n-Type Conjugated Polymer Based on a Carbonyl-Terminated Quinoidal Unit for Transparent Conductor

Simultaneously achieving high electrical conductivity and optical transparency remains a formidable challenge for polymers. In this study, we addressed this challenge by preparing a conjugated polymer (PBT) using a carbonyl-terminated quinoidal unit that was synthesized via a newly developed method. PBT is lightly colored because its absorption band is located in the infrared region with minimal absorption in the ultraviolet and visible regions. This unique feature allows infrared photodetection and imaging without sacrificing visible clarity and minimizing interference from visible light. Upon doping, the infrared absorption band in the spectrum of PBT is almost completely suppressed, resulting in broad-spectrum transparency from 300 to 2500 nm with a maximum transmittance of up to 98%. The excellent optical transparency, combined with a close match between the transmission and solar spectrum, ensures that doped PBT has a minimal impact on the color rendering index of light, thereby preserving the color fidelity of objects. Furthermore, the electrical conductivity of doped PBT exceeds 100 S cm^-1, the highest reported for intrinsically transparent conjugated polymers. As an active material, doped PBT has been successfully used to fabricate transparent thermoelectric devices. These results highlight the potential of PBT for innovative applications in next-generation transparent electronics.