Reducing Voltage Loss via Dipole Tuning for Electron-Transport in Efficient and Stable Perovskite-Silicon Tandem Solar Cells

Abstract

C60 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 (VOC) and fill factor (FF). To overcome this issue, ultra-thin LiF has been widely used as an interlayer between C60 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 C60 and perovskite, and the interlayer further is optimized by introducing an additional oxygen atom on the opposite side of the NH2+. 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 C60 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.