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

该方案的目的是利用时间延迟收集场(TDCF)实验来量化几种聚合物：富勒烯共混物的电场和温度随激发波长的变化，并阐明电荷转移态(CT-)在聚合物基有机太阳能电池中的作用。目前的申请者和其他小组的工作表明，有机施主-接受体异质结太阳能电池中的电荷分离涉及电子驰豫和振荡性热化的CT态。因此，太阳能电池的行为很大程度上受到这些状态分裂效率的影响。我们预计，热化CT激子相对于自由电荷能量的准确能量位置对于有机太阳能电池的光伏功能是至关重要的。因此，该提议的中心点是测量作为几个参数的函数的发电效率，重点是仅激发低能CT态。这些实验将在聚合物：富勒烯共混物上进行，分别具有可变的、可调的施主和受主的电离能和电子亲和力的位置。通过TDCF实验，我们希望检查经常观察到的场相关的产生是主要是热激活的CT态分离的结果还是场辅助隧穿的结果。除了这些测量，我们还将调查从室温下的实验得出的假设，即自由电荷的产生主要由热化的CT态介导，是否普遍有效，即使在低热能的情况下也是如此。三元聚合物：富勒烯1：富勒烯2共混物的选择性CT激发的TDCF实验将被用来显示CT态是否在几个富勒烯上离域。最后，对二元聚合物：低聚合物浓度的富勒烯共混物进行了详细的实验。在这种共混物中，我们期望与聚合物形成两相结构：富勒烯共混域和纯富勒烯域。我们将研究在这样的两相体系中，是否以及在什么情况下CT状态的无激活分离也会发生，就像现在在几个已建立的聚合物：富勒烯混合物中所看到的那样。这项工作的发现将对全面了解有机太阳能电池中的电荷产生具有重要意义，并将为进一步提高太阳能电池的效率奠定基础。

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.