A.V. Moholkar

CZTS based thin film solar cells: a status review

Abstract Today’s thin film photovoltaic technologies comprising CuInS2 (CIS), CuInGaSe2 (CIGS) and CdTe rely on elements that are costly and rare in the earth’s crust (e.g. In, Ga, Te) and are toxic (e.g. Cd). Hence, in future cost reduction and increased production, using abundantly available non-toxic elements, seem to be the main issues. Cu2ZnSnS4 (CZTS), having the kesterite structure, is one of the most promising absorber layer candidates for low cost thin film solar cells, because of its suitable direct band gap between 1·4 and 1·5 eV and large absorption coefficient, over 104 cm−1. Also it is composed of earth abundant and non-toxic elements, promising price reductions in future. Recently, research in this area has gained momentum due to the desirability of producing Ga, In and Cd free absorber layers and the potential to obtain new insights. Hence, a review of recent literature is urgently warranted. The CZTS progress and present status of CZTS thin film solar cells has been reviewed, with the hope of identifying new paths for productive research.

Physical properties of sprayed antimony doped tin oxide thin films: The role of thickness

Transparent conducting antimony doped tin oxide (Sb:SnO2) thin films have been deposited onto preheated glass substrates using a spray pyrolysis technique by varying the quantity of spraying solution. The structural, morphological, X-ray photoelectron spectroscopy, optical, photoluminescence and electrical properties of these films have been studied. It is found that the films are polycrystalline in nature with a tetragonal crystal structure having orientation along the (211) and (112) planes. Polyhedrons like grains appear in the FE-SEM images. The average grain size increases with increasing spraying quantity. The compositional analysis and electronic behaviour of Sb:SnO2 thin films were studied using X-ray photoelectron spectroscopy. The binding energy of Sn3d5/2 for all samples shows the Sn4+ bonding state from SnO2. An intensive violet luminescence peak near 395 nm is observed at room temperature due to oxygen vacancies or donor levels formed by Sb5+ ions. The film deposited with 20 cc solution shows 70 % transmittance at 550 nm leading to the highest figure of merit (2.11 × 10−3Ω−1). The resistivity and carrier concentration vary over 1.22 × 10−3 to 0.89 × 10−3Ωcm and 5.19 × 1020 to 8.52 × 1020 cm−3, respectively.

Visible light catalysis of rhodamine B using nanostructured Fe2O3, TiO2 and TiO2/Fe2O3 thin films

The Fe(2)O(3), TiO(2) and TiO(2)/Fe(2)O(3) composite films are deposited using spray pyrolysis method onto glass and FTO coated substrates. The structural, morphological, optical and photocatalytic properties of Fe(2)O(3), TiO(2) and TiO(2)/Fe(2)O(3) thin films are studied. XRD analysis confirms that films are polycrystalline with rhombohedral and tetragonal crystal structures for Fe2O3 and TiO(2) respectively. The photocatalytic activity was tested for the degradation of Rhrodamine B (Rh B) in aqueous medium. The rate constant (-k) was evaluated as a function of the initial concentration of species. Substantial reduction in concentrations of organic species was observed from COD and TOC analysis. Photocatalytic degradation effect is relatively higher in case of the TiO(2)/Fe(2)O(3) than TiO(2) and Fe(2)O(3) thin film photoelectrodes in the degradation of Rh B and 98% removal efficiency of Rh B is obtained after 20min. The photocatalytic experimental results indicate that TiO(2)/α-Fe(2)O(3) photoelectrode is promising material for removing of water pollutants.

Photoelectrochemical properties of CdS sensitized ZnO nanorod arrays: Effect of nanorod length

The vertically aligned ZnO nanorod arrays were achieved from aqueous chemical route on soda lime and transparent conducting oxide coated glass substrates. The length of nanorods was varied from 1.6 μm to 4.5 μm by varying deposition time. The aspect ratio of ZnO nanorod was increased with increasing deposition time. Cadmium sulfide (CdS) nanoparticles have been subjected to self-assemble onto ZnO nanorods (ZNRs) using chemical bath deposition method. The synthesized CdS/ZnO nanorod arrays were characterized for their optical, structural, and morphological properties with UV-visible absorption spectroscopy (UV-Vis), x-ray diffraction, energy-dispersive x-ray analysis, x-ray photoelectron spectroscopy, contact angle measurement, and scanning electron microscopy. The cross-section images of the samples clearly depict different lengths of ZnO nanorods. UV-vis absorption spectrum shows the significant red shifting after covering of the CdS nanoparticles over the ZnO nanorods. The lengths of ZnO nanorod arrays ...

Photoelectrocatalytic degradation of oxalic acid using WO3 and stratified WO3/TiO2 photocatalysts under sunlight illumination.

The WO3 and stratified WO3/TiO2 thin films are successfully prepared by the spray pyrolysis method. The structural, morphological, compositional and photoelectrocatalytic properties of WO3 and stratified WO3/TiO2 thin films are studied. XRD analysis confirms that films are polycrystalline with monoclinic and tetragonal crystal structures for WO3 and TiO2 respectively. The SEM images clearly show 3D sheeted porous structure of the as-prepared TiO2 forms on WO3 in stratified WO3/TiO2 samples. The synthesized photoelectrodes was used as catalyst for photoelectrocatalytic degradation of oxalic acid in aqueous medium. The rate constant (k) was evaluated as a function of the initial concentration of species. A significant decrease in concentrations of organic species was observed from COD analysis. The photoelectrocatalytic degradation effect is relatively higher in the case of the stratified WO3/TiO2 than WO3 thin film photoelectrode in the degradation of oxalic acid and 83% removal efficiency of oxalic acid is obtained after 180min. Based on the obtained experimental data, the possible photoelectrocatalytic reaction mechanism was proposed. The photoelectrocatalytic experimental results indicate that stratified WO3/TiO2 photoelectrode is the promising material for removing of water pollutants.

Highly selective and sensitive response of 30.5 % of sprayed molybdenum trioxide (MoO3) nanobelts for nitrogen dioxide (NO2) gas detection.

The molybdenum trioxide (MoO3) thin films have been successfully deposited onto the glass substrates using chemical spray pyrolysis (CSP) deposition technique at various substrate temperatures ranging from 300°C to 450°C with an interval of 50°C. The effect of substrate temperature on the structural, morphological, optical and gas sensing properties of MoO3 thin films has been thoroughly investigated. X-ray diffraction analysis reveals that all the films have an orthorhombic crystal structure and are polycrystalline in nature. FE-SEM micrographs depict the formation of nanobelts-like morphology. AFM study reveals that the RMS surface roughness of MoO3 thin films increases from 8.6nm to 12nm with increase in substrate temperature from 300°C to 400°C and then decreases to 11.5nm for substrate temperature of 450°C. Optical results show that the band gap of MoO3 thin films decreases from 3.92eV to 3.44eV. The selectivity studies show that the gas response of various gases varies as NH3<SO2<CO2<CO<H2S<NO2. Moreover, typical MoO3 film deposited at substrate temperature of 400°C is highly selective and sensitive for detection of NO2 gas in comparison with other gases. The maximum response of 30.5 % is obtained towards 100ppm NO2 gas concentration at an operating temperature of 200°C with response and recovery times of 20s and 160s, respectively. Finally, NO2 gas sensing mechanism model based on the chemisorption process is discussed.

Photoelectrocatalytic degradation of benzoic acid using Au doped TiO2 thin films

Highly transparent pure and Au doped TiO2 thin films are successfully deposited by using simple chemical spray pyrolysis technique. The effect of Au doping onto the structural and physicochemical properties has been investigated. The PEC study shows that, both short circuit current (Isc) and open circuit voltage (Voc) are (Isc=1.81mA and Voc=890mV) relatively higher at 3at.% Au doping percentage. XRD study shows that the films are nanocrystalline in nature with tetragonal crystal structure. FESEM images show that the film surface covered with a smooth, uniform, compact and rice shaped nanoparticles. The Au doped thin films exhibit indirect band gap, decreases from 3.23 to 3.09eV with increase in Au doping. The chemical composition and valence states of pure and Au doped TiO2 films are studied by using X-ray photoelectron spectroscopy. The photocatalytic degradation effect is 49% higher in case 3at.% Au doped TiO2 than the pure TiO2 thin film photoelectrodes in the degradation of benzoic acid. It is revealed that Au doped TiO2 can be reused for five cycles of experiments without a requirement of post-treatment while the degradation efficiency was retained.

A Simple Aqueous Precursor Solution Processing of Earth-Abundant Cu2SnS3 Absorbers for Thin-Film Solar Cells

A simple and eco-friendly method of solution processing of Cu2SnS3 (CTS) absorbers using an aqueous precursor solution is presented. The precursor solution was prepared by mixing metal salts into a mixture of water and ethanol (5:1) with monoethanolamine as an additive at room temperature. Nearly carbon-free CTS films were formed by multispin coating the precursor solution and heat treating in air followed by rapid thermal annealing in S vapor atmosphere at various temperatures. Exploring the role of the annealing temperature in the phase, composition, and morphological evolution is essential for obtaining highly efficient CTS-based thin film solar cells (TFSCs). Investigations of CTS absorber layers annealed at various temperatures revealed that the annealing temperature plays an important role in further improving device properties and efficiency. A substantial improvement in device efficiency occurred only at the critical annealing temperature, which produces a compact and void-free microstructure with large grains and high crystallinity as a pure-phase absorber layer. Finally, at an annealing temperature of 600 °C, the CTS thin film exhibited structural, compositional, and microstructural isotropy by yielding a reproducible power conversion efficiency of 1.80%. Interestingly, CTS TFSCs exhibited good stability when stored in an air atmosphere without encapsulation at room temperature for 3 months, whereas the performance degraded slightly when subjected to accelerated aging at 80 °C for 100 h under normal laboratory conditions.

Superior selectivity and enhanced response characteristics of palladium sensitized vanadium pentoxide nanorods for detection of nitrogen dioxide gas

Vanadium pentoxide (V2O5) nanorods have been deposited onto the glass substrates by spraying 75ml of 30mM vanadium trichloride (VCl3) solution at optimized substrate temperature of 400°C. The XRD study confirms the formation of orthorhombic crystal structure of V2O5 nanorods. The FE-SEM micrograph shows the nanorods-like morphology of V2O5. The presence of palladium (Pd) in the Pd-sensitized V2O5 nanorods is confirmed using EDAX study. The gas sensing measurements show that the Pd-sensitized V2O5 sensing material is an outstanding candidate for nitrogen dioxide (NO2) gas detection. Obtained results demonstrate that the Pd-sensitized V2O5 nanorods show the superior selectivity for NO2 gas in comparison with other gases such as NH3, H2S, CO, CO2 and SO2 at an operating temperature of 200°C. It shows the 75% response for 100ppm NO2 gas concentration with response and recovery times of 22s and 126s, respectively. Finally, the gas sensing mechanism based on chemisorption process is proposed to illustrate how Pd nanoparticles affect the gas sensing characteristics (response and response-recovery times).

Influence of Substrate Temperature on

In this paper, nanocrystalline zinc oxide (ZnO) films are deposited onto glass substrates by a novel advanced spray pyrolysis technique, using non-aqueous zinc acetate solution. ZnO films are grown at various substrate temperatures in the range of 423-523 K, keeping the reaction chamber temperature constant. The influence of substrate temperature on film crystallinity and surface morphology electrical properties are investigated. The films are found to be polycrystalline with a wurtzite hexagonal structure. Surface morphological studies reveal columnar growth with enhanced crystallinity and lower activation energy at higher substrate temperature. The H2S gas sensing properties of ZnO films are studied as a function of substrate temperature, operating temperature, and H2S gas concentration. The film grown at a 523 K substrate temeprature exhibits maximum sensitivity (~22%) to 20-ppm H2S exposure at a 573-K working temperature and exhibits good selectivity and stability.