Multilayers strategy with a mixed CdTe/ZnTe absorber layer for optical trapping and efficiency improvement in CdTe-based solar – SCAPS modelling

Abstract

This work is a theoretical contribution to improving the performance of CdTe-based thin-film solar cells (TFSC) by optimising the collection of photons in the absorber structure. The basic data are retrieved from experimental reference work and the reference structure is as follows: CdS/CdTe/ZnTe with an efficiency of 20.16%, where ZnTe is used as a BSF to limit backward recombination. The first approach is to incorporate a ZnTe thin layer at the CdS/CdTe heterojunction, to subdivide the CdTe active layer into two (02) sub-layers and to identify the optimum structure as a function of their position in the stack. Investigating the work function of back contact materials enables to better enhance the device′s performance and stability. To take into consideration the discontinuities in the material properties, grain boundaries and performance loss factors, the impacts of charge carrier capture cross sections, bulk and interfacial defects are investigated. SCAPS software is employed for all the numerical modelling, which enables to calculate the current-voltage (J-V), power-voltage (P-V), external quantum efficiency (EQE) and other PV parameters and to draw energy band diagram to better appraise charge carrier transportation. The doping level in the CdTe active layer, the thicknesses and external temperature are also investigated to optimize our device properties. In terms of the obtained fill factor (FF) and efficiency (PCE), the performances were improved with the following structure CdS/CdTe/ZnTe/CdTe/ZnTe, FF = 81.6% and PCE = 23.45%, with 500 nm thickness of CdTe. These results are opening a promising new perspective in high efficiency CdTe TFSC.