Evaluation of Back Contact in Spray Deposited SnS Thin Film Solar Cells by Impedance Analysis

The role of back metal (M) contact in sprayed SnS thin film solar cells with a configuration Glass/F:SnO₂/In₂S₃/SnS/M (M = Graphite, Cu, Mo, and Ni) was analyzed and discussed in the present study. Impedance spectroscopy was employed by incorporating constant phase elements (CPE) in the equivalent circuit to investigate the degree of inhomogeneity associated with the heterojunction and M/SnS interfaces. A best fit to Nyquist plot revealed a CPE exponent close to unity for thermally evaporated Cu, making it an ideal back contact. The Bode phase plot also exhibited a higher degree of disorders associated with other M/SnS interfaces. The evaluation scheme is useful for other emerging solar cells developed from low cost processing schemes like spray deposition, spin coating, slurry casting, electrodeposition, etc

Facile, Noncyanide Based Etching of Spray Deposited Cu₂ZnSnS₄ Thin Films for Secondary Phase Removal

The coexistence of secondary phases in the quaternary compound kesterite Cu₂ZnSnS₄ (CZTS), a promising photovoltaic absorber, is a major problem while synthesizing under Zn or Cu rich conditions. A large variety of secondary phases, such as CuS, Cu_1.8S, Cu₂S, Cu₂SnS₃, and ZnS exist on the surface unless they are not removed by dedicated surface treatment before the annealing step. Under a carefully chosen concentrations of the starting precursors (usually, Zn-poor and Sn-rich) for spray pyrolyzed CZTS, the fraction of ZnS is minimized. However, under such growth conditions, binary Cu-sulfides become dominant. In this work, a selective noncyanide based chemical etching procedure is demonstrated prior to the deposition of the buffer layer. The absorber surface was treated with hydrogen peroxide that is known to remove Cu_1.8S, Cu₂S, and allied secondary phases to a large extent as compared to conventional KCN based techniques. By this treatment, the optical band gap is changed from 1.8 eV to most suitable 1.5 eV, which ensures improved photon absorption

Photocurrent Enhancement by a Rapid Thermal Treatment of Nanodisk-Shaped SnS Photocathodes

Photocathodes made from the earth-abundant, ecofriendly mineral tin monosulfide (SnS) can be promising candidates for p/n-type photoelectrochemical cells because they meet the strict requirements of energy band edges for each individual photoelectrode. Herein we fabricated SnS-based cell that exhibited a prolonged photocurrent for 3 h at −0.3 V vs the reversible hydrogen electrode (RHE) in a 0.1 M HCl electrolyte. An enhancement of the cathodic photocurrent from 2 to 6 mA cm^–2 is observed through a rapid thermal treatment. Mott–Schottky analysis of SnS samples revealed an anodic shift of 0.7 V in the flat band potential under light illumination. Incident photon-to-current conversion efficiency (IPCE) analysis indicates that an efficient charge transfer appropriate for solar hydrogen generation occurs at the −0.3 V vs RHE potential. This work shows that SnS is a promising material for photocathode in PEC cells and its performance can be enhanced via simple postannealing

Light-Induced All-Transparent Pyroelectric Photodetector

In this work, we demonstrate a new concept for all oxide-based transparent photodetector by employing photoinduced pyroelectric effect. Particularly, a combination of n-type ZnO and p-type NiO heterostructure is used to design a red light-driven transparent photodetector. The device shows a high transmittance (>75%) and very low absorbance in the visible region. An open-circuit voltage of 1.8 V was measured across the detector with the pulsed light illumination (λ = 650 nm, 7 mW cm^–2), which is attributed to the photoinduced pyroelectric effect. The thermometry images confirmed an increment in the surface temperature from 22.9 to 25 °C due to the illumination of pulsed 650 nm. The peak duration corresponding to pyrophototronic effect was 40 μs. This study will open a new avenue to design future advanced transparent optoelectronics devices, including solar cell, photodetectors, and transparent windows

Growth of Wafer-Scale Standing Layers of WS₂ for Self-Biased High-Speed UV–Visible–NIR Optoelectronic Devices

This work describes the wafer-scale standing growth of (002)-plane-oriented layers of WS₂ and their suitability for use in self-biased broad-band high-speed photodetection. The WS₂ layers are grown using large-scale sputtering, and the effects of the processing parameters such as the deposition temperature, deposition time, and sputtering power are studied. The structural, physical, chemical, optical, and electrical properties of the WS₂ samples are also investigated. On the basis of the broad-band light absorption and high-speed in-plane carrier transport characteristics of the WS₂ layers, a self-biased broad-band high-speed photodetector is fabricated by forming a type-II heterojunction. This WS₂/Si heterojunction is sensitive to ultraviolet, visible, and near-infrared photons and shows an ultrafast photoresponse (1.1 μs) along with an excellent responsivity (4 mA/W) and a specific detectivity (∼1.5 × 10¹⁰ Jones). A comprehensive Mott–Schottky analysis is performed to evaluate the parameters of the device, such as the frequency-dependent flat-band potential and carrier concentration. Further, the photodetection parameters of the device, such as its linear dynamic range, rising time, and falling time, are evaluated to elucidate its spectral and transient characteristics. The device exhibits remarkably improved transient and spectral photodetection performances as compared to those of photodetectors based on atomically thin WS₂ and two-dimensional materials. These results suggest that the proposed method is feasible for the manipulation of vertically standing WS₂ layers that exhibit high in-plane carrier mobility and allow for high-performance broad-band photodetection and energy device applications

Thermally Stable Silver Nanowires-Embedding Metal Oxide for Schottky Junction Solar Cells

Thermally stable silver nanowires (AgNWs)-embedding metal oxide was applied for Schottky junction solar cells without an intentional doping process in Si. A large scale (100 mm²) Schottky solar cell showed a power conversion efficiency of 6.1% under standard illumination, and 8.3% under diffused illumination conditions which is the highest efficiency for AgNWs-involved Schottky junction Si solar cells. Indium–tin–oxide (ITO)-capped AgNWs showed excellent thermal stability with no deformation at 500 °C. The top ITO layer grew in a cylindrical shape along the AgNWs, forming a teardrop shape. The design of ITO/AgNWs/ITO layers is optically beneficial because the AgNWs generate plasmonic photons, due to the AgNWs. Electrical investigations were performed by Mott–Schottky and impedance spectroscopy to reveal the formation of a single space charge region at the interface between Si and AgNWs-embedding ITO layer. We propose a route to design the thermally stable AgNWs for photoelectric device applications with investigation of the optical and electrical aspects