Design of blue-sensitive organic photodiode in terms of bottom light absorption

Abstract

CMOS Image Sensor (CIS) is expected to lead the future semiconductor market because cameras are becoming increasingly important in electronic products such as mobile products and high-performance digital cameras. This is because demand for CIS is rapidly increasing in various industries such as tablet PCs, smart phones, medical electronic devices, and automobile sensors, which account for the largest portion [1]. In recent years, as the device size continues to shrink, the pixel size of a high-resolution CIS has been reduced to less than 1 um. That is, the size of the light receiving part is reduced, which leads directly to the problem of reduced sensitivity. Until now, this has been prevented through the use of high-complexity pixel-forming techniques such as BSI, but this also faces limitations [9,10]. In order to overcome the limitations of such a silicon-based photodiode, Organic image sensors having relatively high resolution, high absorption rate and s / n ratio have been developed. In this study, we have studied the performance of blue - sensitive organic photodiodes in terms of structure and thickness. Three different structures were formed on the glass substrate and the difference between the dark current and the photo current was compared and analyzed through the thickness split in each structure. Coumarin6 was used as the donor material and C60 was used as the acceptor material. Among them, P-I-N structure showed the highest on / off ratio. The dark current was 4.69 x 10-9A and the photo currents at 2000lux and 20000lux were 6.67 x 10-7A and 9.62 x 10-6A at reverse bias of 3V. The difference in the results can be explained by how efficiently the free charge is separated due to the potential difference at the interface between the donor and acceptor of the organic material and the lifetime of the free charge flowing from the active layer of the organic material to the electrode.