Enhancing Perovskite Stability and Crystalline Structure through Free Radical Passivation and Recrystallization under High Moisture Fabrication Conditions

Yu-She Huang, I-Ru Chen, Bo-Tau Liu National Yunlin University of Science and Technology, Douliou city, --, Taiwan

Perovskite solar cells (PSCs) stand out as a highly promising photovoltaic technology due to their straightforward manufacturing process and exceptional efficiency in converting solar energy into electricity. However, a significant challenge with perovskite crystals lies in their susceptibility to moisture, particularly during fabrication and storage. Exposure to ambient moisture can hasten crystal growth, leading to inferior morphology, incomplete surface coverage, the formation of pinholes, and a subsequent decrease in efficiency. Consequently, most reported PSCs have been manufactured within controlled environments such as gloveboxes with a nitrogen atmosphere to safeguard against moisture-induced damage. For broader commercial viability and cost-effectiveness in production, the development of a fabrication process for PSCs under ambient conditions is highly sought after. This study introduces UV curable monomers (UVMs) into the perovskite layer using an antisolvent, aiming to enhance the photovoltaic performance of PSCs produced in a moisture-rich atmosphere. Intriguingly, the free radicals generated from the breakdown of photo-initiators and monomers under UV light exposure play a pivotal role in repairing pinholes within the perovskite layer and encouraging crystal growth, thereby enlarging the grain size. This breakthrough in repairing and expanding perovskite crystals holds significant promise. The UVMs interact with Pb atoms by utilizing its lone pairs of electrons, creating a framework over the perovskite layer through in-situ UV polymerization. This process leads to a lower trap-state density, heightened resistance to charge recombination, an extended charge lifetime, and diminished hysteresis. Furthermore, the UVM framework fosters an increased driving force for charge separation at the heterojunction between the electron transport layer and the perovskite layer by adjusting the energy levels of the perovskite. As a result, a PSC featuring a silver top electrode can be fabricated under 70% relative humidity conditions, exhibiting an impressive efficiency and demonstrating long-term stability.