Homeopathic Perovskite Solar Cells: Effect of Humidity during Fabrication on the Performance and Stability of the Device

Rapid degradation in humid environments is a major drawback of methylammonium lead iodide (CH3NH3PbI3), which is the archetypical component of perovskite solar cells. In this work, we have investigated the aging and degradation kinetics of CH3NH3PbI3 films and devices fabricated under controlled conditions as a function of relative humidity (RH) and compared their performance with those that were prepared under dry conditions. The aging and degradation kinetics is monitored by optical absorption and impedance spectroscopy measurements under monochromatic illumination at two different wavelengths. Aged devices show a substantial difference between the recombination rate under red and blue light illumination, which is attributed to the enhancement of local recombination routes upon aging. Interestingly, we observe that this feature is less pronounced in devices prepared under conditions of the highest RH of 50%. In general, we found that these devices keep their original electric properties and withstand a humid environment better. Chemical analysis by X-ray photoelectron spectroscopy reveals the presence of coordinating water in the CH3NH3PbI3 crystalline structure. This indicates that the presence of a small amount of water has a beneficial effect against degradation in a humid environment.