Carr Joshua M, Gish Melissa K, Reid Obadiah G, Rumbles Garry
Materials Science and Engineering Program, University of Colorado Boulder, Boulder, Colorado 80303, United States.
Chemistry and Nanoscience Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States.
ACS Energy Lett. 2024 Feb 8;9(3):896-907. doi: 10.1021/acsenergylett.3c01969. eCollection 2024 Mar 8.
Energy transfer across the donor-acceptor interface in organic photovoltaics is usually beneficial to device performance, as it assists energy transport to the site of free charge generation. Here, we present a case where the opposite is true: dilute donor molecules in an acceptor host matrix exhibit ultrafast excitation energy transfer (EET) to the host, which suppresses the free charge yield. We observe an optimal photochemical driving force for free charge generation, as detected via time-resolved microwave conductivity (TRMC), but with a low yield when the sensitizer is excited. Meanwhile, transient absorption shows that transferred excitons efficiently produce charge-transfer states. This behavior is well described by a competition for the excited state between long-range electron transfer that produces free charge and EET that ultimately produces only localized charge-transfer states. It cannot be explained if the most localized CT states are the intermediate between excitons and the free charge in this system.
在有机光伏器件中，供体 - 受体界面间的能量转移通常对器件性能有益，因为它有助于将能量传输到自由电荷产生的位点。在此，我们展示了一种相反的情况：受体主体基质中的稀供体分子表现出向主体的超快激发能量转移（EET），这抑制了自由电荷产率。我们通过时间分辨微波电导率（TRMC）检测到自由电荷产生存在最佳光化学驱动力，但当敏化剂被激发时产率较低。同时，瞬态吸收表明转移的激子有效地产生电荷转移态。这种行为可以通过产生自由电荷的长程电子转移与最终仅产生局域电荷转移态的EET之间对激发态的竞争很好地描述。如果在此系统中最局域的电荷转移态是激子和自由电荷之间的中间体，那么这种行为就无法解释。
