Reducing UV-Driven Degradation of p-i-n Perovskite Solar Cells Using Strong-Bonding Hole Transport Layers

Promising durability and efficiency have been demonstrated for perovskite solar cells in indoor testing^(<i>1</i>), but outdoor durability to date has been inadequate for commercialization, and the underlying mechanisms for degradation are not clear. Here we report degradation mechanisms of p-i-n structured perovskite solar cells under unfiltered sunlight in comparison with widely used light emitting diodes. The weak chemical bonding between perovskites and polymer hole transport materials (HTMs) and transparent conducting oxides (TCOs) are found to dominate the accelerated A-site cation migration and thus the degradation of perovskite solar cells under sunlight with strong ultraviolet components^(<i>2</i>), instead of the direct degradation of HTMs. An aromatic phosphonic acid, [2-(9-ethyl-9H-carbazol-3-yl)ethyl]phosphonic acid (EtCz3EPA), synthesized as part of this work enhances the bonding at the perovskite/HTM/TCO region with phosphonic acid group bonded to TCOs and nitrogen group interacting with lead in perovskites. A hybrid HTM of EtCz3EPA with strong hole extraction polymers retained high efficiency and improved the UV stability of perovskite devices. The champion perovskite minimodule with the hybrid HTM, independently measured by Perovskite PV Accelerator for Commercializing Technologies (PACT) center, has retained operational efficiency over 16% after 29 weeks of outdoor testing.<br/><br/><b>References</b><br/>1. C. Fei<i> et al.</i>, Lead-chelating hole-transport layers for efficient and stable perovskite minimodules. <i>Science</i> <b>380</b>, 823-829 (2023).<br/>2. C. Fei<i> et al.</i>, Strong-bonding hole-transport layers reduce ultraviolet degradation of perovskite solar cells. <i>Science</i> <b>384</b>, 1126-1134 (2024).