The Role of Charge Transfer States in Free Charge Generation in Organic Donor-Acceptor Solar Cells

该建议的目的是使用时间延迟收集场（TDCF）实验来量化作为激发波长的函数的几种聚合物：富勒烯共混物的场和温度依赖性，并澄清电荷转移（CT-）状态在基于聚合物的有机太阳能电池中的作用。当前申请人和其他小组的工作表明，有机供体-受体本体异质结太阳能电池中的电荷分离涉及电子弛豫和振动热化CT-状态。因此，太阳能电池的行为受到这些状态分裂效率的显著影响。我们预期，准确的能量位置的热化CT-激子的自由电荷的能量是至关重要的有机太阳能电池的光伏功能，因此，中心点的建议是测量发电效率作为几个参数的函数，重点是激发低能量CT-状态。这些实验将进行聚合物：富勒烯共混物与变量，可调位置的电离能和电子亲合势的供体和acceptor，分别与TDCF实验作为电场和温度的函数，我们要检查是否经常观察到的场依赖产生的结果，主要是热激活的CT-状态分离或场辅助隧穿。除了这些测量，我们将调查是否推定，从实验中得出在室温下，即自由电荷的产生主要是介导的热化CT状态是普遍有效的，即使在低热能的情况下。TDCF实验与选择性CT-激发三元聚合物：富勒烯1：富勒烯2共混物将进行显示CT-状态是否离域超过几个富勒烯或没有。最后，详细的实验二元聚合物：富勒烯低聚合物浓度的共混物计划。在这样的共混物中，我们期望形成一个两相结构的聚合物：富勒烯共混域和纯富勒烯域。我们将调查，如果和在何种情况下activationless分离CT状态，现在看到在几个既定的聚合物：富勒烯共混物，也发生在这样的两相系统。这项工作的结果将是重要的，为全面了解电荷产生的有机太阳能电池，并将形成基础，进一步提高太阳能电池的效率。

The aim of this proposal is to use time delayed collection field (TDCF) experiments to quantify the field and temperature dependence of several polymer:fullerene blends as a function of excitation wavelength, and to clarify the role of charge transfer- (CT-) states in polymer-based organic solar cells.Current applicants and other groups work indicated that charge separation in organic donor-acceptor bulk heterojunction solar cells involves electronically relaxed and vibronically thermalized CT-states. Thus, the solar cells behavior is significantly affected by the efficiency of split-up of these states. We expect that the exact energetic position of thermalized CT-excitons in relation to the energy of free charges is of vital importance for the photovoltaic function of organic solar cells.Therefore, the central point of this proposal is to measure generation efficiency as function of several parameters with emphasis on exciting only low energy CT-states. These experiments will be conducted on polymer:fullerene blends with variable, tunable position of the ionization energy and electron affinity of the donor and acceptor, respectively.With TDCF experiments as a function of the electric field and temperature we like to examine whether the often observed field dependent generation is a result of mainly thermally activated separation of CT-states or of field-assisted tunneling. In addition to these measurements, we will investigate whether the presumption, drawn from experiments at room temperature, that free charge generation is mainly mediated by thermalized CT states is generally valid, even in the case at low thermal energies. TDCF experiments with selective CT-excitation on ternary polymer:fullerene1:fullerene2 blends will be conducted to show whether CT-states are delocalized over several fullerenes or not. Finally, detailed experiments on binary polymer:fullerene blends with low polymer concentrations are planned. In such blends, we expect the formation of a two-phase structure with polymer:fullerene blend domains and pure fullerene domains. We will investigate if and under which circumstances activationless separation of CT states, as now seen in several established polymer:fullerene blends, does also occur in such two-phase systems. Findings of this work will be important for a comprehensive understanding of charge generation in organic solar cells and will form the base for further improvement of solar cell efficiency.