Crystal growth, defect passivation and strain release via In-situ Self-polymerization strategy enables efficient and stable perovskite solar cells

The perovskite film fabricated by the currently approbatory solution method with high temperature annealing process is inevitably accompanied by the defects and strains, which are two critical factors affecting the photovoltaic performance of perovskite solar cells (PSCs). Herein, we demonstrate an in-situ self-polymerization (ISP) strategy for high-performance PSCs by incorporating self-polymerizable n-methacrylamide (NMA) monomer additives into the perovskite film. It is revealed that NMA could not only regulate crystal growth, but also passivate grain boundary defects through its own carbonyl groups. Moreover, the self-polymerization of NMA monomer could confine the thermal-expansion of perovskite during thermal crystallization process, thereby releasing the tensile strain of perovskite film. As a result, the optimized devices achieve a champion power conversion efficiency (PCE) of 22.9%. These unencapsulated devices could maintain 91% of their initial PCE after aging 1500 h in ambient air (25 +/- 5 degrees C, 30 +/- 5% relative humidity, dark) and 85% efficiency after annealing 600 h at 65 degrees C in nitrogen atmosphere.