No abstract

This work demonstrates the high performance graphene oxide (GO)/PEDOT:PSS doubled decked hole transport layer (HTL) in the PCDTBT:PC71BM based bulk heterojunction organic photovoltaic device. The devices were tested on merits of their power conversion efficiency (PCE), reproducibility, stability and further compared with the devices with individual GO or PEDOT:PSS HTLs. Solar cells employing GO/PEDOT:PSS HTL yielded a PCE of 4.28% as compared to either of individual GO or PEDOT:PSS HTLs where they demonstrated PCEs of 2.77 and 3.57%, respectively. In case of single GO HTL, an inhomogeneous coating of ITO caused the poor performance whereas PEDOT:PSS is known to be hygroscopic and acidic which upon direct contact with ITO reduced the device performance. The improvement in the photovoltaic performance is mainly ascribed to the increased charge carriers mobility, short circuit current, open circuit voltage, fill factor, and decreased series resistance. The well matched work function of GO and PEDOT:PSS is likely to facilitate the charge transportation and an overall reduction in the series resistance. Moreover, GO could effectively block the electrons due to its large band-gap of ~3.6 eV, leading to an increased shunt resistance. In addition, we also observed the improvement in the reproducibility and stability.

No abstract

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.

No abstract

This work investigates the enhanced stability of organic solar cells (OSCs) fabricated with a hybrid hole-transport layer (HTL) incorporating vanadium pentaoxide (V2O5) nanoparticles in poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS). OSCs have been fabricated in controlled and ambient atmospheric conditions by employing a pristine PEDOT:PSS HTL and its hybrid variant. Stability and degradation analyses were carried out by using photovoltaic and X-ray photoelectron spectroscopy (XPS) measurements, respectively. Normalized photovoltaic characteristics showed that OSCs with hybrid HTL outperformed the pristine device and retained their performance as compared to their pristine counterparts when the fabrication was carried out in a nitrogen-filled glovebox and devices were tested after encapsulation for 7 days. However, OSCs that were fabricated and characterized in ambient air showed severe degradation in photovoltaic performance, mainly due to a drastic decay in the short circuit current and open circuit voltage for both device variants. Further, XPS was applied to probe the stability of HTL variants under aging in ambient air. The device instability was mainly ascribed to indium diffusion from the anode into the HTL, and its concentration increased from 0.4 to 2.8% within 250 h of ambient exposure of pristine HTL, while an insignificant increase was recorded in the indium content of the hybrid HTL. This confirms the remarkable reduction in indium diffusion brought about by the presence of V2O5 nanoparticles.

The fabrication and characterization of a novel co-planar humidity sensor based on organic semiconducting material, vanadyl phthalocyanine (VOPc), is presented in this paper. Here we examine the effect of different humidity conditions on the capacitive and resistive response of VOPc thin films in the Al/VOPc/Pt co-planar structure. The two asymmetric electrodes, aluminum (Al) and platinum (Pt), were deposited through the photolithography technique. Thin films of VOPc were spun-cast on the glass substrate with primarily deposited asymmetric metal electrodes, from a solution of 30 mg ml−1 in chloroform at 3000 rpm. The gap between the electrodes was 17 µm. A 100-fold increase was observed in the capacitance of the VOPc sensing material with an elevation of relative humidity level. The resistance of the sensor reduced from 2.9 GΩ to 2.1 MΩ with increasing level of humidity. The VOPc thin film has been analyzed by x-ray diffraction as well as atomic force microscopy in order to get structural and morphological information on the sample. Adequate sensing properties such as enough sensitivity, good selectivity, linearity and reasonable response and recovery times have been obtained. The humidity-dependent properties of the sensor make it a good match for its potential application in commercial hygrometers.

No abstract