Modulation of Structure and Optical Property of Nitrogen-Incorporated VO2 (M1) Thin Films by Polyvinyl Pyrrolidone

Meinan Wan; Mo Xiong; Shouqin Tian; Xingzhu Chen; Bin Li; Xuesong Lu; Xiujian Zhao

doi:10.3390/ma16010208

Modulation of Structure and Optical Property of Nitrogen-Incorporated VO₂ (M1) Thin Films by Polyvinyl Pyrrolidone

Materials (Basel). 2022 Dec 26;16(1):208. doi: 10.3390/ma16010208.

Authors

Meinan Wan^{1

2

3}, Mo Xiong⁴, Shouqin Tian², Xingzhu Chen⁵, Bin Li², Xuesong Lu^{1

3}, Xiujian Zhao²

Affiliations

¹ School of Architectural Engineering, Huanggang Normal University, Huanggang 438000, China.
² State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology, Wuhan 430070, China.
³ Huanggang Ecological Architecture and Renewable Resources Research Center, Huanggang 438000, China.
⁴ MOE Key Laboratory for Non-Equilibrium Synthesis and Modulation of Condensed Matter, School of Physics, Xi'an Jiaotong University, Xi'an 710049, China.
⁵ KAUST Catalysis Center, King Abdullah University of Science and Technology, Thuwal 23955, Saudi Arabia.

Abstract

VO₂, as a promising material for smart windows, has attracted much attention, and researchers have been continuously striving to optimize the performance of VO₂-based materials. Herein, nitrogen-incorporated VO₂ (M1) thin films, using a polyvinylpyrrolidone (PVP)-assisted sol-gel method followed by heat treatment in NH₃ atmosphere, were synthesized, which exhibited a good solar modulation efficiency (ΔT_sol) of 4.99% and modulation efficiency of 37.6% at 2000 nm (ΔT_{2000 nm}), while their visible integrated transmittance (T_lum) ranged from 52.19% to 56.79% after the phase transition. The crystallization, microstructure, and thickness of the film could be regulated by varying PVP concentrations. XPS results showed that, in addition to the NH₃ atmosphere-N doped into VO₂ lattice, the pyrrolidone-N introduced N-containing groups with N-N, N-O, or N-H bonds into the vicinity of the surface or void of the film in the form of molecular adsorption or atom (N, O, and H) filling. According to the Tauc plot, the estimated bandgap of N-incorporated VO₂ thin films related to metal-to-insulator transition (E_g₁) was 0.16-0.26 eV, while that associated with the visible transparency (E_g₂) was 1.31-1.45 eV. The calculated E_g₁ and E_g₂ from the first-principles theory were 0.1-0.5 eV and 1.4-1.6 eV, respectively. The Tauc plot estimation and theoretical calculations suggested that the combined effect of N-doping and N-adsorption with the extra atom (H, N, and O) decreased the critical temperature (τ_c) due to the reduction in E_g₁.

Keywords: VO2 (M1) thin films; first-principles calculations; nitrogen-incorporated; optical property; polymer-assisted sol–gel method; polyvinyl pyrrolidone (PVP).

Grants and funding

This research was funded by the Natural Science Foundation of Hubei Province (grant number 2019CFB400), the Research Project of the Hubei Provincial Department of Education (grant number Q20192902), the Fundamental Research Funds for the Central Universities (grant number xzy012022024), the Research Project of the Huanggang Eco-Building and Renewable Resources Research Center (grant number 202204304), and the Doctoral Foundation of Huanggang Normal University (grant number 2019033).