Enhanced Radiative Recombination of Excitons and Free Charges Due to Local Deformations in the Band Structure of MAPbBr3 Perovskite Crystals,The Journal of Physical Chemistry C

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Enhanced Radiative Recombination of Excitons and Free Charges Due to Local Deformations in the Band Structure of MAPbBr3 Perovskite Crystals
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2019-05-28 , DOI: 10.1021/acs.jpcc.9b01968
Pushpendra Kumar ₁ , Qi Shi ₁ , Khadga Jung Karki ₁

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We have imaged the emissions from excitons and free charges in a methylammonium lead bromide perovskite (MAPbBr₃) crystal. In a direct band gap semiconductor, dynamics of excited electrons and holes in hybrid lead-halide perovskites is rather complex because of the formation of excitons and the presence of traps and structural inhomogeneities. A recent report by Nah et al. (Nah, S.; Spokoyny, B.; Stoumpos, C.; Soe, C. M. M.; Kanatzidis, M.; Harel, E. Nat. Photonics2017,11, 285–288) has identified spatially segregated populations of excitons and free charges in perovskites. Understanding the cause of segregation and how such distributions contribute to the photoresponse has remained a challenge. Here, we have used phase-modulated two-photon photoluminescence microspectroscopy to separately quantify the emissions from excitons and free charges in a MAPbBr₃ crystal. Our results show that while most of the emission at room temperature is from the recombination of free charges, there are also localized spots where the emissions from excitons dominate. By analyzing the enhancement of the emissions at low temperatures, we show that the trap-mediated nonradiative recombinations are suppressed by local deformations in the band structure. The deformations that are induced by local strains in the crystal prevent excitons and free charges from reaching the traps. Our results indicate that strain engineering through structural designs can improve the performance of perovskite light-emitting diodes.

中文翻译：

由于MAPbBr3钙钛矿晶体的能带结构中的局部变形，激子和自由电荷的增强的辐射复合。

我们已经对甲基铵溴化钙钛矿（MAPbBr ₃）晶体中激子和自由电荷的发射进行了成像。在直接带隙半导体中，由于激子的形成以及陷阱和结构不均匀性的存在，混合卤化钙钛矿中激发电子和空穴的动力学相当复杂。Nah等人的最新报告。（罗，S。; Spokoyny，B。; Stoumpos，C。;梭，CMM; Kanatzidis，M。;哈雷尔，E. 。纳特光子学2017年，11，285-288）确定了钙钛矿中激子和自由电荷在空间上的隔离种群。了解分离的原因以及这种分布如何引起光响应仍然是一个挑战。在这里，我们使用了相位调制的双光子光致发光光谱仪来分别量化MAPbBr _3中激子和自由电荷的发射水晶。我们的结果表明，尽管室温下的大多数排放是由于自由电荷的重组，但在激子的排放中仍存在局部斑点。通过分析低温下发射的增强，我们表明，陷阱能带动的非辐射复合被能带结构中的局部变形所抑制。晶体中局部应变引起的形变阻止了激子和自由电荷到达陷阱。我们的结果表明，通过结构设计进行应变工程可以提高钙钛矿发光二极管的性能。

更新日期：2019-05-28

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