Formation of charge transfer complexes significantly improves the electron transfer process of polymer solar cells

A fluorescent inhibitor, 1-Bromo-4-Nitrobenzene (1-Br-4-NB, C6H4BrNO2), is introduced to poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) active layer of polymer solar cells (PSCs). When the amount of 1-Br-4-NB added is 25 wt%, the device performance of PSCs is optimal. To investigate the means by which the power conversion efficiency (PCE) is improved, external quantum efficiency (EQE), fluorescence spectrum, transient absorption spectroscopy and dynamics photoresponse, X-ray diffraction (XRD) patterns are measured and density functional theory (DFT) calculations are carried out. The results indicate that excitonic recombination to the ground state is reduced and excitonic dissociation at the donor-acceptor interface is enhanced, which explains the inhibitory effect on the generation of fluorescence. Moreover, the electron transfer complexes (P3HT-C6H4BrNO2) is demonstrated to be formed after the addition of 1-Br-4-NB. The PCE of PSCs achieves an improvement of more than 57% compared to the reference solar cell without 1-Br-4-NB. (C) 2015 Elsevier B.V. All rights reserved.