Efficient dialkyl‐difluoro‐substituted quinoxaline‐based medium bandgap polymeric donor for high‐energy‐converting organic solar cells

Abstract

A new medium bandgap polymer incorporating electron‐rich 4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b']dithiophene (BDTT) and electron‐deficient 2,3‐didodecyl‐6,7‐difluoro‐5,8‐di(thiophen‐2‐yl)quinoxaline (2TffQ) units in an alternate manner, namely P(BDTT‐2TffQ), was prepared for organic solar cell (OSC) applications. The optical and electrochemical properties of P(BDTT‐2TffQ) were found to be suitable to use it as an electron donor in OSCs. The absorption band covers the region from 300 to 600 nm with an optical bandgap (Eg) of 1.84 eV, and it highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) were found to be positioned at −5.36 and − 3.52 eV. The OSCs prepared by using P(BDTT‐2TffQ):[6,6]‐Phenyl‐C71‐butyric acid methyl ester (PC70BM) and P(BDTT‐2TffQ):2,2′‐((2Z,2'Z)‐((12,13‐bis(2‐ethylhexyl)‐3,9‐diundecyl‐12,13‐dihydro‐[1,2,5]thiadiazolo[3,4‐e]thieno[2″,3″:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2‐g]thieno[2′,3′:4,5]thieno[3,2‐b]indole‐2,10‐diyl)bis(methanylylidene))bis(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))dimalononitrile (Y6) blends provided a maximum power conversion efficiency (PCE) of 5.50% and 11.65%, respectively. The differences in the photovoltaic performances of OSCs are mainly attributed to their dissimilar short‐circuit current (Jsc), which depends on their absorption spectrum. Herein, we also compared the properties of P(BDTT‐2TffQ) with a structurally similar polymer, namely P(BDTT‐2TfQ), made up of BDTT and 2,3‐didodecyl‐6‐fluoro‐5,8‐di(thiophen‐2‐yl)quinoxaline (2TfQ) units, for better understanding the effects of the incorporation of additional fluorine atom on the backbone of quinoxaline‐based polymers.

Fluorinated Polymer Donors for Nonfullerene Organic Solar Cells

“…[91] Compared with PB-FQx, the performance of PB-DFQx-based devices had clearly improved due to the higher V OC caused by difluoro-substitutions. By introducing thiophene π-bridge, P(BDTT-2TffQ) and P(BDTT-2TfQ) were reported by Park et al [92] Compared with P(BDTT-2TfQ), polymer P(BDTT-2TffQ) has higher absorption coefficient, lower HOMO level and higher film crystallinity because of the difluoro-substitutions. Consequently, the P(BDTT-2TffQ) : Y6based OSCs yielded an PCE of 11.65 %, which is much higher than 6.77 % for P(BDTT-2TffQ):Y6 (Table 4).…”