Chen Zehua, Brocks Geert, Tao Shuxia, Bobbert Peter A
Materials Simulation and Modelling, Department of Applied Physics, Eindhoven University of Technology, Eindhoven, The Netherlands.
Center for Computational Energy Research, Department of Applied Physics, Eindhoven University of Technology, Eindhoven, The Netherlands.
Nat Commun. 2021 May 11;12(1):2687. doi: 10.1038/s41467-021-23008-z.
Mixed halide perovskites that are thermodynamically stable in the dark demix under illumination. This is problematic for their application in solar cells. We present a unified thermodynamic theory for this light-induced halide segregation that is based on a free energy lowering of photocarriers funnelling to a nucleated phase with different halide composition and lower band gap than the parent phase. We apply the theory to a sequence of mixed iodine-bromine perovskites. The spinodals separating metastable and unstable regions in the composition-temperature phase diagrams only slightly change under illumination, while light-induced binodals separating stable and metastable regions appear signalling the nucleation of a low-band gap iodine-rich phase. We find that the threshold photocarrier density for halide segregation is governed by the band gap difference of the parent and iodine-rich phase. Partial replacement of organic cations by cesium reduces this difference and therefore has a stabilizing effect.
在黑暗中热力学稳定的混合卤化物钙钛矿在光照下会发生相分离。这对它们在太阳能电池中的应用来说是个问题。我们基于光生载流子向卤化物组成不同且带隙比母相低的成核相漏斗化导致自由能降低，提出了一种关于这种光致卤化物偏析的统一热力学理论。我们将该理论应用于一系列碘 - 溴混合钙钛矿。在组成 - 温度相图中，分隔亚稳区和不稳定区的旋节线在光照下仅略有变化，而分隔稳定区和亚稳区的光致双节线出现，标志着低带隙富碘相的成核。我们发现卤化物偏析的光生载流子密度阈值由母相和富碘相的带隙差决定。用铯部分取代有机阳离子会减小这种差异，因此具有稳定作用。
