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Bifunctional Etalon-Electrode To Realize HighPerformance Color Filter Free Image Sensor Seongwon Yoon, Kyu Min Sim, and Dae Sung Chung* Department of Energy Science & Engineering, Daegu Gyeongbuk Institute of Science & Technology (DGIST), Daegu 42988, Republic of Korea
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S Supporting Information *
ABSTRACT: Organic photodiodes (OPDs), based on organic semiconductors with high absorption coefficients for visible light, are emerging as potential candidates for replacing silicon photodiodes in image sensors, particularly due to the possibility of realizing a thin thickness and exclusion of color filters, both of which can contribute to a dramatically enhanced degree of integration for image sensors. Despite years of research, techniques have not yet been developed that allow the OPD itself to have color selectivity while maintaining a thin (1012 cm·Hz0.5/W). To solve this issue, we introduce a concept of “etalon-electrode”, which can perform the function of electrode and simultaneously the function of selective wavelength transparency. A strategically designed OPD architecture consisting of an etalon-electrode, a panchromatic organic active layer, and a counter electrode displays well-defined narrowband R-/G-/B-selective detectivity spectra depending on precision-adjusted thickness composition of the etalon-electrode. While a thin thickness of OPD is preserved at less than 800 nm including electrodes, active layer, and other buffer layers for all R-/G-/B-selective OPDs, high average detectivity values over 1012 cm·Hz0.5/W are demonstrated. Furthermore, the characteristic of imparting color selectivity by the etalon-electrode enables a more facile full color patterning, such that a prototype of a 10 × 10 image sensor with a pixel pitch of 500 μm is realized, resulting in accurate picturing of a well-defined full color image. KEYWORDS: etalon-electrodes, high detectivity, organic photodiodes, full-color imaging, color filter free, image sensor, wavelength selectivity
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essential to develop image sensors using better semiconductor materials than conventional Si. Organic semiconductors and inorganic nanomaterials or micromaterials with high absorption coefficients,4−8 and possible wavelength selectivity,9−14 are well suited for such image sensor applications. Recently, color-selective (color filter-free) thin film (thickness 0.3 eV) of organic semiconductors. In this case, polymer-based BHJ has shown the highest EQE among all other combinations of organic semiconductors and thus, here we utilized polymer BHJ structure, but with ternary components, in constructing a solution processed BHJ to implement panchromatic absorption behavior. In a previous report, it was demonstrated that binary BHJ consisting of low bandgap polymer and [6,6]-phenyl-C70butyric acid methyl ester (PCBM) with thick film thickness over 700 nm could achieve broadband spectral response.31 However, to fully utilize the genuine benefits of high absorption coefficient of organic semiconductor, and considering industrial demand for the CMOS image sensor, as well as the small pixel sizes (
