Qayyum Zafar

A Humidity Sensing Organic-Inorganic Composite for Environmental Monitoring

In this paper, we present the effect of varying humidity levels on the electrical parameters and the multi frequency response of the electrical parameters of an organic-inorganic composite (PEPC+NiPc+Cu2O)-based humidity sensor. Silver thin films (thickness ∼200 nm) were primarily deposited on plasma cleaned glass substrates by the physical vapor deposition (PVD) technique. A pair of rectangular silver electrodes was formed by patterning silver film through standard optical lithography technique. An active layer of organic-inorganic composite for humidity sensing was later spun coated to cover the separation between the silver electrodes. The electrical characterization of the sensor was performed as a function of relative humidity levels and frequency of the AC input signal. The sensor showed reversible changes in its capacitance with variations in humidity level. The maximum sensitivity ∼31.6 pF/%RH at 100 Hz in capacitive mode of operation has been attained. The aim of this study was to increase the sensitivity of the previously reported humidity sensors using PEPC and NiPc, which has been successfully achieved.

Humidity sensor based on electrospun MEH-PPV:PVP microstructured composite

The present study demonstrates a solution-processed humidity sensor based on poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]:polyvinylpyrrolidone (MEH-PPV:PVP) organic microstructured composite thin film. The capacitive type humidity sensor has been fabricated in the surface type geometry of Al/MEH-PPV:PVP/Al, wherein organic composite (MEH-PPV:PVP) has been deposited onto the aluminium electrodes by electrospinning technique. The structural and morphological properties of organic thin film have been characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The humidity sensing properties of the sensor have been investigated at ∼1 volt AC operational bias, by measuring the capacitance as a function of a broad range (20–90%) of relative humidity (RH). The temperature and operational frequency dependency of the capacitance of the sensor has also been analyzed in detail. The proposed sensor exhibits high sensitivity (114 fF/% RH @ 100 Hz), small hysteresis (∼2% RH) and fast response (18 s and 8 s for adsorption and desorption processes, respectively). Compared with traditional spin-coated and drop-casted organic humidity sensors, the microstructure composite based sensor has demonstrated significantly improved sensing parameters, highlighting the unique advantages of the electrospinning process for humidity sensor fabrication. The possible humidity sensing mechanism of the proposed capacitive sensor has also been elaborated.

PFO-DBT:MEH-PPV:PC71BM Ternary Blend Assisted Platform as a Photodetector

We present a ternary blend-based bulk heterojunction ITO/PEDOT:PSS/PFO-DBT:MEH-PPV:PC71BM/LiF/Al photodetector. Enhanced optical absorption range of the active film has been achieved by blending two donor components viz. poly[2,7-(9,9-di-octyl-fluorene)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole] (PFO-DBT) and poly(2-methoxy-5(2′-ethylhexyloxy) phenylenevinylene (MEH-PPV) along with an acceptor component, i.e., (6,6)-phenyl-C71 hexnoic acid methyl ester. The dependency of the generation rate of free charge carriers in the organic photodetector (OPD) on varied incident optical power density was investigated as a function of different reverse biasing voltages. The photocurrent showed significant enhancement as the intensity of light impinging on active area of OPD is increased. The ratio of Ilight to Idark of fabricated device at −3 V was ∼3.5 × 104. The dynamic behaviour of the OPD under on/off switching irradiation revealed that sensor exhibits quick response and recovery time of <800 ms and 500 ms, respectively. Besides reliability and repeatability in the photoresponse characteristics, the cost-effective and eco-friendly fabrication is the added benefit of the fabricated OPD.

MEH-PPV/Alq3-based bulk heterojunction photodetector

In this paper, we present the effect of varied illumination levels on the electrical properties of the organic blend bulk heterojuction (BHJ) photodiode. To prepare the BHJ blend, poly(2-methoxy-5(2 0 -ethylhexyloxy) phenylenevinylene (MEH-PPV) and aluminum-tris-(8-hydroxyquinoline) (Alq3) are used as donor and acceptor materials, respectively. In order to fabricate the photodiode, a 40-nm thick film of poly(3, 4-ethylendioxythiophene):poly(styrensulfonate) (PEDOT:PSS) is primarily deposited on a cleaned ITO coated glass substrate by spin coating technique. The organic photosensitive blend is later spun coated on the PEDOT:PSS layer, followed by the lithium fluoride (LiF) and aluminium (Al) thin films deposition by thermal evaporation. The optical properties of the MEH-PPV:Alq3 blend thin films are investigated using photoluminescence (PL) and UV-Vis spectroscopy. The photodiode shows good photo-current response as a function of variable illumination levels. The responsivity value 8 mA/W at 3 V is found and the ratio of photo-current to dark current (IPh/IDark) is found to be 1.24.

Eco-benign visible wavelength photodetector based on phthalocyanine-low bandgap copolymer composite blend

Herein, we demonstrate a novel solution-processed photodetector using an organic composite blend of VOPcPhO and PCDTBT to function as the donor (D) and the acceptor (A) materials, respectively. The absorption spectra of the composite blend have been successfully broadened to encompass almost the entire visible region by exploiting the spectral properties of PCDTBT moiety. The photodetector shows an efficient photo-current response as a function of varied illumination levels. Furthermore, current density–voltage (J–V) characteristics of the device, in the dark, have been employed to extract device parameters such as barrier height and rectification ratio. The conduction mechanisms at the electrode–semiconductor interface have also been investigated. As the proposed photodetector can harvest incident photons over almost the whole visible range, it can be potentially employed for practical applications.

Investigation of charge transport in organic polymer donor/acceptor photovoltaic materials

π-conjugated organic semiconductors have long been used as either holes or electrons transport materials. Recently, ambipolar charge carrier transport in these materials have been reported in many investigations. In this paper, we report on the basis of experimental results that the organic semiconductor (donor/acceptor) materials can be as good electrons transporters as these materials are holes transporters. In our study, the solution-processed unipolar diodes based on organic materials P3HT, VOPCPhO, and their blends with PCBM have been fabricated. The I–V characteristics of these diodes have been analyzed in the space-charge-limited current regime. The values of the electron and hole mobilities for the materials were found in the range of 10−4–10−5 cm2/Vs.