Ziffer Mark E, Jo Sae Byeok, Zhong Hongliang, Ye Long, Liu Hongbin, Lin Francis, Zhang Jie, Li Xiaosong, Ade Harald W, Jen Alex K-Y, Ginger David S
Department of Chemistry , University of Washington , Seattle , Washington 98195-2120 , United States.
Department of Materials Science and Engineering , University of Washington , Seattle , Washington 98195-2120 , United States.
J Am Chem Soc. 2018 Aug 8;140(31):9996-10008. doi: 10.1021/jacs.8b05834. Epub 2018 Jul 26.
Minimization of open-circuit-voltage ( V) loss is required to transcend the efficiency limitations on the performance of organic photovoltaics (OPV). We study charge recombination in an OPV blend comprising a polymer donor with a small molecule nonfullerene acceptor that exhibits both high photovoltaic internal quantum efficiency and relatively high external electroluminescence quantum efficiency. Notably, this donor/acceptor blend, consisting of the donor polymer commonly referred to as PCE10 with a pseudoplanar small molecule acceptor (referred to as FIDTT-2PDI) exhibits relatively bright delayed photoluminescence on the microsecond time scale beyond that observed in the neat material. We study the photoluminescence decay kinetics of the blend in detail and conclude that this long-lived photoluminescence arises from radiative nongeminate recombination of charge carriers, which we propose occurs via a donor/acceptor CT state located close in energy to the singlet state of the polymer donor. Additionally, crystallographic and spectroscopic studies point toward low subgap disorder, which could be beneficial for low radiative and nonradiative losses. These results provide an important demonstration of photoluminescence due to nongeminate charge recombination in an efficient OPV blend, a key step in identifying new OPV materials and materials-screening criteria if OPV is to approach the theoretical limits to efficiency.
要突破有机光伏（OPV）性能的效率限制，需要将开路电压（V）损失降至最低。我们研究了一种OPV共混物中的电荷复合情况，该共混物由一种聚合物给体和一种小分子非富勒烯受体组成，该受体同时具有高光伏内量子效率和相对较高的外部电致发光量子效率。值得注意的是，这种给体/受体共混物，由通常称为PCE10的给体聚合物与一种准平面小分子受体（称为FIDTT - 2PDI）组成，在微秒时间尺度上表现出比纯材料中观察到的更亮的延迟光致发光。我们详细研究了该共混物的光致发光衰减动力学，并得出结论，这种长寿命光致发光源于电荷载流子的辐射非简并复合，我们认为这是通过能量与聚合物给体的单重态接近的给体/受体电荷转移态发生的。此外，晶体学和光谱学研究表明亚带隙无序较低，这可能有利于降低辐射和非辐射损失。这些结果为高效OPV共混物中由于非简并电荷复合引起的光致发光提供了重要证明，如果OPV要接近理论效率极限，这是识别新的OPV材料和材料筛选标准的关键一步。
