Chiral materials are of particular interest and have a wide range of potential applications in life science, material science, spintronic, and optoelectronic devices. Two-dimensional (2D) hybrid organic–inorganic lead halide perovskites have attracted increasing attention. Incorporating the chiral organic ligands into the layered lead iodide frameworks would introduce strong chirality in pure 2D perovskites for potential applications in circularly polarized light (CPL) emission and detection; nonetheless, studies on those aspects are still in their infancy. Here, we report on the strong CPL emission and sensitive CPL detection in the visible-wavelength range in pure chiral (R-/S-MBA)2PbI4 (MBA = C6H5C2H4NH3) 2D perovskites, which are successfully synthesized with a needle shape and millimeter size by incorporating the chiral molecules. The chiral 2D perovskites (R-MBA)2PbI4 and (S-MBA)2PbI4 exhibit an average degree of circularly polarized photoluminescence (PL) of 9.6% and 10.1% at 77 K, respectively, and a maximum degree of the circularly polarized PL of 17.6% is achieved in (S-MBA)2PbI4. The degree of circularly polarized PL dramatically decreases with increasing temperature, implying that the lattice distortion induced by the incorporated chiral molecules and/or temperature-dependent spin flipping might be the origin for the observed chirality. Finally, CPL detection has been achieved with decent performance in our chiral 2D perovskite microplate/MoS2 heterostructural devices. The high degree of the circularly polarized PL and excellent CPL detection together with the layered nature of pure chiral 2D perovskites enables them to be a class of very promising materials for developing and exploring spin associated electronic devices based on the chiral 2D perovskites.

Low-dimensional lead halide perovskite materials are an emerging class of solution-processable semiconductors with promising potential applications in optoelectronic devices. Unfortunately, it is impossible to synthesize high-crystalline-quality low-dimensional perovskite single crystals without using chemotoxic solutions such as dimethylformamide/dimethyl sulfoxide or applying heating. Herein we report an economical and universal aqueous method to synthesize 2D layered and 1D chain perovskite single crystals at room temperature. The resultant chiral 2D perovskites can efficiently and selectively emit and detect circularly polarized light at room temperature. The as-synthesized 1D perovskite single crystals exhibit strong quantum confinement and enhanced self-trapped states that give efficient warm circularly polarized white-light emission. This aqueous synthetic method is general for other high-quality low-dimensional lead halide perovskite single crystals, and thus our findings would motivate more fundamental investigations on low-dimensional perovskites for potential optoelectronic applications.

No abstract

Two-dimensional (2D) organic-inorganic perovskites have recently attracted increasing attention due to their great environmental stability, remarkable quantum confinement effect and layered characteristic. Heterostructures consisting of 2D layered perovskites are expected to exhibit new physical phenomena inaccessible to the single 2D perovskites and can greatly extend their functionalities for novel electronic and optoelectronic applications. Herein, we develop a novel solution method to synthesize (C 4 H 9 NH 3 ) 2 PbI 4 /(C 4 H 9 NH 3 )(CH 3 NH 3 )Pb 2 I 7 single-crystals with the centimeter size, high phase purity, controllable junction depth, high crystalline quality and great stability for highly narrow dual-band photodetectors. On the basis of the different lattice constant, solubility and growth rate between (C 4 H 9 NH 3 ) 2 PbI 4 and (C 4 H 9 NH 3 )(CH 3 NH 3 )Pb 2 I 7 , the newly designed synthesis method allows to first grow the (C 4 H 9 NH 3 ) 2 PbI 4 guided by the self-assembled layer of the organic cations at the water-air interface and subsequently the (C 4 H 9 NH 3 )(CH 3 NH 3 )Pb 2 I 7 layer is formed via diffusion process. Such growth process provides an efficient away for us to readily obtain the (C 4 H 9 NH 3 ) 2 PbI 4 /(C 4 H 9 NH 3 )(CH 3 NH 3 )Pb 2 I 7 single-crystals with various thickness and junction depth by controlling the concentration, reaction 2 temperature and time. The formation of heterostructures has been verified by X-ray diffraction, cross-section photoluminescence and reflection spectroscopy with the estimated junction width below 70 nm. Photodetectors based on such heterostructural single crystal plates exhibit extremely low dark current (∼10 −12 A), high on/off current ratio (∼10 3 ), and highly narrow dual-band spectral response with a full-width at half-maximum of 20 nm at 540 nm and 34 nm at 610 nm due to the high crystalline quality of the synthesized heterostructures and extremely large resistance in the out-of-plane direction leading to the efficient control of photogenerated carrier collection. In particular, the synthetic strategy is general for other 2D perovskites and the narrow dual-band spectral response with all full-width at half-maximum <40 nm can be continuously tuned from red to blue by properly changing the halide compositions. Our findings not only provide an efficient synthetic approach with great simplicity to create 2D perovskite based heterostructural single crystals for investigating the physical processes in those heterostructures, but also offer an alternative strategy to achieve optical-filterless narrow dual-band photodetectors in the entire visible range for multicolor optical sensing.

Two-dimensional (2D) Ruddlesden–Popper perovskites have attracted great interest for their promising applications in high-performance optoelectronic devices owing to their greatly tunable band gaps, layered characteristics, and better environmental stability over three-dimensional (3D) perovskites. Here, we for the first time report on photodetectors based on few-layer MoS2 (n-type) and lead-free 2D perovskite (PEA)2SnI4 (p-type) heterostructures. The heterojunction device is capable of sensing light over the entire visible and near-infrared wavelength range with a tunable photoresponse peak. By using few-layer graphene flakes as the electrical contact, the performance of the heterostructures can be improved with a responsivity of 1100 A/W at 3 V bias, a fast response speed of ∼40 ms under zero bias, and an excellent rectification ratio of 500. Importantly, the quantum efficiency can achieve 38.2% at zero bias, which is comparable or even higher than that of 3D perovskite/2D material photodetectors. Importantly, the spectral response peak of heterojunctions gradually shifts in a wide spectral range from the band edge of MoS2 toward that of (PEA)2SnI4 with the external bias. We believe these 2D perovskite/2D material heterostructures with a great diversity represent an interesting system for investigating the fundamental optoelectronic properties and open up a new pathway toward 2D perovskite-based optoelectronic devices.