Organizing Uniform Phase Distribution in Methylammonium-Free 1.77 eV Wide-Bandgap Inverted Perovskite Solar Cells

Disordered crystallization and poor phase stability of mixed halide perovskite films are still the main factors that compromise the performance of inverted wide bandgap (WBG; 1.77 eV) perovskite solar cells (PSCs). Great difficulties are evidenced due to the very different crystallization rates between I- and Br-based perovskite components through DMSO-alone assisted anti-solvent process. Here, a zwitterionic additive strategy is reported for finely regulating the crystal growth of Cs(0.2)FA(0.8)Pb(I0.6Br0.4)(3), thereby obtaining high-performance PSCs. The aminoethanesulfonic acid (AESA) is introduced to form hydrogen bonds and strong Pb-O bonds with perovskite precursors, realizing the complete coordination with both the organic (FAI) and inorganic (CsI, PbI2, PbBr2) components, balancing their complexation effects, and realizing AESA-guided fast nucleation and retarded crystallization processes. This treatment substantially promotes homogeneous crystal growth of I- and Br-based perovskite components. Besides, this uniformly distributed AESA passivates the defects and inhibits the photo-induced halide segregation effectively. This strategy generates a record efficiency of 19.66%, with a V-oc of 1.25 V and FF of 83.7% for an MA-free WBG p-i-n device at 1.77 eV. The unencapsulated devices display impressive humidity stability at 30 +/- 5% RH for 1000 h and much improved continuous operation stability at MPP for 300 h.

Automated summary

A strategy of introducing a synthetic additive is reported to improve the performance of mixed halide perovskite solar cells, including inverted wide bandgap (1.77 eV) perovskite solar cells. This strategy enables fine regulation of crystal growth and retarded crystallization of Cs(0.2)FA(0.8)Pb(I0.6Br0.4)(3), improving its crystallinity and phase stability. The treatment promotes homogeneous crystal growth and stabilizes the crystal structure to prevent defects and halide segregation.