Influence of polymer side chains on the photovoltaic performance of non-fullerene organic solar cells. Issue 4 (11th January 2017) - Gong, Xue
Abstract : The side chains of polymers had a great influence on their molecular packing, energy level, blend morphology and photovoltaic performance. The PCEs of 7.28% and 1.55% were obtained for alkoxy and alkylthio-substituted polymer based non-fullerene solar cells, respectively. Abstract : Novel polymers comprising a 3-fluoro-5-alkylthiophenyl benzodithiophene donor unit and a 5-fluoro-6-alkoxy (or alkylthio)-2, 1, 3-benzothiadiazole (BT) acceptor unit were synthesized. BothPOF andPSF possess low HOMO and LUMO energy levels due to the incorporation of fluorine atoms. Additionally, alkoxy and alkylthio substitution on the BT unit also had a great influence on the molecular packing and the energy level of the resulting polymers. The introduction of the alkylthio side chains on the BT unit ofPSF led to a significant downshift of the HOMO energy level in comparison to that ofPOF with an alkoxy substituent due to the weaker electron-donating properties of the sulfur atom than that of oxygen. However, the steric hindrance caused by the large sulfur atoms resulted in reduced planarity of the backbone ofPSF, which might influence the charge transport and the morphology of the blend film. As a result, POF based NF-PSCs exhibited a PCE of 7.28%, with a V oc of 0.86 V, a J sc of 14.9 mA cm −2, and an FF of 0.47, while a low PCE of 1.55% with a V oc of 0.95 V, a J sc of 5.6 mA cm −2, and an FF of 0.29 was obtained forPSF based non-fullerene polymer solar cells (NF-PSCs). Therefore, the side chain engineering of the donor polymer is crucial for maximizing both J sc and V oc values to achieve high performance polymer solar cells.