the sputtering process. The Cu deposition time is varied from 2812 s to 3212 s, and the film deposited at 2812 s showed the highest power conversion efficiency (PCE) of 2.39% with an open circuit voltage (V oc ) of 208 mV, a short circuit current density (J sc ) of 28.92 mA/cm 2 and a fill factor (FF) of 39.7%.

Ternary Cu–Sn–S system, Cu2SnS3 (CTS) thin films have been successfully deposited via successive ionic layer adsorption and reaction (SILAR) method. The effect of film thickness on the structural, morphological, wettability and optical properties of CTS material is studied. The XRD studies confirm formation of triclinic (mohite) phase of CTS material. The SEM images show that entire film surface is covered by compact nearly spherical grains over growth of spongy clusters. The Brunauer-Emmett-Teller (BET) analysis revealed that the surface area of CTS material is 2.11 m2 g−1. The wettability study indicates hydrophilic nature of CTS samples. The optical band gap is decreased from 1.36 to 0.98 eV with increase in film thickness. The photoelectrochemical (PEC) study of CTS material shows anodic photocurrent indicating P-type electrical conductivity.

The formation of secondary phases in kesterite-based solar cells plays a critical role, affecting the performances of devices primarily due to the open circuit voltage deficient characteristics. Systematic studies of the phase evolution pathways and the formation of secondary phases in kesterite thin films are desirable. In this paper, the phase evolution pathways and the formation of secondary phases in kesterite Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) thin films during thermal treatment of sputtered Cu-Sn-Zn metallic precursors have been studied using high-resolution X-ray diffraction (XRD), Raman spectroscopy, field-emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). A possible phase evolution process for the kesterite thin films is proposed based on the experimental observations. The Cu-Sn-Zn metallic precursor thin films were prepared using the sputtering technique followed by thermal treatments at different temperatures ranging from 250 °C to 580 °C in a chalcogen atmosphere. XRD and Raman characterizations of the thin films annealed under chalcogen atmospheres indicated that the precursor thin films were completely transformed to the CZTS and CZTSe kesterite phases above 500 °C. However, the TEM analysis of the thin films annealed above 450 °C revealed Cu-based secondary phases. The formation of phase pure CZTS and CZTSe kesterites was observed at annealing temperatures above 500 °C. Based on the experimental observations, the phase evolution pathways for the formation of kesterite and secondary phases from metallic precursors are proposed in this paper.

As an alternative to Cu(In,Ga)(S,Se)2 (CIGS) and Cu2ZnSn(S,Se)4 (CZTS)-based thin film solar cells (TFSCs), the ternary chalcogenide semiconductor Cu2SnS3 (CTS) is an emerging material with suitable optical band gap energy ranging from 0.93 to 1.77 eV and high absorption coefficients (>104 cm−1). In this study, we report the preparation of high-quality CTS thin films by the annealing of the sputtered Cu-Sn metallic precursor under S vapor atmosphere in a graphite box using the RTA process. Furthermore, the influence of different S vapor partial pressures in the graphite box during annealing on the properties of the CTS thin films has been investigated systematically. It is observed that the properties and photovoltaic performance of the CTS thin films are strongly dependent on the S vapor partial pressure during annealing. The monoclinic crystal structure is observed from X-ray diffraction (XRD) of the (1 1 2), (2 2 0), and (3 1 2) planes, and it is further confirmed using Raman spectroscopy by the presence of Raman peaks at 295 and 354 cm−1. The direct band gap energy is found to be 0.91 eV by extrapolation from external quantum efficiency (EQE) measurement of a CTS thin film annealed using 60 mg of S powder. The preliminary best power conversion efficiency (PCE) of 2.21% with a short circuit current density of 29.7 mA/cm2, an open circuit voltage of 179.5 mV, and a fill factor of 41% have been obtained for a CTS thin film annealed using 60 mg of S powder, although the processing parameters have not been optimized.

The possibility of using N-doping to reduce the carrier concentration of zinc oxysulfide (Zn(O,S)) thin films grown by atomic layer deposition (ALD) was investigated. The effect of N-doping on the structural, chemical, and electrical properties of the Zn(O,S) films was investigated using X-ray diffraction, X-ray photoelectron spectroscopy, and Hall measurements. The Zn(O,S) films were applied as alternative n -type buffers replacing conventional CdS for earth-abundant Cu 2 ZnSn(S,Se) 4 thin-film solar cells. With increased O/(O + S) ratio up to ∼0.87–0.90, the fabricated cells suffered severe drops in efficiency, mainly due to the increased shunt conductance coming from excessive carrier concentration of ZnO-like Zn(O,S). Recovery of the rectifying diode behavior and cell efficiency was demonstrated by applying N-doping to the conductive Zn(O,S) buffer layer, further supported by current–voltage and external quantum efficiency measurements.

In the present work, Ge doped CZTGeS thin films are pulsed laser deposited followed by annealing treatment in selenium environment. The influence of selenization condition on the structural, morphological, optical and electrical properties of the absorber thin films are investigated. The thin films characterized using X-ray diffraction (XRD) and Raman spectroscopy techniques confirm the formation of Kesterite CZTGeSSe thin film compound with dominant A1 mode vibration. The morphological and optical studies of the thin films reveal the formation of compact and void free microstructure with optimal band gap in the range of 1–1.2 eV. The impact of selenization temperature on the quality of thin films has been studied and thin film solar cells are fabricated with CZTGeSSe absorbers grown at various annealing temperatures from 525 to 575 ℃ to evaluate the performance of devices as a function of an annealing temperature. The elemental Ge and Sn losses from the absorber compound confirmed from X-ray fluorescence spectroscopy (XRF) depended on the annealing temperature and linearly increased with increasing temperature affecting the optical, compositional and microstructural properties of the thin films. Compositional non uniformity is one of the factors that limit the performance of solar cell device. PLD technique due to its advantage of achieving precise stoichiometry control combined with optimized selenization conditions can potentially address the issue. Compared to solar cell fabricated from absorber compound annealed at 525 and 575 ℃, the solar cell fabricated from the absorber annealed at 550 ℃ exhibited the best conversion efficiency of 3.82% with Voc 434 mV, Jsc 18.33 mA/cm2, FF 47.0% and retained nearly 90% power conversion efficiency (PCE) stability after time period of 60 days.

Cu 2 ZnSn(S,Se) 4 (CZTSSe) thin films with controlled composition, phase, and uniformity were fabricated by sulfo-selenization of stack layer electro-deposited Cu-Sn-Zn precursors. In order to reduce the detrimental bubble phenomenon, Triton X-100 surfactant assisted deposition of the zinc layer was conducted. The effects of Triton X-100 addition on the surface morphology, composition, and solar cell properties were investigated. The results indicated that the addition of Triton X-100 boosted the solar cell performance by many folds. Along with studying the effect of Triton X-100 addition, the composition of the film was finely controlled by varying the deposition time of the Cu layer. Cu poor and Zn rich composition with a Cu/(Zn + Sn) ratio of 0.82 was achieved. The prepared films were characterized by X-ray diffraction, scanning electron microscopy, X-ray fluorescence spectroscopy, and Raman spectroscopy to investigate the structural, morphological, and compositional properties. The highest solar cell performance of approximately 6.06% was achieved for the film in which the Cu-layer was deposited for 15 min.

Zinc oxide (ZnO) thin films have been widely used as an effective gas sensor element. In the present study, nanostructured thin films of ZnO were prepared by using the simplistic and economical successive ion layer adsorption and reaction (SILAR) technique. The effects of SILAR cycles on the structural, optical, surface morphological and electrical properties of nanostructured ZnO thin films were investigated. Characterization techniques such as XRD, UV-vis, PL, FESEM, and Hall measurement were utilized to study the physical and chemical properties of the synthesized films. XRD confirms the formation of hexagonal phase structural ZnO thin films. FE-SEM analysis reveals the formation of well-dispersed ZnO nanoparticles having sizes of ∼18–40 nm. The SILAR cycles play a key role in the synthesis of nanostructured ZnO thin films and it is found that, with increasing SILAR cycles, the grain size continues increasing. Optical studies confirm the presence of oxygen vacancies in synthesized ZnO thin films. Finally, the ZnO thin films were exposed to NO 2 gas with a concentration of 100 ppb–200 ppm and the resulting resistance transient was recorded. The nanostructured ZnO thin films synthesized at 30 SILAR cycles displays an enhancement of gas sensing performance and exhibit significantly higher responses (∼5% per ppm). Moreover, our ZnO thin-film-based gas sensor is sensitive to very low concentrations of dangerous NO 2 (100 ppb). The sensitive gas sensor used to trace level NO 2 detection, synthesized via simple SILAR route proves the novelty of our work. The present report provides a new direction in fabricating nanostructured ZnO thin films for low-cost and efficient gas sensing applications.

Present work portrays surface morphology alteration of CuS thin film with increase in reaction bath temperature. The porous nanoflowers like morphology of CuS offers higher electron transfer and shorten ion diffusion pathway, which facilitates transfer of electrolyte ions. Nanoflowers like morphology of CuS electrode exhibits specific capacitance (Cs) of 1818.2 F g−1 at scan rate of 5 mV s−1 with electrochemical cycling stability of 92%. The symmetric FSS-SCs-PVA-LiClO4 device demonstrates Cs of 172.5 F g−1, specific power density of 1750 W kg−1 and capacity retention of 93% after 2000 CV cycles. More importantly, this device glows the panel of 200 red LEDs.

In present article, temperature dependent surface morphological modification and its subsequent influence on electrochemical performance of hexagonal WO3 (h-WO3) thin films has been investigated. The nanostructured h-WO3 films are synthesized on carbon cloth substrate using simple hydrothermal method. It is observed that h-WO3 thin films prepared at temperature of 413, 433 and 453 K display nanogranule-like, nanoplate-like and nanorod-like suface morphology. The X-ray diffraction study discloses the prominent orientation along (001) and (200) planes which reveals the preferential growth direction of h-WO3 along c and a-axis, respectively. The h-WO3 film prepared at 453 K shows good surface area, pore volume and uniform pore size distribution. The electrochemical measurements exhibit high specific capacitance of 694 F g−1, energy density of 25 Wh Kg−1 and long term cycling performance (87 % capacitance retention after 2,000 cycles) for h-WO3 thin film. The results indicate that h-WO3 nanorods could be a promising electrode material for high performance energy storage devices.

Polyvinyl alcohol is used as a surfactant in the chemical bath deposition of PbS thin films, which causes compact, pinhole free and uniform PbS thin films. Influence of deposition time on the structural, optical, morphological, compositional, electro-chemical and photo-electrochemical (PEC) properties of the PbS thin films are studied. The charge transfer resistance is analysed using electrochemical impedance spectroscopy. The best PEC device fabricated using optimized deposition time (3 h) showed short circuit current density (Jsc) of 1.68 mA. After annealing the optimised P63 sample at 75 °C for 1.5 h the composition changed from Pb rich to near stoichiometric. For typical PA sample Jsc improves to 2.13 mA and photo conversion efficiency advances from 0.045 to 0.072%.