Synthesis of a Conjugated Polymer with Broad Absorption and Its Application in High-Performance Phototransistors

Abstract

An amorphous copolymer (PBDT–BBT) of 4,8-bis(2-thienyl)benzo[1,2-b:4,5-b′]dithiophene and 5,5′-bibenzo[c][1,2,5]thiadiazole was synthesized by Stille coupling polymerization. PBDT–BBT exhibited good solution processability, excellent thermal stability with decomposition temperature of 437 °C, broad absorption (300–800 nm), deep HOMO level (−5.7 eV), and LUMO level (−3.7 eV). The microstructure order of PBDT–BBT thin films is not susceptible to thermal annealing temperature (80–200 °C). Field-effect transistors based on this polymer exhibited a charge-carrier mobility of 6 × 10–3 cm2 V–1 s–1, threshold voltage of −1 V, and on/off current ratio of 106 without any post-treatments. Thin film phototransistors of PBDT–BBT exhibited a photoresponsivity of 3200 mA W–1 and photocurrent/dark current ratio of 4 × 105.