Knight Alexander J, Borchert Juliane, Oliver Robert D J, Patel Jay B, Radaelli Paolo G, Snaith Henry J, Johnston Michael B, Herz Laura M
Department of Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom.
ACS Energy Lett. 2021 Feb 12;6(2):799-808. doi: 10.1021/acsenergylett.0c02475. Epub 2021 Feb 1.
Mixed-halide perovskites offer bandgap tunability essential for multijunction solar cells; however, a detrimental halide segregation under light is often observed. Here we combine simultaneous in situ photoluminescence and X-ray diffraction measurements to demonstrate clear differences in compositional and optoelectronic changes associated with halide segregation in MAPb(BrI) and FACsPb(BrI) films. We report evidence for low-barrier ionic pathways in MAPb(BrI), which allow for the rearrangement of halide ions in localized volumes of perovskite without significant compositional changes to the bulk material. In contrast, FACsPb(BrI) lacks such low-barrier ionic pathways and is, consequently, more stable against halide segregation. However, under prolonged illumination, it exhibits a considerable ionic rearrangement throughout the bulk material, which may be triggered by an initial demixing of A-site cations, altering the composition of the bulk perovskite and reducing its stability against halide segregation. Our work elucidates links between composition, ionic pathways, and halide segregation, and it facilitates the future engineering of phase-stable mixed-halide perovskites.
混合卤化物钙钛矿为多结太阳能电池提供了至关重要的带隙可调性；然而，经常观察到光照下有害的卤化物偏析现象。在此，我们结合同步原位光致发光和X射线衍射测量，以证明在MAPb(BrI)和FACsPb(BrI)薄膜中，与卤化物偏析相关的成分和光电变化存在明显差异。我们报告了MAPb(BrI)中低势垒离子通道的证据，该通道允许卤化物离子在钙钛矿的局部区域重排，而不会对块状材料的成分产生显著变化。相比之下，FACsPb(BrI)缺乏这种低势垒离子通道，因此对卤化物偏析更稳定。然而，在长时间光照下，它在整个块状材料中表现出相当大的离子重排，这可能是由A位阳离子的初始混合引发的，改变了块状钙钛矿的成分，并降低了其对卤化物偏析的稳定性。我们的工作阐明了成分、离子通道和卤化物偏析之间的联系，并有助于未来对相稳定混合卤化物钙钛矿的工程设计。
