Efficient bifacial semi-transparent perovskite solar cells via a dimethylformamide-free solvent and bandgap engineering strategy

Semi-transparent perovskite solar cells (ST-PSCs) featuring high performance and light transmittance are highly desirable for building integrated photovoltaic (BIPV) applications. However, it is challenging to balance the device efficiency and transmittance due to the trade-off between light-harvesting capability and transparency of the perovskite active layer. Herein, we demonstrate a simple solvent- and bandgap-engineering strategy to effectively enhance film transparency of (FAPbI₃)_0.85(MAPbBr₃)_0.15 perovskite while simultaneously preserving its decent light-harvesting capability. N-methyl-2-pyrrolidone (NMP) as the solvent of the perovskite precursor effectively confines the growth of perovskite grains, leading to reduced light-scattering and enhanced average visible transparency (AVT) of the perovskite layer (over 28 %). Meanwhile, the NMP solvent promotes the growth of highly crystalline perovskite films with excellent light-harvesting capability, largely benefiting from stable intermediate adducts due to its intrinsic nature as a coordinative Lewis base. Further bandgap engineering of the perovskite light adsorber (1.6 eV) leads to the design of highly efficient bifacial ST-PSCs, achieving a power conversion efficiency of 15.58 % when illuminated from the conductive glass side and 9.67 % from the top electrode side, both under 1 sun illumination. The best-performing devices also show great promise for indoor applications with an efficiency of 25 % under 1000 lux indoor light illumination.