Chemical And Structural Degradation Of Ch3nh3pbi3 Propagate From Pedot:Pss Interface In The Presence Of Humidity

Understanding interfacial reactions that occur between the active layer and charge-transport layers can extend the stability of perovskite solar cells. In this study, the exposure of methylammonium lead iodide (CH3NH3PbI3) thin films prepared on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)-coated glass to 70% relative humidity (R.H.) leads to a perovskite crystal structure change from tetragonal to cubic within 2 days. Interface-sensitive photoluminescence measurements indicate that the structural change originates at the PEDOT:PSS/perovskite interface. During exposure to 30% R.H., the same structural change occurs over a much longer time scale (>200 days), and a reflection consistent with the presence of (CH3)(2)NH2PbI3 is detected to coexist with the cubic phase by X-ray diffraction pattern. The authors propose that chemical interactions at the PEDOT:PSS/perovskite interface, facilitated by humidity, promote the formation of dimethylammonium, (CH3)(2)NH2+. The partial A-site substitution of CH3NH3+ for (CH3)(2)NH2+ to produce a cubic (CH3NH3)(1-)(x)[(CH3)(2)NH2](x)PbI3 phase explains the structural change from tetragonal to cubic during short-term humidity exposure. When (CH3)(2)NH2+ content exceeds its solubility limit in the perovskite during longer humidity exposures, a (CH3)(2)NH2+-rich, hexagonal phase of (CH3NH3)(1-)(x)[(CH3)(2)NH2](x)PbI3 emerges. These interfacial interactions may have consequences for device stability and performance beyond CH3NH3PbI3 model systems and merit close attention from the perovskite research community.