Filterless narrowband photodetectors can realize color discrimination without filter or bulk spectrometer, thus greatly reducing the system volume and cost for many imaging applications. Charge collection narrowing has been demonstrated to be a successful approach to achieve filterless narrowband photodetections; nevertheless, it sacrifices the sensitivity of the photodetectors. Here we show a highly tunable narrowband photodetector based on two-dimensional perovskite single crystals with high external quantum efficiency (200%), ultralow dark current (10−12 A), and high on–off ratio (103). The spectral response of the narrowband photodetectors can be continuously tuned from red to blue with all full-width at half-maximum < 60 nm and especially < 20 nm in blue wavelength range. The excellent performance can be ascribed to self-trapped states within bandgap and extremely low electrical conductivity in the out-of-plane direction. Our findings open the exciting potential of 2D perovskites for next-generation optoelectronics.

Two-dimensional organic–inorganic perovskites have attracted considerable interest recently. Here, we present a systematic study of the temperature-dependent photoluminescence on phase pure (n-BA)2(MA) n−1Pb n I3n+1 (n = 1–5) and (iso-BA)2(MA) n−1Pb n I3n+1 (n = 1–3) microplates obtained by mechanical exfoliation. The photoluminescence peak position gradually changes from a red-shift for n = 1 to a blue-shift for n = 5 with an increase in temperature in the (n-BA)2(MA) n−1Pb n I3n+1 (n = 1–5) series, while only a monotonous blue-shift has been observed for the (iso-BA)2(MA) n−1Pb n I3n+1 (n = 1–3) series, which can be attributed to the competition between the thermal expansion interaction and electron–phonon interaction. In the (n-BA)2(MA) n−1Pb n I3n+1 (n = 1–5) series, the thermal expansion interaction and electron–phonon interaction are both gradually enhanced and the former progressively dominates the latter from n = 1 to n = 5, resulting in the band gap versus temperature changing from a red-shift to a blue-shift. In contrast, both of these factors show a weaker layer thickness dependence, leading to the monotonous blue-shift in the (iso-BA)2(MA) n−1Pb n I3n+1 (n = 1–3) series.

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.