Highly sensitive polymer photodetectors with a broad spectral response range from UV light to the near infrared region

Abstract

Highly sensitive polymer photodetectors (PPDs) are successfully achieved with a broad spectral response range from UV light to the near infrared region (NIR) based on P3HT : PTB7-Th : PC₇₁BM as the active layer. The highest external quantum efficiency (EQE) values of the PPDs with P3HT : PC₇₁BM (100 : 1) as the active layer are 90 700% and 84 100%, corresponding to 390 nm and 625 nm light illumination under a −25 V bias, respectively. The spectral response range of the PPDs can be extended to the NIR by doping narrow band gap polymer PTB7-Th into P3HT : PC₇₁BM as the active layer. The highest EQE values of the PPDs with P3HT : PTB7-Th : PC₇₁BM (50 : 50 : 1) as the active layer are around 38 000% in the spectral range from 625 nm to 750 nm under a −25 V bias. The high EQE values of the PPDs should be attributed to three points: (i) the rather weak dark current due to the relatively large hole injection barrier; (ii) the enhanced hole tunneling injection due to the interfacial band bending, which is induced by trapped electrons in PC₇₁BM near the Al cathode; and (iii) the efficient hole-only transport in the active layers with the rather low PC₇₁BM content. The broad spectral response range is due to the contribution of PTB7-Th exciton dissociation on the number of trapped electrons in PC₇₁BM near the Al cathode.