Omar Asif

Highly transparent n-type polycrystalline SnS2 and Sn(OxS2-x) thin films were deposited by a modified chemical bath deposition technique using an ionic surfactant t-Octylphenoxy polyethoxy ethanol (abbreviated Tx) activator. X-ray photoelectron spectra (XPS) analysis of the films shows the presence of Sn3d5/2 (486.65 eV) and S2p3/2 (161.7 eV) XPS lines signifying the Sn4+-S2− bonding confirming single phase SnS2 film formation with the addition of < 5 v/v% Tx. With the addition of Tx in higher ≥ 5 v/v% Tx concentration, a strong O1s (531.1 eV) XPS peak attributed to the lattice oxygen matched with the asymmetrical Sn3d5/2 (486.65 and 487.31 eV) XPS peaks confirm the growth of Sn-oxysulfide [Sn(OxS2-x)] film. The Raman spectral analysis based on single intense 314 cm−1 peak suggests the monophasic SnS2 film growth is promoted by Tx addition and complete suppression of the SnS and Sn2S3 phases. Grazing incidence X-ray diffraction show formation of highly crystalline SnS2 film in the hexagonal phase with preferred [100] orientation. Scanning electron micrograph images show uniform lateral growth apparently aided by homogeneous substrate surface nucleation for films deposited with Tx added in the chemiplating solution. The mechanism of SnS2 and Sn(OxS2-x) film growth is discussed in detail based on the reactions which involve controlled dissociation Sn(OH)4 into SnO alongside the SnS2 formation. The photoluminescence (PL) spectrum of deposited films showed a dominant PL peak at ~492 nm attributed to the direct excitonic transitions. The optical transmittance spectra of the Sn(OxS2-x) films are suggestive of sub-bandgap absorption region characterized by gradually decreasing mid-gap states from 2.60 to 2.49 eV and gradually increasing direct bandgap from 3.16 to 3.34 eV indicating increase in oxygen incorporation with increasing concentration of Tx in chemiplating solution. The high optical bandgap and low absorption coefficient in the 900–400 nm range of the Sn(OxS2-x) films is highly suitable for application as an n-type heterojunction layer in thin film solar cells.

In high efficiency organic-inorganic perovskite solar cells formed as a multilayer structure, the hole transporting layer (HTL) at the perovskite absorber layer interface has a critical role. Organic HTLs based on Spiro-OMeTAD and PTAA have led to high efficiencies but displayed poor long-term stability and involves expensive purification processes that hinders universal low-cost commercialization goals for perovskite solar cells. Though as an inorganic alternative, transition metal chalcogenides have been investigated for HTL recently, the hot-injection method often used in synthesis has shown poor reproducibility and difficulty in scaling-up. In this work we demonstrate an ab initio facile inexpensive scalable synthesis of transition metal dichalcogenide (TiS2) by electrodeposition from ionic liquids as a low-cost inorganic HTL for perovskite solar cells. The TiS2 thin films were electrodeposited from choline chloride–urea eutectic based ionic liquid electrolytes at 80°C with Na2S2O3 as sulphur and TiCl4 as titanium source. From cyclic voltammetry studies the deposition potential of TiS2 was optimized at -0.8V vs Pt. The as-deposited TiS2 HTL exhibited polycrystalline structure with preferential growth along (001), (100), (002), (102), (110), (111) planes. The Raman spectroscopy of the films showed peaks around 225 cm−1 and 332 cm−1 attributed to the Eg and A1 g Raman modes respectively. The synthesized thin films demonstrated sharp optical bandgap edge along with bandgap tunability as the bandgap (direct) decreased from 1.53 eV to 1.49 eV, 1.40 eV, and 1.34 eV with gradual change in deposition potential from −0.8 V to −0.9 V, −1.0 V, and −1.1 V vs Pt, respectively. This aspect has potential for alignment of valance band edge in facilitating the hole transport at the perovskite-TiS2 interface. The absorption coefficient in visible-light range of the as-deposited TiS2 thin films likewise has shown a dependence on the synthesis potential which is highly conducive for application as an HTL in multilayer solar cell structure. The TiS2 thin films were observed to be p-type as shown from the Hall effect studies with a carrier mobility up to 14.4 cm2V−1s−1. A detailed study of the effect of the synthesis parameters on the structural, optical, band-edge, and electronic properties of TiS2 thin films suitable for application as HTL in perovskite solar cells is presented.

Electrochemical and energy storage properties of vanadium oxide-graphene composite electrode based solid state supercapacitor using ionic liquid gel electrolyte over flexible stainless-steel foil substrates are discussed. The composite electrode was deposited by a simple technique of spin coating of nano-size graphene dispersed vanadium sol gel followed 300°C -6h air annealing. Graphene mitigates the low electrical resistance limitation of faradaic V2O5 while contributing double layer capacitance to the overall pseudocapacitance. The BMIMBF4 ionic liquid gel with 0.2M LiClO4 dopant acts as high ionic conductivity electrolyte and source of counter ions for redox reactions. The flexible symmetrical V2O5/graphene supercapacitor shows high specific capacitance of 650 Fg-1 and energy and power density values of 30 Wh.kg-1 and 3kW kg-1, respectively at charging potential of 1.5V. The linear charge-discharge, high Coulomb efficiency ~90% and low internal resistance support its use as power source for portable electronics with high energy storage capability.

The chemical bath deposition of wide bandgap n-type SnS2 films and role of sulphur precursor in suppression of p-type SnS phase is described. The as-deposited films are highly polycrystalline in hexagonal crystal structure. Inclusion of oxygen in the film phase is shown by the x-ray photoelectron spectroscopy (XPS) and Raman scattering methods which suggests the CBD films are better described as tin disulfide-oxide (SnS2-xOx) x=0.1. A possible mechanism of film formation is presented. Optical analysis showed energy bandgap 2.76 eV for SnS2-xOx film which decreases to 2.62 eV with the inclusion of the secondary SnS phases.

In this work a review of existing fire-detector types has been carried out along with the development of a low cost, portable, and reliable microcontroller based automated fire alarm system for remotely alerting any fire incidents in household or industrial premises. The aim of the system designed is to alert the distant property-owner efficiently and quickly by sending short message (SMS) via GSM network. A Linear integrated temperature sensor detects temperature beyond preset value whereas semiconductor type sensor detects presence of smoke or gas from fire hazards. The sensor units are connected via common data line to ATMega8L AVR microcontroller. A SIM300CZ GSM kit based network module, capable of operating in standard GSM bands, has been used to send alert messages. The system is implemented on printed circuit board (PCB) and tested under different experimental conditions to evaluate its performances.

Broadband over Power Line (BPL) is an alternative means of providing high-speed Internet access, Voice over Internet Protocol (VoIP), and other broadband services to homes and businesses by using the existing medium voltage (MV) and low voltage (LV) power lines. This paper provides a comprehensive understanding about BPL with its implementation prospects. In this context, the existing power grid infrastructures are discussed elaborately. BPL system functionality with its components and its benefits over other access technologies is also pointed out. Implementation scenarios for various deployment options are illustrated here. The different implementation challenges for BPL system, such as the characteristics of power lines, attenuation problem, noise, potential interference with the other radio frequencies are also presented with their remedies. Comparative analysis between several broadband access technologies shows the feasibility of BPL deployments all over the world.