Competition between the Charge Transfer State and the Singlet States of Donor or Acceptor Limiting the Efficiency in Polymer:Fullerene Solar Cells
Competition between the Charge Transfer State and the Singlet States of Donor or Acceptor Limiting the Efficiency in Polymer:Fullerene Solar Cells
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DOI：
10.1021/ja210029w
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发表时间：
2012-01-11
影响因子：
15
通讯作者：
Nelson, Jenny
中科院分区：
文献类型：
--
作者：
Faist, Mark A.;Kirchartz, Thomas;Nelson, Jenny
我们通过测量高性能聚合物与富勒烯受体的共混薄膜中的电致发光（EL）和光致发光（PL）来研究电荷转移（CT）态的外观和能量。 EL 光谱提供了界面态能量的直接探测，无需依赖原始材料中估计的 LUMO 和 HOMO 能量。对于每种聚合物，我们使用具有不同 LUMO 能级的不同富勒烯作为电子受体，以改变相对于与 [6,6]-苯基 C61-丁酸甲酯 (PCBM) 共混物的 CT 态能量。当CT态发射的能量接近具有较小光学带隙的共混组分的吸收开始时，E-opt,E-min等于min{E-opt,E-donor; E-opt,E-acceptor}，我们观察到 EL 光谱从 CT 发射到带隙较小的组件的单线态发射的转变。组件单线态发射的出现与光电流和填充因子的降低相一致。我们得出的结论是，开路电压 V-OC 受到两个混合组件中较小带隙的限制。根据所研究材料的损耗，我们得出开路电压的经验极限：V-OC 小于或类似于 E-opt,E-min/e - (0.66 +/- 0.08)eV。
We study the appearance and energy of the charge transfer (CT) state using measurements of electroluminescence (EL) and photoluminescence (PL) in blend films of high-performance polymers with fullerene acceptors. EL spectroscopy provides a direct probe of the energy of the interfacial states without the need to rely on the LUMO and HOMO energies as estimated in pristine materials. For each polymer, we use different fullerenes with varying LUMO levels as electron acceptors, in order to vary the energy of the CT state relative to the blend with [6,6]-phenyl C61-butyric acid methyl ester (PCBM). As the energy of the CT state emission approaches the absorption onset of the blend component with the smaller optical bandgap, E-opt,E-min equivalent to min{E-opt,E-donor; E-opt,E-acceptor}, we observe a transition in the EL spectrum from CT emission to singlet emission from the component with the smaller bandgap. The appearance of component singlet emission coincides with reduced photocurrent and fill factor. We conclude that the open circuit voltage V-OC is limited by the smaller bandgap of the two blend components. From the losses of the studied materials, we derive an empirical limit for the open circuit voltage: V-OC less than or similar to E-opt,E-min/e - (0.66 +/- 0.08)eV.