EFFICIENCY ENHANCEMENT OF CD-FREE BUFFER LAYERS on CZTS SOLAR CELL WITH BSF MATERIALS USING WxAMPS

Abstract

CuZnSnS4 (CZTS) is non-toxic earth abundant material and a promising quaternary semiconductor compound of group 1-11-IV-VI having kesterite symmetrical structure. Due to its optimum direct band gap, it has been considered suitable material for absorber layer for photovoltaic solar cell applications. CdS is a toxic material, besides this it is not environment friendly. CdS is used as buffer layer in the CZTS solar cell. This thesis paper presents numerical modeling of experimentally designed bufferless CZTS solar cell by applying CZTSe, ZnTe, Sb2Te3 and SnS as back surface field (BSF) layer individually. Back Surface Field becomes more and more interesting in order to decrease the back surface recombination velocity and to increase collection efficiency. In comparison of the conventional device, the device with back surface field layer gives much greater output voltage. Rollover effect can be overcome by using proper BSF layer and also decreases the barrier height of the back contact and reduces the recombination loss of minority carrier at the back contact. In this work I reproduced results for experimentally designed CZTS solar cell in wxAMPS software. From the ZnO/CdS /CZTS simulative results, it is found that by optimization of the considered structure, optimized value of CZTS, CdS and ZnO thicknesses is 2um, 50 nm and .1um; doping concentration of CZTS layer is 2e14 and an improvement of the resulting efficiency which, respectively increases from 10% to 30.29% (30.39 is the maximum efficiency at 300 K) has been obtained. Using CZTSe BSF with CdS buffer layer CZTS solar cell has maximum 31.37% efficiency at 300 K temperature. Among bufferless CZTS solar cells with BSF, ZnTe BSF has maximum efficiency (33.55%) at 300 K temperature. CZTSe and Sb2Te3 has 33.51% and 33.54% efficiency respectively at 300 K. SnS has the lowest efficiency (30.36%). Bufferless CZTS solar cell with BSF has greater efficiency than CZTS solar cell with CdS buffer layer. Increasing temperature of CZTS solar cell decreases efficiency. Cadmium free bufferless CZTS solar cell with BSF can be a significant solar cell because it has greater efficiency than CdS buffer layer solar cell.