Liu Albert, Almeida Diogo B, Bonato Luiz G, Nagamine Gabriel, Zagonel Luiz F, Nogueira Ana F, Padilha Lazaro A, Cundiff S T
Department of Physics, University of Michigan, Ann Arbor, MI 48109, USA.
Instituto de Química, Universidade Estadual de Campinas, 13083-970 Campinas, São Paulo, Brazil.
Sci Adv. 2021 Jan 1;7(1). doi: 10.1126/sciadv.abb3594. Print 2021 Jan.
Advances in optoelectronics require materials with novel and engineered characteristics. A class of materials that has garnered tremendous interest is metal-halide perovskites, stimulated by meteoric increases in photovoltaic efficiencies of perovskite solar cells. In addition, recent advances have applied perovskite nanocrystals (NCs) in light-emitting devices. It was found recently that, for cesium lead-halide perovskite NCs, their unusually efficient light emission may be due to a unique excitonic fine structure composed of three bright triplet states that minimally interact with a proximal dark singlet state. To study this fine structure without isolating single NCs, we use multidimensional coherent spectroscopy at cryogenic temperatures to reveal coherences involving triplet states of a CsPbI NC ensemble. Picosecond time scale dephasing times are measured for both triplet and inter-triplet coherences, from which we infer a unique exciton fine structure level ordering composed of a dark state energetically positioned within the bright triplet manifold.
光电子学的进步需要具有新颖和工程特性的材料。一类引起极大关注的材料是金属卤化物钙钛矿，钙钛矿太阳能电池光伏效率的迅速提高激发了人们对它的兴趣。此外，最近的进展已将钙钛矿纳米晶体（NCs）应用于发光器件。最近发现，对于铯铅卤化物钙钛矿纳米晶体，其异常高效的发光可能归因于一种独特的激子精细结构，该结构由三个明亮的三重态组成，它们与近端暗单重态的相互作用极小。为了在不分离单个纳米晶体的情况下研究这种精细结构，我们在低温下使用多维相干光谱来揭示涉及CsPbI纳米晶体集合三重态的相干性。测量了三重态和三重态间相干性的皮秒时间尺度退相时间，由此我们推断出一种独特的激子精细结构能级排序，其中暗态在能量上位于明亮的三重态流形内。
