Incorporating formamidinium into 4-fluoro-phenethylammonium based quasi-2D perovskite films and their application in n-i-p perovskite solar cells

Recently, perovskite solar cells (PSCs) basing on quasi-two-dimensional (quasi-2D) perovskites with hydrophobic bulky organic cations have received a lot of interests owing to their superior moisture stability. While quasi-2D perovskites have achieved great success in planar p-i-n PSCs, their application in planar n-i-p devices and the corresponding efficiencies lag far behind. In our work, (FPEA)2(MA)4Pb5I16 perovskite films with high crystallinity, compact and smooth surface were deposited on electron transport layer with NH4SCN as an additive. Formamidinium (FA+) were then incorporated into the FPEA based perovskite films to partially replace methylammonium (MA+), and effects of FA+ on the film's vertical orientation, light absorption capacity, carrier lifetime, defect density and electron mobility were studied. It was found that when molar ratio of FA/MA = 0.5/9.5, the film had the highest vertical orientation, enhanced light absorption, less carrier recombination loss. The obtained (FPEA)2(FA0.05MA0.95)4Pb5I16 based n-i-p PSCs gave a maximum efficiency of 12.17% under standard illumination, retaining 83% of the initial efficiency after stored in air environment (25–30 °C) with 40 ± 5% RH for 1080 h. The results demonstrate an efficient approach to prepare high-quality quasi-2D perovskite films in a n-i-p structure as well as improved device efficiency and stability.