Copolymers of benzo[1,2-b:4,5-b′]dithiophene and bithiazole for high-performance thin film phototransistors

A series of conjugated polymers based on benzo[1,2-b:4,5-b′]dithiophene and bithiazole were systematically investigated for applications of polymer field-effect transistors and thin film phototransistors. Grazing incidence X-ray diffraction and atomic force microscopy were employed to investigate the solid state molecular organization and film morphology. The solution processability, solid state molecular organization, film morphology, charge transport and phototransistor performance can be tuned by elaborately optimizing the polymer backbone and side chains synchronously. For the optimized polymer (P5), a charge-carrier mobility of 0.194 cm2 V−1 s−1, a threshold voltage of −6 V and an on/off current ratio of 106 were achieved. Phototransistors based on this polymer showed a highest photoresponsivity of 132 A W−1 and a photocurrent/dark current ratio of 2 × 105.