Photodegradation of Metal Oxide Interlayers in Polymer Solar Cells

The effect of 1 sun illumination for 24 h on encapsulated inverted organic photovoltaic devices is studied through a series of electrical and optical characterizations for donor/acceptor polymer solar cells based on poly(dithienogermole-alt-thienopyrrolodione)/[6,6]-phenyl C71 butyric acid methyl ester blends. Power conversion efficiency is significantly reduced after light exposure due to a 45% drop in the device fill factor and a 40% drop in both the open circuit voltage and short circuit current. The decrease in open circuit voltage is attributed to a reduction in the built-in field in the device due to photodegradation of the ZnO interlayer. The reduction in fill factor and short circuit current is shown to be due to the formation of an extraction barrier for hole collection as a result of photodegradation of the MoOx interlayer. Using a 400 nm long pass filter to block the UV light, device stability is significantly enhanced, resulting in a decrease in power conversion efficiency of less than 5% under the same operation conditions.