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

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.