In the field of organic photovoltaics (OPVs), triplet materials are expected to be good candidates for improving power conversion efficiency (PCE) due to their long-lifetime and energy-tunable triplet excitons. A comparative photophysical analysis (including absorption spectra, exciton diffusion lengths, singlet and triplet charge transfer dynamics and so on) of PTB7/PC₇₁BM and PTB7Ir/PC₇₁BM cell devices was investigated, by DFT and TD-DFT methods, to explore why PTB7Ir/PC₇₁BM device has obvious higher PCE (8.71%) than PTB7/PC₇₁BM device (6.64%) in the same condition. The results manifest that the enhanced PCE of the PTB7Ir/PC₇₁BM device is mainly attributed to the improving exciton diffusion lengths owing to the longer lifetime and increasing diffusivity of triplet excitons. Besides, to reveal the structure-property relationships of the polymer donor materials, we calculated the values of driving force for charge recombination to the triplet (CRT) with the changes of torsional angles between electron donating and electron withdrawing units of PTB7 and PTB7Ir. It is found that suitably increasing the angle and number of torsional angles of polymer donors to limit conjugation extent will prevent the CRT process at donor/acceptor interface and thus improve photovoltaic performance. This work would provide theoretical guidelines for the molecular design of high-efficiency triplet-material-based OPVs.

在有机光伏（OPV）领域中，由于三重态材料的使用寿命长且可调节能量的三重态激子，有望成为提高功率转换效率（PCE）的良好选择。通过DFT和TD-DFT方法研究了PTB7 / PC ₇₁ BM和PTB7Ir / PC ₇₁ BM细胞装置的比较光物理分析（包括吸收光谱，激子扩散长度，单重态和三重态电荷转移动力学等），以探索为什么在相同条件下PTB7Ir / PC ₇₁ BM设备的PCE明显高于PTB7 / PC ₇₁ BM设备（6.64％）。结果表明，PTB7Ir / PC _71的PCE增强BM装置主要归因于三重态激子的更长寿命和增加的激子扩散长度。此外，为揭示聚合物供体材料的结构-性质关系，我们计算了电荷复合到三重态（CRT）的驱动力值，该值与给电子和吸电子单元PTB7和PTB7Ir之间的扭转角变化有关。已经发现，适当地增加聚合物供体的角度和扭转角的数量以限制共轭程度将防止在供体/受体界面处的CRT过程，从而改善光伏性能。这项工作将为基于高效三重态材料的OPV的分子设计提供理论指导。