Solution-processed copper(i) iodide via co-doping for enhanced hole selective contacts in p-type crystalline silicon solar cells

Abstract

In studies addressing contact recombination, carrier-selective contacts (CSCs) have played a key role in crystalline silicon (c-Si) solar cells resulting in a higher photoelectrical conversion efficiency (PCE). Recently, wide-bandgap metal compound materials with extreme work functions or suitable energy band alignment have drawn considerable interest for CSC materials. Among them, cuprous iodide (CuI) is a very promising hole-selective layer, however, very little research has been conducted for c-Si solar cells. In this work, we have demonstrated that solution-processed CuI films act as effective full-area hole-selective contact layers for p-Si solar cells. Moreover, iodine (I₂) doping suppresses the generation of I⁻ vacancies (V_I), and enhances the film conductivity due to an increase in copper vacancies (V_Cu). Aluminum ion (Al³⁺) doping further promotes the generation of more V_Cu and increases the work function of the CuI film. The proposed I₂ and Al³⁺ co-doping strategy for CuI films significantly improves the passivating contact performance of the Al³⁺–I₂:CuI/p-Si heterojunction, contributing to the significantly improved PCE from 15.12% to 18.28%, which is the highest for solution-processed copper-based hole transport layers for c-Si solar cells to date. The results demonstrate the great potential of the CuI hole-selective layer applied for highly efficient c-Si solar cells.