Enhanced bending stability of flexible perovskite solar cells on stainless steel substrates via C60 buffer layer integration

Abstract

Flexible perovskite solar cells (PSCs) based on stainless steel (SS) substrates offer a highly promising platform for next-generation Building-Integrated Photovoltaics (BIPV) and Vehicle-Integrated Photovoltaics (VIPV), owing to their superior durability, mechanical strength, and thermal resilience. However, achieving long-term operational stability under bending stress remains a significant hurdle. In this work, we identify fractures in the TiO₂ electron transport layer as the dominant source of performance degradation under mechanical deformation. To address this issue, we introduce a C₆₀ buffer layer atop the TiO₂, which serves dual functions: mechanical protection and enhanced interfacial charge extraction. The C₆₀ layer functions by redistributing strain through a shift of the neutral axis closer to the TiO₂ layer and by passivating interfacial trap states, as confirmed by SEM, AFM, PL, TRPL, and EIS analyses. As a result, SS-based PSCs with an optimized 20 nm C₆₀ layer demonstrate a remarkable ∼5% increase in PCE before bending and an ∼92.84% improvement in PCE retention after bending, compared to control devices. Furthermore, devices maintained superior performance over 100 bending cycles and continuous bending for 100 hours. These findings establish the C₆₀ buffer layer as a powerful strategy for enabling flexible PSCs with both high efficiency and mechanical reliability, accelerating their practical deployment in BIPV and VIPV systems where mechanical stress is unavoidable.