Multifunctional Additives Suppressed Phase Segregation of Wide-Bandgap Perovskites for Semitransparent Solar Cells

Metal halide perovskite with a bandgap of ~ 1.68 eV attracts increasing attention due to its crucial role in tandem solar cells. This perovskite is commonly fabricated by incorporating Br^- and Cs⁺ into I-based perovskites. However, the mismatch in ionic radii among these constituent ions perturbs the crystallization kinetics and lattice stability, often resulting in perovskite films with reduced grain sizes, elevated defect densities, inefficient carrier transport, and pronounced photo-induced phase segregation, ultimately compromising device efficiency and operational stability. Herein, we design a targeted multifunctional molecule, (S)-methyl 2-amino-3-(3,4-dihydroxyphenyl)propanoate hydrochloride (DMECl), incorporating ester, amino, and catechol moieties. These functional groups enable coordination with undercoordinated Pb²⁺ and hydrogen bonding with I^- and FA⁺, thereby regulating perovskite crystallization, reducing defect density, and suppressing phase segregation. This strategy enables semi-transparent perovskite solar cells to deliver a power conversion efficiency of 19.7% with enhanced operational stability, retaining over 85% of the initial efficiency after 1000 hr of maximum power point tracking. When integrated into two terminal monolithic perovskite-silicon tandem solar cells, the DMECl strategy further enables an efficiency of 29%.