Silver Nanowire-Based Transparent Electrodes for V₂O₅ Thin Films with Electrochromic Properties

The development of electrochromic systems, known for the modulation of their optical properties under an applied voltage, depends on the replacement of the state-of-the-art ITO (In₂O₃:Sn) transparent electrode (TE) as well as the improvement of electrochromic films. This study presents an innovative ITO-free electrochromic film architecture utilizing oxide-coated silver nanowire (AgNW) networks as a TE and V₂O₅ as an electrochromic oxide layer. The TE was prepared by simple spray deposition of AgNWs that allowed for tuning different densities of the network and hence the resistance and transparency of the film. The conformal oxide coating (SnO₂ or ZnO) on AgNWs was deposited by atmospheric-pressure spatial atomic layer deposition, an open-air fast and scalable process yielding a highly stable electrode. V₂O₅ thin films were then deposited by radio frequency magnetron sputtering on the AgNW-based TE. Independent of the oxide's nature, a 20 nm protective layer thickness was insufficient to prevent the deterioration of the AgNW network during V₂O₅ deposition. On the contrary, crystalline V₂O₅ films were grown on 30 nm thick ZnO or SnO₂-coated AgNWs, exhibiting a typical orange color. Electrochromic characterization demonstrated that only V₂O₅ films deposited on 30 nm thick SnO₂-coated AgNW showed characteristic oxidation-reduction peaks in the Li⁺-based liquid electrolyte associated with a reversible orange-to-blue color switch for at least 500 cycles. The electrochromic key properties of AgNW/SnO₂ (30 nm)/V₂O₅ films are discussed in terms of structural and morphological changes due to the AgNW network and the nature and thickness of the two protective oxide coatings.