Efficient MA-free perovskite solar cells with balanced carrier transport achieved using 4-trifluorophenylammonium iodide

The treatment of a 3D perovskite film with 2D perovskite segments has been recognized as a promising approach to improve the device performance of perovskite solar cells (PSCs), which have received much less attention in methylammonium (MA)-free devices than that in the MA-containing counterparts. We explored a novel fluorine-containing aromatic ammonium salt, 4-trifluorophenylammonium iodide (TFPAI) to form a 2D/3D junction on top of a Cs/FA-based perovskite. It was found that the hole and electron transport were more balanced for the 2D/3D configuration than for the pristine one, leading to a boosted fill factor (FF) and decreased hysteresis in the resultant devices. The formation of the 2D layer further increased the PL intensity, prolonged the carrier lifetimes, and significantly suppressed nonradiative recombination. Consequently, an impressive power conversion efficiency (PCE) of 22.7% was delivered for TFPAI modified devices with 2D/3D heterostructures, which is among the most efficient Cs/FA-based PSCs. Owing to the inherent hydrophobic characteristics of the 2D capping segment, the resultant PSCs exhibited remarkable moisture tolerance and thermal stability. This study provides an insight into the molecule design to deliver an efficient 2D/3D junction for high-performance PSCs.