Pinhole Patching by Free Radicals for Highly Efficient Perovskite Solar Cells Fabricated in High-Moisture Environments

2-Hydroxy-2-methylpropiophenone (HMPP) and pentaerythritol triacrylate (PETA) are introduced into the perovskite layer via an antisolvent to enhance the photovoltaic performance of perovskite solar cells (PSCs) fabricated in a moisture atmosphere. Interestingly, the free radicals created from the decomposition of HMPP and PETA by irradiating UV light can effectively patch pinholes in the perovskite layer and regrow the crystal to enlarge the grain size. PETA can interact with Pb atoms via its lone pairs of electrons and forms a framework over the perovskite layer by in situ UV polymerization, resulting in a low trap-state density, high charge recombination resistance, long charge lifetime, and reduced hysteresis. Additionally, the PETA framework induces an enhanced driving force for charge separation at the heterojunction of the electron transport layer and the perovskite layer by adjusting the energy level of the perovskite. Consequently, a PSC with a silver top electrode can be fabricated under 70% RH conditions, exhibiting a high efficiency of 19.52% and good long-term stability. This enhancement surpassed most reported values in the literature for PSCs fabricated in a highly moist atmosphere.