As a wide‐bandgap semiconductor material, titanium dioxide (TiO2), which possesses three crystal polymorphs (i.e., rutile, anatase, and brookite), has gained tremendous attention as a cutting‐edge material for application in the environment and energy fields. Based on the strong attractiveness from its advantages such as high stability, excellent photoelectric properties, and low‐cost fabrication, the construction of high‐performance photodetectors (PDs) based on TiO2 nanostructures is being extensively developed. An elaborate microtopography and device configuration is the most widely used strategy to achieve efficient TiO2‐based PDs with high photoelectric performances; however, a deep understanding of all the key parameters that influence the behavior of photon‐generated carriers, is also highly required to achieve improved photoelectric performances, as well as their ultimate functional applications. Herein, an in‐depth illustration of the electrical and optical properties of TiO2 nanostructures in addition to the advances in the technological issues such as preparation, microdefects, p‐type doping, bandgap engineering, heterojunctions, and functional applications are presented. Finally, a future outlook for TiO2‐based PDs, particularly that of further functional applications is provided. This work will systematically illustrate the fundamentals of TiO2 and shed light on the preparation of more efficient TiO2 nanostructures and heterojunctions for future photoelectric applications.

Application of Nanostructured TiO2 in UV Photodetectors: A Review

A General Strategy to Ultrasensitive Ga2O3 Based Self-Powered Solar-blind Photodetectors

Tunable work function has a high profile for the MXene‐based optoelectronic devices, and surface modification provides the huge potential to shift its Fermi level and modulate the work function. In this work, the window of MXene's work function is engineered from 4.55 to 5.25 eV by surface modification with LiF, Se, and polyethylenimine ethoxylated (PEIE). The vertical p‐CsCu2I3/n‐Ca2Nb3‐xTaxO10 junction photodetectors are constructed on the basis of the above surface‐modified MXenes, which changes the Schottky barrier between n‐Ca2Nb3‐xTaxO10 and the electrodes. In particular, the rectification effect is significantly enhanced by utilizing PEIE‐decorated MXene electrodes, resulting in a high rectification ratio of 16 136 and improved UV responsivity of 81.3 A W–1. Such high‐performance devices based on MXenes electrodes are compatible with the standard clean room fabrication process, realizing large‐scale flexible UV detectors that maintain 80% of the original current after 5000 times bending. Meanwhile, a photodetector array stimulated with UV of different wavelengths is constructed to reveal its potential for image sensing. Finally, functional “AND” and “OR” optoelectronic logic gates are developed for UV communication using Au/CsCu2I3/Ca2Nb3‐xTaxO10/MXene–PEIE photodetectors, enriching the application of MXene‐based optoelectronic devices. This work on tuning MXene work function via surface modification demonstrates that MXene is a promising candidate for future optoelectronics.

Work‐Function‐Tunable MXenes Electrodes to Optimize p‐CsCu2I3/n‐Ca2Nb3‐xTaxO10 Junction Photodetectors for Image Sensing and Logic Electronics

Tunable work function has a high profile for the MXene-based optoelectronic devices, and surface modification provides the huge potential to shift its Fermi level and modulate the work function. In this work, the window of MXene's work function is engineered from 4.55 to 5.25 eV by surface modification with LiF, Se, and polyethylenimine ethoxylated (PEIE). The vertical p-CsCu2I3/n-Ca2Nb3-xTaxO10 junction photodetectors are constructed on the basis of the above surface-modified MXenes, which changes the Schottky barrier between n-Ca2Nb3-xTaxO10 and the electrodes. In particular, the rectification effect is significantly enhanced by utilizing PEIE-decorated MXene electrodes, resulting in a high rectification ratio of 16 136 and improved UV responsivity of 81.3 A W–1. Such high-performance devices based on MXenes electrodes are compatible with the standard clean room fabrication process, realizing large-scale flexible UV detectors that maintain 80% of the original current after 5000 times bending. Meanwhile, a photodetector array stimulated with UV of different wavelengths is constructed to reveal its potential for image sensing. Finally, functional “AND” and “OR” optoelectronic logic gates are developed for UV communication using Au/CsCu2I3/Ca2Nb3-xTaxO10/MXene–PEIE photodetectors, enriching the application of MXene-based optoelectronic devices. This work on tuning MXene work function via surface modification demonstrates that MXene is a promising candidate for future optoelectronics. 

Work‐Function‐Tunable MXenes Electrodes to Optimize p‐CsCu
 2
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 Nb
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Photodetectors are light sensors in widespread use in image sensing, optical communication, and consumer electronics. In current smart optoelectronic technology, conventional semiconductors have encountered a bottleneck caused by inflexibility and opacity. With the ever-increasing demands for versatile optoelectronic applications, perovskite-type 2D materials demonstrate great potential for advanced photodetectors inspired by molecularly thin 2D materials. Through the reduction of thickness to thin or molecularly thin levels, single-crystalline 2D perovskites can exhibit superior optoelectronic performance characteristics, such as tunable absorption property by chemical design, enhanced carrier separation by remarkable photosensing capability, and improved carrier extraction by versatile band engineering. More importantly, perovskite-type 2D materials exhibit great potential for large-scale monolithic integration to achieve all-in-one sensing-memory-computing optoelectronic devices. In this Perspective, recent progress in 2D perovskite-based photodetectors is presented in detail. The focus is on growth strategies for reducing thickness, thickness-dependent optical and electrical properties, device engineering, heterojunction fabrication, and device performance. Finally, the current challenges and future prospects in this field are presented.

Yihan Chen

Papers

Switch type PANI/ZnO core-shell microwire heterojunction for UV photodetection