Poly-(3-hexylthiophene)/graphene composite based organic photodetectors: The influence of graphene insertion

Highlights: • P3HT:graphene composite photodetectors have been fabricated and characterized. • Photocurrent in photodetectors enhanced by graphene incorporation. • Diode parameters depend significantly on graphene concentration. • Detectivity and responsivity comparable with that of inorganic photodetectors. • Photocurrent is not limited by space-charge effects. -- Abstract: Currently, graphene has emerged as the prominent material for numerous applications in the field of optoelectronic devices. Herein we report an organic photodetector fabricated using solution processed composites of poly-(3-hexylthiophene) (P3HT) and graphene. The UV/Vis/NIR absorption spectra reveal that the composites exhibit absorption in the visible range. Incorporation of graphene introduces slight red shifts in the absorption spectra of P3HT indicative of the increase in the conjugation length of P3HT. The effects of various amount of graphene on electrical performance of devices are investigated. Results show that the device with 5 wt% graphene concentration demonstrates best performance, exhibiting detectivity of 1.8 × 10⁸ Jones and responsivity of 0.25 A/W at –9 V. Intensity and voltage dependent photocurrent studies predict that the photocurrent is not limited by the space charge effect in the device. Impedance spectroscopy analysis is carried out, and the obtained data are fitted to the suitable equivalent circuit to extract the internal device parameters, including junction resistance and capacitance, that are further used to estimate the bandwidth of photodetector. We believe that this report helps in the basic understanding of the impact of graphene insertion in polymer devices that will contribute towards the development of polymer/graphene composite based organic optoelectronic devices.