Improving the photovoltaic performance of fluorinated 2, 2′-bithiophene core-based D(A–Ar)2 type small molecules via strategically end-capped heteroaromatic substitution. Issue 39 (23rd September 2019)

• Record Type: Journal Article
• Authors: Li, Min; Wang, Shichao; Bao, Chengjia; Liu, Zuoji; Bai, Dan; Yang, Zhen; Zhu, Weiguo; Peng, Qiang; Liu, Yu
• Is Part Of: Journal of materials chemistry. Volume 7:Issue 39(2019)
• Page Start: 12217
• Page End: 12230
• Publication Date: 2019-09-23
• Subjects: Materials -- Periodicals; Chemistry, Analytic -- Periodicals; Optical materials -- Research -- Periodicals; Electronics -- Materials -- Research -- Periodicals; 543.0284
• DOI: 10.1039/c9tc03577j
• Languages: English
• ISSNs: 2050-7526

Abstract

Abstract : Three novel D(A–Ar)2 type small molecules were obtained for application in OSCs. Especially, the V oc, J sc and FF values for FBT(TDPP-TS)2 -based cells were synergistically improved by inserting both N and S atoms onto the terminal groups. Abstract : To reveal the influences of introducing various end-capping units onto small-molecule (SM) donors, in this article, 2-octylthio-thiophene (TS), 2-octyl-thiazole (TZ) and 2-octylthiothiazole (TZS) are strategically selected as end-capping units to combine with a fluorinated 2, 2′-bithiophene (FBT) core and thiophene-flanked diketopyrrolopyrrole (TDPP) units as electron acceptors to afford three novel D(A–Ar)2 type SM donors, namely FBT(TDPP-TS)2, FBT(TDPP-TZ)2 and FBT(TDPP-TZS)2 . The structure-property relationships provoked by slight changes in the terminal groups were systematically evaluated. In particular, TZS end-units make FBT(TDPP-TZS)2 possess better molecular stacking, higher mobility and better miscibility in the blend with PC71 BM in comparison with the other two SMs. As a result, the introduction of TZS end-groups has been found to enhance the open-circuit voltage ( V oc ), short circuit current density ( J sc ) and fill factor (FF) simultaneously. After optimization, an outstanding power conversion efficiency (PCE) of 8.91% with a V oc of 0.80 V, a J sc of 16.75 mA cm −2 and a FF of 66.93% was obtained for the FBT(TDPP-TZS)2 based device, which is among the top values of the D(A–Ar)2 type single junction small molecular BHJ-OSCs. Our results obtained here indicate that strategic hetero-substitution of end-capping units in D(A–Ar)2 type SMs is an efficient strategy to improve photovoltaic performance.