Red-Shifted Photoluminescence from Crystal Edges Due to Carrier Redistribution and Reabsorption in Lead Triiodide Perovskites

Abstract

Photoluminescence (PL) of CH3NH3PbI3 perovskites depends strongly on sample preparation, atmosphere, crystal size, and so forth. However, the origin of these dependencies is always misunderstood because of the co-works of many different factors. Herein, we prepared hexagonal-shaped single crystals with tens of micrometers in size and observed a red-shifted PL emission (800–830 nm) mainly from the crystal edges besides the usual band-to-band transition (760 nm) from the central regions. Also, significantly different time-resolved dynamics and excitation power dependencies were observed. To summarize, we conclude that the red-shifted component comes from the depth of the crystal, where monomolecular recombination occurs involving photogenerated charges and unintentional doped charges, while the normal PL is emitted by bimolecular recombination from the surface layers. These results showed the significance of pure optical effects in perovskite crystals and would promote detailed understanding of the charge dynamics and recombination in perovskite crystalline materials of different geometries and sizes.

Investigating the Tetragonal‐to‐Orthorhombic Phase Transition of Methylammonium Lead Iodide Single Crystals by Detailed Photoluminescence Analysis

“…In general, it has been shown that self‐absorption effects can play an important role and need to be considered when analyzing measured PL spectra. [ 16–22 ] We recently demonstrated that self‐absorption can even lead to additional peaks in measured PL. With a relatively simple optical model it was possible to reproduce and analyze the additional peaks in the case of pure tetragonal or orthorhombic crystal phases.…”

Photoluminescence properties of hybrid perovskites in solar cells with TiO2 and Mg0.2Zn0.8O electron transport layers

“…The inclusion of a different crystal phase, an atmosphere effect and a degradation of the sample, reabsorption effects, radiative recombination involving shallow trapping levels and luminescence from the crystal edges [28] could all be possible reasons for the red shift. We attributed this red shift to the relative change between the intensities of the two lowest energy peaks.…”

“…The distance between the second and third peaks is 62 and 7 meV for samples S1 and S2, respectively. A possible reason of this separation can be attributed to the presence of another phase of perovskite [42][43][44], different grain sizes [45] and emissions from the interior or boundaries of the grains [28,45,46]. However, the addition of small amounts of cesium (Cs) in a triple cation (Cs/MA/FA) configuration resulted in the formation of monolithic grains of a purer perovskite [47] and in the suppression of possible phase transitions [32].…”

“…However, the addition of small amounts of cesium (Cs) in a triple cation (Cs/MA/FA) configuration resulted in the formation of monolithic grains of a purer perovskite [47] and in the suppression of possible phase transitions [32]. Meanwhile, emissions from the interior and boundaries of the grains should show a different tendency of PL decay [28,46]. An- other possible explanation for the presence of these three peaks could be the band edge and two kinds of local phases, distinguished as ordered and disordered crystallites [48].…”

Mechanisms of Spontaneous and Amplified Spontaneous Emission in CH3NH3PbI3 Perovskite Thin Films Integrated in an Optical Waveguide

“…Finally, such a specific method of optical pumping, based on the tail of the TE 4 mode traveling along the PMMA cladding layer, provides a quasiuniform excitation of the MAPI layer over the whole length of the waveguide (mm scale). Moreover, since the whole MAPI film is excited, the PL reabsorption effect, which is a well-known issue in MHP layers [39,40], is minimized with this scheme, even below the ASE threshold. Indeed, a study of ASE in waveguides of different lengths reveals that the reabsorption-induced redshift of the PL line is only 10 meV (5 nm) for the longest (3 mm) waveguides, as observed in Fig.…”