Water-resistant self-doped conducting polymer-based transparent and semi-transparent electrodes for underwater organic solar cells

We investigated SELFTRON®, a self-doped conducting polymer, as a water-resistant electrode material for underwater organic photovoltaics (OPVs). After 100 bending cycles, SELFTRON® and CNT-containing SELFTRON® (SELFTRON®:CNTs) retained over 85% of their initial conductivity, whereas indium tin oxide showed substantial degradation. After storage at 25 °C and 100% relative humidity for 24 h, SELFTRON® and SELFTRON®:CNTs retained 97% and approximately 100% of their initial conductivity, respectively, outperforming PEDOT:PSS. Incorporating CNTs increased conductivity from 207 to 683 S cm⁻¹, enabling SELFTRON®:CNTs to serve as a rear current-collecting electrode. A SELFTRON®/SELFTRON®:CNTs bilayer fabricated by thermocompression lamination replaced moisture-sensitive PEDOT:PSS while maintaining carrier selectivity. The resulting PEDOT:PSS-free OPV retained over 90% of its initial efficiency after 150 h in water, demonstrating the potential of flexible, water-resistant SELFTRON®-based electrodes for underwater OPVs.