Improvement of photovoltaic performance by ternary blending of amorphous and semi-crystalline polymer analogues with PCBM

Ternary blending of amorphous and semi-crystalline anthracene-containing poly(p-phenyleneethynylene)-alt-poly(p-phenylene-vinylene) (PPE-PPV) copolymers (AnE-PVs) with PCBM was investigated in bulk heterojunction solar cells. In general, a strong impact on all photovoltaic parameters was observed by increasing the amount of amorphous AnE-PVba-derivative in relation to its semi-crystalline counterpart AnE-PVab. Interestingly, small additions of the amorphous copolymer were beneficial for overall solar cell performance. The observed performance increase of the ternary blend could be related to an improved open-circuit voltage, despite the fact that the binary blend of the amorphous copolymer and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) did not exhibit a larger photovoltage than the binary blend based on the semi-crystalline copolymer. These results indicate that a certain amorphous fraction of the donor polymer may be required for obtaining optimal bulk heterojunction morphologies, yielding maximum photovoltaic performance.