Interface modification of hole transport layer in tin-based halide perovskite solar cells

Abstract

PEDOT:PSS is one of the most widely used hole transport materials in tin-based perovskite solar cells. However, the acid residues in the PEDOT:PSS caused chemical/physical reactions with the ITO electrode. In this study, we utilized the [2-(3,6-dimethoxy-9H-carbazol-9-yl) ethyl] phosphonic acid (MeO-2PACz) and [4-(3,6-dimethyl-9H-carbazol-9-yl) butyl] phosphonic acid (Me-4PACz) as buffer layer between PEDOT:PSS and ITO. The charge carrier transport ability of the SAM/PEDOT:PSS layer was significantly improved compared to the pure PEDOT:PSS layer. With the SAM/PEDOT:PSS as the bottom layer, the tin-based perovskite films showed an improved morphology, suppressed Sn2+/Sn4+ oxidation, and prolonged carrier lifetime; meanwhile, the perovskite film obtained a reduced defect density, especially the deep-level defect densities. Consequently, the champion tin-based devices achieve an increase in PCE from 5.7% (control device) to 7.3% (Me-4PACz/PEDOT:PSS device), while also retaining 80% of the initial PCE after 750 hours storage in the N2 environment.