UV organic photodetector employing dithienylethene as a photochromic tuner

Abstract

Organic photodiodes (OPDs), crucial components in logical circuits, have long been a focus of extensive research. Nonetheless, the development of multifunctional diodes, especially those capable of adapting to light variations, remains a formidable challenge. In this study, we designed a novel simplistic solution-processed OPD by incorporating the photochromic molecule 3,3′-(perfluorocyclopent-1-ene-1,2-diyl)bis(5-bromo-2-methylthiophene) (DTE-Br) into a P3HT and PC₆₁BM system. The performance of the OPD could be tuned under ultraviolet (UV) or visible (vis) light exposure. Notably, the small molecule DTE-Br exhibited exemplary compatibility with P3HT and PC₆₁BM. When the doping weight ratio of DTE-Br reached 30%, the dark current of the fabricated OPD remained unaffected compared with the undoped reference. After the devices were irradiated under UV illumination (254 nm) for a certain period, the external quantum efficiency (EQE) and specific detectivity of the DTE-Br doped OPDs increased from 10% and 6 × 10¹¹ Jones in the dark to 19% and 2.3 × 10¹² Jones under an excitation of 320 nm. Additionally, after the devices were irradiated under vis illumination, the EQE and detectivity of the DTE-Br doped OPDs underwent a reversible change to 5% and 2.0 × 10¹¹ Jones. Upon analysis, this result was attributed to the adjustment of the energy bandgap and change in the stacking states of the active layer with the reorganisation of DTE-Br molecules under UV light irradiation. These findings have profound implications for advancing multifunctional photodetectors and near-future UV OPD research.