Enhancing Efficiency and Stability of Inverted Flexible Perovskite Solar Cells via Multi-Functionalized Molecular Design

Inverted flexible perovskite solar cells (f-PSCs) are promising candidates for mechanical photovoltaic applications due to their ease of preparation, lightweight, and portability. However, the weak interface connections, residual strain, and the nonradiative recombination loss among adjacent layers are critical challenges that restrict f-PSCs development. To address these issues, a functionalized molecule with multiple hydrogen bond acceptors, 4-Carboxyphenylboronic acid (4-BBA), is designed in the perovskite precursor for modulating perovskite crystallization, which achieves uniform and stress-relaxation perovskite film and forms a robust bridging structure anchored at the buried interface. Theoretical calculation and experimental results show that the C═O group passivates Pb²⁺ with I⁻ vacancy defect through Lewis acid-base interactions, reducing trap-assisted recombination. Furthermore, the designed 4-BBA is preferentially deposited at the buried layer interface between the perovskite and substrate, forming hydrogen bonds with the self-assembled monolayer via B─OH bonds, creating a mechanically stable bridge between the layers. As a result, the power conversion efficiency of the champion f-PSC reached 25.30% (25.13% certified). And the f-PSC open-circuit voltage set a record of 1.21V. Importantly, the unencapsulated f-PSC using 4-BBA retains 95.3% of its original performance after 5000 cycles at a bending radius of 10mm, demonstrating extraordinary bending stability.