Abstract

Abstract C 60 is a widely used electron selective material for p–i–n perovskite cells, however, its energy level does not match well with that of a wide‐bandgap perovskite, resulting in low open‐circuit voltage (V OC ) and fill factor ( FF ). To overcome this issue, ultra‐thin LiF has been widely used as an interlayer between C 60 and perovskite layers facilitating efficient electron extraction but resulting in instability. In this work, the use of a piperidinium bromide (PpBr) is reported as an interlayer between C 60 and perovskite, and the interlayer further is optimized by introducing an additional oxygen atom on the opposite side of the NH 2 + . This results in morpholinium bromide (MLBr) with increased dipole moment. Because of this, MLBr is highly effective in minimizing the energy band mismatch between perovskite and C 60 layer for electron extraction while at the same time passivating defects. The champion single junction 1.67 eV MLBr solar cell produced a PCE of 21.9% and the champion monolithic MLBr perovskite‐Si tandem cell produced a PCE of 28.8%. Most importantly, both encapsulated MLBr and PpBr devices retain over 97% of their initial efficiency after 400 thermal cycles (between −40 and 85 °C), twice the number of cycles specified by the International Electrotechnical Commission (IEC) 61215 photovoltaic module standard.