Organic photovoltaics incorporating electron conducting exciton blocking layers

We demonstrate that 3,4,9,10 perylenetetracarboxylic bisbenzimidazole (PTCBI) and 1,4,5,8-napthalene-tetracarboxylic-dianhydride (NTCDA) can function as electron conducting and exciton blocking layers when interposed between the acceptor layer and cathode. A low-resistance contact is provided by PTCBI, while NTCDA acts as an exciton blocking layer and optical spacer. Both materials serve as efficient electron conductors, leading to a fill factor as high as 0.70. By using an NTCDA/PTCBI compound blocking layer structure in a functionalized-squaraine/C-60-based device, we obtain a spectrally corrected power conversion efficiency of 5.1 +/- 0.1% under 1 sun, AM 1.5G simulated solar illumination, an improvement of >25% compared to an analogous device using a conventional bathocuproine layer that has previously been shown to conduct electrons via damage-induced midgap states. (C) 2011 American Institute of Physics. [doi:10.1063/1.3598426]