Panchromatic small molecules for UV-Vis-NIR photodetectors with high detectivity

摘要

Two donor-acceptor-donor (D-A-D) type low-bandgap small molecules, Ml and M2, with bis(2-thienyl)-N-alkylpyrrole (TPT) as the donor and thieno[3,4-b]thiadiazole (TT) as the acceptor were designed and synthesized. The absorption, transmission, electrochemical, thermal and film properties were studied. The compounds showed panchromatic absorption in the spectral range of 300-1000 nm. Moreover, they also exhibited semi-transparent property in the visible region (400-700 nm). Small molecule photodetectors (SMPDs) based on Ml and M2 were fabricated and studied. For the SMPD with BCP as the hole blocking layer (HBL), a detectivity of 5.0 × 10~(11) Jones at 800 nm at -0.1 V was obtained, which is among the highest detectivities reported for NIR SMPDs. With a sufficiently thin silver electrode, visibly transparent PDs with an average transmittance of 45% in the visible region were obtained for the first time. The transparent PDs exhibited fairly constant and high detectivity between 10~(11) and 10~(12) Jones over a broad spectral range of 300-900 nm. In addition, side chains of the compounds exhibited a great influence on the device performance, which could be assigned to their film absorption coefficient, molecular packing and active layer morphology.