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.
Typical CMOS colour image sensors consist of Si-based photodetectors (PDs) attached with colour filter arrays (i.e., the Bayer pattern). Recent trends on the development of high resolution image sensors, however, require downsizing the pixel dimension, which inevitably results in the loss of sensitivity due to the reduction in the photon acquisition. Very recently, hybrid stacks of organic photodetectors (OPDs) on conventional CMOS technologies have been proposed as one of the promising approaches to realise highly sensitive image sensors by doubling the light detecting area in the limited pixel size. Specifically, OPDs with orthogonal photosensitivity to green light and Si-based PDs with red and blue colour filters serve as the top and bottom photo-conversion layers, respectively. In this presentation, we will introduce the recent development of high performance green light sensitive OPDs and the demonstration of colour images from hybrid CMOS image sensors proposed.
OPDs consisting of small molecule organic bulk heterto-junction structures, hole/electron buffer layers, and transparent top/bottom ITO electrodes exhibited peak external quantum efficiencies of 60-65% at 550-560 nm wavelengths and full width at half maximum of ~120 nm at reverse bias of 3 V. Extremely low dark current densities in the range of 0.2-0.5 nA/cm2 at reverse bias of 3V and consequently high specific detectivities over 2×10^13 Jones were obtained from the developed OPD system. Further investigations in terms of the molecular structures of organic light absorbing materials, buffer materials, layer sequences, and even integration issues of the OPD on the CMOS will be described in detail.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.