Distinct conducting layer edge states in two-dimensional (2D) halide perovskite

Abstract

Two-dimensional (2D) lead halide perovskite with a natural “multiple quantum well” (MQW) structure has shown great potential for optoelectronic applications. Continuing advancement requires a fundamental understanding of the charge and energy flow in these 2D heterolayers, particularly at the layer edges. Here, we report the distinct conducting feature at the layer edges between the insulating bulk terrace regions in the (C4H9NH3)2PbI4 2D perovskite single crystal. The edges of the 2D exhibit an extraordinarily large carrier density of ~1021 cm−3. By using various mapping techniques, we found the layer edge electrons are not related to the surface charging effect; rather, they are associated with the local nontrivial energy states of the electronic structure at the edges. This observation of the metal-like conducting feature at the layer edge of the 2D perovskite provides a different dimension for enhancing the performance of the next-generation optoelectronics and developing innovative nanoelectronics.

Molecular Intercalation and Electronic Two Dimensionality in Layered Hybrid Perovskites

“…Therefore, the edges of the crystals can be considered as those locations where the Pb–I layers interact predominantly, introducing the pseudo 2D nature in the system. These results agree with the recent report that showed edges could conduct electricity unlike other parts of (BA) 2 PbI 4 single crystal . It is to be noted here that electron injection/extraction, required for any electronic and optoelectronic applications, occur through these edge states because the terraces of layered perovskites are insulating.…”

“…It is to be noted here that the edge‐state emission from our (BA) 2 PbI 4 is different than the previously reported edge‐state emission from (C 4 H 9 NH 3 ) 2 (CH 3 NH 3 ) 2 Pb 3 I 10 and (C 4 H 9 NH 3 ) 2 (CH 3 NH 3 ) 3 Pb 4 I 13 with ( n ≥2). For samples with n ≥2, the small A‐site cations CH 3 NH 3 + leads to the formation of 3D perovskite compositions at the edges.…”

“…For example, a single crystal of (BA) 2 PbI 4 and other layered hybrid perovskite systems exhibit two (band edge) excitonic absorption and emission features, as if the same crystal has two band gaps! Further, Wang et al. found that the edges of (BA) 2 PbI 4 single crystals are significantly more electrically conducting than their terraces . We hypothesize that some of these unusual experimental observations might arise from possible electronic interactions between the Pb–I layers.…”

Structurally Tunable Two-Dimensional Layered Perovskites: From Confinement and Enhanced Charge Transport to Prolonged Hot Carrier Cooling Dynamics

“…In fact, the distinct metal-like conducting features reported at the layer-edge of 2D perovskites provide a different dimension for enhancing the performance of next-generation photovoltaics. 38 The vast potential for tuning the optical and electronic properties of 2D perovskites by varying their elemental composition (e.g., the choice of metals, halides, and small organic cations), organic spacers, and number of layers (i.e., thickness) holds considerable promise for further system optimization. Additionally, charge-carrier collection can be supported through optimized deposition and process engineering, 36 , 39 − 41 additive engineering (e.g., SCN – and MACl), 42 − 44 and doping approaches 45 − 48 that favor vertical growth and preferential out-of-plane charge transport.…”

Photoinduced Trap Passivation for Enhanced Photoluminescence in 2D Organic–Inorganic Hybrid Perovskites

“…More recently, 2D organic–inorganic hybrid perovskites with a layered multiquantum‐well structure, have been demonstrated to possess more outstanding properties, such as a larger exciton binding energy, a greater tunability, and a better stability . Encouraged by the impressive features, 2D perovskites have become potential candidates for next‐generation optoelectronic devices like high‐efficiency light emitting devices and high‐performance solar cells .…”