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.