Engineering Titania based Planar Heterojunction for Hysteresis-Less Perovskite Solar Cells

We adopted a procedure to achieve an optimised CH3NH3PbI3 layer in a planar TiO2 based Planar Heterojunction, which finally results in hysteresis-less and high-efficiency solar cells. We explored the optimisation of the perovskite film thickness, by using a super-saturated solution of CH3NH3I and PbI2 precursors, which also impact on the quality and size of perovskite domains, and the fine-tuning of the perovskite layer surface by a thermal-vacuum post-deposition treatment. Using this procedure, we have obtained a pinhole-free perovskite film with large grain size, reduced surface defects, and generate high photovoltaic performance almost independent on the voltage scan direction. Through photophysical characterization, we proved that the fine setting of the combined thermal-vacuum treatments results in extra-large grains, simultaneously offsetting film defect concentration. Our finding suggests how hysteresis can be efficiently stemmed by simply optimising perovskite processing conditions targeting different device layouts.[1] Moreover, we present a well know p-type doping material as an additive for the Hole Transport Material (HTM), 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane, i.e. F4TCNQ: we have tested various doping concentration in the two most used HTM material for perovskite-based solar cells, Spiro-OMeTAD and P3HT, defining the best doping condition and testing stability in months.