Synthesis and application of benzooxadiazole-based conjugated polymers in high performance phototransistors

Abstract

Four planar conjugated polymers called CZ-BO8, CZ-BO12, CZ-BT8 and CZ-BT12 with carbazole as the donor unit and benzooxadiazole or benzothiadiazole as the acceptor unit have been synthesized and characterized. These four polymers have medium band gaps (1.95–1.97 eV), low lying highest occupied molecular orbital energy levels (below −5.5 eV), relatively high hole mobilities (in the range of 0.026–0.1 cm² V⁻¹ s⁻¹), and on/off current ratio of 10⁶ without any post-treatment. Furthermore, high performance thin film phototransistors based on these four polymers have also been fabricated with high photocurrent/dark current ratios (5.7 × 10³–8.2 × 10³). Interestingly, phototransistors based on CZ-BO8 and CZ-BO12 show a faster photoresponse than that based on CZ-BT8 and CZ-BT12, providing valuable molecular design guidelines for high performance photoresponse polymers.