Sweet Zwitterionic Aspartame for High‐Performance Wide‐Bandgap Perovskite Solar Cells and Tandem Devices

Abstract The development of high‐quality wide‐bandgap (WBG) perovskite films is essential for achieving high‐efficiency and stable tandem solar cells (TSCs). However, WBG perovskites often suffer from high trap‐state densities and significant non‐radiative recombination, leading to substantial voltage losses. To address these challenges, aspartame (ASP), a food sweetener, is designed to serve as a multifunctional additive to regulate the microstructure of the precursor solution and optimize the crystallization dynamics, enabling the fabrication of high‐quality perovskite films. The resulting films exhibit reduced defect density and enhanced charge extraction properties. Consequently, single‐junction perovskite solar cells (PSCs) with a bandgap of 1.67 eV achieve power conversion efficiency (PCE) as high as 23.20%, while perovskite/Si TSCs reach PCE as high as 30.68%. Furthermore, the ASP‐treated devices exhibit enhanced photostability and operational durability, retaining 95% of their initial PCE after 1900 h in ambient conditions. This work demonstrates the potential of molecular engineering through zwitterionic additives to optimize the optoelectronic properties and stability of WBG perovskite films, paving the way for high‐performance TSCs.