Multi-purpose overcoating layers based on PVA/silane hybrid composites for highly transparent, flexible, and durable AgNW/PEDOT:PSS films

Flexible hybrid overcoating layers with antireflective properties are fabricated by a catalyzed two-step sol-gel process using poly(vinyl alcohol) (PVA) and silane precursors, followed by simple bar coating. Hydrolysis of alkoxysilanes followed by the condensation reaction forms chemical bonds between Si-OH and C-OH groups. A glass substrate with the hybrid overcoating layer shows higher transmittance than a bare glass substrate because the overcoating provides an antireflective layer with an intermediate refractive index. Haziness and surface roughness of the hybrid overcoating decrease with increasing PVA content. Further, complexation of PVA and silanes yields greater mechanical flexibility. Various silanes functionalized with methyl, epoxy, amino, and phenyl groups are also incorporated into the hybrid overcoating to adjust the hydrophobicity, transparency, and protective properties. A methyltrimethoxysilane (MTMS)-based hybrid overcoating shows the best optical transparency and water repellency. Application of a PVA/MTMS hybrid overcoating over silver nanowire (AgNW)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) conducting films dramatically improves the long-term stability of the sheet resistance through enhanced resistance to moisture penetration. Consequently, highly stable and durable AgNW/PEDOT:PSS conducting films (sheet resistance, 20 Ω sq^-1; transmittance, 95.4%) are fabricated by passivating them on both sides with the hybrid overcoating.