Surface Modification of Al-Doped ZnO Transparent Conducive Thin Films with Polycrystalline Zinc Molybdenum Oxide

Abstract

High-work function (WF) transparent conductive thin films improve the performance of solar cells and organic light-emitting diodes by facilitating interfacial charge carrier transport. Al-doped ZnO (AZO) becomes a very promising transparent conductive material because of nontoxicity, abundant material resources, and low cost. To increase the WF of AZO without enhancing the series resistance of the device, a high-WF and low-resistance surface modifier of polycrystalline zinc molybdenum oxide (ZMO) was developed by utilizing thermal evaporation of MoO3 on the surface of AZO and a subsequent two-step annealing treatment. The first step of air annealing causes the formation of monoclinic ZnMoO4 nanocrystals in the ZMO modifier. This improves the WF of AZO from 3.83 to 4.86 eV by increasing the group electronegativity and cation oxidation state. Furthermore, the second step of N2 annealing decreases the resistivity of the polycrystalline ZMO by increasing the donor states of oxygen vacancies. The surface modification effect is verified by applying the ZMO-modified AZO to the front electrode of hydrogenated amorphous silicon thin-film solar cells. The low-resistance polycrystalline ZMO modifier not only increases light harvesting in the solar cells by improving interfacial refractive index matching but also improves the open-circuit voltage by modifying the interfacial band alignment. In particular, the modifier increases the fill factor by ca. 13% by reducing the series resistance of the device. These enable a gain of ca. 23% in photoelectric conversion efficiency compared to the unmodified AZO. The results suggest the feasibility to tune the WF and conductivity of a material independently.

NiAl-LDH-Modified Core–Shell Rod-like ZnO@ZnS Heterostructures for Enhanced Photocatalytic Hydrogen Precipitation

“…ZnO, with a high surface area-to-volume ratio, non-toxicity, and a rich morphology, has been extensively studied in many applications, , such as photocatalysts, transparent conductive films, photoconductors, and gas sensors. − ZnO semiconductor photocatalysts have low photocatalytic efficiency due to photocorrosion and fast photogenerated electron–hole pair complexation. , Many efforts have been made to improve the catalytic properties of ZnO-based materials. For example, Yu et al constructed Pt-doped ZnO spheres to promote electron transfer and inhibit photocorrosion.…”

Structural, Optoelectronic, and Electrochemical Properties of Zn1–x(Ga0.5Al0.5)xO Nanoparticles for Supercapacitor Applications

“…The NBE feature is because of the free excitonic transition and is a characteristic signature to ZnO attributed to band-edge emission or donor-band excitation . The DLE is known for the intrinsic defects in ZnO, such as Vo, O i , or Zn i and O Zn . , The spectral color and intensity of the DLE depends strongly on the synthesis route and the growth environment of the material. Dopants are responsible for not only creating new energy levels but also can introduce or enhance the latent defects.…”

“…34 The DLE is known for the intrinsic defects in ZnO, such as Vo, 35 O i , 36 or Zn i and O Zn . 7,37 The spectral color and intensity of the DLE depends strongly on the synthesis route and the growth environment of the material. Dopants are responsible for not only creating new energy levels but also can introduce or enhance the latent defects.…”

A hybrid zeolitic imidazolate framework-derived ZnO/ZnMoO4heterostructure for electrochemical hydrogen production

“…2c, the Zn 2p 3/2 and Zn 2p 1/2 peaks shift toward the higher binding energy after ZnMoO 4 modification, indicating the interaction of ZnO and ZnMoO 4 . 43 In the highresolution Mo 3d spectrum, the doublet located at the higher binding energy is attributed to the Mo 6+ species, while the doublet with the lower binding energy originates from Mo δ+ (δ < 6) (Fig. 2d).…”