New Strategy for Two-Step Sequential Deposition: Incorporation of Hydrophilic Fullerene in Second Precursor for High-Performance p-i-n Planar Perovskite Solar Cells

In p-i-n planar perovskite solar cells (pero-SCs) based on methylammonium lead iodide (MAPbI(3)) perovskite, high-quality MAPbI(3) film, perfect interfacial band alignment and efficient charge extracting ability are critical for high photovoltaic performance. In this work, a hydrophilic fullerene derivative [6,6]-phenyl-C61-butyric acid-(3,4,5-tris(2-(2-(2-methoxyethoxy)ethoxy)ethoxy) phenyl) methanol ester (PCBB-OEG) is introduced as additive in the methylammonium iodide precursor solution in the preparation of MAPbI3 perovskite film by two-step sequential deposition method, and obtained a top-down gradient distribution with an ultrathin top layer of PCBB-OEG. Meanwhile, a high-quality perovskite film with high crystallinity, less trap-states, and dense-grained uniform morphology can well grow on both hydrophilic (poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid)) and hydrophobic (polytriarylamine, PTAA) hole transport layers. When the PCBB-OEG-containing perovskite film (pero-0.1) is prepared in a p-i-n planar pero-SC with the configuration of ITO/PTAA/pero-0.1/[6,6]-phenyl-C61-butyric acid methyl ester/Al, the device delivers a promising power conversion efficiency (PCE) of 20.2% without hysteresis, which is one of the few PCE over 20% for the p-i-n planar pero-SCs. Importantly, the pero-0.1-based device shows an excellent stability that can retain 98.4% of its initial PCE after being exposed for 300 h under ambient atmosphere with a high humidity, and the flexible pero-SCs based on pero-0.1 also demonstrate a promising PCE of 18.1%.