Strain Release via Glass Transition Temperature Regulation for Efficient and Stable Perovskite Solar Cells

Thermally induced tensile strain that remains in perovskite films after annealing is one of the key reasons for diminishing the performance and operational stability of perovskite solar cells (PSCs). Herein, a glass transition temperature (T_g) regulation (TR) strategy is developed by introducing two polymerizable monomers, 2-(N-3-Sulfopropyl-N,N-dimethyl ammonium)ethyl methacrylate (SBMA) and 2-Hydroxyethyl acrylate (HEA), into the perovskite layer. SBMA and HEA undergo in situ polymerization, which regulates the nucleation and crystal growth of the perovskite film. In addition, adjusting the ratio of SBMA and HEA to lower the T_g of the resulting polymer effectively releases the strain in the perovskite film. The modified film exhibits significantly reduced tensile strain, decreased trap density and improved stability. As a result, the optimized PSCs achieve a champion power conversion efficiency (PCE) of 26.15% (certified as 25.59%). Furthermore, the encapsulated device demonstrates prominent enhanced operation stability, maintaining 90.3% of its initial efficiency after 500 h of continuous sunlight exposure.