Minimizing the VOC deficit by regulating facets of wide-bandgap perovskite for monolithic perovskite/silicon tandem solar cells

Perovskite/silicon tandem solar cells have recently exceeded the Shockley–Queisser efficiency limit for single-junction photovoltaics. Further minimizing the loss of open-circuit voltage ( V OC ) in wide-bandgap perovskite sub-cells is crucial for realizing the full potential of tandem devices. In this study, the plant growth regulator Forchlorfenuron (CPPU) is introduced to dynamically regulate the crystallization of wide-bandgap perovskite. The selective adsorption between CPPU with lead halide and dimethylsulfoxide adducts enhances 001 crystal orientation, and promotes the formation of optimum (100) facets during perovskite crystallization, which efficiently suppresses non-radiative recombination and reduces trap states in wide-bandgap perovskites. We achieve a certified steady-state efficiency of 23.46% and a high V OC of 1.295 V for 1.67 eV wide-bandgap perovskite solar cells with enhanced photo-thermal stability. The monolithic perovskite/silicon tandem device with the efficient perovskite sub-cells demonstrates a PCE of 32.17%, with a certified efficiency of 31.93% (1.00 cm 2 ). • Forchlorfenuron (CPPU) selectively adsorbs onto lead halide adducts, steering the crystallization toward perovskites with preferential (100)-oriented facets. • The 1.67 eV wide-bandgap perovskite devices achieve a certified steady-state efficiency of 23.46% and a V OC of 1.295 V. • Unencapsulated CPPU-treated devices retain 94% of their initial efficiency for over 850 h at 85 °C under MPPT in N 2 atmosphere.