Pyrrolo[3,4-g]quinoxaline-6,8-dione-based conjugated copolymers for bulk heterojunction solar cells with high photovoltages
2015 (English)In: Polymer Chemistry, ISSN 1759-9954, Vol. 6, no 25, 4624-4633 p.Article in journal (Refereed) Published
A new electron-deficient building block 5,9-di(thiophen-2-yl)-6H-pyrrolo[3,4-g]quinoxaline-6,8(7H)-dione (PQD) was synthesized via functionalizing the 6- and 7-positions of quinoxaline (Qx) with a dicarboxylic imide moiety. Side chain substitution on the PQD unit leads to good solubility which enables very high molecular weight copolymers to be attained. The fusion of two strong electron-withdrawing groups (Qx and dicarboxylic imide) makes the PQD unit a stronger electron-deficient moiety than if the unit had just one electron-withdrawing group, thus enhancing the intramolecular charge transfer between electron-rich and deficient units of the copolymer. Four PQD-based polymers were synthesized which feature deep-lying highest occupied molecular orbital (HOMO) levels and bathochromic absorption spectra when compared to PBDT-Qx and PBDT-TPD analogues. The copolymers incorporated with benzo[1,2-b:4,5-b]dithiophene (BDT) units show that the 1D and 2D structural variations of the side groups on the BDT unit are correlated with the device performance. As a result, the corresponding solar cells (ITO/PEDOT:PSS/polymer: PC71BM/LiF/Al) based on the four copolymers feature very high open-circuit voltages (V-oc) of around 1.0 V. The copolymer PBDT-PQD1 attains the best power conversion efficiency of 4.9%, owing to its relatively high absorption intensity and suitable film morphology. The structure-property correlation demonstrates that the new PQD unit is a promising electron-deficient building block for efficient photovoltaic materials with high V-oc.
Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY , 2015. Vol. 6, no 25, 4624-4633 p.
IdentifiersURN: urn:nbn:se:liu:diva-120071DOI: 10.1039/c5py00394fISI: 000356298900009OAI: oai:DiVA.org:liu-120071DiVA: diva2:839930
Funding Agencies|Swedish Research Council; Swedish Energy Agency; EU ; China Scholarship Council; program for the Excellent Doctoral Dissertations of Guangdong Province [ybzzxm201114]2015-07-062015-07-062015-07-06