Synthesis and properties of mono‐ and di‐fluoro‐substituted 2,3‐didodecylquinoxaline‐based polymers for polymer solar cells

• Published in: Journal of polymer science. Part A, Polymer chemistry Polymer chemistry, 2019-02, Vol.57 (4), p.545-552
• Main Authors: Agneeswari, Rajalingam, Kang, Yeongkwon, Lee, Jihoon, Kwon, Ji Hyeon, Tamilavan, Vellaiappillai, Park, Seong Soo, Park, Sung Heum, Jin, Youngeup
• Format: Article
• Language: English
• Subjects: Absorption spectra; Chemical synthesis; Circuits; Energy conversion efficiency; fluorine atom; Maximum power; Molecular orbitals; Photovoltaic cells; polymer; polymer solar cell; Polymers; Solar cells; synthesis; Weight loss
• ISSN: 0887-624X; 1099-0518
• DOI: 10.1002/pola.29293

ABSTRACT We synthesized two new alternating polymers, namely P(Tt‐FQx) and P(Tt‐DFQx), incorporating electron rich tri‐thiophene and electron deficient 6‐fluoroquinoxaline or 6,7‐difluoroquinoxaline derivatives. Both polymers P(Tt‐FQx) and P(Tt‐DFQx) exhibited high thermal stabilities and the estimated 5% weight loss temperatures are 425 and 460 °C, respectively. Polymers P(Tt‐FQx) and P(Tt‐DFQx) displayed intense absorption band between 450 and 700 nm with an optical band gap (Eg) of 1.78 and 1.80 eV, respectively. The determined highest occupied/lowest unoccupied molecular orbital's (HOMO/LUMO) of P(Tt‐DFQx) (−5.48 eV/−3.68 eV) are slightly deeper than those of P(Tt‐FQx) (−5.32 eV/−3.54 eV). The polymer solar cells fabricated with a device structure of ITO/PEDOT:PSS/P(Tt‐FQx) or P(Tt‐DFQx):PC70BM (1:1.5 wt %) + 3 vol % DIO/Al offered a maximum power conversion efficiency (PCE) of 3.65% with an open‐circuit voltage (Voc) of 0.59 V, a short‐circuit current (Jsc) of 10.65 mA/cm2 and fill factor (FF) of 59% for P(Tt‐FQx)‐based device and a PCE of 4.36% with an Voc of 0.69 V, a Jsc of 9.92 mA/cm2, and FF of 63% for P(Tt‐DFQx)‐based device. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 545–552 Two new polymeric donor materials, namely P(Tt‐FQx) and P(Tt‐DFQx), comprising tri‐thiophene and mono‐ or difluoro‐substituted quinoxaline derivatives are synthesized for polymer solar cell applications. Mono‐fluoro‐substituted quinoxaline‐based polymer P(Tt‐FQx) showed more improved absorption than that of di‐fluoro‐substituted quinoxaline‐based polymer P(Tt‐DFQx), while P(Tt‐DFQx) exhibited deeper HOMO level than that of P(Tt‐FQx). Conversely, P(Tt‐FQx) offered higher photocurrent while P(Tt‐DFQx) gave higher open‐circuit voltage. Therefore, both polymers provided comparable photovoltaic performance of 3.65% and 4.36%, respectively, for the polymer solar cell devices made by using P(Tt‐FQx) or P(Tt‐DFQx):PC70BM blends.