Surface Engineering of Perovskite Single Crystals by Atomic Layer Deposited Tin Oxide for Optical Communication.

Perovskite single crystals with excellent physical properties have broad prospects in the field of optoelectronics. However, the presence of dangling bonds, surface dislocations, and chemical impurities results in high surface defect density and sensitivity to humidity. Unfortunately, there are relatively few surface engineering strategies for single perovskite single crystals. We present a strategy utilizing atomic layer deposited SnOx to passivate surface defects in perovskite single crystals. The photodetector prepared based on the modified FAPbBr3 single crystals exhibits a low dark current of 1.89 × 10-9 A at a 5 V bias, close to 4 times lower with respect to the pristine device, a high detectivity of 2.3 × 1010 jones, and a fast response time of 27 µs. Moreover, the photodetectors feature long-term operational stability because the presence of a dense SnOx capping layer hinders the ingress of moisture and diffusion of ions. We further demonstrate the promise of our perovskite single crystal detectors for real-time subaqueous optical communication.

Sensitive photodetection below silicon bandgap using quinoid-capped organic semiconductors.

High-sensitivity organic photodetectors (OPDs) with strong near-infrared (NIR) photoresponse have attracted enormous attention due to potential applications in emerging technologies. However, few organic semiconductors have been reported with photoelectric response beyond ~1.1 µm, the detection limit of silicon detectors. Here, we extend the absorption of organic small-molecule semiconductors to below silicon bandgap, and even to 0.77 eV, through introducing the newly designed quinoid-terminals with high Mulliken-electronegativity (5.62 eV). The fabricated photodiode-type NIR OPDs exhibit detectivity (D*) over 1012 Jones in 0.41 to 1.2 µm under zero bias with a maximum of 2.9 × 1012 Jones at 1.02 µm, which is the highest D* for reported OPDs in photovoltaic-mode with response spectra beyond 1.1 µm. The high D* in 0.9 to 1.2 µm is comparable to those of commercial InGaAs photodetectors, despite the detection limit of our OPDs is shorter than InGaAs (~1.7 µm). A spectrometer prototype with a wide measurable region (0.4 to 1.25 µm) and NIR imaging under 1.2-µm illumination are demonstrated successfully in OPDs.

Highly Sensitive Tin-Lead Perovskite Photodetectors with Over 450 Days Stability Enabled by Synergistic Engineering for Pulse Oximetry System.

Low-bandgap tin (Sn)-lead (Pb) halide perovskites can achieve near-infrared response for photodetectors. However, the Sn-based devices suffer from notorious instability and high defect densities due to the oxidation propensity of Sn2+ . Herein, a multifunctional additive 4-amino-2,3,5,6-tetrafluorobenzoic acid (ATFBA) is presented, which can passivate surface defects and inhibit the oxidation of Sn2+ through hydrogen bonds and chelation coordination from the terminal amino and carboxyl groups. The perfluorinated benzene ring structure of ATFBA affords the passivator assembled at the grain boundaries to enhance the water resistance. With the synergistical passivation of these functional groups, the Sn-Pb perovskite photodetector exhibits a remarkable responsivity of 0.52 A W-1 and an excellent specific detectivity of 5.34 × 1012 Jones at 850 nm, along with remaining 97% of its initial responsivity over 450 days. Benefitting from high sensitivity, the photodetector is integrated into a pulse oximetry sensor visualization system, yielding accurate blood oxygen saturation and heart rate with less than 2% error. This work paves the avenue toward constructing high-performance and stable Sn-Pb perovskite photodetectors for practical applications.

Searching for High-Quality Halide Perovskite Single Crystals toward X-ray Detection.

Metal halide perovskite materials, which combine outstanding physical properties, large absorption coefficient, tailored composition, and low-cost solution-processing, have aroused wide attention for use in various optoelectronic devices. Recently, perovskite single crystals have been rapidly outpacing traditional semiconductor materials in the field of radiation detection. As a prerequisite, achieving high-quality single crystals under controllable solution-phase growth must be tackled to fulfill their full potential as a new paradigm in this stagnated field. This Perspective summarizes the advances in X-ray detectors based on lead halide perovskite single crystals, presenting a comprehensive picture of the relationship among composition engineering, synthesis, and device properties. Additionally, we share our thoughts on several outstanding challenges of perovskite single crystals as promising X-ray detectors and propose possible approaches to the unresolved issues. We anticipate that this Perspective can open up new opportunities to improve their optoelectronic properties, which confers fascinating photonics applications with above and beyond state-of-the-art performance.

Broadband Photodetector Based on Inorganic Perovskite CsPbBr3 /GeSn Heterojunction.

Photodetectors with broadband response spectrum have attracted great interest in many application areas such as imaging, gas sensing, and night vision. Here, a high performance broadband photodetector is demonstrated with inorganic perovskite CsPbBr3 /GeSn heterojunction, detection range can be covered from 450 to 2200 nm. The responsivity of heterojunction device can achieve as high as 129 mA W-1 under illuminated light of 532 nm, which is 4.92 times larger than that of a GeSn based device. As the CsPbBr3 can also act as anti-reflective coating for infrared wavelength, the infrared band responsivity at wavelength of 2200 nm can also be raised by 1.42 times. In addition, the device with all inorganic components is showed good stability, while keeping in the dry environment, the device can sustain its 90% original after 550 h storage. These results show the inorganic perovskite/GeSn heterojunction device is of great potential in broadband photodetection with high responsivity.

Stable Perovskite Solar Cells with Bulk-Mixed Electron Transport Layer by Multifunctional Defect Passivation.

Multifarious electron transport layers (ETLs), especially fullerene derivatives, have been applied in organic-inorganic hybrid perovskite (OIHP) devices owing to their superior optoelectronic properties. However, a PCBM Lewis acid molecule can only passivate the iodine-rich defect sites, which cannot solve the problem of uncoordinated Pb2+ and water oxygen erosion due to the high volatility of halide I- and the hydrophilicity of organic cation MA+. Herein, we introduce a Lewis base, TBA-Azo with an electron-donating Azo moiety, and hydrophobic long alkyl chains into the PCBM layer to form a multifunctional bulk-mixed electron transport layer (MBE). PCBM of MBE can combine with iodine-rich trap sites at the surface and grain boundaries of perovskite. TBA-Azo molecules of MBE can passivate uncoordinated Pb2+ by forming Lewis adducts and isolate water/oxygen at the perovskite surface with hydrophobic alkyl chains. It results in a decrease of trap densities with 1 order of magnitude, effectively inhibiting both bimolecular and trap-induced recombination and thus elongating the carrier lifetime. The passivation of MBE can effectively improve the open-circuit voltage from 1.05 to 1.10 V. Furthermore, three long carbon chain structures of TBA-Azo in MBE can improve the water-resistant ability of OIHP devices, which can maintain 90% of the original PCE after 500 h at the humidity of 50 ± 10%. We believe that the MBE with multifunctional defect passivation provides a strategy for simultaneously achieving high-performance and high-stability OIHP optoelectronic devices.

Fast Response Organic Tandem Photodetector for Visible and Near-Infrared Digital Optical Communications.

Organic photodetectors (OPDs), which usually work as photodiodes, photoconductors, or phototransistors, have emerged as candidates for next-generation light sensing. However, low response speed caused by low carrier mobility and resistance-capacitance (RC) time constant, severely hinders the commercialization of OPDs. Herein, the authors demonstrate a state-of-the-art OPD with a record response speed of 146.8 ns by employing tandem structure to simultaneously reduce both the carrier transit time and RC time constant of the device, which is faster than that of previously reported OPDs as far as they know. Moreover, benefitting from the multi-level barrier enhancement and voltage division engendered by tandem structure, an ultralow noise current of 7.82 × 10-14 A Hz-1/2 is obtained, as well as a wide detection range in 300-1000 nm. In addition, the tandem OPDs are successfully integrated into the optical communication system as signal receivers, demonstrating the precise digital signal communication from visible to near-infrared light. It is believed that tandem OPDs have promising application potential in the wireless transmission system.

High-Temperature Stable FAPbBr3 Single Crystals for Sensitive X-ray and Visible Light Detection toward Space.

Organolead trihalide perovskite single crystals (SCs) offer unprecedented opportunity for X-ray and visible light detection. Nevertheless, it remains a challenge to keep simultaneous high-performance and stability at a high-temperature working mode. Herein, formamidinium lead bromide (FAPbBr3) SCs are developed to successfully address these issues. Low-temperature crystallized induced FAPbBr3 SCs possess an excellent mobility-lifetime product and an ultralow surface charge recombination velocity, thus exhibiting an X-ray dose rate as low as 0.3 µGyair s-1 as a sensitive radiation detector. Furthermore, it also contributes a specific detectivity as high as 3.5 × 1012 cm Hz1/2 W-1, keeping stable at high-temperature of 460 K as a photodetector. A prototype of an imaging system with diffuse reflection mode is constructed using detectors as receivers, enabling defined scanning images in a high temperature environment. The bifunctional FAPbBr3 SC detectors will motivate new strategies for stable detection in an extreme space environment.

Sensitive and Stable Tin-Lead Hybrid Perovskite Photodetectors Enabled by Double-Sided Surface Passivation for Infrared Upconversion Detection.

Tin(Sn)-based perovskite is currently considered one of the most promising materials due to extending the absorption spectrum and reducing the use of lead (Pb). However, Sn2+ is easily oxidized to Sn4+ in atmosphere, causing more defects and degradation of perovskite materials. Herein, double-sided interface engineering is proposed, that is, Sn-Pb perovskite films are sandwiched between the phenethylammonium iodide (PEAI) in both the bottom and top sides. The larger organic cations of PEA+ are arranged into a perovskite surface lattice to form a 2D capping layer, which can effectively prevent the water and oxygen to destroy bulk perovskite. Meanwhile, the PEA+ can also passivate defects of iodide anions at the bottom of perovskite films, which is always present but rarely considered previously. Compared to one sided passivation, Sn-Pb hybrid perovskite photodetectors contribute a significant enhancement of performance and stability, yielding a broadband response of 300-1050 nm, a low dark current density of 1.25 × 10-3 mA cm-2 at -0.1 V, fast response speed of 35 ns, and stability beyond 240 h. Furthermore, the Sn-Pb broadband photodetectors are integrated in an infrared up-conversion system, converting near-infrared light into visible light. It is believed that a double-sided passivation method can provide new strategies to achieving high-performance perovskite photodetectors.