Facile precursor stoichiometry engineering for efficient inverted perovskite solar cells without any dopants

Abstract Full coverage of MAPbI3 layer could be easily obtained by two-step method, while the perovskite precursor stoichiometry ratio is very sensitive to the performance of the perovskite solar cells (PSCs). Here, we demonstrated the high quality MAPbI3 film can be formed on the hydrophobic poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) without any surface treatment and dopant. We systematically adjusted the stoichiometry ratio of the first PbI2:MAI precursor from 1.1:0.3 to 1.3:0.3 and the surface morphology as well as optoelectronic properties of perovskite films were also measured. Benefits from the more uniform surface, higher crystallinity and lower trap states, the high photoelectric conversion efficiency (PCE) of 18.38% and lower hysteresis were achieved based on the optimized ratio of PbI2:MAI. That is one of highest performance of the inverted PSCs based on free-dopants both in MAPbI3 active layer and PTAA hole transport layer. In addition, the devices also showed good stability, and the PCE could maintain 73.85% of its initial value when they were exposed in air and 95.63% in N2 for 216 h. This work suggested a facile precursor stoichiometry engineering to obtain efficient and stable MAPbI3 PSCs based on free-dopants.