Influence of Substrate Temperature on Structural and Optical Properties of Co-Evaporated Cu2SnS3/ITO Thin Films

In this study report the structural and optical properties of Copper Tin Sulfide (Cu2SnS3) thin films on indium tin oxide (ITO) substrate using co-evaporation technique. High purity of copper, tin and sulfur were taken as source materials to deposit Cu2SnS3 (CTS) thin films at different substrate temperatures (200-350 °C). Further, the effect of different substrate temperature on the crystallographic, morphological and optical properties of CTS thin films was investigated. The deposited CTS thin films shows tetragonal phase with preferential orientation along (112) plane confirmed by X-ray diffraction. Micro-Raman studies reveled the formation of CTS thin films. The surface morphology, average grain size and rms values of the deposited films are examined by Scanning electron spectroscopy (SEM) and Atomic Force Microscopy (AFM). The Energy dispersive spectroscopy (EDS) shows the presence of copper, tin and sulfur with a nearly stoichiometric ratio. The optical band gap (1.76-1.63 eV) and absorption coefficient (~105 cm-1) of the films was calculated by using UV-Vis-NIR spectroscopy. The values of refractive index, extinction coefficient and permittivity of the deposited films were calculated from the optical transmittance data.

Study of a Lead-Free Perovskite Solar Cell Using CZTS as HTL to Achieve a 20% PCE by SCAPS-1D Simulation

In this paper, a n-i-p planar heterojunction simulation of Sn-based iodide perovskite solar cell (PSC) is proposed. The solar cell structure consists of a Fluorine-doped tin oxide (FTO) substrate on which titanium oxide (TiO2) is placed; this material will act as an electron transporting layer (ETL); then, we have the tin perovskite CH3NH3SnI3 (MASnI3) which is the absorber layer and next a copper zinc and tin sulfide (CZTS) that will have the function of a hole transporting layer (HTL). This material is used due to its simple synthesis process and band tuning, in addition to presenting good electrical properties and stability; it is also a low-cost and non-toxic inorganic material. Finally, gold (Au) is placed as a back contact. The lead-free perovskite solar cell was simulated using a Solar Cell Capacitance Simulator (SCAPS-1D). The simulations were performed under AM 1.5G light illumination and focused on getting the best efficiency of the solar cell proposed. The thickness of MASnI3 and CZTS, band gap of CZTS, operating temperature in the range between 250 K and 350 K, acceptor concentration and defect density of absorber layer were the parameters optimized in the solar cell device. The simulation results indicate that absorber thicknesses of 500 nm and 300 nm for CZTS are appropriate for the solar cell. Further, when optimum values of the acceptor density (NA) and defect density (Nt), 1016 cm−3 and 1014 cm−3, respectively, were used, the best electrical values were obtained: Jsc of 31.66 mA/cm2, Voc of 0.96 V, FF of 67% and PCE of 20.28%. Due to the enhanced performance parameters, the structure of the device could be used in applications for a solar energy harvesting system.

High-detectivity tin disulfide nanowire photodetectors with manipulation of localized ferroelectric polarization field

Tin sulfide semiconductor nanowires (NWs) have been widely investigated for photodetection applications because of their good optical and electrical properties. Herein, we synthesized n-type SnS2 NWs and then fabricated SnS2 NW photodetectors with a ferroelectric polymer side-gate. The strong electric field induced by ferroelectric polymer can effectively suppress the dark current and improve the detectivity in SnS2 NW photodetectors. The photodetectors after polarization depletion exhibit a high photoconductive gain of 4.0 × 105 and a high responsivity of 2.1 × 105 A W−1. Compared with devices without polarization depletion, the detectivity of polarization-depleted photodetectors is improved by at least two orders of magnitude, and the highest detectivity is 1.3 × 1016 Jones. Further, the rise and fall time are 56 and 91 ms respectively, which are about tens of times faster than those without polarization depletion. The device also shows a good spectral response from ultraviolet to near-infrared. This study demonstrates that ferroelectric materials can enhance optoelectronic properties of low-dimensional semiconductors for high-performance photodetectors.

Advances in low-cost and nontoxic materials based solar cell devices

Photovoltaics (PV) have become increasingly popular and reached as the third-largest renewable energy source. Thin-film solar cells made from earth-abundant, inexpensive and environmentally friendly materials are needed to replace the current PV technologies whose large-scale applications are limited by material and/or resource constraints. Near optimum direct optical bandgap of 1.3 eV, high absorption coefficient (>104 cm−1), less toxic, and abundant raw resources along with considerable scalability have made tin sulfide (SnS) as a strategic choice for next-generation PVs. In this review, limitations of leading commercial PV technologies and the status of a few alternate low-cost PV materials are outlined. Recent literature on crucial physical properties of SnS thin-films and the present status of SnS thin-film-based solar cells are discussed. Deficiency and adequacy of some of the key properties of SnS including carrier mobility (μ), minority carrier lifetime (τ), and absorption coefficient (α) are discussed in comparison of existing commercial solar cell materials. Future research trends on SnS based solar cells to enhance their conversion efficiencies towards the theoretical maximum of 24% from present ~5% and its prospectus as next-generation solar cell is also discussed.