Synthesis of conductive and transparent PEDOT:P(SS-co-PEGMA) with excellent water-, weather-, and chemical-stabilities for organic solar cells

Abstract

The water-, weather- and chemical-resistant conductive poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)-co-poly(ethylene glycol methacrylate) (PEDOT:P(SS-co-PEGMA)) copolymer was successfully synthesized with thermally curable P(SS-co-PEGMA) copolymers. The PSS and P(SS-co-PEGMA) copolymers were synthesized by solution polymerization and PEDOT:PSS and PEDOT:P(SS-co-PEGMA) were synthesized by Fe⁺-catalyzed oxidative polymerization. PSS and P(SS-co-PEGMA) were characterized by Fourier-transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance spectroscopy (NMR). The electrical properties of the conductive PEDOT:P(SS-co-PEGMA) thin films were characterized in two parts; first, the mechanism and characterization of the conductivity change, and second, the characterization of the water-, chemical-, and weather-stability of the films. The conductivity and transmittance, respectively, of PEDOT:P(SS-co-PEGMA) at 550 nm under optimized conditions were maintained at the levels found in PEDOT:PSS, 160.3 S cm⁻¹ and 86.7%. The introduction of PEGMA to the PSS copolymer improved the mechanical properties and weather stability. The PEDOT:P(SS-co-PEGMA) was highly stable to chemical solvents and independent of the type of solvents used for stability analysis. The conductivity in the weather stability test of PEDOT:PSS decreased by 44.9%, on the other hand, the conductivity of PEDOT:P(SS-co-PEGMA) was decreased by only 22.2%. The PEDOT:PSS and PEDOT:P(SS-co-PEGMA) copolymers were used as buffer layers in organic solar cells (OSC) and showed as high efficiency as conventional PEDOT:PSS materials. The decrease of OSC efficiency with PEDOT:P(SS-co-PEGMA) was 30% less than the OSCs with the commercial and reference PEDOT:PSS buffer layers.