Influence of pH of spray solution on optoelectronic properties of cadmium oxide thin films

Highly conducting transparent cadmium oxide thin films were prepared by the conventional spray pyrolysis technique. The pH of the spray solution is varied by adding ammonia/hydrochloric acid. The effect of pH on the morphology, crystallinity and optoelectronic properties of these films is studied. The structural analysis showed all the films in the cubic phase. For the films with pH 〈 7（acidic condition）, the preferred orientation is along the（111） direction and for those with pH 〉7（alkaline condition）, the preferred orientation is along the（200） direction.A lowest resistivity of 9.9×10^4 cm（with carrier concentration D5.1×10^20cm^3, mobility D12.4 cm^2/（V s））is observed for pH12. The resistivity is tuned almost by three orders of magnitude by controlling the bath pH with optical transmittance more than 70%. Thus, the electrical conductivity of CdO films could be easily tuned by simply varying the pH of the spray solution without compromising the optical transparency.

Modulating the degree of O vacancy defects to achieve selective control of electrochemical CO_(2) reduction products

Conversion of CO_(2) into high-value products using electrochemical CO_(2) reduction(ECR)technology is an effective way to alleviate global warming and reach carbon neutrality.The oxygen vacancies in heterogenous catalysis are generally considered as a powerful method to enhance the performance of ECR by promoting CO_(2) adsorption and activation.However,the extent of defects in oxygen vacancies-activity relation has rarely been studied.Herein,we prepared Cu-Cd bimetallic catalysts with adjustable oxygen defect degree by controlling the amount of cadmium addition.Fourier transform infrared spectroscopy characterization results reveal that the formation of oxygen vacancies is attributed to the asymmetric stretching of Cu-O by the addition of cadmium.Electrochemical results show that the oxygen defect degree can modulate the selectivity of ECR products.A low degree of oxygen defects(CuO)is generally associated with lower product Faraday efficiency(FE_(C2)/FE_(C1)≈114%),but overabundant oxygen vacancies(CuO_(2.625)-CdO_(0.375))are not entirely favorable to improving ECR activity(FE_(C2)/FE_(C1)≈125%)and single selectivity,while an appropriate degree of oxygen vacancies(CuO_(2.75)-CdO_(0.25))can facilitate the ECR process toward single product selective production(FE_(C2)/FE_(C1)≈296%).The theoretical calculation showed that the O vacancy formed on CuO and the interface between CdO and CuO were conducive to enhancing the formation of ^(*)COOH intermediate and promoting the generation of ethylene products.This study provides a new approach and insight into the selective production of single products for future industrial applications of ECR.

Influence of substrate temperature on the structural and properties of In-doped CdO films prepared by PLD

Transparent indium-doped cadmium oxide （In-CdO） thin films were deposited on quartz glass sub- strates by pulsed laser deposition （PLD） from an ablating Cd-In metallic target. The effect of substrate temperature on the structural, optical and electrical properties of In-doped CdO thin films were studied in detail. The optical transmittance of In doped CdO films are obviously influenced by the substrate temperature. All films exhibit a transmittance higher than 75% in the visible region. More significantly, In-doping leads to an evident widening of optical band gap from 2.56 to 2.91 eV; and the increase in optical band gap is found to depend on the deposition temperature. It is also seen that the electrical properties of these films strongly depend on the substrate temperature. The ln-CdO thin film grown at 300 ℃ has low resistivity （1.15 × 10^4 Ω.cm）, high carrier concentration （5.35 ×10^20 cm^-3）, and high mobility （101.43 cm2/（V-s））.