Spontaneous Formation of 2D/3D Heterostructures on the Edges of 2D Ruddlesden–Popper Hybrid Perovskite Crystals

Abstract

The observation of low-energy edge photoluminescence and its beneficial effect on the solar cell efficiency of Ruddlesden−Popper perovskites has unleashed an intensive research effort to reveal its origin. This effort, however, has been met with more challenges as the underlying material structure has still not been identified; new modelings and observations also do not seem to converge. Using twodimensional (2D) (BA) 2 (MA) 2 Pb 3 Br 10 as an example, we show that threedimensional (3D) MAPbBr 3 is formed due to the loss of BA on the edge. This self-formed MAPbBr 3 can explain the reported edge emission under various conditions, while the reported intriguing optoelectronic properties such as fast exciton trapping from the interior 2D perovskite, rapid exciton dissociation, and long carrier lifetime can be understood via the self-formed 2D/3D lateral perovskite heterostructure. The 3D perovskite is identified by submicron infrared spectroscopy, the emergence of X-ray diffraction (XRD) signature from freezer-milled nanometer-sized 2D perovskite, and its photoluminescence response to external hydrostatic pressure. The revelation of this edge emission mystery and the identification of a self-formed 2D/3D heterostructure provide a new approach to engineering 2D perovskites for high-performance optoelectronic devices.

Momentarily trapped exciton polaron in two-dimensional lead halide perovskites

“…Previous studies on 2D lead halide perovskites also have shown asymmetric PL line shape and attributed to extrinsic below gap trap states at surfaces/interfaces 33 , 43 . Layer edge states can also contribute the lower emission due the stochastic loss of organic ligands and formation of bulk CsPbBr3 perovskites 2 , 32 , 44 – 47 . However, lower energy emissions from below gap states or layer edge states exhibit longer lifetime compared with the band edge emission from 2D perovskites and persist at cryogenic temperature, if not be more pronounced 2 , 32 , 33 , 46 , 48 .…”

Kinetic Molecular Cationic Control of Defect-Induced Broadband Light Emission in 2D Hybrid Lead Iodide Perovskites

“…1,3,[23][24][25] In addition, other studies indicate the presence of electronic states on the edges and dislocations of crystals correlate with broadband, subgap light emission from SAQW samples possessing the Ruddlesden-Popper structure. [26][27][28] Given the variation in experimental observations of the characteristics of subgap PL from hybrid SAQWs with so many different parameters of material formation, the general understanding of the mechanisms by which different types of electronic states participate in the trapping and recombination of excitons and charge carriers remains incomplete.…”

“…13,19,21 Most importantly, we find this light emission feature is red-shifted by nearly 200 nm from the narrow photoluminescence emitted due free exciton recombination and possesses the broad bandwidth consistent with PL caused by so-called edge states in mixed cation, Ruddlesden-Popper hybrid perovskites reported by numerous authors. [26][27][28] Contrasting with previous studies, however, the 532 nm laser in our experiments excites the free exciton directly and allows us determine how the concentrations of molecular constituents in precursor solutions affect the photophysical properties of hybrid SAQWs. In particular, driving the exciton resonantly not only allows us to discount trapping of charge carriers photo-generated promptly with higher energy light, but also allows us to use power-dependent PL spectra and investigate the excited state processes driving subgap PL in our samples, as we discuss in more detail below.…”

Kinetic Molecular Cationic Control of Defect-Induced Broadband Light Emission in 2D Hybrid Lead Iodide Perovskites

“…1,3,[23][24][25] In addition, other studies indicate the presence of electronic states on the edges and dislocations of crystals correlate with broadband, subgap light emission from SAQW samples possessing the Ruddlesden-Popper structure. [26][27][28] Given the variation in experimental observations of the characteristics of subgap PL from hybrid SAQWs with so many different parameters of material formation, the general understanding of the mechanisms by which different types of electronic states participate in the trapping and recombination of excitons and charge carriers remains incomplete.…”