Synthesis and characterization of two new benzothiadiazole- and fused bithiophene based low band-gap D–A copolymers: Application as donor bulk heterojunction polymer solar cells. (18th May 2015)

• Record Type: Journal Article
• Authors: Keshtov, M.L.; Sharma, G.D.; Kuklin, S.A.; Ostapov, I.Е.; Godovsky, D.Yu.; Khokhlov, A.R.; Chen, F.C.
• Is Part Of: Polymer. Volume 65(2015)
• Page Start: 193
• Page End: 201
• Publication Date: 2015-05-18
• Subjects: D–A copolymers -- Bulk heterojunction solar cells -- Power conversion efficiency; Polymers -- Periodicals; Polymerization -- Periodicals; Polymères -- Périodiques; Polymérisation -- Périodiques; 547.7
• DOI: 10.1016/j.polymer.2015.03.058
• Languages: English
• ISSNs: 0032-3861

Abstract

Abstract: Two new narrow bandgap D–A conjugated copolymersP1 andP2 containing different fused thiophene donor unit and same benzothiadiazole acceptor unit were synthesized by Stille cross-coupling polymerization, and characterized by 1 H NMR, elemental analysis and GPC, TGA, DSC. Cyclic voltammetry measurement showed that the HOMO energy level both copolymers is deep lying (−5.10 and −5.35 eV forP1 andP2, respectively) which show that copolymers has good stability in the air and assured a higher open circuit voltage when it photovoltaic application. These copolymer were used as donor along with PC71 BM and the BHJ polymer solar cells based onP1 :PC71 BM andP2 :PC71 BM processed with chloroform (CF) solvent showed over all PCE of 4.54% and 4.36%, respectively. Additionally, the PCE was improved up to 5.62% and 5.24% forP1 :PC71 BM andP2 :PC71 BM active layer processed with DIO (4 v%)/CF solvent. The enhancement in the PCE has been attributed to improved nanoscale morphology and crystalline nature of active layer as well as charge transport in the device with the addition of DIO, due to the higher boiling point of DIO causing slow evaporation rate during the film formation. Graphical abstract: Highlights: CopolymersP1 andP2 compromises of different weak donors and same strong acceptor units were synthesized. Deeper highest occupied molecular orbital (HOMO) energy levels and beneficial for high open circuit voltage (Voc). PCE of 5.62% and 5.24% forP1 :PC71 BM andP2 :PC71 BM active layer processed with DIO (4 v%)/CF solvent. Weak donor and strong acceptor will be an ideal choice for high efficiency polymer solar cells.