High‐Efficiency (21.4%) Carbon Perovskite Solar Cells via Cathode Interface Engineering by using CuPc Hole‐Transporting Layers

Carbon perovskite solar cells (C‐PSCs) represent a promising photovoltaic technology that addresses the long‐term operating stability needed to compete with commercial Si solar cells. However, the poor interface contacts between the carbon electrode and the perovskite result in a gap between C‐PSC's performances and state‐of‐the‐art PSCs based on metallic back electrodes. In this work, Cu (II) phthalocyanine (CuPc) was rediscovered as an effective hole‐transporting material (HTM) to be coupled with carbon electrodes. In particular, based on computional studies and VASP calculations, it is found that the tetragonal structure of CuPc could efficiently coordinated to perovskite layer via N and Cu atoms to Pb and I atoms, respectively. By systematically optimizing the concentration of the CuPc HTL solution, and screening the coupling of CuPc HTL with two types of carbon electrodes, based on carbon black:graphite mixture and reduced graphene oxide, respectively, a maximum power conversion efficiency of 21.4% has been achieved. In addition, our cells demonstrate satisfactory stability under thermal ageing at 85°C; 20% PCE loss after more than 200 h and shelf‐life ageing 20 days with 1.3% PCE loss in ambient conditions (ISOS‐D‐1). These findings are interesting in developing commercially competitive C‐PSCs, as they combine both high PCE and stability.