An alternating polymer (PFOFTQx) with 9,9-dioctylfluorene (FO) as electron-rich unit and fluorine substituted quinoxaline (FTQx) as electron-withdrawing unit was synthesized and characterized. PFOFTQx showed similar absorption property with that of the counterpart polymer without fluorine atom (synthesized APFO-15). However, the low-lying highest occupied molecular orbit (HOMO) energy level of PFOFTQx was -5.37 eV, about 0.07 eV smaller than that of synthesized APFO-15. In order to study the photovoltaic properties of the materials, polymer solar cells (PSCs) were fabricated with PFOFTQx as donor blended with [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) as acceptor. The power conversion efficiency (PCE) of PSC was 1.77% with a high open-circuit voltage (V-oc) of 0.90 V for an optimized PFOFTQx:PC61BM weight ratio of 1:5, in comparison with that of synthesized APFO-15-based device (PCE of 1.60% with V-oc of 0.77 V). This study indicated that fluorine substituted quinoxaline-based polymers would be promising material with a higher V-oc for the application in polymer solar cells. (C) 2013 Elsevier Ltd. All rights reserved.
Side-Chain Engineering of Benzodithiophene-Fluorinated Quinoxaline Low-Band-Gap Co-polymers for High-Performance Polymer Solar Cells
AbstractA new series of donor–acceptor co‐polymers based on benzodithiophene and quinoxaline with various side chains have been developed for polymer solar cells. The effect of the degree of branching and dimensionality of the side chains were systematically investigated on the thermal stability, optical absorption, energy levels, molecular packing, and photovoltaic performance of the resulting co‐polymers. The results indicated that the linear and 2D conjugated side chains improved the thermal stabilities and optical absorptions. The introduction of alkylthienyl side chains could efficiently lower the energy levels compared with the alkoxyl‐substituted analogues, and the branched alkoxyl side chains could deepen the HOMO levels relative to the linear alkoxyl chains. The branched alkoxyl groups induced better lamellar‐like ordering, but poorer face‐to‐face packing behavior. The 2D conjugated side chains had a negative influence on the crystalline properties of the co‐polymers. The performance of the devices indicated that the branched alkoxyl side chains improved the Voc, but decreased the Jsc and fill factor (FF). However, the 2D conjugated side chains would increase the Voc, Jsc, and FF simultaneously. For the first time, our work provides insight into molecular design strategies through side‐chain engineering to achieve efficient polymer solar cells by considering both the degree of branching and dimensionality.
Performance comparison of fluorinated and chlorinated donor–acceptor copolymers for polymer solar cells
作者:Yubao Zhang、Fumeng Ren、Qinghua Li、Zhixuan Zhang、Xingdao He、Zhongping Chen、Jiulin Shi、Guoli Tu
DOI:10.1039/c8tc00948a
日期:——
Chlorination could be an effective and simple strategy to develop highly efficient polymer donors.