Effect of Bulk Engineering on Energy Level Pinning and Ionic Driven Degradation Pathways for 1.72 eV Wide Bandgap Perovskite
Alena A Pakhomova, Lev O Luchnikov, Polina K Sukhorukova, Irina A Chuyko, Kirill A Bulgakov, Dmitri Yu Dorofeev, Igor A Salimon, Andrey P Morozov, Alexandra A Feklistova, Yuriy Yu Lebedinskii, Yuriy N Luponosov, Danila S SaraninAbstract
Wide-bandgap perovskites (1.6-1.8 eV) are promising top sub-cells for tandem and indoor photovoltaics, but high bromine content induces halide segregation and accelerated degradation. In this work, we systematically investigate three bulk modifiers: Ti3C2Tx (2D flakes), Methylammonium chloride (crystallization additive), and the self-assembled monolayer 4-(pyridin-4-yl)triphenylamine in CsFAPb(I-Br)3 (1.72 eV) p-i-n solar cells. Notably, Ti3C2Tx modified devices deliver a champion power conversion efficiency of 18.84 % for 1.72 eV wide-bandgap perovskites, maximizing efficiency through optimized energy-level alignment and reduced series resistance.
To address operational stability, we identified two distinct ion-migration-driven degradation pathways. Local ion interactions at the hole-transport interface causes void formation and photocurrent loss, which is effectively suppressed by methylammonium chloride. In contrast, ion accumulation at extraction interfaces primarily degrades the fill factor. By immobilizing mobile ions, the 4-(pyridin-4-yl)triphenylamine self-assembling monolayer prevents void formation, improves fill factor thermal resilience, and achieves an 80 % operational lifetime of over 800 hours under continuous stress (ISOS-L-2, 65 °C). These findings demonstrate that managing ionic dynamics and passivating traps are complementary strategies for stabilizing wide-bandgap perovskite solar cells.