The conventional silicon based photo diodes have high photoelectric conversion efficiency and photosensitivity. However, inorganic based photo diodes have a low visible-wavelength sensitivity due to their infrared-wavelength absorption. Recently, organic based photo diodes (OPDs) have been greatly attracted due to their flexibility, a low production cost, and a high photosensitivity in visible wavelength ranges.^{[1, 2]}

In this work, we investigated the effect of inserting inorganic interlayer between metal electrode and organic layers in order to enhance photosensitivity of OPDs. The device structure was consist of vertically stacted bottom indium-tin-oxide (ITO) electrode/bottom inorganic interlayer (NiO_x)/organic layer (DMQA:Me-PTC)/top inorganic interlayer (MoO_x)/top aluminum electrode on a glass substrate. The bottom NiO_x inorganic interlayer was inserted between bottom ITO electrode and DMQA:Me-PTC photo-organic layer and its thickness was varied from 1 to 5 nm. It was found that the highest photocurrent/dark current ratio of OPDs was 1.34 x 10⁴ at 4-nm-thick NiO_x. In addition, the top MoO_x:Al (1:1) inorganic interlayer was inserted between top aluminum electorde and DMQA:Me-PTC photo-organic layer and its thickness was varied from 1 to 3 nm. It was also observed that the highest photocurrent/dark current ratio was 4.51 x 10⁴ at 2-nm-thick MoO_x:Al. In our presentation, we will present the mechanism by which the photosensitivity is enhanced by varying inserted inorganic interlayer (NiO_x or MoO_x) via investigating the dependency of energy band gap on the inserted inorganic interlayer thickness and that of the chemical composition profiles of OPDs.

* This work was financially supported by LG Electronics Inc. and Brain Korea 21 Plus Program in 2017.

[1] Baeg, K.-J., Binda, M., Natali, D., Caironi, M. & Noh, Y.-Y. Organic light detectors: photodiodes and phototransistors. Adv. Mater. 25, 4267–4295 (2013).

[2] Yao, Y. et al. Plastic near-infrared photodetectors utilizing low band gap polymer. Adv. Mater. 19, 3979–3983 (2007)