Ceratti D R, Cohen A V, Tenne R, Rakita Y, Snarski L, Jasti N P, Cremonesi L, Cohen R, Weitman M, Rosenhek-Goldian I, Kaplan-Ashiri I, Bendikov T, Kalchenko V, Elbaum M, Potenza M A C, Kronik L, Hodes G, Cahen D
Weizmann Institute of Science, Department of Materials and Interfaces, 7610001, Rehovot, Israel.
Mater Horiz. 2021 May 1;8(5):1570-1586. doi: 10.1039/d1mh00006c. Epub 2021 Mar 30.
We find significant differences between degradation and healing at the surface or in the bulk for each of the different APbBr single crystals (A = CHNH, methylammonium (MA); HC(NH), formamidinium (FA); and cesium, Cs). Using 1- and 2-photon microscopy and photobleaching we conclude that kinetics dominate the surface and thermodynamics the bulk stability. Fluorescence-lifetime imaging microscopy, as well as results from several other methods, relate the (damaged) state of the halide perovskite (HaP) after photobleaching to its modified optical and electronic properties. The A cation type strongly influences both the kinetics and the thermodynamics of recovery and degradation: FA heals best the bulk material with faster self-healing; Cs protects the surface best, being the least volatile of the A cations and possibly through O-passivation; MA passivates defects via methylamine from photo-dissociation, which binds to Pb. DFT simulations provide insight into the passivating role of MA, and also indicate the importance of the Br defect as well as predicts its stability. The occurrence and rate of self-healing are suggested to explain the low effective defect density in the HaPs and through this, their excellent performance. These results rationalize the use of mixed A-cation materials for optimizing both solar cell stability and overall performance of HaP-based devices, and provide a basis for designing new HaP variants.
我们发现，对于每种不同的APbBr单晶（A = CHNH，甲胺（MA）；HC(NH)，甲脒（FA）；以及铯，Cs），其表面或内部的降解和愈合存在显著差异。通过单光子和双光子显微镜以及光漂白技术，我们得出结论：动力学主导表面过程，而热力学主导整体稳定性。荧光寿命成像显微镜以及其他几种方法的结果，将光漂白后卤化物钙钛矿（HaP）的（受损）状态与其改性的光学和电子性质联系起来。A阳离子类型强烈影响恢复和降解的动力学及热力学：FA对整体材料的愈合效果最佳，自我愈合速度更快；Cs对表面的保护效果最佳，它是挥发性最低的A阳离子，可能通过氧钝化作用；MA通过来自光解离的甲胺钝化缺陷，甲胺与Pb结合。密度泛函理论（DFT）模拟深入了解了MA的钝化作用，同时也表明了Br缺陷的重要性并预测了其稳定性。自我愈合的发生和速率被认为可以解释HaP中低有效缺陷密度，并由此解释其优异性能。这些结果为使用混合A阳离子材料优化基于HaP的器件的太阳能电池稳定性和整体性能提供了理论依据，并为设计新型HaP变体提供了基础。
