有机半导体器件中准费米能级分裂的直接量化
Direct quantification of quasi-Fermi level splitting in organic semiconductor devices
摘要：
开路电压的非辐射损耗是限制有机光伏器件的功率转换效率的主要因素。占主导地位的非辐射损耗是有源层固有的，可以从准费米能级分裂（QFLS）和光电压的辐射热力学极限来确定。由于光激发的激子性质和与器件结构相关的非辐射损耗的额外来源，具有低迁移率的薄膜器件中的QFLS的量化是具有挑战性的。这项工作概述了一种基于电调制光致发光的实验方法，该方法可用于直接测量开路电压的固有非辐射损耗，从而量化QFLS。漂移扩散模拟表明，该方法准确地预测QFLS在大部分的设备，而不管设备相关的非辐射损失。国家的最先进的PM6：Y6为基础的有机太阳能电池作为一个模型来测试的实验方法，QFLS被量化，并显示为独立的设备架构。这项工作提供了一种方法来量化的QFLS的有机太阳能电池在工作条件下，充分表征开路电压的非辐射损耗的不同贡献。所报道的方法将不仅有助于表征和理解有机太阳能电池中的损耗，而且还有助于其他器件平台，如发光二极管和光电探测器。
英文摘要：
Non-radiative losses to the open-circuit voltage are a primary factor in limiting the power conversion efficiency of organic photovoltaic devices. The dominant non-radiative loss is intrinsic to the active layer and can be determined from the quasi-Fermi level splitting (QFLS) and the radiative thermodynamic limit of the photovoltage. Quantification of the QFLS in thin film devices with low mobility is challenging due to the excitonic nature of photoexcitation and additional sources of nonradiative loss associated with the device structure. This work outlines an experimental approach based on electro-modulated photoluminescence, which can be used to directly measure the intrinsic non-radiative loss to the open-circuit voltage; thereby, quantifying the QFLS. Drift-diffusion simulations are carried out to show that this method accurately predicts the QFLS in the bulk of the device regardless of device-related non-radiative losses. State-of-the-art PM6:Y6-based organic solar cells are used as a model to test the experimental approach, and the QFLS is quantified and shown to be independent of device architecture. This work provides a method to quantify the QFLS of organic solar cells under operational conditions, fully characterizing the different contributions to the non-radiative losses of the open-circuit voltage. The reported method will be useful in not only characterizing and understanding losses in organic solar cells, but also other device platforms such as light-emitting diodes and photodetectors.
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