Fabrication of Planar Heterojunction Perovskite Solar Cells by Controlled Low-Pressure Vapor Annealing

A new method for achieving high efficiency planar CH3NH3PbI3-xClx perovskite photovoltaics, based on a low pressure, reduced temp. vapor annealing is demonstrated. Heterojunction devices based on this hybrid halide perovskite exhibit a top power conversion efficiency of 16.8%, reduced c.d.-voltage hysteresis, and highly repeatable performance without need for a mesoporous or nanocryst. metal oxide layer. Our findings demonstrate that large hysteresis is not an inherent feature of planar heterojunctions, and that efficient charge extn. can be achieved with uniform halide perovskite materials with desired compn. X-ray diffraction, valence band spectroscopy, and transient absorption measurements of these thin films reveal that structural modifications induced by chlorine clearly dominate over chem. and electronic doping effects, without affecting the Fermi level or photocarrier lifetime in the material.