Organic photodetector
performance for
enhancing the sensing abilities of an organic photoplethysmography
sensor was investigated. The optimized organic photodetector with
an anode interlayer and a cathode interlayer showed a reverse dark
current density of 22 nA cm–2 at −2 V and
an external quantum efficiency of 53.3% at 0 V. This organic photodetector
was fabricated monolithically with an organic light-emitting diode
on a glass substrate to achieve a reflectance-mode photoplethysmography
sensor, demonstrating the impact of organic photodetector device performance
on the measured photoplethysmography signal for sensing applications.
Furthermore, we estimated the optimal sensor design for circular geometry
in terms of device area and distance between the organic light-emitting
diode and organic photodetector to maximize the signal-to-noise ratio
and lower the power consumption of organic photoplethysmography sensor
devices. For the most favorable photoplethysmography sensor design,
a signal strength of 130 mV with 600 μW power consumption was
measured.
This paper compares the structural design of two organic biosensors that minimize power consumption in wireless photoplethysmogram (PPG) waveform monitoring. Both devices were fabricated on the same substrate with a red organic light-emitting diode (OLED) and an organic photodiode (OPD). Both were designed with a circular OLED at the center of the device surrounded by OPD. One device had an OLED area of 0.06 cm2, while the other device had half the area. The gap distance between the OLED and OPD was 1.65 mm for the first device and 2 mm for the second. Both devices had an OPD area of 0.16 cm2. We compared the power consumption and signal-to-noise ratio (SNR) of both devices and evaluated the PPG signal, which was successfully collected from a fingertip. The reflectance-based organic pulse meter operated successfully and at a low power consumption of 8 µW at 18 dB SNR. The device sent the PPG waveforms, via Bluetooth low energy (BLE), to a PC host at a maximum rate of 256 kbps data throughput. In the end, the proposed reflectance-based organic pulse meter reduced power consumption and improved long-term PPG wireless monitoring.
This paper demonstrated a new design structure for minimizing the power consumption of a pulse meter. Monolithic devices composed of a red (625 nm) organic light-emitting diode (OLED) and an organic photodiode (OPD) were fabricated on the same substrate. Two organic devices were designed differently. One had a circle-shaped OLED in the center of the device and was surrounded by the OPD, while the other had the opposite structure. The external quantum efficiency (EQE) of the OLED and the OPD were 7% and 37%, respectively. We evaluated and compared the signal-to-noise ratio (SNR) of the photoplethysmogram (PPG) signal on different parts of the body and successfully acquired clear PPG signals at those positions, where the best signal was obtained from the fingertip at a SNR of about 62 dB. The proposed organic pulse meter sensor was operated successfully with a power consumption of 0.1 mW. Eventually, the proposed organic biosensor reduced the power consumption and improved the capability of the pulse meter for long-term use.
The low mobility and large contact resistance in organic thin-film transistors (OTFTs) are the two major limiting factors in the development of high-performance organic logic circuits. Here, solution-processed high-performance OTFTs and circuits are reported with a polymeric gate dielectric and 6,6 bis (trans-4-butylcyclohexyl)-dinaphtho[2,1-b:2,1-f]thieno[3,2-b]thiophene (4H–21DNTT) for the organic semiconducting layer. By optimizing and controlling the fabrication conditions, a high saturation mobility of 8.8 cm2 V−1 s−1 was demonstrated as well as large on/off ratios (> 106) for relatively short channel lengths of 15 μm and an average carrier mobility of 10.5 cm2 V−1 s−1 for long channel length OTFTs (> 50 μm). The pseudo-CMOS inverter circuit with a channel length of 15 μm exhibited sharp switching characteristics with a high signal gain of 31.5 at a supply voltage of 20 V. In addition to the inverter circuit, NAND logic circuits were further investigated, which also exhibited remarkable logic characteristics, with a high gain, an operating frequency of 5 kHz, and a short propagation delay of 22.1 μs. The uniform and reproducible performance of 4H–21DNTT OTFTs show potential for large-area, low-cost real-world applications on industry-compatible bottom-contact substrates.
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