Optimal negative electrodes for poly(3-hexylthiophene): [6,6]-phenyl C61-butyric acid methyl ester bulk heterojunction photovoltaic devices

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Abstract
The role of the work function and interfacial chemistry on organic device performance was investigated by using a series of contact materials. The active layer was a standard blend of poly(3-hexylthiophene) and [6-6]-phenyl C61-butyric acid methyl ester. Over 100 devices were fabricated and measured to obtain good statistics. Ba∕Al and Ca∕Al electrodes performed best, with similar open-circuit voltages and power conversion efficiencies. Device stability studies showed devices with these two electrodes remained similar after six weeks with degradation of 11%–16% in net conversion efficiency observed. The incorporation of silver into the electrodes led to considerably more degradation than other electrode types.