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.

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.

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 ...

The incorporation of chloride (Cl) into methylammonium lead iodide (MAPbI3) perovskites has attracted much attention because of the significantly improved performance of the MAPbI3‐based optoelectronic devices with a negligible small amount of Cl incorporation. It is expected that the Cl incorporation in 2D perovskites with layered nature would be much more efficient and thus can greatly alter the morphology, optical properties, phase transition, and charge transport; however, studies on those aspects in 2D perovskites remain elusive up to date. Here, a one‐pot solution method to synthesize the Cl‐doped lead‐free 2D perovskite (BA)2SnI4 with various Cl incorporation concentrations is reported and how the Cl incorporation affects the morphology change, photoluminescence, phase transition, and charge transport is investigated. The Cl element is successfully incorporated into the crystal lattice in the solution‐processed perovskite materials, confirmed by X‐ray photoelectron spectroscopy and energy dispersive X‐ray spectroscopy measurements. The temperature‐dependent photoluminescence studies indicate that the emission properties and phase transition behavior in (BA)2SnI4−xClx can be tuned by varying the Cl incorporation concentration. Electrical measurement suggests that the charge transport behavior can also be greatly altered by the Cl doping concentration and the electrical conductivity can be significantly improved under a higher Cl incorporation concentration.

Zircon water content is an important physicochemical parameter for many geological processes, yet its measurement by the secondary ion mass spectrometry (SIMS) technique is hampered by the lack of suitable reference materials and high water background, especially if large-geometry (LG)-SIMS is used.

All‐inorganic lead halide perovskites have been extensively studied in the past several years due to their superior stability against moisture, oxygen, light, and heat compared with their organic–inorganic counterparts. CsPbBr3 with suitable band gap and ultrahigh photoluminescence quantum yield is a promising candidate for pure green emitter in the backlighting display to fill the so‐called “green gap.” Here, vapor‐phase growth of CsPbBr3 microspheres is reported for highly efficient pure green light emission. The as‐synthesized microspheres exhibit a stronger photoluminescence (PL) intensity with a photoluminescence quantum yield of 75% resulting from the lower energy of longitudinal optical phonons revealed by temperature dependent PL studies. Importantly, with the diameter increasing from 2 to 50 µm the PL peak positions of the microspheres can be readily tuned from 527 to 539 nm, well filling the so‐called “green gap.” The red‐shift with increasing diameter can be ascribed to the reabsorption process during the photon propagation inside the microspheres. The studies provide a route to improve the photoluminescence quantum yield in all‐inorganic lead halide perovskites, but also suggest an alternative approach to achieve the pure green emission for the backlighting display.

Abstract Two-dimensional (2D) organic-inorganic hybrid perovskites have attracted growing attention recently due to their naturally formed quantum-well structure, unique photoelectric properties and better environmental stability compared to three-dimensional perovskites. The reduced screening and enhanced Coulomb interaction in 2D perovskites result in the formation of excitonic complexes. While the properties of free excitons have been well investigated, studies on biexcitons remain elusive. Here, we report on the biexcitons in 2D (iso-BA)2PbI4 (BA=C4H9NH3) crystals. The biexciton emission can be observed under a very low excitation power density of 6.4 W/cm2 at 78 K. The biexciton exhibits a large biexciton binding energy of 46 meV due to the large exciton binding energy of (iso-BA)2PbI4. Furthermore, the biexcitons exhibit a favorable polarization orientation, resulting in different anisotropy between biexcitons and excitons. Our findings would motivate more studies on biexcitons in 2D perovskites and pave the way for exploiting the many-body physics for biexciton lasing and optical storage devices.

Recently, a two-dimensional Dion–Jacobson (DJ) perovskite (AMP)­PbI4 (AMP = 4-(aminomethyl)­piperidinium) is emerging with remarkable Rashba effect and ferroelectricity. However, the origin of the giant Rashba splitting remains elusive and the current synthetic strategy via slow cooling is time- and power-consuming, hindering its future applications. Here, we report on an economical aqueous method to obtain (AMP)­PbI4 crystals and clarify the origin of the giant Rashba effect by temperature- and polarization-dependent photoluminescence (PL) spectroscopy. The strong temperature-dependent PL helicity indicates the thermally assisted structural distortion as the main origin of the Rashba effect, suggesting that valley polarization still preserves at high temperatures. The Rashba effect was further confirmed by the circular photogalvanic effect near the indirect bandgap. Our study not only optimizes the synthetic strategies of this DJ perovskite but also sheds light on its potential applications in room/high-temperature spintronics and valleytronics.