Grain Engineering for Perovskite/Silicon Monolithic Tandem Solar Cells with Efficiency of 25.4%

Organic-inorganic halide perovskites are promising semiconductors to mate with silicon in tandem photovoltaic cells due to their solution processability and tunable complementary bandgaps. Herein, we show that a combination of two additives, MACl and MAH2PO2, in the perovskite precursor can significantly improve the grain morphology of wide-bandgap (1.64–1.70 eV) perovskite films, resulting in solar cells with increased photocurrent while reducing the open-circuit voltage deficit to 0.49–0.51 V. The addition of MACl enlarges the grain size, while MAH2PO2 reduces non-radiative recombination through passivation of the perovskite grain boundaries, with good synergy of functions from MACl and MAH2PO2. Matching the photocurrent between the two sub-cells in a perovskite/silicon monolithic tandem solar cell by using a bandgap of 1.64 eV for the top cell results in a high tandem Voc of 1.80 V and improved power conversion efficiency of 25.4%.