Kamat Prashant V, Kuno Masaru
Acc Chem Res. 2021 Feb 2;54(3):520-531. doi: 10.1021/acs.accounts.0c00749. Epub 2021 Jan 21.
ConspectusThe optical and electronic properties of metal halide perovskites provide insight into the operation of solar cells as well as their long-term operational stability. Halide mobility in perovskite films is an important factor influencing solar cell performance. One can visualize halide ion migration through halide exchange between two nanocrystal suspensions or between physically paired films of two different metal halide perovskites. The ability to tune band gap by varying halide ratios (Cl:Br or Br:I) allows the synthesis of mixed halide perovskites with tailored absorption and emission across the entire visible spectrum. Interestingly, mixed halide (e.g., MAPb(BrI)) films undergo phase segregation to form Br-rich and I-rich sites under steady state illumination. Upon halting illumination, segregated phases mix to restore original mixed halide compositions. Introducing multiple cations (Cs, formamidinium) at the A site or alloying with Cl greatly suppresses halide mobilities. Long-term irradiation of MAPb(BrI) films also cause expulsion of iodide leaving behind Br-rich phases. Hole trapping at I-rich sites in MAPb(BrI) is considered to be an important step in inducing halide mobility in photoirradiated films. This Account focuses on halide ion migration in nanocrystals and nanostructured films driven by entropy of mixing in dark and phase segregation under light irradiation.
综述
金属卤化物钙钛矿的光学和电子性质有助于深入了解太阳能电池的运行及其长期运行稳定性。钙钛矿薄膜中的卤化物迁移率是影响太阳能电池性能的一个重要因素。人们可以通过两种纳米晶体悬浮液之间或两种不同金属卤化物钙钛矿的物理配对薄膜之间的卤化物交换来观察卤离子迁移。通过改变卤化物比例（Cl:Br或Br:I）来调节带隙的能力使得能够合成在整个可见光谱范围内具有定制吸收和发射特性的混合卤化物钙钛矿。有趣的是，混合卤化物（例如MAPb(BrI)）薄膜在稳态光照下会发生相分离，形成富Br和富I的位点。停止光照后，分离的相会混合以恢复原始的混合卤化物组成。在A位点引入多个阳离子（Cs、甲脒）或与Cl合金化会极大地抑制卤化物迁移率。长期照射MAPb(BrI)薄膜也会导致碘化物排出，留下富Br相。MAPb(BrI)中富I位点的空穴捕获被认为是在光辐照薄膜中诱导卤化物迁移的一个重要步骤。本综述重点关注由黑暗中的混合熵和光照下的相分离驱动的纳米晶体和纳米结构薄膜中的卤离子迁移。
