All organic near ultraviolet photodetectors based on bulk hetero-junction of P3HT and DH6T

Abstract

The effect of oligomer concentration on the performance of polymer and oligomer blended system based photo-detectors was investigated. Improvement in dark rectification ratio and photoresponse of diode were observed in the blended system photodetectors compared to pristine polymer based photodetectors. The photodetectors fabricated with poly(3-hexylthiophene) (P3HT) and α, ω-di-hexyl-sexithiophene (DH6T) were tuned to two different wavelengths namely 525 nm and 400 nm respectively, corresponding to the maximum of the absorption of polymer and oligomer materials respectively. It was observed that the effective conjugation length and disorder in the polymer chains critically affect the photoresponse of organic optoelectronic devices. In this study, improvement in effective conjugation length and disorder were observed as the concentration of DH6T in the blend was increased; leading to the enhancement in the photoresponse of the fabricated device with these blends. Herein, with the increase of DH6Tconcentartion in the blended thin films, the photoresponsivity of fabricated photodetectors towards near UV at ∼400 nm wavelength in addition to the 525 nm wavelength was found to be increased. Comparable photosensitivity (∼1.6 × 103) and responsivity (∼18 A W−1) were achieved for both the wavelengths separately, in the blended photodetectors fabricated with a DH6T concentration of 40%. Such devices tuned to dual wavelength may also find their application in the field of optically switched logic gates.