Monitoring the stability of organometallic perovskite thin films†
Organometallic halide perovskites have emerged as a revolutionary class of light-absorbing semiconductors that have demonstrated a rapid increase in efficiency within a few years of active research. However, chemical stability is a major issue that hampers their large-scale implementation. Therefore being able to monitor the degradation rate of perovskite thin films may help understand the key factors governing the stability of this material system. Here, we use grazing incidence X-ray diffraction (GIXRD) measurements to elucidate the role of chlorine and the substrate in the stability of perovskite CH3NH3Pb(I1−xClx)3 (MAPbI) films for solar cells exposed to ambient atmosphere for more than 30 days. MAPbI films with different concentrations of chlorine were deposited on glass, ITO, and Si substrates. We found that the degradation rate of the perovskite that decomposes into PbI2 depends on the used substrate as well as the concentration of Cl. Through first principles calculations, we propose a mechanism on how chlorine affects the perovskite film properties. Furthermore, the power conversion efficiency of the fabricated perovskite planar heterojunction solar cells is investigated. The highest device performance with an efficiency of 15.7% is obtained with the 10% Cl film at the cost of stability. These findings lead to an improved understanding of more controllable processing schemes for hybrid perovskites. They also offer a potential route to control the degradation rate so as to create more favorable ways of producing stable films and devices from these materials.