Abstract
This paper investigates the crystal structure and optical absorption of Ge-doped Nb-oxide (Nb-Ge-O) thin films prepared by RF sputtering. A wide-gap material, Nb2O5, is selectively produced as a matrix to disperse Ge nanocrystals through compositional optimization with Ge chip numbers and oxygen ratio in argon. The optical-absorption spectra are obviously shifted to visible (vis) and near-infrared (NIR) regions, suggesting that a composite thin film with Ge nanocrystals dispersed in Nb2O5 matrix exhibits quantum-size effects. Accordingly, the two valuable characteristics of the Nb2O5 matrix and the vis-NIR absorption are found to be retained simultaneously in Nb-Ge-O thin films.
Highlights
Quantum-dot solar cells have attracted much attention because of their potential to increase conversion efficiency [1]
The present study proposes a new composite thin film with Ge nanocrystals dispersed in Nb2O5 matrix by radio frequency (RF) sputtering
Onset absorption can be confirmed at 1.0 eV with 1.5 at.% Ge, favorably covering the desirable energy region for high conversion efficiency [14]
Summary
Quantum-dot solar cells have attracted much attention because of their potential to increase conversion efficiency [1]. The optical band gap can be tuned to the effective energy region for absorbing the maximum intensity of the solar radiation spectrum. Wide-gap materials such as TiO2 and ZnO can only absorb the ultraviolet (UV) part of the solar radiation spectrum. The wide-gap semiconductor ZnO was investigated, since the band gap and the energetic position of the valence band maximum and conduction band minimum of ZnO are very close to that of TiO2 [9]. Most of these composite materials were synthesized through chemical techniques, physical deposition, such as sputtering, is useful.
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