Even though the mesoporous-type perovskite solar cell (PSC) is known for high efficiency, its planar-type counterpart exhibits lower efficiency and hysteretic response. Herein, we report success in suppressing hysteresis and record efficiency for planar-type devices using EDTA-complexed tin oxide (SnO2) electron-transport layer. The Fermi level of EDTA-complexed SnO2 is better matched with the conduction band of perovskite, leading to high open-circuit voltage. Its electron mobility is about three times larger than that of the SnO2. The record power conversion efficiency of planar-type PSCs with EDTA-complexed SnO2 increases to 21.60% (certified at 21.52% by Newport) with negligible hysteresis. Meanwhile, the low-temperature processed EDTA-complexed SnO2 enables 18.28% efficiency for a flexible device. Moreover, the unsealed PSCs with EDTA-complexed SnO2 degrade only by 8% exposed in an ambient atmosphere after 2880 h, and only by 14% after 120 h under irradiation at 100 mW cm−2.

Surface plasmon resonances (SPRs) have been found to promote chemical reactions. In most oxidative chemical reactions oxygen molecules participate and understanding of the activation mechanism of oxygen molecules is highly important. For this purpose, we applied surface-enhanced Raman spectroscopy (SERS) to find out the mechanism of SPR-assisted activation of oxygen, by using p-aminothiophenol (PATP), which undergoes a SPR-assisted selective oxidation, as a probe molecule. In this way, SPR has the dual function of activating the chemical reaction and enhancing the Raman signal of surface species. Both experiments and DFT calculations reveal that oxygen molecules were activated by accepting an electron from a metal nanoparticle under the excitation of SPR to form a strongly adsorbed oxygen molecule anion. The anion was then transformed to Au or Ag oxides or hydroxides on the surface to oxidize the surface species, which was also supported by the heating effect of the SPR. This work points to a promising new era of SPR-assisted catalytic reactions.

Even though the power conversion efficiency (PCE) of rigid perovskite solar cells is increased to 22.7%, the PCE of flexible perovskite solar cells (F-PSCs) is still lower. Here, a novel dimethyl sulfide (DS) additive is developed to effectively improve the performance of the F-PSCs. Fourier transform infrared spectroscopy reveals that the DS additive reacts with Pb to form a chelated intermediate, which significantly slows down the crystallization rate, leading to large grain size and good crystallinity for the resultant perovskite film. In fact, the trap density of the perovskite film prepared using the DS additive is reduced by an order of magnitude compared to the one without it, demonstrating that the additive effectively retards transformation kinetics during the thin film formation process. As a result, the PCE of the flexible devices increases to 18.40%, with good mechanical tolerance, the highest reported so far for the F-PSCs. Meanwhile, the environmental stability of the F-PSCs significantly enhances by 1.72 times compared to the device without the additive, likely due to the large grain size that suppresses perovskite degradation at grain boundaries. The present strategy will help guide development of high efficiency F-PSCs for practical applications.

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.

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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...

Proteins perform vital functional and structural duties in living systems, and the in-depth investigation of protein in its native state is one of the most important challenges in the postgenomic era. Surface-enhanced Raman spectroscopy (SERS) can provide the intrinsic fingerprint information of samples with ultrahigh sensitivity but suffers from the reproducibility and reliability issues. In this paper, we proposed an iodide-modified Ag nanoparticles method (Ag IMNPs) for label-free detection of proteins. The silver nanoparticles provide the huge enhancement to boost the Raman signal of proteins, and the coated iodide layer offers a barrier to prevent the direct interaction between the proteins and the metal surface, helping to keep the native structures of proteins. With this method, highly reproducible and high-quality SERS signals of five typical proteins (lysozyme, avidin, bovine serum albumin, cytochrome c, and hemoglobin) have been obtained, and the SERS features of the proteins without chromophore were almost identical to the respective normal Raman spectra. This unique feature allows the qualitative identification of them by simply taking the intensity ratio of the Raman peaks of tryptophan to phenylalanine residues. We further demonstrated that the method can also be used for label-free multiplex analysis of protein mixture as well as to study the dynamic process of protein damage stimulated by hydrogen peroxide. This method proves to be very promising for further applications in proteomics and biomedical research.

Single crystalline perovskites exhibit high optical absorption, long carrier lifetime, large carrier mobility, low trap-state-density and high defect tolerance. Unfortunately, all single crystalline perovskites attained so far are limited to bulk single crystals and small area wafers. As such, it is impossible to design highly demanded flexible single-crystalline electronics and wearable devices including displays, touch sensing devices, transistors, etc. Herein we report a method of induced peripheral crystallization to prepare large area flexible single-crystalline membrane (SCM) of phenylethylamine lead iodide (C6H5C2H4NH3)2PbI4 with area exceeding 2500 mm2 and thinness as little as 0.6 μm. The ultrathin flexible SCM exhibits ultralow defect density, superior uniformity and long-term stability. Using the superior ultrathin membrane, a series of flexible photosensors were designed and fabricated to exhibit very high external quantum efficiency of 26530%, responsivity of 98.17 A W−1 and detectivity as much as 1.62 × 1015 cm Hz1/2 W−1 (Jones).