An Lili, Huang Yubo, Wang Xu, Liang Zezhou, Li Jianfeng, Tong Junfeng
Key Laboratory for Utility of Environment- Friendly Composite Materials and Biomass in University of Gansu Province, School of Chemical Engineering, Northwest Minzu University, Lanzhou 730030, China.
School of Materials Science and Engineering, Lanzhou Jiaotong University, Lanzhou 730070, China.
Polymers (Basel). 2020 Feb 25;12(3):504. doi: 10.3390/polym12030504.
Two two-dimensional (2D) donor-acceptor (D-A) type conjugated polymers (CPs), namely, PBDT-TVT-BT and PBDT-TVT-FBT, in which two ((E)-(4,5-didecylthien-2-yl)vinyl)- 5-thien-2-yl (TVT) side chains were introduced into 4,8-position of benzo[1,2-b:4,5-b']dithiophene (BDT) to synthesize the highly conjugated electron-donating building block BDT-TVT, and benzothiadiazole (BT) and/or 5,6-difluoro-BT as electron-accepting unit, were designed to systematically ascertain the impact of fluorination on thermal stability, optoelectronic property, and photovoltaic performance. Both resultant copolymers exhibited the lower bandgap (1.60 ~ 1.69 eV) and deeper highest occupied molecular orbital energy level (E, -5.17 ~ -5.37 eV). It was found that the narrowed absorption, deepened E and weakened aggregation in solid film but had insignificant influence on thermal stability after fluorination in PBDT-TVT-FBT. Accordingly, a PBDT-TVT-FBT-based device yielded 16% increased power conversion efficiency (PCE) from 4.50% to 5.22%, benefited from synergistically elevated V, J, and FF, which was mainly originated from deepened E, increased μ, μ, and more balanced μ/μ ratio, higher exciton dissociation probability and improved microstructural morphology of the photoactive layer as a result of incorporating fluorine into the polymer backbone.
两种二维（2D）供体-受体（D-A）型共轭聚合物（CPs），即PBDT-TVT-BT和PBDT-TVT-FBT，其中两个（（E）-（4,5-二癸基噻吩-2-基）乙烯基）-5-噻吩-2-基（TVT）侧链被引入到苯并[1,2-b:4,5-b']二噻吩（BDT）的4,8位以合成高度共轭的给电子结构单元BDT-TVT，并且苯并噻二唑（BT）和/或5,6-二氟-BT作为电子受体单元，被设计用于系统地确定氟化对热稳定性、光电性能和光伏性能的影响。两种所得共聚物均表现出较低的带隙（1.601.69 eV）和更深的最高占据分子轨道能级（E，-5.17-5.37 eV）。研究发现，在PBDT-TVT-FBT中氟化后，吸收变窄、E加深且固体薄膜中的聚集减弱，但对热稳定性影响不显著。因此，基于PBDT-TVT-FBT的器件的功率转换效率（PCE）从4.50%提高到5.22%，提高了16%，这得益于V、J和FF协同提高，这主要源于E加深、μ、μ增加以及μ/μ比值更平衡、激子解离概率更高以及由于氟掺入聚合物主链而改善了光活性层的微观结构形态。
