From Event: SPIE Organic Photonics + Electronics, 2017
Organic photodetectors (OPDs) are attracting interest as various sensing platforms such as photo/chemical sensors, healthcare sensors, x-ray scanner, and image sensors. In particular, a distinct advantage of organic materials, i.e., orthogonal photosensitivity to the specific wavelength such as blue (B), green (G), red (R), and even infrared has recently facilitated promising applications to organic full colour image sensors. For instance, vertical stacks of G-wavelength selective organic photoconversion layers on conventional Si CMOS imagers with B/R color filters have been made to realize highly sensitive image sensors by doubling the light detecting area compared to the planar R/G/B pixel structure.
Our recent investigations on small molecule OPDs with bulk heterojunction structure have shown high peak external quantum efficiencies over 60% and extremely low dark current densities below 0.1 nA/cm2 at reverse bias of 3V, which are comparable to the typical performance of Si-based PDs. On the other hand, their photoresponse characteristics have not been systematically studied. For example, the Si PD exhibited the rising time of photoresponse speed as fast as 10 us at 99.9% of the peak photocurrent, whereas the OPD showed 20 times slower response time plausibly due to the reduced charge carrier mobility. Thus, in order to investigate the practical use of OPDs as image sensor applications, we will present the current status of dynamic characteristics of OPDs in terms of photoresponse speed, frequency response, and transient photocurrent. Further, the possible origin of photoresponse characteristics of OPDs will be described.
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