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Unique Optical Properties of Methylammonium Lead Iodide Nanocrystals Below the Bulk Tetragonal-Orthorhombic Phase Transition
Nano Letters ( IF 10.8 ) Pub Date : 2018-01-12 00:00:00 , DOI: 10.1021/acs.nanolett.7b04099
Benjamin T. Diroll 1 , Peijun Guo 1 , Richard D. Schaller 1, 2
Affiliation  

Methylammonium (MA) and formamidinium (FA) lead halides are widely studied for their potential as low-cost, high-performance optoelectronic materials. Here, we present measurements of visible and IR absorption, steady state, and time-resolved photoluminescence from 300 K to cryogenic temperatures. Whereas FAPbI3 nanocrystals (NCs) are found to behave in a very similar manner to reported bulk behavior, colloidal nanocrystals of MAPbI3 show a departure from the low-temperature optical behavior of the bulk material. Using photoluminescence, visible, and infrared absorption measurements, we demonstrate that unlike single crystals and polycrystalline films NCs of MAPbI3 do not undergo optical changes associated with the bulk tetragonal-to-orthorhombic phase transition, which occurs near 160 K. We find no evidence of frozen organic cation rotation to as low as 80 K or altered exciton binding energy to as low as 3 K in MAPbI3 NCs. Similar results are obtained in MAPbI3 NCs ranging from 20 to over 100 nm and in morphologies including cubes and plates. Colloidal MAPbI3 NCs therefore offer a window into the properties of the solar-relevant, room-temperature phase of MAPbI3 at temperatures inaccessible with single crystals or polycrystalline samples. Exploiting this phenomenon, these measurements reveal the existence of an optically passive photoexcited state close to the band edge and persistent slow Auger recombination at low temperature.

中文翻译:

块状四方正交相变以下的甲基铵碘化铅纳米晶体的独特光学性质

甲基铵(MA)和甲ami(FA)卤化铅由于其作为低成本,高性能光电材料的潜力而得到了广泛研究。在这里,我们介绍了从300 K到低温温度下的可见光和IR吸收,稳态和时间分辨的光致发光的测量值。尽管发现FAPbI 3纳米晶体(NCs)的行为与已报道的整体行为非常相似,但MAPbI 3的胶体纳米晶体却偏离了整体材料的低温光学行为。使用光致发光,可见光和红外吸收测量,我们证明了与MAPbI 3的单晶和多晶膜NCs不同不会发生与大块四方相到正​​交相变相关的光学变化(发生在160 K附近)。我们没有发现冷冻有机阳离子旋转至低至80 K或激子结合能降低至3 K的证据。 MAPbI 3 NC。在从20 nm到100 nm以上的MAPbI 3 NC以及包括立方体和平板的形态中都获得了相似的结果。胶体MAPbI 3因此的NC提供一个窗口,MAPbI的太阳能相关,室温相的特性3在单晶或多晶样品无法达到的温度下。利用这种现象,这些测量揭示了在带边缘附近存在光被动光激发态以及在低温下持续缓慢的俄歇复合。
更新日期:2018-01-12
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