Efficient inverted polymer solar cells incorporating doped organic electron transporting layer

An efficient inverted polymer solar cell is enabled by incorporating an n-type doped wide-gap organic electron transporting layer (ETL) between the indium tin oxide cathode and the photoactive layer for electron extraction. The ETL is formed by a thermal-deposited cesium carbonate-doped 4,7-diphenyl-1,10-phenanthroline (Cs2CO3:BPhen) layer. The cell response parameters critically depended on the doping concentration and film thickness of the Cs2CO3:BPhen ETL. Inverted polymer solar cell with an optimized Cs2CO3:BPhen ETL exhibits a power conversion efficiency of 4.12% as compared to 1.34% for the device with a pristine BPhen ETL. The enhanced performance in the inverted device is associated with the favorable energy level alignment between Cs2CO3:BPhen and the electron-acceptor material, as well as increased conductivity in the doped organic ETL for electron extraction. The method reported here provides a facile approach to optimize the performance of inverted polymer solar cells in terms of easy control of film morphology, chemical composition, conductivity at low processing temperature, as well as compatibility with fabrication on flexible substrates.

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► An efficient inverted polymer solar cell is demonstrated.
► The electron transporting layer is formed by a thermal-deposited Cs2CO3:BPhen layer.
► Efficient electron extraction is achieved due to favorable energy level alignment.