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.

Interlayer excitons have been extensively studied in monolayer transition metal dichalcogenide (TMD) heterobilayers mainly due to the long lifetime, which is beneficial for a wide range of optoelectronic applications. To date, the majority of investigations of interlayer excitons in TMD heterobilayers have been focusing on the geometric arrangement of structures, spin–valley lifetime, and interlayer valley excitons with interlayer hopping rules. Nevertheless, interlayer excitons in TMD heterobilayers strongly depend on the local atomic registry and coupling strength, which increase the complexity of the device fabrication. Here, we report pronounced interlayer exciton emission in two-dimensional (2D) perovskite/monolayer TMD heterostructures without the need of thermal annealing or specific geometric arrangements, and the interlayer exciton emission is rather general among 2D perovskites and monolayer TMDs. Such interlayer exciton emission completely dominates the emission spectrum at 78 K regardless of the stacking sequence, suggesting the robust interlayer coupling in 2D perovskite/monolayer TMD heterostructures. Furthermore, the interlayer exciton emission shows a large blue-shift with increasing laser intensity due to the repulsive dipole–dipole interaction and can persist above 220 K. Importantly, the interlayer exciton emission also possesses robust circular polarization in chiral 2D perovskite/monolayer WSe2 heterostructures, which can be applied to manipulate the valley degree of freedom for valleytronic devices. Our findings would provide a favorable platform to explore interlayer coupling and related physical processes in 2D perovskites and TMDs and further provoke more investigations into the understanding and controlling of excitonic effects and associated optoelectronic applications in van der Waals heterostructures over a broad-range spectral response.

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Circularly polarized luminescent (CPL) materials are promising in applications such as 3D displays and quantum communication. Hybrid organic–inorganic copper­(I) iodides have been rapidly developed due to their intense photoluminescence and structural diversity; nevertheless, the reported Cu–I clusters rarely show CPL activities. In this study, we introduced chiral organic molecules R/S-methylbenzylammonium (R/S-MBA) into Cu–I inorganic skeletons to achieve chiral tetranuclear (R/S-MBA)4Cu4I4 clusters with intense orange luminescence and CPL activity at room temperature. These enantiomeric (R/S-MBA)4Cu4I4 clusters show oppositely signed circular dichroism (CD) signals, which agree well with their simulated electronic CD spectra. The crystallization-induced helical arrangement of (R/S-MBA)4Cu4I4 clusters and their largely distorted polynuclear configuration demonstrate a new platform for the study of chiral-related properties.

with a proper selected optical filter. [8] Nevertheless, this method increases both the cost and complexity of the system and also is limited by the available filters. To address those issues, several strategies have been developed to achieve filterless narrowband photodetections, which include: (1) specially designing the absorber with narrowband absorption; [9][10][11] (2) utilizing the plasma effect to intentionally enhance the absorption at a designed wavelength range; [12] (3) engineering the charge collection efficiency via charge collection narrowing (CCN) mechanism. [13,14] In particular, filterless narrowband photodetectors based on CCN mechanism have been recently demonstrated with decent performance in both 2D perovskite single crystals and 3D perovskite single crystals and films. [15] While in 2D perovskite single crystals the narrowband photoresponse is assisted by the self-trapped states within bandgap, the band-tail states play the dominant role in 3D perovskite based narrowband photodetectors. [16][17][18] The CCN mechanism is to manipulate the charge collection efficiency to a desired spectral region so that the photo response can be controlled in the designed spectral range. In brief, the photogenerated carriers are mainly distributed close to the crystal surface for the above-gap photons due to the large absorption coefficient (termed as surface generation) while the light can penetrate deep into the crystal for the subgap photons because of the smaller absorption coefficient (termed as volume generation). The collection efficiency of surface-generation carriers is greatly suppressed due to the recombination loss due to the imbalanced carriers' transit time, higher local carrier density, and severe surface-charge recombination while the collection efficiency of volume-generation carriers is much less affected by those factors. As a result, the charge collection efficiency of volume-generation carriers is much larger than that of surface-generation carriers. For the photons with energy far below the bandgap energy of materials, the photons cannot be absorbed by the materials, and thus cannot contribute to the photocurrent again. Therefore, under such situation, only photons with energy near or slight below bandgap energy can significantly contribute to the photocurrent, leading to the narrowband spectral response. [4] Polarization-sensitive photodetectors can sense the polarization of light in addition to the intensity and wavelength of the Polarization-sensitive narrowband photodetectors can respond to a narrow spectral range of light together with the ability to sense the polarization of light. Traditionally, expensive filters combined with polarizers are utilized to realize the polarization-sensitive narrowband photodetections. To reduce the cost and simplify optical system, here a polarization-sensitive narrowband photodetector based on 2D perovskite single crystals without any additional optical components is reported. The photodetector shows a linear dichroic ratio of 1.56 at 552 nm under ...

2D layered halide perovskites have attracted significant attention. Apart from the linear optical properties, it is also intriguing to explore the nonlinear optics of 2D layered halide perovskites and their heterostructures. Previous nonlinear optical (NLO) studies of 2D perovskites primarily focus on the thin films or microplates. Herein, the NLO properties of (n‐C4H9NH3)2PbI4/(n‐C4H9NH3)2(CH3NH3)Pb2I7 heterostructures with centimeter size are systematically studied. The NLO properties can be continuously tuned by changing the thickness. A giant two‐photon absorption (2PA) coefficient up to 44 cm MW−1 is obtained for the heterostructures with a total thickness of 20 µm based on the nonlinear transmittance measurement. Additionally, strong multiphoton‐induced photoluminescence is observed in the heterostructures. It is proposed that the giant 2PA coefficient might arise from the small thickness (≈1 µm) of (n‐C4H9NH3)2(CH3NH3)Pb2I7 layer and possibly the nonradiative energy transfer between the different constituting layers within the heterostructures through an antenna‐like effect. Finally, benefiting from the giant 2PA coefficient, direct detection of 980 nm light is demonstrated with a responsivity of 10−7 A W−1 in the heterostructures. The findings suggest the promising applications of 2D perovskite heterostructures in the infrared photodetection and some other nonlinear absorption related optoelectronic devices.