Ultraviolet‐Resistant Flexible Perovskite Solar Cells with Enhanced Efficiency Through Attachable Nanophotonic Downshifting and Light Trapping

Abstract Despite the many promising properties of perovskite solar cells (PSCs), ultraviolet (UV)‐induced degradation remains a critical issue for their long‐term reliability. One potential solution is the selective inhibition of UV exposure before it reaches the PSCs; however, this approach leads to a reduction in PSC efficiency due to limited photon utilization. In this regard, here a universally applicable method is presented to address the UV stability issue of PSCs without compromising their high‐level efficiency while also providing device flexibility. A UV‐absorbing colorless polyimide (CPI) substrate serves as a flexible protective shield against UV illumination. The photocurrent loss in CPI‐based PSCs is mitigated by a nanostructured photonic sticker that incorporates a UV‐to‐visible downshifting medium, which can be easily integrated with the fabricated PSC substrate. Through the combined effects of downshifting and synergistic light trapping, the efficiency of UV‐resistant CPI‐based PSCs is improved from 18.6% to 20.4%, making it comparable to the performance of UV‐damageable glass‐based PSCs. Together with numerical modeling, various experimental characterizations of optical and photovoltaic properties, as well as stability assessments under UV, bending, and off‐normal incidence conditions, provide insights into the underlying physical phenomena and optimal design considerations for successful application.