Surface-tension release in PTAA-based inverted perovskite solar cells

Perovskite solar cells (PSCs) with inverted planar heterojunction (p-i-n) structure have attracted wide attention due to their facile preparation and flexible application. So far, poly(bis{4-phenyl}{2,4,6-trimethylphenyl}amine) (PTAA) as the hole-transport material has promised the state-of-the-art performance for p-i-n PSCs. However, the hydrophobic nature of PTAA has two contradictory impacts on the PSCs performance, namely the perfect resistance of corrosion and hygroscopicity versus the large surface-tension and incomplete surface coverage of the photoactive perovskite film. To address this challenge, an inorganic potassium fluoride (KF) buffer layer was introduced onto the PTAA substrate to regulate the surface-energy difference between PTAA and the perovskite precursor. As a result, superb quality perovskite film was synthesized. In addition, the KF treatment also downward shifts the valence-band maximum (VBM) of the polymer toward the VBM of perovskite thus facilitating the hole extraction from the perovskite to PTAA and in turn enlarging both the short-circuit current density (JSC) and open-circuit voltage (VOC) Therewith, the planar inverted perovskite solar cell aided by KF realizes a champion power conversion efficiency (PCE) of 21.51% with a JSC of 23.95 mA/cm2, VOC of 1.09 V, and fill factor of 82.4%. It is also important that optimized devices exhibit excellent long-term stability, with 90% of the original PCE retained after 30 days under ambient conditions (60% humidity).