Effect of CdS and CdSe pre-treatment on interdiffusion with CdTe in CdS/CdTe and CdSe/CdTe heterostructures

Abstract

High efficiency CdTe solar cell structure has the configuration of CdS/CdSe/CdTe. Depending on the deposition and post deposition techniques employed, this stack is often subjected to high temperatures, often in presence of CdCl2, which leads to various degrees of interdiffusion at the CdS/CdSe and CdSe/CdTe interfaces. Such interdiffusion greatly influences device performance. Therefore, understanding and controlling these interdiffusion processes are important. In this contribution, interdiffusion between CdS-CdTe and CdSe-CdTe pairs were studied using CdS/CdTe and CdSe/CdTe stacks annealed at 673 K. Effect of pre-treating the CdS and CdSe layers with CdCl2 before the CdTe deposition on this interdiffusion was investigated. CdS films were grown by CBD and CdSe and CdTe films were vacuum evaporated. CdTe thickness was intentionally kept at the low 150–200 nm range to more easily identify alloy phases formed. GA-XRD measurements demonstrated that in absence of any CdCl2 pre-treatment, there was more interdiffusion between CdSe and CdTe compared to CdS and CdTe. In all cases CdCl2 pre-treatment of CdS or CdSe before the deposition of the CdTe film was found to reduce diffusion of S and Se into CdTe.