Vacancy defect regulation in Copper(I) thiocyanate hole selective layer for efficient and stable crystalline silicon solar cells

Recently, p-type inorganic copper-based compounds have attracted increasing interest as hole-selective layers for crystalline silicon (c-Si) heterojunction solar cells. Among them, copper(I) thiocyanate (CuSCN) has a small valence band offset with c-Si and high stability, however, it has not been explored in c-Si solar cell applications. Herein, we successfully demonstrate that solution-processed CuSCN film acts as an effective hole-selective contact layer for p-Si solar cells. Nevertheless, the p-Si/CuSCN heterostructure suffers from an unsatisfactory surface passivation and a relatively high contact resistivity originated from the uncontrollable vacancy defects in the film. The I- doping of CuSCN film (CuSCN:I-) not only suppresses the generation of SCN vacancies, but also increases the Cu vacancies, significantly improving the hole selectivity. Moreover, a better energy band alignment is formed based on CuSCN:I-/MoO3 bilayer for hole selective contact of p-Si substrate, achieving a remarkably high photoelectric conversion efficiency (PCE) of 19.42 %. The PCEs of unencapsulated p-Si/CuSCN heterojunction solar cells maintain over 92 % of the initial values under storing in air atmosphere for 1200 h or after annealing at 350 degrees C. This work highlights that CuSCN is a very promising hole selective layer with superior stability for c-Si solar cell applications.