Energy Level Tuning in Conjugated Donor Polymers by Chalcogen Exchange for Low Dark Current Organic Photodetectors

The performance of organic photodetectors (OPDs) using conjugated polymer donors and molecular acceptors has improved rapidly, but many polymers are difficult to upscale due to their complex structures. This study examines two low-complexity thiophene copolymers with substituted benzooxadiazole (<b>FO6-BO-T</b>) or benzothiadiazole (<b>FO6-T</b>). Substituting sulfur with oxygen in <b>FO6-BO-T</b> increased its ionization energy without affecting the optical gap. When blended with the nonfullerene acceptor IDSe, <b>FO6-BO-T</b> showed a significantly lower dark current density (2.06·10^-9 A cm^-2 at -2 V) compared to <b>FO6-T</b>. Grazing incidence wide-angle X-ray scattering (GIWAXS) measurements demonstrated that pristine <b>FO6-BO-T</b> exhibited a more ordered morphology than <b>FO6-T</b>. However, blending resulted in a significant disruption to the ordered domains in both cases, with a loss of orientational order, suggesting that <b>FO6-BO-T</b>'s improved performance is largely related to its increased ionization energy. This study demonstrates the potential of chalcogen atom engineering to enhance the performance of the OPD in scalable polymers.