Chemical Physics and Nano Lund, Lund University, Box 124, Lund, 22100, Sweden.
Helmholtz-Zentrum Berlin GmbH, Institut fur Silizium Photovoltaik, Kekuléstrasse 5, Berlin, 12489, Germany.
Nat Commun. 2017 Jun 26;8(1):34. doi: 10.1038/s41467-017-00058-w.
Solution-processed organometal halide perovskites are hybrid crystalline semiconductors highly interesting for low-cost and efficient optoelectronics. Their properties are dependent on the crystal structure. Literature shows a variety of crystal phase transition temperatures and often a spread of the transition over tens of degrees Kelvin. We explain this inconsistency by demonstrating that the temperature of the tetragonal-to-orthorhombic phase transition in methylammonium lead triiodide depends on the concentration and nature of local defects. Phase transition in individual nanowires was studied by photoluminescence microspectroscopy and super-resolution imaging. We propose that upon cooling from 160 to 140 K, domains of the crystal containing fewer defects stay in the tetragonal phase longer than highly defected domains that readily transform to the high bandgap orthorhombic phase at higher temperatures. The existence of relatively pure tetragonal domains during the phase transition leads to drastic photoluminescence enhancement, which is inhomogeneously distributed across perovskite microcrystals.Understanding crystal phase transition in materials is of fundamental importance. Using luminescence spectroscopy and super-resolution imaging, Dobrovolsky et al. study the transition from the tetragonal to orthorhombic crystal phase in methylammonium lead triiodide nanowires at low temperature.
溶液处理的有机金属卤化物钙钛矿是混合结晶半导体，对低成本和高效光电非常有趣。它们的性质取决于晶体结构。文献表明，各种晶相转变温度，并且经常在数十摄氏度的范围内转变。我们通过证明碘化甲基铵铅中的四方-正交相转变的温度取决于局部缺陷的浓度和性质，解释了这种不一致性。通过光致发光微光谱和超分辨率成像研究了个别纳米线中的相转变。我们提出，在从 160 到 140 K 冷却时，含缺陷较少的晶体域比容易在较高温度下转变为高带隙正交相的高度缺陷域在四方相中停留更长时间。在相变期间存在相对纯净的四方域会导致荧光强度急剧增强，这在钙钛矿微晶中呈不均匀分布。了解材料的晶体相变具有重要的基础意义。Dobrovolsky 等人使用发光光谱和超分辨率成像研究了低温下碘化甲基铵铅纳米线中从四方相到正交相的转变。
