By fine-tuning the crystal nucleation and growth process, a low-temperature-gradient crystallization method is developed to fabricate high-quality perovskite CH NH PbBr single crystals with high carrier mobility of 81 ± 5 cm V s (>3 times larger than their thin film counterpart), long carrier lifetime of 899 ± 127 ns (>5 times larger than their thin film counterpart), and ultralow trap state density of 6.2 ± 2.7 × 10 cm (even four orders of magnitude lower than that of single-crystalline silicon wafers). In fact, they are better than perovskite single crystals reported in prior work: their application in photosensors gives superior detectivity as high as 6 × 10 Jones, ≈10-100 times better than commercial sensors made of silicon and InGaAs. Meanwhile, the response speed is as fast as 40 µs, ≈3 orders of magnitude faster than their thin film devices. A large-area (≈1300 mm ) imaging assembly composed of a 729-pixel sensor array is further designed and constructed, showing excellent imaging capability thanks to its superior quality and uniformity. This opens a new possibility to use the high-quality perovskite single-crystal-based devices for more advanced imaging sensors.

X-ray detectors have attracted significant attention because they are widely used in applications such as computed tomography (CT), homeland security, and environmental monitoring. [1,2] In particular, there is an ever-increasing demand to invent better semiconductor material and device design to attain even higher sensitivity and lower manufacturing cost. [3,4] In the past decades, various traditional semiconductors have been studied for X-ray detection applications, like silicon (Si), [5] high-purity germanium (HP-Ge), [6] amorphous selenium (α-Se), [7] mercury iodide (HgI 2), [8] cadmium zinc telluride (CdZnTe), [9] and so on. Unfortunately, none of them is very ideal, more specifically, neither HP-Ge nor CdZnTe is costeffective; Si and CdZnTe require high working voltage; Si and α-Se have low X-ray absorption coefficient and large leakage current. Also, the CdZnTe, Si, and HP-Ge require very high growth temperature exceeding 500 °C, Hg and Cd are highly toxic. Recently, solution-processable organic-inorganic metal-halide perovskites have been demonstrated as a promising candidate for high performance X-ray detectors. They are advantageous in strong X-ray absorption, processable at low temperature, low-cost fabrication, and superior semiconducting properties like low defect density, large mobility-lifetime product (μτ), long carrier diffusion length, etc. Noticeably, the recently reported X-ray detectors based on 3D perovskites including MAPbI 3 [4,10-12] and CsFAMA [13] microcrystalline thin films or MAPbX 3 (X = Cl, Br, I and their mixture), [14-24] Cs x FA 1−x PbI 3 , [25] CsPbBr 3 , [26-29] and Cs 2 AgBiBr 6 [30-32] single crystals have realized high sensitivity with the highest up to 2.1 × 10 4 µC Gy air-1 cm-2 , significantly larger than the state-of-the-art α-Se X-ray detectors. [33] Unfortunately, the dark current is too high and as is the photocurrent drift in X-ray detectors made of these hybrid organic and inorganic 3D perovskites, and this is expected based on serious ion migration in the materials. Even worse, ionic migration is recognized as the main root cause for material decomposition and performance degradation in perovskite devices. In order to obtain perovskites with low ion migration, low-dimensional perovskite single crystals, like inchsized 0D MA 3 Bi 2 I 9 [34-37] and Cs 3 Bi 2 I 9 , [38-40] 2D Cs 2 TeI 6 [41] and (NH 4) 3 Bi 2 I 9 , [42] have been adventured first by our group and Low ionic migration is required for a semiconductor material to realize stable high-performance X-ray detection. In this work, successful controlled incorporation of not only methylammonium (MA +) and cesium (Cs +) cations, but also bromine (Br-) anions into the FAPbI 3 lattice to grow inch-sized stable perovskite single crystal (FAMACs SC) is reported. The smaller cations and anions, comparing to the original FA + and Ihelp release lattice stress so that the FAMACs SC shows lower ion migration, enhanced hardness, lower trap density, longer carrier lifetime and diffusion length, higher charge mobility and the...

The two-dimensional (2D) perovskites stabilized by alternating cations in the interlayer space (ACI) define a new type of structure with different physical properties than the more common Ruddlesden−Popper counterparts. However, there is a lack of understanding of material crystallization in films and its influence on the morphological/optoelectronic properties and the final photovoltaic devices. Herein, we undertake in situ studies of the solidification process for ACI 2D perovskite (GA)(MA) n Pb n I 3n+1 (⟨n⟩ = 3) from ink to solid-state semiconductor, using solvent mixture of DMSO:DMF (1:10 v/v) as the solvent and link this behavior to solar cell devices. The in situ grazing-incidence X-ray scattering (GIWAXS) analysis reveals a complex journey through disordered sol−gel precursors, intermediate phases, and ultimately to ACI perovskites. The intermediate phases, including a crystalline solvate compound and the 2D GA 2 PbI 4 perovskite, provide a scaffold for the growth of the ACI perovskites during thermal annealing. We identify 2D GA 2 PbI 4 to be the key intermediate phase, which is strongly influenced by the deposition technique and determines the formation of the 1D GAPbI 3 byproducts and the distribution of various n phases of ACI perovskites in the final films. We also confirm the presence of internal charge transfer between different n phases through transient absorption spectroscopy. The high quality ACI perovskite films deposited from solvent mixture of DMSO:DMF (1:10 v/v) deliver a record power conversion efficiency of 14.7% in planar solar cells and significantly enhanced long-term stability of devices in contrast to the 3D MAPbI 3 counterpart.

light-emitting diodes, [5][6][7] and photodetectors, [8,9] because of their remarkable structural flexibility, tunability, and excellent stability compared with their 3D perovskite counterparts. [10][11][12] 2D perovskites are generally a class of quantum wells (QWs), including Ruddlesden-Popper (RP), [13][14][15] Dion-Jacobson (DJ), [16][17][18] and alternating cations in the interlayer space (ACI) perovskites. [19,20] The RP and DJ families adopt the general formulas A′ 2 A n−1 M n X 3n+1 and BA n−1 M n X 3n+1 , respectively, where A is a univalent organic cation: methylammonium (MA + ) or formamidinium (FA + ), A′ is a large univalent organic spacer cation like phenylethylammonium (PEA + ), [8,21] or butylammonium (BA + ), etc., [3,22] B is a divalent organic cation like 3-(aminomethyl)piperidinium (3AMP 2+ ) [10] or 1,3-propanediamine. [23] Much work on 2D perovskites to date has focused on the RP and DJ families. For example, it was found that the incorporation of large organic spacer cations leads to the formation of a QW structure with strong quantum confinement, which leads to a higher bandgap and large exciton binding energy. [14,[24][25][26][27] The RP and DJ perovskites feature poor charge dissociation and transportation within the bulk polycrystalline film, which significantly limits the power conversion efficiency (PCE) of solar cells. [28][29][30] To address the issue, a hot-casting strategy was developed to achieve preferential outof-plane alignment of RP QWs. [3] A systematic understanding of how RP perovskites are formed as well as the charge transfer between QWs were also demonstrated, which guided development of the dynamic control of the phase transformation during QWs growth for better compositional and orientation control. [31][32][33][34][35][36] Compositional and solvent engineering were also developed to fabricate high-quality DJ films with significantly improved charge transport. [23,37] For the RP and DJ families, much has been achieved toward a deep understanding of the relationships between molecular chemistry, crystal structure, film quality and optoelectronic properties, leading to outstanding PCEs of 15.42% and 13.3% for PR and DJ perovskite solar cells, respectively. [23,38] The hybrid halide ACI perovskites, which are derived from the oxide perovskite family, are a very new entry in the class 2D perovskites stabilized by alternating cations in the interlayer space (ACI) represent a very new entry as highly efficient semiconductors for solar cells approaching 15% power conversion efficiency (PCE). However, further improvements will require understanding of the nature of the films, e.g., the thickness distribution and charge-transfer characteristics of ACI quantum wells (QWs), which are currently unknown. Here, efficient control of the film quality of ACI 2D perovskite (GA)(MA) n Pb n I 3n+1 (〈n〉 = 3) QWs via incorporation of methylammonium chloride as an additive is demonstrated. The morphological and optoelectronic characterizations unambiguously demonstrate that the additive ena...

Layered Ruddlesden–Popper (RP) phase (2D) halide perovskites have attracted tremendous attention due to the wide tunability on their optoelectronic properties and excellent robustness in photovoltaic devices. However, charge extraction/transport and ultimate power conversion efficiency (PCE) in 2D perovskite solar cells (PSCs) are still limited by the non‐eliminable quantum well effect. Here, a slow post‐annealing (SPA) process is proposed for BA2MA3Pb4I13 (n = 4) 2D PSCs by which a champion PCE of 17.26% is achieved with simultaneously enhanced open‐circuit voltage, short‐circuit current, and fill factor. Investigation with optical spectroscopy coupled with structural analyses indicates that enhanced crystal orientation and favorable alignment on the multiple perovskite phases (from the 2D phase near bottom to quasi‐3D phase near top regions) is obtained with SPA treatment, which promotes carrier transport/extraction and suppresses Shockley–Read–Hall charge recombination in the solar cell. As far as it is known, the reported PCE is so far the highest efficiency in RP phase 2D PSCs based on butylamine (BA) spacers (n = 4). The SPA‐processed devices exhibit a satisfactory stability with <4.5% degradation after 2000 h under N2 environment without encapsulation. The demonstrated process strategy offers a promising route to push forward the performance in 2D PSCs toward realistic photovoltaic applications.