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• Mo incorporated CZTS with no secondary phases deposited by magnetron co-sputtering. • Formation of bilayer CZTS absorber with different grain microstructure and porosity. • Mo enhances P -type conductivity and absorbance of CZTS for wavelengths <600 nm. • V oc deficit, J sc , and FF improved for CZTS/CdS devices with optimized Mo content. • PCE of optimized Mo incorporated CZTS solar cell increased to 5.49% from 1.63% Molybdenum (Mo) incorporated Cu 1.69 ZnSnS 4 (CZTS) absorber has been deposited onto Mo-coated soda lime glass (SLG) by co-sputtering of Mo and non-stoichiometric quaternary compound targets. After sulfurization at 600 °C, Mo incorporation into CZTS was confirmed by X-ray diffraction (XRD) and secondary ion mass spectrometry (SIMS). From the observed shifts for the (1 1 2) and (2 2 0) peaks, both lattice parameters a and c of the CZTS unit cell were found to decrease with increasing Mo incorporation suggesting cationic substitution by Mo. The Mo incorporated CZTS has a bilayer microstructure in which the lower sub-layer adjacent to the substrate has a smaller grain size and higher porosity than the upper sub-layer. The lower sub-layer is also richer in Mo and has a graded Mo profile. Sheet resistance measurements on Mo incorporated CZTS films deposited on SLG and on quartz show resistivity that decreases with the amount of Mo in CZTS and Mo acts as an acceptor dopant. The energy band gap of CZTS on SLG increases from 1.38 eV to about 1.68 eV as a result of Mo incorporation and the absorbance of Mo incorporated CZTS is increased for wavelengths shorter than 600 nm. When Mo is co-deposited at the optimized DC sputtering power of 10 W, Mo incorporated CZTS/CdS solar cells attain a maximum power conversion efficiency (PCE) of 5.49% versus 1.63% for the reference device under 1 Sun AM 1.5 illumination. Device efficiency enhancement is due to back surface field, increased carrier concentration and reduced band tailing. [ABSTRACT FROM AUTHOR]

Highlights • Suppression of molybdenum (Mo) reaction with Sulphur (S) and secondary phase formation. • Non-stoichiometric CZTS (Cu 1.69 ZnSnS 4) reduces interfacial MoS 2 thickness below 40 nm. • Integration of ultrathin tantalum nitride intermediate layer (TaN IL) of thickness 3–12 nm. • TaN IL shows high chemical reactivity towards S vapor and reduces S concentration in Mo. • TaN IL avoids creation of MoS 2 layer and reduces void formation at the back interface. Abstract Ultrathin tantalum nitride (TaN) intermediate layers (IL) with thickness from 3 nm to 12 nm have been used to limit the undesirable interfacial reaction between molybdenum (Mo) and copper-zinc-tin-sulphide (CZTS). The morphology, chemical and structural properties of the samples were characterized by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, X-ray diffraction analysis, and scanning transmission electron microscopy (STEM). Time-of-flight secondary ion mass spectrometry (TOFSIMS), energy-dispersive X-ray spectroscopy (EDX), and electron energy loss spectroscopy (EELS) have been used for elemental analysis. Thin TaN IL shows chemical reactivity towards sulphur (S) vapor at 600 °C and the incorporation of S in TaN reduces the S concentration in Mo films at the sub-surface region and thus improves electrical conductivity of sulphurised Mo. The use of a non-stoichiometric quaternary compound CZTS target along with TaN IL enables to minimise thickness of MoS 2 layer and reduce void formation at the Mo/CZTS interface. Furthermore, incorporation of TaN IL improves scratch hardness of CZTS/Mo films to soda-lime glass substrate. [ABSTRACT FROM AUTHOR]

The dielectric properties of AC powder electroluminescent devices were measured and analyzed using complex impedance spectroscopy to determine the relaxation processes occurring within the devices. The relaxation processes identified were ascribed to the electrode polarization caused by ion accumulation at the electrode/resin interfaces, the Maxwell-Wagner-Sillars effects at the (ZnS or BaTiO 3 ) particle/resin interfaces, and the dipolar reorientation of polymer chains in the resin matrix. Each relaxation process was represented by its corresponding equivalent circuit component. Space charge polarization at the electrodes were represented by a Warburg element, a resistor, and a constant phase element. The resin matrix, ZnS/resin and BaTiO 3 /resin interfaces could each be modeled by a resistor and a capacitor in parallel. The simulated equivalent circuits for three different printed structures showed good fitting with their experimental impedance results. [ABSTRACT FROM AUTHOR]

[Display omitted] • Introduction to basic photovoltaic and water splitting technologies with nomenclature. • Challenges and relative advantages of integrated PV-PEC over PV-EC for cost effective clean H 2. • Current status of designs and material choices for affordable and scalable devices. • Special emphasis on earth abundant multi-functional metal oxides such as copper oxides. The Sun is an inexhaustible source of renewable energy, although under-utilized due to its intermittent nature. Hydrogen fuel is another clean, storable, and renewable energy as it can be readily produced by electrolysis of water, a naturally abundant resource. However, the necessary voltage for water electrolysis (>1.23 V) is high for the process to be cost effective, and therefore requires photoelectrocatalytic (PEC) cells for lowering the voltage. Powering the PEC cells with solar driven photovoltaic (PV) devices offers an all-clean efficient technology purely relying on renewable sources and therefore warrants large research attention. This review aims to provide an up to date account of the PV-PEC integrated technology for green hydrogen. We begin with the fundamentals of PV and water splitting technologies (electrolysis, photocatalysis, electrocatalysis (EC), photoelectrocatalysis (PEC)), as well as why and how the unassisted solar water splitting technology gradually progressed from PV with external electrolysers (PV-EC) to integration of PV with EC (IPV-EC) and PEC (PV-PEC). We then discuss the major challenges in PV-PEC integration and outline the major breakthroughs in design and materials development for high Solar to Hydrogen (STH) efficiency and long device lifetime. The importance of material selection and metal-oxide semiconductor nanostructures for PV-PEC integration are also discussed with a special focus on Cu-oxide as an emerging material. An outlook toward commercialization including the major guiding factors and related technologies (for e.g., PV-Thermal integration) that can maximize solar energy utilization to reduce payback time has been discussed. [ABSTRACT FROM AUTHOR]