Efficiency improvement of current gain in organic up-conversion devices by maintaining hole blocking property at interface of anode/charge generation layer

Abstract

The organic donor/acceptor of chloroaluminum phthalocyanine and C70 as a charge generation layer (CGL) enabled a realization of near-infrared (NIR) image sensing for a highly efficient organic up-conversion device. The well-alignment energy level of CGL played an important role in controlling the conduction-path of a hole carrier for our device (i.e., electron-rich type), which effectively blocked the injection carrier at the interface of the anode/CGL. The proposed up-converter used was a device configuration of ITO/CGL/1,1-bis(di-4-tolylaminophenyl) cyclohexane/4,4'-Bis(N-carbazolyl)-1,1'-biphenyl doped with fac-tris (2-phenylpyridine) iridium (III)/2-phenyl-9-(3-(2-phenyl-1,10-phenanthrolin-9-yl)phenyl)-1,10-phenanthroline/CS2CO3/Ag to provide a green emission under NIR illumination. As a result, an optimal device with a current gain as high as 10 000 (i.e., on-off ratio from dark to light testing) at a driving voltage of 3 V was successfully achieved. In addition, our transparent device (i.e., device with ultra-thin cathode of ~ 12 nm Ag) was proposed from a clear three-dimensional image of a real object with a high resolution of 420 dots per inch, indicating the high sensitivity of this organic device for NIR sensing.