Phenyltrimethylammonium as an Interlayer Spacer for Stable Formamidinium-Based Quasi-2D Perovskite Solar Cells

Quasi-2D perovskite materials possess great potential in improving the stability of perovskite solar cells due to their superior chemical and structural stableness compared to 3D counterparts. Here, commonly-used 3D formamidinum lead iodide (FAPbI₃) perovskite is alloyed by addition of quaternary cation phenyltrimethylammonium (PTMA) up to 33% (n = 5), which forms quasi-2D perovskite phase that acts beneficial to charge transport and stability. Since the detailed structural analyses regarding this quaternary ammonium salt is still lacking, we attempt to provide how the presence of 2D perovskite affects the crystal structure based on x-ray diffraction techniques. It is shown that PTMA cations directs FAPbI₃ to have textured orientation and reduced strains. This led to enhanced extraction of photogenerated carriers and reduced defects, making it promising material for solar cell applications. The champion device remains stable under 60 °C or 1 sun for 700 h, demonstrating its potential for optoelectronic devices requiring long-term stability.