Wang Long, Liu Xuncheng, Shi Xiaomei, Anderson Christopher L, Klivansky Liana M, Liu Yi, Wu Yishi, Chen Junwu, Yao Jiannian, Fu Hongbing
Key Laboratory of Interface Science and Engineering in Advanced Materials, Ministry of Education, Taiyuan University of Technology, Taiyuan 030024, China.
The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley 94720, United States.
J Am Chem Soc. 2020 Oct 21;142(42):17892-17896. doi: 10.1021/jacs.0c06604. Epub 2020 Oct 12.
The exploitation of singlet fission (SF) in photovoltaic devices is restricted by the limited number of SF materials available and the conflicting requirement of intermolecular interactions to satisfy both efficient SF and subsequent triplet extraction. Intramolecular SF (iSF) represents an emerging alternative and may prove simpler to implement in devices. On account of the excellent chemical structure tunability and solution processability, conjugated polymers have emerged as promising candidates for iSF materials despite being largely underexplored. It remains a significant challenge to develop SF-capable conjugated polymers and achieve efficient dissociation of the formed triplet pairs simultaneously. In this contribution, we present a new iSF material in a -azaquinodimethane-based quinoidal conjugated polymer. Using transient optical techniques, we show that an ultrafast iSF process dominates the deactivation of the excited state in such polymer, featuring ultrafast population (<1 ps) and stepwise dissociation of triplet pairs. Notably, these multiexciton states could further diffuse apart to produce long-lived free triplets (tens of μs) in strongly coupled aggregates in solid thin film. Such findings not only introduce a new iSF-active conjugated polymer to the rare SF material family but also shed unique insight into interchain interaction-promoted triplet pair dissociation in aggregates of conjugated polymers, thus openning new avenues for developing next-generation SF-based photovoltaic materials.
光伏器件中三线态裂变（SF）的应用受到可用SF材料数量有限以及分子间相互作用的矛盾要求的限制，即需要同时满足高效SF和随后的三线态提取。分子内SF（iSF）是一种新兴的替代方案，在器件中可能更容易实现。由于具有出色的化学结构可调节性和溶液可加工性，共轭聚合物尽管在很大程度上尚未得到充分探索，但已成为iSF材料的有前途的候选者。开发具有SF能力的共轭聚合物并同时实现所形成的三线态对的有效解离仍然是一项重大挑战。在本论文中，我们展示了一种基于氮杂喹二亚甲基的醌型共轭聚合物中的新型iSF材料。使用瞬态光学技术，我们表明超快iSF过程主导了此类聚合物中激发态的失活，其特征在于超快布居（<1 ps）和三线态对的逐步解离。值得注意的是，这些多激子态可以进一步扩散分开，在固体薄膜中的强耦合聚集体中产生长寿命的自由三线态（数十微秒）。这些发现不仅为稀有的SF材料家族引入了一种新型的具有iSF活性的共轭聚合物，还为共轭聚合物聚集体中链间相互作用促进的三线态对解离提供了独特的见解，从而为开发下一代基于SF的光伏材料开辟了新途径。
