Organic Photodetectors With Indium-Tin-Oxide Grids

A 110-nm-thick indium tin oxide (ITO) grid is placed on an ITO layer using photolithography, sputtering, and lift-off processes. The organic photodetector (OPD) with the ITO grid is obtained after a titanium dioxide (TiO2) layer, an active layer, and an aluminum layer are deposited on the ITO grid sequentially. The dark current density (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${8.41} \times {10}^{-}9 $ </tex-math></inline-formula> A/cm2) of the OPD with the ITO grid is lower than that (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${1.36} \times {10}^{-}7 $ </tex-math></inline-formula> A/cm2) of an OPD without an ITO grid at zero bias voltage. The light current density (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${2.67} \times {10}^{-}4 $ </tex-math></inline-formula> A/cm2) of the OPD with the ITO grid is higher than that (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${1.97} \times {10}^{-}4 $ </tex-math></inline-formula> A/cm2) of the OPD without an ITO grid at zero bias voltage. The OPD with the ITO grid has a 21 times larger light-to-dark current ratio than an OPD without an ITO grid. The large light-to-dark current ratio of the OPD with the ITO grid is verified by its low series resistance and high electron-hole recombination resistance and arises from the protrusive structure of the ITO grid. This structure increases the surface areas and directional charge transport channels of the TiO2 layer, active layer, and aluminum layer, facilitating the transportation of the electrons and holes in the OPD. The response time (14.54 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>s) of the OPD with the ITO grid is 24% faster than that (19.17 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>s) of the OPD without an ITO grid at zero bias voltage. The OPD with the ITO grid has the potential for image capturing and monitoring.