Photon Reabsorption Masks Intrinsic Bimolecular Charge-Carrier Recombination in CH3NH3PbI3 Perovskite
Photon Reabsorption Masks Intrinsic Bimolecular Charge-Carrier Recombination in CH3NH3PbI3 Perovskite
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DOI：
10.1021/acs.nanolett.7b02834
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发表时间：
2017-09-01
期刊：
影响因子：
10.8
通讯作者：
Herz, Laura M.
中科院分区：
文献类型：
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作者：
Crothers, Timothy W.;Milot, Rebecca L.;Herz, Laura M.
了解载流子复合过程对于开发用于光伏应用的混合金属卤化物钙钛矿至关重要。我们表明，CH3NH3PbI3 中辐射双分子复合常数的典型测量受到光子重吸收的强烈影响，光子重吸收掩盖了更大的本征双分子复合速率常数。通过研究一组厚度在 50 至 533 nm 之间的薄膜，我们发现随着薄膜厚度的增加，双分子电荷复合速率似乎减慢了一个数量级。然而，通过使用考虑光子重吸收和电荷载流子扩散的动力学模型，我们确定，无论薄膜厚度如何，所有样品都有一个值为 6.8 X 10(-10) cm(3)s(-1) 的单一本征双分子复合系数。因此，我们假设报道的此类系数的广泛文献值部分归因于具有影响光散射的不同尺寸的晶粒或介孔支架的样品之间的光子输出耦合的差异，而更薄的薄膜或折射率匹配的周围层可以降低光子重吸收的可能性。我们讨论了光子限制对薄光伏层中自由电荷载流子保留的关键作用，并重点介绍了一种通过瞬态光谱测量评估此类方案成功与否的方法。
An understanding of charge-carrier recombination processes is essential for the development of hybrid metal halide perovskites for photovoltaic applications. We show that typical measurements of the radiative bimolecular recombination constant in CH3NH3PbI3 are strongly affected by photon reabsorption that masks a much larger intrinsic bimolecular recombination rate constant. By investigating a set of films whose thickness varies between 50 and 533 nm, we find that the bimolecular charge recombination rate appears to slow by an order of magnitude as the film thickness increases. However, by using a dynamical model that accounts for photon reabsorption and charge-carrier diffusion we determine that a single intrinsic bimolecular recombination coefficient of value 6.8 X 10(-10) cm(3)s(-1) is common to all samples irrespective of film thickness. Hence, we postulate that the wide range of literature values reported for such coefficients is partly to blame on differences in photon out-coupling between samples with crystal grains or mesoporous scaffolds of different sizes influencing light scattering, whereas thinner films or index-matched surrounding layers can reduce the possibility for photon reabsorption. We discuss the critical role of photon confinement on free charge-carrier retention in thin photovoltaic layers and highlight an approach to assess the success of such schemes from transient spectroscopic measurement.