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In this study, we demonstrate a novel approach to use vanadium pentaoxide (V2O5) as a single material that can simultaneously function as both electron blocking and transport layers (EBLs and ETLs) in an organic photo-detector (OPD). Composite of V2O5 and PEDOT:PSS was introduced as hole transport layer (HTL) whereas, single V2O5 film was utilised as an ETL. The resultant device had the ITO/PEDOT:PSS+V2O5/PCDTBT:PC71BM/ V2O5/Al architecture and exhibited a new range of photo-current as well as showed an enhanced photo-response. For comparison, we also fabricated devices with ITO/PCDTBT:PC71BM/Al, ITO/PEDOT:PSS/PCDTBT:PC71BM/Al and ITO/PEDOT:PSS+V2O5/PCDTBT:PC71BM/Al architectures. The device with ITO/PCDTBT:PC71BM/Al architecture showed a photo-response in the range of ∼2.3 (OFF) to ∼6.7 mA/cm2 (ON) which increased to almost double after the inclusion of PEDOT:PSS as an HTL and reached to ∼2.3 and ∼12.6 mA/cm2 in OFF and ON states, respectively. In the third variant of devices with the addition of V2O5 in PEDOT:PSS to form a composite HTL, the photo-response narrowed down to ∼5.4 (OFF) and ∼12.6 mA/cm2 (ON). Lastly, the new approach with the addition of an ultrathin V2O5 layer as an ETL along with composite HTL demonstrated a new range of photo-current with enhanced photo-response in the range of 13.2 mA/cm2 (OFF) and ∼20.7 mA/cm2 (ON). The findings of the current work suggest that addition of V2O5 based ETL has tuned both photo-current and response range of the OPDs. In addition, inclusion of V2O5 into the PEDOT:PSS could effectively block the electrons due to its large band-gap.

In this paper, composite micro-structures of Vanadyl 2,9,16,23-tetraphenoxy-29H,31H-phthalocyanine) (VOPcPhO) and Poly (3-hexylthiophene-2,5-diyl) (P3HT) complex with nano-porous surface morphology have been developed by electro-spraying technique. The structural and morphological characteristics of the VOPcPhO:P3HT composite films have been studied by field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The multidimensional VOPcPhO:P3HT micro-structures formed by electro-spraying with nano-porous surface morphology are very promising for the humidity sensors due to the pore sizes in the range of micro to nano-meters scale. The performance of the VOPcPhO:P3HT electro-sprayed sensor is superior in term of sensitivity, hysteresis and response/recovery times as compared to the spin-coated one. The electro-sprayed humidity sensor exhibits ∼3 times and 0.19 times lower hysteresis in capacitive and resistive mode, respectively, as compared to the spin-coated humidity sensor.

In this work, we report on the application of a newly synthesized macroporous polythiophene derivative, benzo[b]thiophene end-capped dioctyloxy-benzene(PBObzT2), in the fabrication of a capacitive humidity sensor. The sensor has been fabricated by spin-coating polymer solution in the gap between pre-deposited aluminum electrodes to form a coplanar Al/PBObzT2/Al capacitive humidity sensor. We have also demonstrated how effectively thermal annealing has improved the physical aspects of the active layer and sensing properties of the sensor. The sensor's capacitance is measured against RH variations at different frequencies. Particularly, at an optimum annealing temperature of 75 �C, the sensor exhibits high sensitivity, fast response and low hysteresis. The hydrophobic nature of the polymer makes it highly appropriate to be used in the humidity sensors Authors are thankful to the Ministry of Education, Malaysia , for the financial support under High Impact Research (HIR) grant UM.S/625/3/HIR/MOE/26 with account number UM.0000080/HIR.C3, Fundamental Research Grant Scheme (FRGS) FP046-2015A and University Malaya under University Malaya Research Grant (UMRG) RP007A-13AFR and RP007A/2011A . Fakhra Aziz would like to acknowledge the support of Higher Education Commission (HEC) of Pakistan through Post Doctoral Fellowship. The authors are also grateful to the University Kebangsaan Malaysia (UKM) for providing the research funds through grant FST-06-FRGS0095-2010 . Appendix A Scopus

In this study, we developed a miniaturized InGaN blue μLED-based excitation source intended for an implantable lens-less brain imaging system. To enhance its implantability, the μLED was thinned further through the laser lift-off process. A filtering component comprising a short-pass interference filter and a low-NA fiber optic plate (FOP), was loaded onto the μLED. The addition of an interference filter reduced normal incident green-end band emissions from the μLED by two orders of magnitude. The application of FOP enables the resolution of the angle-dependent problem of the interference filter. Further, a fluorescent imaging experiment was carried out on the proposed excitation source. The proposed device produced bright fluorescence images that are sufficient for implantable in vivo application. The thickness of the proposed excitation device was 180 μm, making it suitable for implantable brain fluorescent imaging applications.

We present herein the effect of varied humidity levels on the electrical parameters of the (E)-2-{4-[2-(3,4,5-trimethoxybenzylidene) hydrazinyl]phenyl}ethylene-1,1,2-tricarbonitrile (TMBHPET) organic dye based humidity sensor. TMBHPET dye has been synthesized bearing an additional methoxy group substituent at the terminal benzene ring of previously reported (E)-2-(4-(2-(3,4-dimethoxybenzeylidene)hydrazinyl)phenyl)ethane-1,1,2-tricarbonitrile (DMBHPET) dye. The strategic dye design is believed to increase the π-electron polarizability in the dye structure. Capacitive type humidity sensor has been fabricated in planar geometry of Al/TMBHPET/Al and its capacitance has been monitored as a function of relative humidity (RH) level at varied frequencies of ∼1 v AC input bias. A maximum sensitivity ∼46 fF/%RH at 1 kHz has been observed which is almost seven times higher as that of DMBHPET based humidity sensor which may be attributed to the porous surface morphology of TMBHPET sensing film. The sensor has also shown reversible changes in its capacitance with variation in humidity level and hysteresis value has been observed to be 2.4%. The motive of the present study was to increase the sensing parameters of the previously reported humidity sensor utilizing DMBHPET dye, which has been successfully achieved.

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. Authors are thankful to the Ministry of Education for the financial support under High Impact Research (HIR) grant UM.S/625/3/HIR/MOE/26 with account number UM.0000080/HIR.C3 and University Malaya Research Grant (UMRG) under grant number RP007A-13AFR. This project was also partially funded by the University Malaya postgraduate grant PG089-2012B. Scopus

In this work, surface-type humidity sensors with P3HT (organic) and P3HT–TiO2 (organic–inorganic hybrid) active layers have been fabricated. The surface morphology of the humidity active films has been studied by atomic force microscopy, whereas their crystalline structure has been studied by X-ray diffraction. We have aimed at improving the sensing parameters of P3HT-based humidity sensor, by embedding nano-anatase TiO2 powder in pristine organic P3HT moiety. The capacitance versus relative humidity (%RH) response curves of the organic and hybrid humidity sensors have been examined in 30–98%RH range (dark ambient condition, room temperature). In general, an increase in capacitance has been observed in both sensors with the increment in RH level. The observed response of both humidity sensors is believed to be associated with polarization change due to the adsorption of water molecules and transfer of charge carriers due to the formation of charge transfer complexes. The hybrid-based humidity sensor has shown significantly improved humidity-sensing parameters, i.e., fivefold higher sensitivity, with hysteresis reduced to one-third as compared to that of pristine organic humidity sensor. A relatively faster response and recovery time has also been obtained by the hybrid sample.

We have investigated the influence of relative humidity on the electrical response of a bottom gate organic field-effect transistor (OFET) with poly(3,4-ethylenedioxythiophene)/poly(4-styrene sulfonate) (PEDOT:PSS) as an active channel material. For sensor fabrication, the organic polymer PEDOT:PSS has been spun-cast on highly doped n-Si wafer with preliminary thermally deposited gold, source and drain electrodes. The structural characterization and surface morphology study of active layer has been performed by XRD and FESEM, respectively. From the transfer characteristic curve, the p-type hole conductivity in PEDOT:PSS thin film is confirmed. Whereas from the output current-voltage (I�V) characteristic of the OFET, the Ion/Ioff ratio has been measured to be ?2.6, when operated at relative humidity (RH) ?60%. The humidity sensing characteristics of the OFET have further been investigated by exposing the proposed OFET to varied RH levels (40�80% RH) at room temperature (26.2 �C). Within the humidity range examined, the channel current has been observed to amplify by nearly 29.4 times of its magnitude. 2017 Elsevier B.V. Authors are thankful to the Ministry of Education for the financial support under High Impact Research (HIR) grant UM.S/625/3/HIR/MOE/26 with account number UM.0000080/HIR.C3 and University Malaya Research Grant (UMRG) under grant number RP007A-13AFR . Q. Zafar is thankful to Erasmus Mundus (EM) INTACT program for Post-Doc mobility. Dr. Qayyum Zafar was born in 1986 at Lahore-city, Pakistan. He graduated in Physics from Government College University (GCU), Lahore in 2008. He received his MS degree from Ghulam Ishaq Khan Institute of Engineering Sciences and Technology (GIKI), Swabi in 2011. He served as Research Associate at Nano sensors.catalysis lab at COMSATS Institute, Islamabad for one year. He obtained his PhD in Applied Physics (Organic Electronics) from Department of Physics, University of Malaya, Malaysia. He later joined Solar/Photovoltaic Materials Research Group as a Postdoctoral Research Fellow in 2015. Currently he is serving as ERASMUS MUNDUS (INTACT) postdoctoral Research Fellow at Department of Electrical Engineering, Frederick University, Cyprus. Dr. Shahino Mah Abdullah was born in Johor, Malaysia in 1987. He completed his B.Sc. and Ph.D. degrees in Physics from the University of Malaya, Malaysia. He joined Low Dimensional Materials Research Centre (LDMRC) at Department of Physics, University of Malaya as a postdoctoral research fellow in 2016. His research interests encompass fabrication of electrochemical and organic semiconducting devices including solar cells, light-emitting diodes, and field-effect transistors. Currently, he is a Research Fellow at International Institute of Advanced Islamic Studies (IAIS) Malaysia, with interest in Science, Technology, Environment and Ethics. Mohamad Izzat Azmer was born at Ipoh, Perak in 1989. He completed his BSc. (Hons.) in Materials Technology in 2013 at Universiti Teknologi Mara (UiTM), Shah Alam, Selangor, Malaysia. He has recently completed his MS applied Physics from Solar/Photovoltaic Materials Research Group, Department of Physics, University of Malaya, Malaysia. Dr. Mansoor Ani Najeeb received his Bachelors in Physiotherapy from Calicut University (India) and M.Tech in Biomedical Engineering from VIT University (India). He completed his Ph.D in Biomedical Engineering & Nanotechnology from Noorul Islam University (India). Prior to his Ph.D, he was working as an Assistant Professor at the Department of Biomedical Engineering, Noorul Islam University. He joined Solar/Photovoltaic Materials Research Group as a Postdoctoral Research Fellow in 2014. Currently, he is working as PostDoc Research Fellow at Center for Advanced Materials, Qatar University, Qatar . His current research interests are Organic Semiconductor based biosensors, Thin Films and Nano Biomaterials. Dr. Karwan Wasman Qadir was born in Dbis-Kerkuk, Kurdistan, Iraq in 1982. He did his B.Sc in Physics in 2005 and M.Sc in Solar Radiation Physics in 2010 from Salahaddin University, Erbil, Iraq. His M.Sc research title was Study and Analysis of Global Solar Radiation in Kurdistan Region-Iraq. He earned his PhD in Applied Physics from Universiti Malaya. Currently, he is working as lecturer and researcher at Salahaddin University, Erbil, Iraq. Dr. Khaulah Sulaiman is an Associate Professor at Department of Physics, Faculty of Science, University of Malaya, Kuala Lumpur, Malaysia. Her current research interests are organic semiconductor device physics, solution process-able organic semiconductor thin films, organic/metal interface and organic solar cells. Scopus

In this paper, we investigate the humidity sensing properties of an organic dye material (E)-2-(4-(2-(3,4-dimethoxybenzeylidene)hydrazinyl)phenyl)ethane-1,1,2-tricarbonitrile (DMBHPET). The sensors were fabricated by making pairs of aluminum electrodes on glass substrates. The gap between the electrodes was ∼40 μm. The active layer was deposited in the gap using the drop casting technique. The resistive and capacitive outputs of the sensors under the different %RH levels have been recorded which have been further analyzed and simulated by a mathematical expression. The data analysis demonstrates a linear behavior for the both resistance–humidity and capacitance–humidity measurements. Furthermore, hysteresis and response/recovery measurements have also been performed.

This research work demonstrates compositional engineering of an organic-inorganic hybrid nano-composites for modifying absolute threshold of humidity sensors. Vanadyl-2,9,16,23-tetraphenoxy-29H,31H-phthalocyanine (VOPcPhO), an organic semiconductor, doped with Titanium-dioxide nanoparticles (TiO

This research work demonstrates compositional engineering of an organic-inorganic hybrid nano-composites for modifying absolute threshold of humidity sensors. Vanadyl-2,9,16,23-tetraphenoxy-29H,31H-phthalocyanine (VOPcPhO), an organic semiconductor, doped with Titanium-dioxide nanoparticles (TiO2 NPs) has been employed to fabricate humidity sensors. The morphology of the VOPcPhO:TiO2 nano-composite films has been analyzed by atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM). The sensors have been examined over a wide range of relative humidity i.e. 20-99% RH. The sensor with TiO2 (90 nm) shows reduced sensitivity-threshold and improved linearity. The VOPcPhO:TiO2 (90 nm) nano-composite film is comprised of uniformly distributed voids which makes the surface more favorable for adsorption of moisture content from environment. The VOPcPhO:TiO2 nano-composite based sensor demonstrates remarkable improvement in the sensing parameter when equated with VOPcPhO sensors. Scopus

a b s t r a c t In this paper, we report on the fabrication and characterization of organic based pressure sensor and displacement transducer. For the purpose, an organic semi-conductor, Vanadyl 2,9,16,23-tetraphenoxy- 29H,31H-phthalocyanine (VOPcPhO), is employed as an active material. The fabrication was done on the PEDOT:PSS coated ITO-glass substrates by the methods of spincoating and dropcasting for the displace- ment transducer and pressure sensor, respectively. By considering the elastic properties of the devices under external mechanical pressure, reversible measurements of the devices' electrical outputs have been demonstrated. The pressure-capacitance and displacement-capacitance relationships have been obtained from the measurement of the capacitance output of the devices, which afterwards further ana- lyzed and modeled using mathematical expressions. The data analysis suggests a linear pattern of the capacitance-pressure from the devices in the specific ranges of the pressure and displacement.

In this paper, the formation of poly(2-methoxy-5-(2-ethylhexyl-oxy)-p-phenylenevinylene) (MEH-PPV) and polyvinylpyrrolidone (PVP) composite microstructures by an electrospinning technique has been reported. MEH-PPV:PVP composites have been prepared by using chloroform as solvent. Novel microstructures have been successfully formed at the varying concentrations of PVP at 1 wt%, 3 wt%, and 5 wt%. The morphological study of these structures has been characterized by Field Emission Scanning Electron Microscopy (FESEM), while their optical properties have been investigated by UV–vis, XRD, and photoluminescence (PL) microscopies. Enhancement in optical properties for the novel microstructures has been observed. The microstructures obtained from this study seem very promising for the applications in optoelectronic devices.

In this study, we report the enhanced sensing parameters of previously reported TMBHPET-based humidity sensor. Significant improved sensing performance has been demonstrated by coupling of TMBHPET moisture sensing thin film with cobalt ferrite nanoparticles (synthesized by eco-benign ultrasonic method). The mean size of CoFe2O4 nanoparticles has been estimated to be ~ 6.5 nm. It is assumed that the thin film of organic–ceramic hybrid matrix (TMBHPET:CoFe2O4) is a potential candidate for humidity sensing utility by virtue of its high specific surface area and porous surface morphology (as evident from TEM, FESEM, and AFM images). The hybrid suspension has been drop-cast onto the glass substrate with preliminary deposited coplanar aluminum electrodes separated by 40 µm distance. The influence of humidity on the capacitance of the hybrid humidity sensor (Al/TMBHPET:CoFe2O4/Al) has been investigated at three different frequencies of the AC applied voltage (V rms ~ 1 V): 100 Hz, 1 kHz, and 10 kHz. It has been observed that at 100 Hz, under a humidity of 99 % RH, the capacitance of the sensor increased by 2.61 times, with respect to 30 % RH condition. The proposed sensor exhibits significantly improved sensitivity ~560 fF/ % RH at 100 Hz, which is nearly 7.5 times as high as that of pristine TMBHPET-based humidity sensor. Further, the capacitive sensor exhibits improved dynamic range (30–99 % RH), small hysteresis (~2.3 %), and relatively quicker response and recovery times (~12 s, 14 s, respectively). It is assumed that the humidity response of the sensor is associated with the diffusion kinetics of water vapors and doping of the semiconductor nanocomposite by water molecules.

A hybrid solar cell (HSC) based on a ZnSe and CdSe QDs-composite with improved conversion efficiency has been demonstrated. A novel approach of incorporating a QDs-composite (CdSe and ZnSe QDs simultaneously), in the poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT-PSS) matrix by a simple cost effective solution processing technique, has been adopted. The combination of the QDs produced a 33% increase in the photo-conversion efficiency with a corresponding 67% enhancement in the fill factor (FF) when compared with the reference device. The micro-Raman analysis revealed effective strong coupling between both ZnSe and CdSe QDs, which promotes smooth charge transfer. This improved efficiency due to enhanced FF was achieved through interfacial engineering of the solution-processed hole transport layer, leading to facilitated charge transport and restrained bimolecular recombination. The present approach, outdoing the need of a cascaded layered structure, is compatible with the state-of-the-art hybrid solar cells, thus offering better throughput and a low cost manufacturing process for an improved-performance device. 2016 The Royal Society of Chemistry. Scopus