Effects of Substrate Radial-Position Relative to the Sputter-Gun Axis on the Electrical, Optical and Structural Properties of ZnO Thin Films Deposited by Reactive Direct Current Magnetron Sputtering

ZnO thin films were deposited using reactive direct current (dc) magnetron sputtering on glass substrates placed at seven variable radial positions (-1, 0, 1, 2, 3, 4 and 5 cm)  relative to the sputter-gun (target) axis. A pure zinc target was used and sputtering carried out in argon and oxygen atmosphere with flow rates of 50 sccm and 6 sccm, respectively. XRD characterization showed that, all films crystallized homogeneously in the wurtzite phase with a strong (002) and a weak (004) orientations. Film crystallinity was very low at substrate positions located less than or equal to 1 cm from the target axis but rapidly improved as substrate position increased beyond 1 cm. Film thickness decreased steadily (from 320 to 160 nm) with increase in substrate position from 1 to 5 cm. Film resistivity was much higher (over ~104 Ω cm) at substrate positions located less than 2 cm from the target axis and rapidly decreased with increase in substrate position reaching the order ~10– 3 Ω cm at 3 cm and leveled out. Optical transmittance was homogeneous with 86% in the wavelength range 380 – 2500 nm. Band gap increased dramatically (from 3.15 eV to 3.28 eV) with increase in substrate position.Keywords: Magnetron sputtering, substrate radial position, properties of ZnO thin films

Influence of Pore Size on the Optical and Electrical Properties of Screen Printed TiO

Influence of pore size on the optical and electrical properties of TiO2 thin films was studied. TiO2 thin films with different weight percentages (wt%) of carbon black were deposited by screen printing method on fluorine doped tin oxide (FTO) coated on glass substrate. Carbon black decomposed on annealing and artificial pores were created in the films. All the films were 3.2 µm thick as measured by a surface profiler. UV-VIS-NIR spectrophotometer was used to study transmittance and reflectance spectra of the films in the photon wavelength of 300–900 nm while absorbance was studied in the range of 350–900 nm. Band gaps and refractive index of the films were studied using the spectra. Reflectance, absorbance, and refractive index were found to increase with concentrations of carbon black. There was no significant variation in band gaps of films with change in carbon black concentrations. Transmittance reduced as the concentration of carbon black in TiO2 increased (i.e., increase in pore size). Currents and voltages (I-V) characteristics of the films were measured by a 4-point probe. Resistivity (ρ) and conductivity (σ) of the films were computed from the I-V values. It was observed that resistivity increased with carbon black concentrations while conductivity decreased as the pore size of the films increased

Stability Investigation in the Optical Properties of Thermally Evaporated Ge5Se95-x Znx Thin Films

Selenium-based chalcogenides are useful in telecommunication devices like infrared optics and threshold switching devices. The investigated system of Ge5Se95-xZnx (0.0 ‰¤ x ‰¤ 4 at.%) has been prepared from high purity constituent elements. Thin films from the bulk material were deposited by vacuum thermal evaporation. Optical absorbance measurements have been performed on the as-deposited thin films using transmission spectra. The allowed optical transition was found to be indirect and the corresponding band gap energy determined. The variation of optical band gap energy with the average coordination number has also been investigated based on the chemical bonding between the constituents and the rigidity behaviour of the systems network

Improved Light Soaking and Thermal Stability of Organic Solar Cells by Robust Interfacial Modification

The most widely used material in electron transport layers (ETL) of inverted organic solar cells (iOSCs) is zinc oxide (ZnO). However, the brittleness, inorganic nature, surface defects, and photocatalytic activity of ZnO lead to poor stability in iOSCs. Herein, the light‐soaking and thermal stability of iOSCs are substantially improved by modifying ZnO surface with polyurethane diacrylate (SAR) or urethane acrylate (OCS)‐based ultraviolet (UV) resins. The UV resins significantly reduce the energy barrier, suppress surface defects, and improve interfacial contact between ZnO ETL and the organic photoactive layer. Notably, the SAR and OCS resins mitigate the photocatalytic activity of ZnO, electrical leakage, and interfacial resistance during photoaging of OSCs. As a result, iOSCs based on modified ZnOs retain over 80% of initial efficiency under 1 sun illumination for light soaking 1000 h. Furthermore, SAR and OCS resins on ZnO surfaces form a robust crosslinked network with excellent solvent resistant properties, which result in enhanced thermal stability. These results reveal that this simple and effective approach is a promising procedure to fabricate high‐performance iOSCs