Halide perovskites exhibit diverse properties depending on their compositions. However, integrating desired properties into one material is still challenging. Here, a facile solution-processed epitaxial growth method to grow 2D perovskite single crystal on top of 3D perovskite single crystal, which can passivate the surface defects for improved device performance is reported. Short formamidine (FA + ) ions are replaced by long organic cations, which can fully align and cover the single crystal surface to prevent the ions migration or short FA + ions volatilization. The thickness of epitaxial layer can be finely adjusted by controlling the growth time. The defect density of single crystals heterojunction is only 3.18 × 10 9 cm −3 , and the carrier mobility is 80.43 cm 2 V −1 s −1 , which is greater than that of the control 3D perovskite single crystal. This study for the first time realized large area 3D/2D perovskite single crystals heterojunction, which suppressed ions migration and exhibited advanced performance in hard X-rays detection applications. This strategy also provides a way to grow large area 2D perovskite single crystal from solution processes.
Sphere imagers featuring specific wavelength recognition and wide-angle imaging are required to meet the fast development of modern technology. However, it is still challenging to deposit high-quality photosensitive layers on sphere substrates from low-cost solution processes. Here we report spray-coated quasi-two-dimensional phenylethylammonium/formamidinium lead halide (PEA2FAn-1PbnX3n+1) perovskite hemispherical photodetectors. The crystallization speed is manipulated by perovskite compositions, and the film thickness can be controlled by spray-coating cycles and solution concentration from tens of nanometers to hundreds of micrometers with a fast velocity of 1.28 × 10−4 cm3 s−1. The lens-free hemispherical photodetectors allow light response at a wide incident angle of 180°. Simultaneously, the wavelength selective response from visible to the near-infrared range is achieved with full width at half maximums (FWHMs) of ~20 nm, comparable to single-crystal devices. Wide-angle and wavelength-selective imaging are also demonstrated, which can find potential applications in intelligent recognition and intraoperative navigated surgery.
Both semiconductors and scintillators have their own advantages in direct and indirect X-ray detection, respectively. However, they are also limited by their intrinsic properties and detection mechanisms. Here, a low-cost and large-area flat X-ray detector is reported by combining a cesium silver bismuth bromide (Cs 2 AgBiBr 6 ) perovskite semiconductor with a ethylenebistriphenylphosphonium manganese (II) bromide ((C 38 H 34 P 2 )MnBr 4 ) scintillator through fast tableting processes. Cs 2 AgBiBr 6 and (C 38 H 34 P 2 )MnBr 4 can attenuate the X-ray photons to induce charge carriers that are collected through the continuous Cs 2 AgBiBr 6 grains. (C 38 H 34 P 2 )MnBr 4 blocks the Cs 2 AgBiBr 6 ions migration paths at the grain boundaries to reduce the device dark current/noise and improves the working stability. Most charges generated by (C 38 H 34 P 2 )MnBr 4 are transferred to the adjacent Cs 2 AgBiBr 6 , and recombined charges radiate light through scintillation, which will be further absorbed by the surrounding Cs 2 AgBiBr 6 perovskite, and further induce collectable charges for indirect X-ray detection, avoiding the unwanted light scattering, self-absorption, or afterglow effects of scintillators. The hybrid X-ray detector displays a high sensitivity of 114 µC Gy air −1 cm −2 to 120 keV p hard X-rays with a lowest detectable dose rate of 0.2 µGy air s −1 , showing 75 times lower detection limit compared to (C 38 H 34 P 2 )MnBr 4 scintillator, which provides a new path for X-ray flat-panel design.
Near-infrared (NIR) II detection at weak flux intensity is required in medical imaging and is especially urgent in light of the low quantum efficiency of NIR-II dyes. The low responsivity of traditional photodetectors in this region limits image quality. Here, we report a NIR-II photodetector with high gain based on perovskite coupled PbS colloidal quantum dots (CQDs). Tailoring the trap density of CQDs by designing surface ligands with dual functionality contributed to control over trap-induced charge-injection upon light illumination. As a result, a detector with high gain is realized, showing external quantum efficiency of 1260% at 1200 nm and achieving the lowest detectable light intensity, that is, as low as 0.67 pW cm–2 with a linear dynamic range of 200 dB. Devices maintain over 90% of responsivity after 150 days of storage. We acquired images of a butterfly wing, showing the skeleton texture with a maximum spatial resolution of 3.9 lp/mm.
The diversity of organic cations greatly enriches the species of 2D perovskites; traditional 2D Ruddlesden‐Popper (RP) and Dion‐Jacobson (DJ) perovskites are synthesized by two different organic amines. Here, according to the difference in pKa values between conjugated acids of monoprotonated and biprotonated 4‐(2‐Aminoethyl)pyridine (4AEPy) ions, the 2D perovskites of RP (4AEPy)2PbI4 and DJ (4AEPy)PbI4 from same organic amine is reported, which can realize reversible transformation under the treatment of HI and NH3, respectively. The interaction of N‐H···N hydrogen bond between adjacent organic molecules in (4AEPy)2PbI4 leads to the bending conformation of ethylamine groups, which results in a 2.4 Å reduction in layer spacing compared to typical phenylethylamine lead iodine ((PEA)2PbI4) 2D perovskite. Besides, the ethylamine groups of organic layers in (4AEPy)PbI4 are deeply inserted into octahedral cavities and directly participate in the construction of the conduction band minimum, which leads to a small exciton binding energy of 27.3 meV to generate free charges. The stronger coupling between the organic and inorganic layers and the minor exciton binding energy can promote the DJ phase to possess a more stable structure and better optoelectronic properties. Thus the (4AEPy)PbI4 device displays better light response and X‐ray detection capability with a high sensitivity of 5627 µC Gyair‐1 cm‐2 and the lowest detectable dose rate of 20 nGyair s‐1.
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