Vapor phase polymerized high-performance Poly(3,4-ethylenedioxythiophene) using polyethyleneimine (PEI) as the base inhibitor and grafting agent for electrochromic medical face shields

Abstract

Synthesizing of highly conductive conjugated polymers on target substrates must consider both the reaction regime and adhesion. Vapor phase polymerization (VPP) with a relatively simple procedure and mild reaction temperature (40–50 °C) is favorable for polymerization of poly(3,4-ethylenedioxythiophene) (PEDOT) on PET substrates. However, achieving high conductivity and good surface adhesion with target substrates has been challenging. Addressing this, we report that weak alkalinity and enriched amine groups of polyethyleneimine (PEI) were used as a base inhibitor and grafting agent during VPP to improve the PEDOT film's electrical and mechanical properties. The base-inhibited VPP results in a needle-like morphology with enhanced crystallinity in PEDOT, and with this, the conductivity of 1980 S/cm has been achieved. Moreover, many amine groups with high chemical activity in PEI make it successfully grafted on the polydopamine (PDA)-coated substrates. The surface grafting of PEI in PEDOT with PDA through Schiff base and Michael addition reactions make the PEDOT film resistant to ultrasonic cleaning in water or organic electrolyte, presenting significant potential in applying washable and cleanable electronics. We then demonstrate an anti-ultrasonic cleaning electrochromic display based on vapor phase polymerized PEDOT. This work experimentally confirms that PEI is critical in ensuring high-performance PEDOT films. Incorporating this technique on a PET-based medical face shield renders robust wearable electronics.