Fast and sensitive polymer photodetectors with extra high external quantum efficiency and large linear dynamic range at low working voltage bias

摘要

An extra high quantum efficiency (EQE) exceeding 100% can be obtained in organic photomultiplication photodetectors which generally exhibit either low response speed or high working voltage. In this work, a fast and sensitive polymer photoconductive detector with an over 10000% EQE is demonstrated, which requires a low negative working voltage of around -0.8 V. In the device, a poly (3-hexylthiophene) (P3HT):(phenyl-C61-butyric-acid-methyl-ester) (PC61BM) bulk heterojunction (BHJ) film is used as the photo-active layer with a polyethylenimine ethoxylated (PEIE) modified ITO electrode. By adjusting the PC61BM: P3HT weight ratio from 2: 3 to 9: 1 gradually in the device, the photodetector performances can be dramatically varied: the EQEs can achieve from about 1000% to 12000%; the responsivities can reach from 4 A/W to 54 A/W; and the detectivities are up to 10(12) Jones. Among these devices, the optimized device has a high EQE of about 12000%, a fast response time of 24 mu s (rise time), and a large linear dynamic range of 79 dB at around -0.8 V bias. With the help of transmission electron microscope images (TEM), light-assisted capacitance-voltage (C-V), and transient photocurrent measurements, the fullerene concentration effect in the device has been investigated. This methodology provides a universal guidance for understanding and developing photomultiplication type polymer photodetectors with various spectral responses.