Unveiling the Effect of Side Chains and Fluorination on the Photovoltaic Performance of D-A Copolymers: A Comparative Study of P-HBT-T, P-FBT-T and P-FBT-O

• Published in: Materials today energy 2023-08, Vol.36, p.101369, Article 101369
• Main Authors: Yilmaz, Eda Alemdar, Cevher, Sevki Can, Cevher, Duygu, Hizalan, Gonul, Cirpan, Ali
• Format: Article
• Language: English
• Subjects: Benzodithiophene; Conjugated Polymer; Organic Solar Cells; Thienopyrroledione
• ISSN: 2468-6069; 2468-6069
• DOI: 10.1016/j.mtener.2023.101369

Three random D-A copolymers containing thienopyrroledione (TPD) and benzodithiophene (BDT) named P-HBT-T, P-FBT-T and P-FBT-O were synthesized. The effects of side chains on BDT and fluorination to benzothiadiazole on the photovoltaic performances of fabricated solar cells were investigated. The HOMO levels of the polymers were −5.51, −5.57, and −5.65 eV for P-HBT-T, P-FBT-T, and P-FBT-O, respectively, suggesting low-lying HOMO energy levels. The optimized weight ratios of the polymer to PC71BM were determined as 1:2 with 24 mg/mL blend concentration for all polymers, and the maximum PCEs of the devices were 7.35%, 7.76%, and 9.21% for P-HBT-T, P-FBT-T, and P-FBT-O, respectively, after optimizations with 1,8-diiodooctane (DIO) and 1-chloronaphthalene (CN). Trap-assisted recombination and bimolecular recombination loss mechanisms, which are power conversion efficiency (PCE) limiting mechanisms, were examined for all devices. The morphological and topographical properties were investigated using transmission electron microscopy (TEM) and atomic force microscopy (AFM), respectively. Our findings demonstrate that P-FBT-O bearing OSCs emerged as the best-performing device due to its deeper HOMO level, high molecular weight, lower trap-assisted and bimolecular recombination and superior morphology. [Display omitted] •The study investigates and compares the electrochemical, optical, photoluminescence and photovoltaic properties of three BDT and TPD polymers (P-HBT-T, P-FBT-T, P-FBT-O), and includes a comparison to the previously studied di-fluorinated counterpart, PF.•Effects of fluorine groups attached to benzothiadiazole groups and alkoxy and alkylthienyl groups attached to benzodithiophene groups were examined.•P-FBT-O exhibited the greatest photovoltaic performance among the polymers with 9.21% PCE, 60.33 FF, and 0.95V VOC.•Molecular weight and morphology are important factors in determining the PCE value, in addition to the polymer structure.•Bimolecular and trap-assisted recombinations were investigated, and TEM and AFM analyseswere performed. These complementary analyses provided further validation of the J-V results.