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 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. In an approach towards thickness reduction, numerical modelling are carried out using SCAPS software, which enables to calculate the current-voltage (J-V), power-voltage (P-V) and external quantum efficiency (EQE) output characteristics employing only 500 nm of absorber layer. The discontinuities in the material properties are assumed by modelling the interfaces at the heterojunctions, recombination and defect densities. The effects of defects states density, doping level in the CdTe active layer and external temperature were also investigated to gain a deeper understanding of how these factors can affect performances. 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.