Search

Herein, ultrathin Al2O3 is investigated as a rear interface passivation layer for kesterite solar cells with F:SnO2 (FTO) back contact for potential performance improvement. On the passivation layer, a thin Mo layer is deposited to improve the FTO's ohmicity. Further, NaF is evaporated on the copper zinc tin sulfide (CZTS) precursors to create openings at the passivation layer and achieve Na‐induced benefits in the absorber. The CZTS absorbers deposited directly on the Al2O3‐coated FTO peel off, while those with Mo interlayer do not. For pure sulfide kesterite devices, the Al2O3 layer reduces the short‐circuit current density (JSC), resulting in poor device efficiency. On the other hand, significantly higher JSC is realized for mixed sulfide and selenide kesterite devices with Al2O3 passivation layer, with the current density–voltage curve suggesting a reduced barrier height at the rear interface. As a result, the efficiency is improved from 1.5% for devices without Al2O3 to 4.6% for those with Al2O3. Likewise, improved external quantum efficiency response is observed in the devices with passivation layer for backside and frontside illumination. Therefore, contribution of Al2O3 passivation layer to the performance of kesterite‐based solar cells is evident from the results of this study. [ABSTRACT FROM AUTHOR] more...

This study investigated the impact of Ag layer thickness on the properties of rapid thermal annealed Ag/ITO bilayer films, aimed at addressing conductivity loss in ITO substrates used as a back contact for optoelectronic applications, such as bifacial CZTS solar cells. Ag layers of varying thickness (10 nm, 20 nm, 30 nm, and 40 nm) were sputter-deposited onto a commercially acquired ITO-coated glass substrate and rapidly thermally annealed. The samples' characterization was performed using AFM, XRD, four-point probe, Hall Effect measurements, and UV-VIS-NIR spectrophotometry. Results indicated that thinner Ag layers exhibited relatively stable surfaces with uniformly distributed grains, smaller roughness, and higher electrical conductivity due to increased carrier mobility and concentration. The XRD analysis showed a preferential delafossite AgInO2 structure for thinner Ag layers. Optical measurements revealed that the sample with thinner Ag layers had lower solar transmittance and bandgap narrowing, while thicker layers showed bandgap broadening. The samples had bandgaps within reported ITO bandgaps (3.38 to 4.15 eV). Ag/ITO films with thinner layers achieved a high average transmittance of 76%, lower sheet resistance of 13.2 and enhanced micro-strain and crystallite size properties. These results suggest that thinner Ag/ITO bilayer films hold potential for use in optoelectronic applications, particularly as back contacts in bifacial CZTS solar cells. [ABSTRACT FROM AUTHOR] more...

Clean cooking energy is a global priority, especially in developing countries where firewood and charcoal remain the primary cooking fuels. Solar cooking is an attractive alternative in these countries since it is eco-friendly and utilises freely available solar radiation. Utilisation of solar cookers however is still very low mainly due to the perceived complexity and lack of confidence in the available solar cooker models. In this work, the enhanced box and parabolic solar cookers were designed, fabricated and tested taking into consideration standard solar cookers and local cooking requirements. The enhanced box solar cooker was designed with booster mirrors making an effective aperture area of 0.68 m², a double glass glazing and a glass wool insulator between the double walls of the cooking box. The parabolic cooker was designed with polished aluminium paraboloid with a net aperture area of 1.44 m², a parabola depth of 0.47 m and manual solar tracking. In field tests in Isimani Tanzania, the enhanced solar cooker attained a maximum temperature and cooking power of 129.8 °C and 101.9 W, respectively, and was able to boil 2 litres of water in 100 minutes. The parabolic cooker on the other hand registered a maximum cooking power of 513 W at solar noon and was able to boil 2 and 5 litres of water in reasonable times of 30 and 60 minutes, respectively. [ABSTRACT FROM AUTHOR] more...

Several studies have attempted to overcome the sudden volume expansion of the precursor during sulfurization by the use of oxygen-containing precursors when growing the CZTS absorber. This work demonstrates the influence of precursor stacking orders on the properties of the CZTS thin film absorber layer from DC-sputtered oxygenated precursors for solar cell applications. CZTS absorber layers were prepared from three types of DC-sputtered stacks, namely, Zn-O/Sn/Cu, Sn/Zn-O/Cu, and Sn/Cu/Zn-O. The precursors were sequentially deposited on a soda lime glass (SLG) using DC-magnetron sputtering and annealed in a sulfur and nitrogen ambient. X-ray diffractometry (XRD) and Raman spectroscopy analyses reveal the formation of crystalline kesterite CZTS structure regardless of the precursor stacking order. Atomic force microscope (AFM) analysis showed that CZTS thin films grown from precursor stacks SLG/Zn-O/Sn/Cu and SLG/Sn/Zn-O/Cu had improved morphological properties with densely packed large grains compared to that with stack SLG/Sn/Cu/Zn-O. SLG/Zn-O/Sn/Cu is the best stack among the studied stacking orders since it exhibits large grains in the absorber layer, which is preferential for high-efficiency thin film solar cells. The use of oxygenated precursor with order Sn/Zn-O/Cu promises improved CZTS absorber properties as it exhibits better morphological properties. [ABSTRACT FROM AUTHOR] more...

Thermochromic W/Zr co-doped VO2-based thin films with different concentrations of Zr were successfully deposited on soda lime glass substrates by direct current (DC) magnetron sputtering of V(99)W(01) alloy and Zr targets at a substrate temperature of 425 °C. The films were characterized by x-ray diffraction (XRD), atomic force microscopy (AFM), Rutherford backscattering spectroscopy (RBS), two-point probe and UV/VIS/NIR spectroscopy. The film's structural properties evolution was significantly influenced by Zr concentration in the films. The transition temperature and hysteresis loop widths of the films were found to decrease with increasing Zr concentration. For the Zr concentrations of 0.21 at.%, 0.23 at.% and 0.36 at.% the films' transition temperatures were 38.1oC, 35.7 oC and 33.7 oC, respectively, whereas the corresponding hysteresis widths were 12.9 °C, 5.7 °C and 2.6 °C. Films with 0.36 at.% Zr demonstrated a high value of solar transmittance modulation at 8%, albeit with some compromise in luminous transmittance. These results reveal that a controlled amount of Zr in the W-doped VO2 films can potentially improve the films' thermochromic properties for smart Windows applications. [ABSTRACT FROM AUTHOR] more...

Sputter deposition of thermochromic VO2 thin films for smart window applications has been faced with several challenges including the need for high deposition temperature, extremely precise and narrow range of oxygen/argon flow ratio and target poisoning during sputtering. Deposition of VO2 at room temperature without oxygen followed by post-deposition annealing has been cited as one of the potential mitigations to the challenge. In this study, the effects of post-deposition annealing conditions on the structural, electrical and optical properties of VO2 thin films are reported. The films were prepared on soda lime glass substrates using DC magnetron sputtering of metallic vanadium target in argon atmosphere, at room temperature without oxygen followed by post-deposition annealing. The working pressure and argon flow rate were 5.2 - 5.6 x 10-3 mbar and 76 ml/min, respectively. Thereafter, the films were annealed in a low vacuum environment at different temperatures and times. The XRD results confirmed that all films annealed at different temperatures and times were monoclinic VO2 except for films annealed at a temperature of 300 oC. The results indicate that 400 oC and 20 minutes are the optimum annealing temperature and time, respectively, for fabrication of highquality VO2 films with improved stoichiometry and crystallinity. The films had resistivity change between the semiconducting and metallic phases of one order of magnitude and the transition temperature between ~ 58 oC and 63 oC. The highest peak transmittance and best optical switching of the annealed VO2 films was 53% and 18%, respectively, at a wavelength of 2500 nm for film thickness of 44 nm. The results suggest that room temperature deposition without oxygen followed by post-deposition annealing in a low vacuum environment may be adequate for the fabrication of switching VO2 thin films. [ABSTRACT FROM AUTHOR] more...

Magnesium doped zinc oxide (ZnO:Mg) thin films were deposited on soda lime glass slides by DC magnetron sputtering method. Atomic force microscope (AFM), and UV/VIS spectrophotometer were used to investigate the effect of sputtering power and substrate temperature on the surface morphology and optical properties of ZnO:Mg thin films. AFM images revealed that sputtering power and deposition temperature have significant influence on surface morphology of the ZnO:Mg thin films. For all sputtering powers and substrate temperatures investigated, ZnO:Mg films had peak transmittance above 85%. Samples deposited at 110 W sputtering power and 450 °C substrate temperature showed the best peak transmittance of > 90% at 560 nm (visible range). Optical band gap of ZnO:Mg films was in the range of 3.44-3.69 eV depending on the substrate temperature. The results indicated the potential of the films for transparent conductor applications. [ABSTRACT FROM AUTHOR] more...

DC magnetron sputtering at a substrate temperature of 425 °C was used to successfully deposit W/Zn-doped VO2 thin films on soda lime glass (SLG) substrates. The aim was to investigate the influence of Zn doping levels on the transition temperature (τc), luminous transmittance (Tlum) and solar transmittance modulation (ΔTsol) of VO2-based thin films. UV/VIS/NIR spectrometer, X-ray Diffraction (XRD), Atomic Force Microscope (AFM), and Rutherford Backscattering Spectroscopy (RBS) were used to characterise the thin films. It was revealed that W/Zn co-doped VO2 thin films with ~ 10.8 at.% Zn showed a luminous transmittance of ~ 40.4%, with excellent solar transmittance modulation of 10.2%. Furthermore, the transition temperature obtained for the Zn and W co-doped VO2 films with ~ 10.8 at.% Zn was lower at 23.1 °C compared to 25.6 °C and 26.8 °C for thin films with ~ 3.9 at.% Zn and ~ 2.8 at.% Zn, respectively. It was not possible to deposit the films with Zn doping level above 10.8 at.% due to some technical limitations. These findings indicate that thin films with a controlled proportion of Zn in the W/Zn co-doped VO2-based thin films have the potential to be employed for applications such as smart windows. [ABSTRACT FROM AUTHOR] more...