Dangling Octahedra Enable Edge States in 2D Lead Halide Perovskites

Abstract

The structural reconstruction at the crystal layer edges of 2D lead halide perovskites (LHPs) leads to unique edge states (ES), which are manifested by prolonged carrier lifetime and reduced emission energy. These special ES can effectively enhance the optoelectronic performance of devices, but their intrinsic origin and working mechanism remain elusive. Here it is demonstrated that the ES of a family of 2D Ruddlesden–Popper LHPs [BA2CsPb2Br7, BA2MAPb2Br7, and BA2MA2Pb3Br10 (BA = butylammonium; MA = methylammonium)] arise from the rotational symmetry elevation of the PbBr6 octahedra dangling at the crystal layer edges. These dangling octahedra give rise to localized electronic states that enable an effective transport of electrons from the interior to layer edges, and the population of electrons in both the interior states and the ES can be manipulated via controlling the external fields. Moreover, the abundant phonons, activated by the dangling octahedra, can interact with electrons to facilitate radiative recombination, counterintuitive to the suppressive role commonly observed in conventional semiconductors. This work unveils the intrinsic atomistic and electronic origins of ES in 2D LHPs, which can stimulate the exploration of ES‐based exotic optoelectronic properties and the corresponding design of high‐performance devices for these emergent low‐dimensional semiconductors.

Coherent Spin Dynamics of Electrons in Two-Dimensional (PEA)2PbI4 Perovskites

“…12 In photovoltaics a power conversion efficiency above 17% 13,14 was reached, and long-term stability was reported. 15 A variety of optical methods, like four-wave mixing, 16 spatially resolved spectroscopy, 14 second harmonic generation, 17 and strong coupling in cavities, 8 were used to address the optical properties of exciton complexes in 2D perovskites. The application of high magnetic fields up to 60 T delivered information about the exciton binding energy, effective mass, fine structure, and g-factor.…”

“…A variety of optical methods, like four-wave mixing, spatially resolved spectroscopy, second harmonic generation, and strong coupling in cavities, were used to address the optical properties of exciton complexes in 2D perovskites. The application of high magnetic fields up to 60 T delivered information about the exciton binding energy, effective mass, fine structure, and g -factor. − Time-resolved transmission was used to study the exciton spin dynamics at picosecond and subpicosecond time scales. − However, in these reports, performed at temperatures above liquid nitrogen temperature up to ambient conditions, the spin dynamics was significantly limited, and spin relaxation times exceeding a few picoseconds have not been reported so far.…”

Enantiomeric Hydrogen-bonded Chains Driving Ferroelectric and Nonlinear Optical Behavior

“…Furthermore, the anisotropy of the SHG intensity for the crystals of [HDABCO]­[ l - and d -MA] was verified through polarization SHG measurement (Figures a and S6b). In addition, Figure c displays that the SHG intensity of [HDABCO]­[ l -MA] increases with the rise of the particle size and tends to maximum, which indicates the phase matching property. , …”

Navigating the Site-Distinct Energy Conversion Properties of Perovskite Quantum Wells

“…(d) Schematic illustration of the dangling [PbBr 6 ] octahedra at the edge of 2D HPs. Reproduced with permission from ref . Copyright 2022, John Wiley and Sons.…”