Gutsev Lavrenty Gennady, Nations Sean, Ramachandran Bala Ramu, Gutsev Gennady Lavrenty, Wang Shengnian, Aldoshin Sergei, Duan Yuhua
Institute for Micromanufacturing, Louisiana Tech University, Ruston, LA 71272, USA.
Federal Research Center for Problems of Chemical Physics and Medicinal Chemistry of RAS, Semenov Prospect 1, Chernogolovka 142432, Russia.
Nanomaterials (Basel). 2023 Jan 9;13(2):276. doi: 10.3390/nano13020276.
The logic in the design of a halide-mixed APb(I1−xBrx)3 perovskite is quite straightforward: to combine the superior photovoltaic qualities of iodine-based perovskites with the increased stability of bromine-based perovskites. However, even small amounts of Br doped into the iodine-based materials leads to some instability. In the present report, using first-principles computations, we analyzed a wide variety of α-CsPbI2Br and β-CsPbI2Br phases, compared their mixing enthalpies, explored their oxidative properties, and calculated their hole-coupled and hole-free charged Frenkel defect (CFD) formations by considering all possible channels of oxidation. Nanoinclusions of bromine-rich phases in α-CsPbI2Br were shown to destabilize the material by inducing lattice strain, making it more susceptible to oxidation. The uniformly mixed phase of α-CsPbI2Br was shown to be highly susceptible towards a phase transformation into β-CsPbI2Br when halide interstitial or halide vacancy defects were introduced into the lattice. The rotation of PbI4Br2 octahedra in α-CsPbI2Br allows it either to transform into a highly unstable apical β-CsPbI2Br, which may phase-segregate and is susceptible to CFD, or to phase-transform into equatorial β-CsPbI2Br, which is resilient against the deleterious effects of hole oxidation (energies of oxidation >0 eV) and demixing (energy of mixing <0 eV). Thus, the selective preparation of equatorial β-CsPbI2Br offers an opportunity to obtain a mixed perovskite material with enhanced photostability and an intermediate bandgap between its constituent perovskites.
卤化物混合的APb(I1−xBrx)3钙钛矿的设计逻辑相当简单：将碘基钙钛矿优异的光伏性能与溴基钙钛矿增强的稳定性相结合。然而，即使向碘基材料中掺入少量溴也会导致一些不稳定性。在本报告中，我们使用第一性原理计算分析了多种α-CsPbI2Br和β-CsPbI2Br相，比较了它们的混合焓，探究了它们的氧化性质，并通过考虑所有可能的氧化通道计算了它们的空穴耦合和无空穴带电弗伦克尔缺陷（CFD）的形成。结果表明，α-CsPbI2Br中富含溴的相的纳米夹杂物会通过引起晶格应变使材料不稳定，使其更容易被氧化。当卤化物间隙或卤化物空位缺陷引入晶格时，α-CsPbI2Br的均匀混合相显示出极易转变为β-CsPbI2Br。α-CsPbI2Br中PbI4Br2八面体的旋转使其要么转变为高度不稳定的顶端β-CsPbI2Br，后者可能会发生相分离且易受CFD影响，要么相转变为赤道β-CsPbI2Br，后者能抵抗空穴氧化（氧化能>0 eV）和相分离（混合能<0 eV）的有害影响。因此，选择性制备赤道β-CsPbI2Br为获得一种具有增强光稳定性且其组成钙钛矿之间具有中间带隙的混合钙钛矿材料提供了机会。
