Copper Bromide Hole Transport Layer for Stable and Efficient Perovskite Solar Cells

We demonstrate that replacing poly(3,4-ethylenedioxythiophene)-polystyrenesulfonate (PEDOT:PSS) with copper bromide (CuBr) as a hole transport layer (HTL) leads to highly efficient and stable inverted perovskite solar cells (PSCs). The CuBr-based devices showed an average power conversion efficiency (PCE) of 15.73% and a maximum PCE of 17.65%. Devices with PEDOT:PSS as the HTL had an average PCE of 10.94%. The active layer films fabricated on CuBr showed larger grain size distribution and improved crystallinity. Ultraviolet photoelectron spectroscopy and Kelvin probe force microscopy data reveal a favorable valence band alignment of CuBr with MAPbI3. We also found that CuBr-based devices exhibit a large built-in potential of 1.03 V compared to 0.77 V in PEDOT:PSS devices, which favors efficient hole extraction in the former. Compared to PEDOT:PSS, the CuBr-based PSCs also exhibited long-term stability in inert and humid environments.