Nonradiative Energy Losses in Bulk-Heterojunction Organic Photovoltaics
Nonradiative Energy Losses in Bulk-Heterojunction Organic Photovoltaics
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DOI：
10.1103/physrevx.8.031055
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发表时间：
2018-09-07
影响因子：
12.5
通讯作者：
Nelson, Jenny
中科院分区：
文献类型：
--
作者：
Azzouzi, Mohammed;Yan, Jun;Nelson, Jenny
基于分子电子材料的太阳能电池的性能受到相对高的非辐射电压损耗的限制。有机供体-受体异质结器件中非辐射复合的主要途径被认为是电荷转移（CT）激发态经由能量转移到振动模式而衰减到基态。最近，非辐射电压损失已经与电荷转移状态的性质有关，例如描述CT和基态振动状态重叠的弗兰克-康登因子，因此与CT状态的能量有关。然而，实验数据并不总是遵循简单模型所建议的趋势。在这里，我们扩展这个复合模型，包括影响非辐射衰减速率常数的其他因素，因此开路电压，但尚未详细探讨。我们使用扩展的模型来理解所观察到的一系列小分子的行为：富勒烯共混物设备，其中开路电压出现不敏感的非辐射损耗。这种趋势只能用依赖于微观结构的CT态振子强度来解释，表明CT态能量以外的参数可以控制非辐射复合。我们提出了通过控制材料参数来提高开路电压的设计规则，并对有机太阳能电池的功率转换效率提出了一个现实的限制。
The performance of solar cells based on molecular electronic materials is limited by relatively high nonradiative voltage losses. The primary pathway for nonradiative recombination in organic donor-acceptor heterojunction devices is believed to be the decay of a charge-transfer (CT) excited state to the ground state via energy transfer to vibrational modes. Recently, nonradiative voltage losses have been related to properties of the charge-transfer state such as the Franck-Condon factor describing the overlap of the CT and ground-state vibrational states and, therefore, to the energy of the CT state. However, experimental data do not always follow the trends suggested by the simple model. Here, we extend this recombination model to include other factors that influence the nonradiative decay-rate constant, and therefore the open-circuit voltage, but have not yet been explored in detail. We use the extended model to understand the observed behavior of series of small molecules: fullerene blend devices, where open-circuit voltage appears insensitive to nonradiative loss. The trend could be explained only in terms of a microstructure-dependent CT-state oscillator strength, showing that parameters other than CT-state energy can control nonradiative recombination. We present design rules for improving open-circuit voltage via the control of material parameters and propose a realistic limit to the power-conversion efficiency of organic solar cells.