Wang Jun, Huang Yuting, Wang Yajing, Durbeej Bo, Blancafort Lluís
School of Chemistry and Chemical Engineering, Huaiyin Normal University, No. 111 West Changjiang Road, Huaian 223300, China.
Division of Theoretical Chemistry, IFM, Linköping University, SE-581 83 Linköping, Sweden.
Molecules. 2024 Nov 14;29(22):5348. doi: 10.3390/molecules29225348.
Poly-CPDTBT, as typical low-band gap copolymers, have potential applications in organic bulk heterojunction solar cells. To have a clear picture of its excited-state processes, the first task is to understand their excited states, in particular, electronic character and relevant optical absorption. Herein, the low-lying singlet excited states of Poly-CPDTBT oligomers were investigated via Algebraic Diagrammatic Construction Second Order (ADC(2)) and time-dependent density functional theory (TDDFT) method with several functionals. Six CPDTBT (N = 1-6) oligomers were taken as prototypes to study their excited states in detail. The results provide interesting clues to extrapolate the photophysical properties of such polymers with potential applications in photovoltaic materials. The result provided by ωB97XD functional gives good agreement with the experiment result. The vertical excitation energies of the four lowest excited states decrease almost linearly with increasing polymerization degree (N) for CPDTBT (N = 1-6). The transition density analysis indicates that the local excitations (LE) and the short-distance charge transfer (CT) excitations between two adjacent CPDT and BT units are dominant for low-lying excited states for short oligomers. For the long-chain oligomers (trimer to hexamer), the transition density shows a ladder (or zigzag) pattern along the diagonal blocks at the planar geometry. For long oligomers, the whole chain is involved in the transitions, and the CT excitations only exist between two adjacent CPDT and BT units. The present work provides a valuable basis for understanding the excited-state processes of Poly-CPDTBT and other conjugated polymers that conduct solar energy conversions, which has great significance for the development of new solar cells.
聚（咔唑并[3,2-b:4,5-b']二噻吩-2,6-二(3-十二烷基噻吩)）（Poly-CPDTBT）作为典型的低带隙共聚物，在有机本体异质结太阳能电池中具有潜在应用。为了清晰了解其激发态过程，首要任务是了解其激发态，特别是电子特性和相关的光吸收。在此，通过代数图示构造二阶微扰理论（ADC(2)）和含时密度泛函理论（TDDFT）方法，并结合多种泛函，研究了聚（咔唑并[3,2-b:4,5-b']二噻吩-2,6-二(3-十二烷基噻吩)）低聚物的低激发单重态。选取六种聚（咔唑并[3,2-b:4,5-b']二噻吩-2,6-二(3-十二烷基噻吩)）（N = 1 - 6）低聚物作为原型，详细研究它们的激发态。这些结果为推断此类聚合物在光伏材料中的光物理性质提供了有趣的线索，ωB97XD泛函给出的结果与实验结果吻合良好。对于聚（咔唑并[3,2-b:4,5-b']二噻吩-2,6-二(3-十二烷基噻吩)）（N = 1 - 6），四个最低激发态的垂直激发能几乎随聚合度（N）的增加呈线性下降。跃迁密度分析表明，对于短低聚物的低激发态，两个相邻的咔唑并[3,2-b:4,5-b']二噻吩（CPDT）和苯并噻二唑（BT）单元之间的局域激发（LE）和短程电荷转移（CT）激发占主导。对于长链低聚物（三聚体到六聚体），在平面几何结构中，跃迁密度沿对角块呈现阶梯状（或锯齿状）图案。对于长低聚物，整个链参与跃迁，且CT激发仅存在于两个相邻的CPDT和BT单元之间。本工作为理解聚（咔唑并[3,2-b:4,5-b']二噻吩-2,6-二(3-十二烷基噻吩)）以及其他进行太阳能转换的共轭聚合物的激发态过程提供了有价值的基础，这对新型太阳能电池的开发具有重要意义。
