In this study, double-layered TCO (transparent conductive oxide) films were produced by depositing two distinct TCO materials: SnO₂ works as an n-type layer and ITO (indium-doped tin oxide) serves as a transparent conductor. Both transparent conductive oxide-films were sequentially deposited by sputtering. The electrical and optical properties of single-layered TCO films (SnO₂) and double-layered TCO (ITO/SnO₂) films were investigated. A TCO-embedding photodetector was realized through the formation of an ITO/SnO₂/p-Si/Al layered structure. The remarkably high rectifying ratio of 400.64 was achieved with the double-layered TCO device, compared to 1.72 with the single-layered TCO device. This result was attributed to the enhanced electrical properties of the double-layered TCO device. With respect to the photoresponses, the photocurrent of the double-layered TCO photodetector was significantly improved: 1,500% of that of the single-layered TCO device. This study suggests that, due to the electrical and optical benefits, double-layered TCO films are effective for enhancing the photoresponses of TCO photodetectors. This provides a useful approach for the design of photoelectric devices, including solar cells and photosensors.

Molybdenum oxide (MoO₃) offers pivotal advantages for high optical transparency and low light reflection. Considering device fabrication, n-type MoO₃ semiconductor can spontaneously establish a junction with p-type Si. Since the energy bandgap of Si is 1.12 eV, a maximum photon wavelength of around 1,100 nm is required to initiate effective photoelectric reaction. However, the utilization of infrared photons is very limited for Si photonics. Hence, to enhance the Si photoelectric devices, we applied the wide energy bandgap MoO₃ (3.7 eV) top-layer onto Si. Using a large-scale production method, a wafer-scale MoO₃ device was fabricated with a highly crystalline structure. The MoO₃/p-Si heterojunction device provides distinct photoresponses for long wavelength photons at 900 nm and 1,100 nm with extremely fast response times: rise time of 65.69 ms and fall time of 71.82 ms. We demonstrate the high-performing MoO₃/p-Si infrared photodetector and provide a design scheme for the extension of Si for the utilization of long-wavelength light.

An all-transparent photodetector was fabricated by structuring Cu₂O/ZnO/AZO/ITO on a glass substrate. The visible-range transmittance was as high as 80%, which ensures clear vision forhuman eyes. High-transparency metal conductive oxides (p-type Cu₂O and n-type ZnO) were appliedto form the transparent p/n junction. The functional AZO layer was adopted to improve the transparent photodetector performance between the ZnO and ITO, improving the photoresponses because of its electrical conductivity. To clarify the AZO functionality, a comparator device was prepared without the AZO layer in the formation of Cu₂O/ZnO/ITO/Glass. The Cu₂O/ZnO/AZO/ITO device provided a rectifying ratio of 113.46, significantly better than the 9.44 of the Cu₂O/ZnO/ITO device. In addition, the Cu₂O/ZnO/AZO/ITO device`s photoresponses at short wavelengths were better than those of the comparator. The functioning AZO layer provides ahigh-performing transparent Cu oxide photodetector and may suggest a route for the design of efficient photoelectric devices.

Transparent n-type metal-oxide semiconductor of MoO_x was applied on a p-type Si substrate for high-performing heterojunction photodetector. The formation of MoO_x on Si spontaneously established a rectifying current flow with a high rectification ratio of 1,252.3%. Under light illumination condition, n-type MoO_x/p-type Si heterojunction device provided significantly fast responses (rise time : 61.28 ms, fall time : 66.26 ms). This transparent metal-oxide layer (MoO_x) would provide a functional route for various photoelectric devices, including photodetectors and solar cells.

Transparent UV photodetector was achieved by using wide bandgap metal oxide materials. In order to realize transparent heterojunction UV photodetector, n-type ZnO and p-type NiO metal oxide materials were employed. High light-absorbing SnS layer was inserted into the n-ZnO and p-NiO layers. High-performing UV photodetector was realized by ZnO/SnS/NiO/ITO structures to provide extremely fast response times (Fall time: 7 μ s and rise time: 13 μs) and high rectifying ratio. The use of functional SnS-embedded photodetector would provide a route for high functional photoelectric devices.