Bio-based PEDOT: nanocellulose hybrids as efficient hole-transport layers for photoelectrochemical devices

Developing sustainable hole-transport materials that can match the performance of conventional poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) remains a key challenge for environmentally compatible optoelectronic devices. In this work, nanocrystalline cellulose (NCC) is demonstrated as a renewable dopant and stabilizer for PEDOT, forming bio-based hybrids with competitive photoelectrochemical performance. Two crystalline allomorphs, NCC Type I and NCC Type II, were compared as templates for aqueous oxidative polymerization of EDOT, producing stable dispersions of PEDOT nanoparticles (50-100 nm) electrostatically anchored to the NCC surface. Spectroscopic and thermal analyses revealed that the higher ester sulfate content and distinct morphology of NCC-II promoted enhanced polaron stabilization and 10-15% higher PEDOT incorporation compared to NCC-I. FTIR and UV-vis spectroscopy showed more pronounced polaronic bands for PEDOT:NCC-II hybrids, evidencing enhanced charge delocalization and doping. Optimal performance was achieved for the PEDOT:NCC-II (50 : 50) composition, which formed stable, conductive networks and served as an efficient hole-transport layer in poly(3-hexylthiophene)-based photoelectrochemical devices. These bio-based electrodes achieved photocurrent densities above 18 µA cm^-2, matching or exceeding PEDOT:PSS reference, and maintained stable operation over 300 s of cycling (>10 light/dark cycles at 0.3 Hz) with reproducible ON/OFF photoresponse. These findings establish nanocellulose-doped PEDOT as a sustainable alternative for next-generation optoelectronic interfaces.