Solution-processed inorganic copper(i) thiocyanate (CuSCN) hole transporting layers for efficient p–i–n perovskite solar cells

Abstract

CuSCN is a highly transparent, highly stable, low cost and easy to solution process HTL that is proposed as a low cost replacement to existing organic and inorganic metal oxide hole transporting materials. Here, we demonstrate hybrid organic–inorganic perovskite-based p–i–n planar heterojunction solar cells using a solution-processed copper(I) thiocyanate (CuSCN) bottom hole transporting layer (HTL). CuSCN, with its high work function, increases the open circuit voltage (V_oc) by 0.23 V to 1.06 V as compared with devices based on the well-known poly(3,4-ethylenedioxythiophene) : poly(styrenesulfonate) (PEDOT : PSS) (0.83 V), resulting in a superior power conversion efficiency (PCE) of 10.8% without any notable hysteresis. Photoluminescence measurements suggest a similar charge transfer efficiency at the HTL/perovskite interface to PEDOT : PSS. However, we observe more efficient light harvesting in the presence of CuSCN at shorter wavelengths despite PEDOT : PSS being more transparent. Further investigation of the microstructure and morphology reveals differences in the crystallographic texture of the polycrystalline perovskite film, suggesting templated perovskite growth on the surface of CuSCN. The successful demonstration of the solution-processed inorganic HTL using simple and low temperature processing routes bodes well for the development of reliable and efficient flexible p–i–n perovskite modules or for integration as a front cell in hybrid tandem solar cells.