High‐Performance Fullerene Free Polymer Solar Cells Based on New Thiazole ‐Functionalized Benzo[1,2‐b:4,5‐b′]dithiophene D‐A Copolymer Donors

• Published in: ChemistrySelect (Weinheim) 2021-07, Vol.6 (28), p.7025-7036
• Main Authors: Keshtov, Mukhamed. L., Konstantinov, Igor O., Kuklin, Sergei A., Khokhlov, Aleksei R., Ostapov, Ilya E., Xie, Zhiyuan, Komarov, Pavel V., Alekseev, Vladimir G., Dahiya, Hemraj, Sharma, Ganesh D.
• Format: Article
• Language: English
• Subjects: fullerene free polymer solar cells; low energy loss; power conversion efficiency; Wide bandgap copolymers
• ISSN: 2365-6549; 2365-6549
• DOI: 10.1002/slct.202101824

Two new wide bandgaps D−A copolymers compromising of same benzo [1,2‐b:4, 5‐b′]dithiophene functionalized with thiazole side‐chain donor unit and different acceptors units, i. e., fluorinated benzotriazole (FBTA) (PBDTTZ‐FBTA) and bis‐thiophene‐thieno‐benzothiazole (BTZ) (PBDTTZ‐BTZ) were synthesized and their optical and electrochemical properties were investigated. These copolymers exhibit appropriate frontier energy levels and complementary absorption to most middle and narrow bandgap non‐fullerene small molecule non‐fullerene acceptors. We have explored using these two copolymers as donors combined with a narrow bandgap non‐fullerene acceptor, namely BThIND−Cl, for the construction of polymer solar cells. The optimized polymer solar cells employing PBDTTZ‐FBTA: BThIND−Cl showed overall power conversion efficiency of 14.96 % (with energy loss of 0.51 eV), which is higher than that for PBDTTZ‐BTZ: BThIND−Cl (11.68 % with energy loss of 0.56 eV). Although the PBDTTZ‐BTZ exhibits a broader absorption profile than that of PBDTTZ‐FBTA, the higher power conversion efficiency of the later copolymer may be correlated with the high charge carrier mobility, suppression of the bimolecular and trap‐assisted recombination due to appropriate phase separation and compact π‐π stacking distance in the active layer and low energy loss. The donor‐acceptor (D−A) copolymer poly (benzo[2,2‐b:4,5‐b′] dithiophene‐4,7‐bis(5‐bromothiophen‐2‐yl)‐2‐dodecyl‐5,6‐difluoro‐2H‐benzo[d] [1,2,3]triazole) (PBDTTZ‐FBTA) with fluoro‐2H‐benzo[d] [1,2,3] triazole (FBTA) acceptor unit showed higher power conversion efficiency of about 14.96 %, which is higher than that copolymer poly (benzo[2,2‐b:4,5‐b′] dithiophene‐4,7‐bis(5‐bromothiophen‐2‐yl)‐ bisthiophen‐[2‐yl]bisthieno[3,2‐e:2′,3′‐g][1.3] benzothiazole) (PBDTTZ‐BTZ) with bisthiophen‐[2‐yl]bisthieno[3,2‐e:2′,3′‐g][1.3] benzothiazole (BTZ) acceptor unit (11.68 %).