Improving Performance of Organic Photodetectors by Using TCNQ Doped Copper Thiocyanate as the Anode Interfacial Layer

The responsivity and specific detectivity are critical figures of merits for organic photodetectors; however, it remains challenging to simultaneously enhance two such parameters, since enhancing external quantum efficiency corresponding to responsivities will inevitably increase leakage current and noises, resulting in decreased specific detectivity. To address such a trade-off, an effective anode interfacial layer of 7,7,8,8-tetracyanoquinodimethane (TCNQ) doped copper thiocyanate (CuSCN) is developed herein, which can enhance shunt resistance, increase depletion width, enhance hole extraction efficiency, as well as reduce trap density of states of organic photodetectors. The organic photodetectors based on doped CuSCN present a very low dark current density of 4.4 x 10-11 A cm-2 and an impressively high specific detectivity of 1.1 x 1014 Jones. As evidenced by X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy measurements, the energy levels of the doped CuSCN:TCNQ film are deepened, associated with the occurrence of dopant bonding and charge transfer. In addition, it is found that increasing the delay time can suppress the hysteresis effects of current density-voltage characteristics of organic photodetectors and make the minimum dark current density obtainable at 0 V. These findings demonstrate the great potential of using molecular doping to adjust the anode interfacial layer for developing high-performance organic photodetectors. An anode interfacial layer based on 7,7,8,8-tetracyanoquinodimethane-doped copper thiocyanate is developed for application in organic photodetectors, which shows enhanced hole extraction capability and electron-blocking capability, resulting in a high specific detectivity of over 1014 Jones in the near-infrared region. image