Intermediate phase-assisted solution preparation of two dimensional CsPbCl3 perovskite for efficient ultraviolet photodetection

Air-Stable Self-Driven UV Photodetectors on Controllable Lead-Free CsCu2I3 Microwire Arrays

The rapid evolution of the Internet of Things has engendered increased requirements for low-cost, self-powered UV photodetectors. Herein, high-performance self-driven UV photodetectors are fabricated by designing asymmetric metal-semiconductor-metal structures on the high-quality large-area CsCu2I3 microwire arrays. The asymmetrical depletion region doubles the photocurrent and response speed compared to the symmetric structure device, leading to a high responsivity of 233 mA/W to 355 nm radiation. Notably, at 0 V bias, the asymmetric device produces an open-circuit voltage of 356 mV and drives to a short-circuit current of 372 pA; meanwhile, the switch ratio (Iph/Idark) reaches up to 103, indicating its excellent potential for detecting weak light. Furthermore, the device maintains stable responses throughout 10000 UV-light switch cycles, with negligible degradation even after 90-day storage in air. Our work establishes that CsCu2I3 is a good candidate for self-powered UV detection and thoroughly demonstrates its potential as a passive device.

Low-Temperature Vapor-Phase Anion-Exchange Strategy for Wide-Bandgap Double-Perovskite Cs2AgBiCl6 Films toward Weak Ultraviolet Light Imaging

Low-temperature synthesis of high-quality, high-stability, wide-bandgap perovskite films by solution methods is still challenging. Herein, large-scale wide-bandgap Cs₂AgBiCl₆ (CABC) double perovskite films are synthesized by a vapor-phase anion-exchange strategy. By dedicatedly designing an ultrathin TiO₂ modification layer between the substrate and double perovskites, high-quality heterojunctions with matched energy band alignment are formed, contributing to a remarkably enhanced ON/OFF ratio of 2.4 × 10⁴ (86 times) and a responsivity of 16 mA W^-1 (12 times). Additionally, the ultraviolet photodetectors (UV PDs) exhibit an excellent UV detection limit of 1.18 μW cm^-2 (20 nW), a broad linear dynamic range of 146 dB, and a high specific detectivity of 2.06 × 10¹¹ Jones, as well as long-term stability. Finally, we further demonstrate a weak UV imaging system using CABC UV PDs as imaging sensors. The system is capable of imaging weak UV signals as low as 2.94 μW cm^-2 (50 nW). Our results provide a feasible approach for low-temperature fabrication of wide-bandgap perovskite UV PDs and explore the promising application for weak UV detection and imaging.

Boosting the Performance of Self-Powered CsPbCl3-Based UV Photodetectors by a Sequential Vapor-Deposition Strategy and Heterojunction Engineering

All-inorganic CsPbCl₃ perovskite in ultraviolet (UV) detection is drawing increasing interest owing to its UV-matchable optical band gap, ultrahigh UV stability, and superior inherent optoelectronic properties. Almost all of the reported CsPbCl₃ photodetectors employ CsPbCl₃ nano- or microstructures as sensitive components, while CsPbCl₃ polycrystalline film-based self-powered photodetectors are rarely studied on account of the terrible precursor solubility. Herein, a novel sequential vapor-deposition technique is demonstrated to fabricate CsPbCl₃ polycrystalline film for the first time. High-quality CsPbCl₃ films with excellent optical, electronic, and morphological features are obtained. A self-powered photodetector based on the CsPbCl₃ film is constructed without any charge transport layer, showing a high UV detection performance. A thin p-type PbS buffer layer is further introduced to passivate the surface defects of the CsPbCl₃ layer and decrease the interfacial energy barrier by forming a type-II heterojunction, contributing to a faster hole extraction rate and a suppressed dark current level. The best-performing device achieves an ultrafast response time of 1.92 μs, an ultrahigh on/off ratio of 2.22 × 10⁵, and a responsivity of 0.22 A/W upon 375 nm UV illumination at 0 V bias. This comprehensive performance is the best among all of the CsPbCl₃ photodetectors reported to date. The as-prepared photodetectors also present an eminent UV irradiation and long-term durability in ambient air. Furthermore, a large-area and uniform 625-pixel UV image sensor is fabricated and attains a prominent imaging capability. Our work opens a new avenue for the scalable production of CsPbCl₃-based optoelectronics.

Highly-efficient and stable photocatalytic activity of lead-free Cs2AgInCl6 double perovskite for organic pollutant degradation

Photocatalytic applications of halide perovskites have attracted increasing attention. However, lack of stability and lead toxicity of lead halide perovskites have hindered their applications. Metal halide double perovskite (DP) Cs₂AgInCl₆ is a stable, environment-friendly semiconductor with direct band gap, and then the best promising alternative to lead halide perovskites. Here, the applications of Cs₂AgInCl₆ DP to photocatalytic degradation of organic pollutants have been developed, in which the octahedral Cs₂AgInCl₆ DP particles (~3.33 eV) were prepared by precipitation from acid solutions. The as-prepared samples exhibit high photocatalytic activity, which can degrade about 98.5% of water-insoluble carcinogen Sudan Red III in only 16 min, and have a good stability for 5 cycle operations. Furthermore, the Cs₂AgInCl₆ DP also can degrade Rhodamine B, Methyl orange and Methyl red efficiently, demonstrating a highly-efficient and stable ethanol solvent-based photocatalytic system for organic pollutants degradation. The high photocatalytic activity could be attributed to direct band gap and long carrier lifetime of Cs₂AgInCl₆ DP. These unique features of Cs₂AgInCl₆ DP indicate that it could have a good application prospect for photocatalytic degradation of organic pollutants.

Dual-Phase CsPbCl3-Cs4PbCl6 Perovskite Films for Self-Powered, Visible-Blind UV Photodetectors with Fast Response

All-inorganic, Cl-based perovskites are promising for visible-blind UV photodetectors (PDs), particularly the self-powered ones. However, the devices are rarely reported until now since the low solubility of raw materials hinders significantly the thickness and electronic quality of solution-processed Cl-based perovskite films. Herein, we demonstrate a simple intermediate phase halide exchange method to prepare desired dual-phase CsPbCl₃-Cs₄PbCl₆ films. It is achieved by spin-coating of a certain dose of CH₃NH₃Cl/CsCl solution onto a CsI-PbBr₂-dimethyl sulfoxide (DMSO) intermediate phase film, followed by thermal annealing. The inclusion of CsCl species in the solution is crucial to a stable dual-phase CsPbCl₃-Cs₄PbCl₆ film, while a high annealing temperature contributes to improving its quality. Therefore, the dual-phase CsPbCl₃-Cs₄PbCl₆ film with an absorption onset of ∼420 nm, microsized grains, a few defects, and a proper work function is obtained by optimizing the annealing temperature. The final self-powered, visible-blind UV PD exhibits the superior performance, including a favored response range of 310-420 nm, a high responsivity (R) peak value of 61.8 mA W^-1, an exceptional specific detectivity (D*) maximum of 1.35 × 10¹² Jones, and a particularly fast response speed of 2.1/5.3 μs, together with amazing operational stability. This work represents the first demonstration of solution-processed, self-powered, visible-blind UV PDs with all-inorganic, Cl-based perovskite films.