Dong-seok Leem

Green-sensitive organic photodetectors with high sensitivity and spectral selectivity using subphthalocyanine derivatives.

Green-sensitive organic photodetectors (OPDs) with high sensitivity and spectral selectivity using boron subphthalocyanine chloride (SubPc) derivatives are reported. The OPDs composed of SubPc and dicyanovinyl terthiophene derivative (DCV3T) demonstrated the highest green-sensitivity with maximum external quantum efficiency (EQE) of 62.6 % at an applied voltage of -5 V, but wide full-width-at-half-maximum (FWHM) of 211 nm. The optimized performance considering spectral selectivity was achieved from the composition of N,N-dimethyl quinacridone (DMQA) and SubPc showing the high specific detectivity (D*) of 2.34 × 10(12) cm Hz(1/2)/W, the EQE value of 60.1% at -5 V, and narrow FWHM of 131 nm. In spite of the sharp absorption property of SubPc with the maximum wavelength (λmax) at 586 nm, the EQE spectrum showed favorable green-sensitivity characterized by smooth waveform with λmax at 560 nm, which is induced from the high reflectance of SubPc centered at 605 nm. The photoresponsivity of the OPD devices was found to be consistent with their absorptance. Optimized DMQA/SubPc device showed the lowest value of blue crosstalk (0.42) and moderate red crosstalk (0.37), suggesting its promising application as a green-sensitive OPD.

Dipolar donor–acceptor molecules in the cyanine limit for high efficiency green-light-selective organic photodiodes

We report on two novel p-type small molecules with a donor–acceptor molecular structure for application to green-light-selective organic photodiodes (OPDs). To achieve the requirement of high light selectivity and sensitivity, an electron-donating aryl amino moiety is combined with two respective electron-accepting heterocycles so that the molecules approach cyanine-like character, characterized by intense and sharp absorption. Molecular stacking is controlled by the addition of bulky aryl functional groups to the main backbone to further control the electrical charge transport properties. With this molecular design, a maximum external quantum efficiency close to 61% (λmax = 550 nm) and a dark-current density below 1.6 nA cm−2 (or specific detectivity D* = 1.19 × 1013 cm Hz1/2 W−1) at an applied reverse bias of 3 V are obtained when mixed with fullerene (C60) in an inverted-structure bulk heterojunction OPD composed of two transparent electrodes. The potential construction of a full-color photodetector or an image sensor is demonstrated by combining the green-light-selective OPD with a silicon photodiode containing solely blue and red color filters in a stacked architecture.

A high performance green-sensitive organic photodiode comprising a bulk heterojunction of dimethyl-quinacridone and dicyanovinyl terthiophene

A fullerene-free bulk-heterojunction (BHJ) organic photodiode (OPD) with high efficiency and green-color selectivity is reported. Using N,N-dimethyl quinacridone (DMQA) as a donor and dibutyl-substituted dicyanovinyl-terthiophene (DCV3T) as an acceptor, a maximum external quantum efficiency (EQE) of over 67% at 540 nm was achieved at −5 V bias. The OPD performance together with their electrical and optical behaviors were investigated by varying the ratio of donor and acceptor components and measuring the absorption coefficient, charge carrier generation, and charge transport. The composition rich in DMQA exhibited a high yield of photogenerated charge carriers and a low absorption intensity, whereas the material rich in DCV3T had a high absorption intensity and low yield of charge carriers. It was found that the 1u2006:u20061 ratio of components showed the best device performance due to its relatively high absorption and efficient photogeneration of charge carriers. Furthermore, electrical characterization of our BHJ OPDs indicated that a balance of electron and hole mobilities is important for enhancing EQE.

Recent developments in green light sensitive organic photodetectors for hybrid CMOS image sensor applications(Conference Presentation)

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.