Porphyrins with di-alkoxy-thiophene side chains for organic solar cells

Abstract

The crystallinity of electron donors and their compatibility with electron acceptors play important roles for the performance of bulk-heterojunction organic solar cells. Considering that large electronegative atoms such as O and S atoms are often introduced into active materials to enhance intermolecular interactions and poly(3,4-ethylenedioxythiophene) (PEDOT) is a highly conductive polymer, here in, we introduce dimethoxythiophene (DMOT) and ethylene dioxyl-thiophene (EDOT) side chains at two of the meso positions of a porphyrin core to synthesize two small molecular donors, ZnP-DMOT and ZnP-EDOT, and PCEs of 9.63% and 9.06%, respectively, are achieved for the OSCs with PC₆₁BM as the acceptor. These PCEs are very close to the state-of-the-art among fullerene-based OSCs. In addition, when non-fullerene acceptor 6TIC was employed, the ZnP-DMOT and the ZnP-EDOT binary devices showed PCEs of 11.55% and 10.86%, respectively. Experimental results show that di-alkoxy groups improve not only the crystallinity of the porphyrins but also their compatibility with PC₆₁BM and 6TIC. Furthermore, the introduction of PC₆₁BM as the third component into 6TIC based binary layers significantly improves the electron mobility and the balance of hole and electron transport. As a result, the ternary ZnP-DMOT:6TIC:PC₆₁BM and ZnP-EDOT:6TIC:PC₆₁BM devices achieve PCEs of 13.32% and 12.96%, respectively.