Deep-ultraviolet photodetector based on pulsed-laser-deposited Cs3Cu2I5 films/n-Si heterojunction

Recent Progress of 2D Materials-Based Photodetectors from UV to THz Waves: Principles, Materials, and Applications

Photodetectors are one of the most critical components for future optoelectronic systems and it undergoes significant advancements to meet the growing demands of diverse applications spanning the spectrum from ultraviolet (UV) to terahertz (THz). 2D materials are very attractive for photodetector applications because of their distinct optical and electrical properties. The atomic-thin structure, high carrier mobility, low van der Waals (vdWs) interaction between layers, relatively narrower bandgap engineered through engineering, and significant absorption coefficient significantly benefit the chip-scale production and integration of 2D materials-based photodetectors. The extremely sensitive detection at ambient temperature with ultra-fast capabilities is made possible with the adaptability of 2D materials. Here, the recent progress of photodetectors based on 2D materials, covering the spectrum from UV to THz is reported. In this report, the interaction of light with 2D materials is first deliberated on in terms of optical physics. Then, various mechanisms on which detectors work, important performance parameters, important and fruitful fabrication methods, fundamental optical properties of 2D materials, various types of 2D materials-based detectors, different strategies to improve performance, and important applications of photodetectors are discussed.

Highly stable mixed-phase Cs-Cu-I films with tunable optoelectronic properties for UVB photodetector applications

Ultraviolet (UV) photodetector plays an important role in military, civilian and people's daily life, and is an indispensable part of spectral detection. However, photodetectors target at the UVB region (280-320 nm) are rarely reported, and the devices detected by medium-wave UV light generally have problems such as low detection rate, low sensitivity, and poor stability, which are difficult to meet the market application needs. Herein, Cs-Cu-I films with mixed-phase have been prepared by vacuum thermal evaporation. By adjusting the proportion of evaporation sources (CsI and CuI), the optical bandgaps of mixed-phase Cs-Cu-I films can be tuned between 3.7 eV and 4.1 eV. This absorption cut-off edge is exactly at both ends of the UVB band, which indicating its potential application in the field of UVB detection. Finally, the photodetectors based on Cs-Cu-I/n-Si heterojunction are fabricated. The photodetector shows good spectral selectivity for UVB band, and has a photoresponsivity of 22 mA/W, a specific detectivity of 1.83*1011 Jones, an EQE over 8.7% and an on/off ratio above 20.

Recent Advances and Opportunities of Eco-Friendly Ternary Copper Halides: A New Superstar in Optoelectronic Applications

Recently, the newly-emerging lead-free metal-halide materials with less toxicity and superior optoelectronic properties have received wide attention as the safer and potentially more robust alternatives to lead-based perovskite counterparts. Among them, ternary copper halides (TCHs) have become a vital group due to their unique features, including abundant structural diversity, ease of synthesis, unprecedented optoelectronic properties, high abundance, and low cost. Although the recent efforts in this field have made certain progresses, some scientific and technological issues still remain unresolved. Herein, a comprehensive and up-to-date overview of recent progress on the fundamental characteristics of TCH materials and their versatile applications is presented, which contains topics such as: i) crystal and electronic structure features and synthesis strategies; ii) mechanisms of self-trapped excitons, luminescence regulation, and environmental stability; and iii) their burgeoning optoelectronic devices of phosphor-converted white light-emitting diodes (WLEDs), electroluminescent LEDs, anti-counterfeiting, X-ray scintillators, photodetectors, sensors, and memristors. Finally, the current challenges together with future perspectives on the development of TCH materials and applications are also critically described, which is considered to be critical for accelerating the commercialization of these rapidly evolving technologies.

Room-Temperature Solid-State Synthesis of Cs3Cu2I5 Thin Films and Formation Mechanism for Its Unique Local Structure

Blue-emitting Cs₃Cu₂I₅ has attracted attention owing to its near-unity PL quantum yield and applications in DUV photodetectors and scintillators. Its PL properties originate from the unique local structure around the luminescent center, the [Cu₂I₅]^3- polyhedron iodocuprate anion consisting of the edge-shared CuI₃ triangle and the CuI₄ tetrahedron dimer, which is isolated by Cs⁺ ions. We found that solid-state reactions between CsI and CuI occur near room temperature (RT) to form Cs₃Cu₂I₅ and/or CsCu₂I₃ phases. High-quality thin films of these phases were obtained by the sequential deposition of CuI and CsI by thermal evaporation. We elucidated that the formation of interstitial Cu⁺ and the antisite of I^- at the Cs⁺ site in the CsI crystal through Cu⁺ and I^- diffusion results in the RT synthesis of Cs₃Cu₂I₅. The unique structure formation of the luminescent center was revealed using a model based on the low packing density of the CsCl-type crystal structure, similar sizes of Cs⁺ and I^- ions, and the high diffusivity of Cu⁺. The self-aligned patterning of the luminous regions on thin films was demonstrated.