Organic diradicals enabled N-type self-doped conjugated polyelectrolyte with high transparency and enhanced conductivity

Conjugated polyelectrolytes (CPEs) have achieved vast success in organic electronics due to their appealing opt-electrical properties and convenient solution-processability. However, most of the existing n-type CPEs commonly exhibit distinct light capture in visible region. The attainment of novel n-type CPEs possessing both high electron conductivity and high visible light transparency is significant while still challenging. Herein, optimized amount of organic diradicals achieved by benzobisthiadiazo (BBT) unit are intentionally introduced into the backbone of the representative wide-band-gap polyfluorene-based conjugated polyelectrolyte via ternary copolymerization. The incorporation of diradical canonical structure could promote the quinoid resonance of conjugated skeleton, leading to increased self-doping effect. Consequently, the copolymerized CPE exhibits high visible light transmittance (AVT over 85%) and enhanced electron conductivity compared to the referenced CPE. The fabricated organic solar cell devices with the new-designed polyelectrolyte as the cathode interface layer can achieve high power conversion efficiencies of more than 16%, which is not susceptible to the thickness up to 50 nm. This work provides a feasible molecular modification strategy via organic diradicals regulation to obtain high performance n-type self-doped conjugated polyelectrolytes.