层状钙钛矿中的光致碘化物排斥和卤化物分层
Photoinduced iodide repulsion and halides-demixing in layered perovskites
摘要：
在金属卤化物钙钛矿（MHP）中混合卤化物是调节MHP带隙以用于叠层太阳能电池的有效方法。然而，混合卤化物（MH-）MHP在连续光照下发生光诱导相分离（LIPS）。因此，了解LIPS的机制对于开发稳定的MH-MHPs是必要的。在这项工作中，我们研究了层状（L）MHP中的LIPS，并发现了间隔阳离子在LIPS中的关键作用。通过对LIPS化学变化的研究，揭示了LIPS过程中光照区碘离子排斥和富Br相的形成。这一发现也为三维（3D）MHP中的LIPS过程提供了深入了解。通过进一步研究LIPS在3D MHP中的作用，我们发现LIPS不仅诱导了富Br和富I畴的形成，而且还诱导了卤化物沿膜厚度方向分布的整体变化，这可以影响电子能量的取向，从而影响MHP器件的性能。此外，由于光生载流子的更大群体，LIPS在本体中更显著。总之，本研究揭示了LIPS在MHP中的化学机理及其对器件性能的潜在影响，为理解LIPS机理和提高MHP的稳定性提供了见解。
英文摘要：
Mixing halides in metal halide perovskites (MHPs) is an effective approach to adjust MHPs bandgap for applications in tandem solar cells. However, mixed-halide (MH-) MHPs undergo light-induced-phase-segregation (LIPS) under continuous illumination. Therefore, understanding the mechanism of LIPS is necessary for developing stable MH-MHPs. In this work, we investigated LIPS in layered (L) MHPs and discovered a critical role of spacer cations in LIPS. Through probing chemical changes of LIPS, we unveil light-induced-iodide-repulsion and the formation of Br-rich-phase in illuminated regions during LIPS. This discovery also gives insight into LIPS process in three dimensional (3D) MHPs. By further investigating LIPS in 3D MHPs, we reveal that LIPS induces not only the formation of Br-rich and I-rich domains but also an overall change of halide distribution along the film thickness direction, which can affect the electronic energy alignment and consequently MHPs devices performance. Moreover, LIPS is more significant in the bulk due to larger population of photogenerated charge carriers. Overall, this study reveals the chemical mechanism of LIPS in MHPs and its potential effect on device performance, offering insight into understanding LIPS mechanism and improving the stability of MHPs.
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