Valencia, 11th November 2019
Raquel Chulia-Jordan, Natalia Fernández-Delgado, Emilio Jose Juarez-Perez, Iván Mora Seró, Miriam Herrera-Collado, Sergio Molina and Juan Martínez-Pastor
Inhibition of light emission from metastable tetragonal phase at low temperatures in island-like films of lead iodide perovskites
Nanoscale, in press (2019).
Photonic applications based on halide perovskites, namely CH3NH3PbI3 (MAPbI3), have recently attracted remarkable attention due to the high efficiencies reported for photovoltaic and light emitting devices. Despite these outstanding results, there are many temperature-, laser excitation power-, and morphology-dependent phenomena that require further research to be completely understood. In this work, we have investigated in detail the nature of exciton optical transitions and recombination dynamics below and above the orthorhombic/tetragonal (‘O‘-/‘T‘-) temperature phase transition (∼150 K) depending on the material continuity (continuous-like) or discontinuity (island-like) in MAPbI3 films. At low temperatures, continuous thin films of perovskite can exhibit strain inhomogeneities associated to the formation of different ‘T‘-defective domains leading to an energy spread of states over more than 200 meV. On the opposite, a single photoluminescence line peak related to the perovskite ‘O‘-phase (associated to the distortion of the [PbI3]- anion) is observed in the island-like sample that we attribute to strain relaxation for this morphology. Moreover, the predominantly radiative recombination dynamics of the continuous-like sample is mainly originated from nongeminate electron-hole formation of excitons in the ‘O‘-phase and the internal dynamics with carrier trapping levels. This observation is in strong contrast to the free exciton recombination dominant found in the island-like sample.
Valencia, 4th November 2019
J. Navarro-Arenas, I. Suárez, V. S. Chirvony, A. F. Gualdrón-Reyes, I. Mora-Seró, J. P. Martínez-Pastor,
Single-Exciton Amplified Spontaneous Emission in Thin Films of CsPbX3 (X=Br, I) Perovskite Nanocrystals
J. Phys. Chem. Lett. 10, 6389−6398 (2019).
CsPbX3 perovskite nanocrystals (PNCs) have emerged as an excellent material for stimulated emission purposes, with even more prospective applications than conventional colloidal quantum dots. However, a better understanding of the physical mechanisms responsible for amplified spontaneous emission (ASE) is required to achieve more ambitious targets (lasing under continuous wave optical or electrical excitation). Here, we establish the intrinsic mechanisms underlying ASE in PNCs of three different band gaps (CsPbBr3, CsPbBr1.5I1.5, and CsPbI3). Our characterization at cryogenic temperatures does not reveal any evidence of the biexciton mechanism in the formation of ASE. Instead, the measured shift toward long wavelengths of the ASE band is easily explained by the reabsorption in the PNC layer, which becomes stronger for thicker layers. In this way, the threshold of ASE is determined only by optical losses at a given geometry, which is the single-exciton mechanism responsible for ASE. Experimental results are properly reproduced by a physical model.
Valencia, 17th October 2019
DROP-IT has received funding from the European Union’s Horizon 2020 FET-OPEN research programme under grant agreement No 862656.