A polymer electron donor based on isoindigo units bearing branched oligo(ethylene glycol) side chains for polymer solar cells

• Published in: Polymer chemistry Vol. 8; no. 36; pp. 5496 - 5503
• Main Authors: Chen, Xingxing, Zhang, Zijian, Liu, Jun, Wang, Lixiang
• Format: Journal Article
• Language: English
• Published: 28.09.2017
• ISSN: 1759-9954; 1759-9962
• DOI: 10.1039/C7PY01089C

For solution processability of polymer solar cells (PSCs), polymer electron donors are almost always composed of conjugated main chains and flexible alkyl side chains. In this paper, we report a polymer electron donor based on isoindigo units bearing branched oligo(ethylene glycol) (OEG) side chains, P-OEG. Compared with the control polymer bearing alkyl side chains (P-Alkyl), P-OEG exhibits not only a smaller π–π stacking distance and redshifted absorption spectra, but also larger surface energy for better compatibility with the [6,6]-phenyl-C 71 -butyric acid methyl ester (PC 71 BM) electron acceptor. The PSC device of P-OEG exhibits an open-circuit voltage ( V OC ) of 0.73 V, short-circuit current density ( J SC ) of 13.92 mA cm −2 , and fill factor (FF) of 0.50, corresponding to the power conversion efficiency (PCE) of 5.10%. This performance is higher than that of P-Alkyl (PCE = 3.0%), which is attributed to the finer phase separation morphology of the P-OEG:PC 71 BM blend than that of the P-Alkyl:PC 71 BM blend. These results suggest that the branched OEG side chain is an effective approach to improve the PSC device performance of some polymer electron donors.