Here,
a smart strategy for decreasing the active layer thickness of the
organic photodiode down to 70 nm is demonstrated by utilizing a trap-assisted
photomultiplication mechanism with the optimized chemical composition.
Despite the presence of a high dark current, dramatically enhanced
external quantum efficiency (EQE) via photomultiplication can allow
significantly reduced active layer thickness, yielding high detectivity
comparable to that of conventional Si. To achieve this, a spatially
confined and electrically isolated optical sensitizer, 2,2′-((2Z,2′Z)-((4,4,9,9-tetrahexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-2,7-diyl)bis(methanylylidene))bis(3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (IDIC) was introduced
strategically between a hole transport active layer and a cathode.
A nonfullerene acceptor, IDIC, turned out to be a much more efficient
sensitizer than the conventional fullerene-based acceptors, as confirmed
by the effective lowering of the Schottky barrier under illumination,
as well as the highest EQE exceeding 130 000%. Due to its favorable
electronic structure as well as two-dimensional molecular structure,
a high detectivity over 1012 Jones was successfully demonstrated
while maintaining the active layer thickness as 70 nm.
In this work, we present a screen-printed humidity sensor fabricated on a flexible polyvinyl chloride (PVC) substrate. A comparative analysis has been carried out for printed graphene-carbon electrode with and without Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) modification in the humidity sensing range of 25 -90 %RH. The sensor modified with PEDOT:PSS demonstrated enhanced performance ( ~ 1 %/%RH versus ~ 0.8 %/%RH of unmodified sensor). Further, the enhancement in the performance of the modified sensor was found to be prominent in the low to moderate humidity range (≤60 %RH). The repeatability, response and recovery time were also analysed for both types of sensors and their applicability has been demonstrated for neonatal care by monitoring the humidity level of a wet baby diapers. This demonstration shows the potential application of presented humidity sensors in areas such as environmental monitoring, healthcare, industrial, and agriculture.
Screen printing is one of the widely used methods for printed sensors and electronics. The performance of these devices could vary with the printing parameters such as thickness of the printed layer, the squeeze length and pressure applied for printing etc. Whilst sensor design and the ink used for the printing of sensitive layers have been studied previously, the vital printing parameters has not attracted much attention. This paper reports the influence of thickness of printed sensor on their electrochemical sensing property. Carbon ink is used to print sensors with three-electrode geometry and their working electrode is modified with MoS2 to study the detection of ascorbic acid. The thicknesses of the sensitive layers varied from ~4 m to 120 m as the number of printed layers of ink increased from 1 to 5, 10 and 20. The cyclic voltammetry, differential pulse voltammetry and impedance spectroscopy are used to investigate the electrochemical performance. It was noted that the peak current indicating the oxidation of ascorbic acid at 0.04 V, increased with the increase in the thickness of electrode or the number of printed layers. The higher current values and lower series resistance was measured for layers 10 and 20, indicating the ideal printed thickness of sensors for low power operation and easy interfacing with read out electronics.
Monitoring of heavy metal ions in aquatic environment can be a tedious process, especially in harsh, logistically challenging field conditions. This work demonstrates the detection of copper ions in water using a low-cost screen printed 2D molybdenum disulfide (MoS2) nanoparticle based electrochemical sensor. To deal with the common field-testing challenges, an easily disposable, flexible, compact sized reliable sensor was fabricated using a screen-printing technique. The developed sensor shows an excellent performance with a linear range of 5 µM to 1000 µM, a low limits of detection (LOD) value of just 0.3125 µM, and high repeatability with standard deviation less than 0.5%. With this performance and attractive attributes such as flexible form factor, low-cost fabrication and disposability etc. the presented sensor shows a great potential for practical applications in soil and water monitoring.
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