He Baitian, Tang Luting, Zhang Jinming, Xiao Manjun, Chen Guiting, Dai Chuanbo
School of Chemistry and Environment, Guangdong Rare Earth Photofunctional Materials Engineering Technology Research Center, Jiaying University Meizhou 514015 P. R. China
College of Chemistry, Key Lab of Environment-Friendly Chemistry and Application (Ministry of Education), Xiangtan University Xiangtan 411105 P. R. China
RSC Adv. 2023 Oct 4;13(41):29035-29042. doi: 10.1039/d3ra05647c. eCollection 2023 Sep 26.
The design and synthesis of polymer donors with a low-lying highest occupied molecular orbital (HOMO) level are crucial for increasing open-circuit voltages () and achieving high-performance non-fullerene polymer solar cells. Here, we developed two copolymers using non-fluorinated or fluorinated thienyl-conjugated benzodithiophenes as electron donor units, and difluoro-quinoxaline with a naphthalimide substituent (DNB) as the electron acceptor unit. These copolymers, namely PDNB and PDNB-2F, exhibited deep HOMO levels owing to the strong electron-withdrawing ability of the naphthalimide substituent. Density-functional theory calculations demonstrated that the skeletons of the two copolymers featured good coplanarity. Owing to the fluorination, PDNB-2F displayed an increased absorption coefficient and deeper HOMO level than PDNB. Moreover, the blended film based on PDNB-2F:Y6 demonstrated enhanced carrier mobility, decreased bimolecular recombination as well as favorable phase-separation regions. Consequently, the PDNB-2F:Y6-based device yielded a superior power conversion efficiency (PCE) of 12.18%, whereas the device based on PDNB:Y6 showed a comparatively lower PCE of 8.83%. These results indicate that difluoro-quinoxaline with a naphthalimide substituent is a prospective electron-deficient building block to develop donor polymers with low-lying HOMO levels to achieve efficient non-fullerene polymer solar cells.
设计和合成具有低最高占据分子轨道（HOMO）能级的聚合物供体对于提高开路电压（）和实现高性能非富勒烯聚合物太阳能电池至关重要。在此，我们使用非氟化或氟化的噻吩基共轭苯并二噻吩作为电子供体单元，以及带有萘二甲酰亚胺取代基的二氟喹喔啉（DNB）作为电子受体单元，开发了两种共聚物。由于萘二甲酰亚胺取代基具有强吸电子能力，这些共聚物，即PDNB和PDNB - 2F，表现出较深的HOMO能级。密度泛函理论计算表明，这两种共聚物的骨架具有良好的共平面性。由于氟化作用，PDNB - 2F比PDNB表现出更高的吸收系数和更深的HOMO能级。此外，基于PDNB - 2F:Y6的共混膜表现出增强的载流子迁移率、降低的双分子复合以及良好的相分离区域。因此，基于PDNB - 2F:Y6的器件产生了12.18%的优异功率转换效率（PCE），而基于PDNB:Y6的器件表现出相对较低的PCE，为8.83%。这些结果表明，带有萘二甲酰亚胺取代基的二氟喹喔啉是开发具有低HOMO能级的供体聚合物以实现高效非富勒烯聚合物太阳能电池的一种有前景的缺电子结构单元。
