Engineering Electrochromism in Ni-Deficient NiO through Defect, Dopant, and Strain Coupling

TL;DR

This study uses density functional theory to explore how dopants, vacancies, and strain influence electrochromism in Ni-deficient NiO, revealing mechanisms for charge trapping and optical switching.

Contribution

It systematically investigates the effects of Cu, Sn, and V dopants, as well as strain, on the electronic and optical properties of Ni-deficient NiO for electrochromic applications.

Findings

V-doping preserves charge compensation and leads to conventional bleaching.

Sn doping traps injected charge, reversing electrochromic response.

Strain enhances Li insertion but reduces optical contrast.

Abstract

The electrochromic response of Ni-deficient NiO is governed by vacancy-mediated electronic processes that can be strongly influenced by dopant chemistry and lattice deformation. Using density functional theory, we systematically investigated Cu-, Sn-, and V-doped Ni-deficient NiO(001) surfaces and examined alkali-ion insertion at surface Ni vacancies. Li insertion proceeds as nearly complete ionic electron donation (~+0.9 e), but the fate of the injected electron depends on dopant identity. V-doping preserves framework-dominated charge compensation and leads to conventional bleaching through filling of vacancy-associated hole states. In contrast, Sn actively traps the injected charge, generating dopant-assisted optical transitions and reversing the electrochromic response, while Cu produces an intermediate spectral redistribution without significant dopant reduction. Substitution of Li by Na or K in the V-doped system does not alter the switching mechanism, confirming that vacancy-state filling governs the optical behavior. Biaxial tensile strain enhances the energetics of Li insertion but reduces optical contrast by altering the defect electronic structure. These results establish dopant activity, vacancy stabilization, and lattice strain as key parameters controlling electrochromism in NiO-based materials.