Direct, simple, rapid, and real‐time monitoring of ultraviolet B level in sunlight using a self‐powered and flexible photodetector

Abstract

Sunlight-originated ultraviolet B (UVB) rays influence daily life in both beneficial and detrimental ways, depending upon light power and exposure time. Therefore, precise and timely UVB irradiance control is of great importance to humans. This study proposes a self-powered and wearable zinc sulfide (ZnS) nanoparticle (NP)-based UVB-C detector for the in situ monitoring of UVB levels in ambient environments. The performance of the ZnS-based photodetector can be markedly enhanced by constructing a vertical p-n heterojunction for testing the feasibility of a self-powered UVB-C detector, employing a thin polyethylenimine (PEI) film for inhibiting current leakage and charge recombination, and introducing a poly(9,9-dioctylfluorene-alt-N-[4-s-butylphenyl]-diphenylamine) (TFB) film as a hole transport layer to increase the photocurrent and enhance the response speed. In particular, we demonstrate that the ZnS NP/TFB junction in the device enables the direct monitoring of narrow and specific UVB bands from sunlight owing to its unique energy band structure and light absorption characteristics. The optimized device has a fast rise/fall time of 50/62 ms, high specific detectivity of 8.20 Â 10 10 Jones, and good stability over long-term storage and against mechanical bending under 254-nm light illumination. Our study provides new insights into self-powered devices that can be implemented for the facile, precise, and rapid estimation of UVB levels under sunlight for various personal healthcare applications.

Nature of Photoconductivity in Self-Powered Single-Atomic-Layered Nb-Doped WSe2 Phototransistors

“…The Ti/Nb-doped WSe 2 depletion exhibited a higher V bi (0.5 V) than the 0.2 V of the undoped WSe 2 photodetectors (Figure S4b), which facilitated charged carrier dissociation (step (ii)) . Moreover, the downshifting of the Fermi level reduced the energy mismatch between the VB of WSe 2 and the Fermi level of Pd from 0.4 to 0.1 eV (Figure S4b), which promoted the transport of photogenerated holes from Nb-doped WSe 2 to the Pd electrode (step (iii)) . Overall, the p-type Nb dopants introduced V Se , which provided numerous electron-trapping sites to escalate the photogating-dominated current.…”

“…43 Moreover, the downshifting of the Fermi level reduced the energy mismatch between the VB of WSe 2 and the Fermi level of Pd from 0.4 to 0.1 eV (Figure S4b), which promoted the transport of photogenerated holes from Nb-doped WSe 2 to the Pd electrode (step (iii)). 44 Overall, the p-type Nb dopants introduced V Se , which provided numerous electron-trapping sites to escalate the photogating-dominated current. Additionally, the supply of Nb into the WSe 2 ML generated defecttolerant shallow levels of Nb W , which caused a downshift in the Fermi level of the WSe 2 ML, thereby modifying the band alignment of the asymmetrical MSM structure to boost the photovoltaic-dominated current.…”

Self-Powered Flexible Ultraviolet Photodetectors Based on CuI/a-ZTO Heterojunction Processed at Room Temperature

“…Combined with the energy band structure analysis, since the light is incident from the CuI side, and the CuI has a remarkable ability to absorb ultraviolet irradiation, we propose that CuI plays a more important role in the conversion of optical signals. At the same time, besides the conventional conduction mechanisms, there are also several pathways for photoelectric conversion based on amorphous oxides: − (1) molecule O 2 is often adsorbed at the interface of the two materials as negatively charged O 2– . Under illumination, the photogenerated holes will neutralize the oxygen ions, and numerous free electrons will be left at the interface, resulting in a considerate photogenerated current.…”

Self-Powered ZTO/ZnO Nanowire-Based Photodetectors with Ultrahigh Photosensitivity for Advanced UV Sensing

“…ZnO is an essential element in the conversion of optical signals because of its capacity to absorb UV energy. Amorphous oxides and ubiquitous conduction processes are further methods for photoelectric conversion. , At the interface between the two materials, the O 2 molecule typically becomes adsorbed and acquires the negative charge of O 2 – . When exposed to light, the oxygen ion’s negative charge will be balanced by the holes produced by the photons, creating a considerable buildup of free electrons at the interface.…”