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• The investigation of the defect-related carrier dynamics of CZTSe conducted in this study provided the experimental characterization of the existence of [2Cu Zn − + Sn Zn 2+] defect clusters. From the results, it is important to consider the possibility of factors such as the presence of [2Cu Zn − + Sn Zn 2+] defect clusters when determining the source of the performance degradation of CZTSe solar cells. In this work, a systematic investigation of the effects of point defects on the efficiency of a Cu 2 ZnSnSe 4 (CZTSe) thin film solar cell was conducted using temperature-/power-dependent photoluminescence (PL) and time-resolved photo-luminescence (TRPL). The studied stoichiometric CZTSe absorber layer for a CZTSe solar cell with an efficiency of 4.4 % was prepared using the low-toxicity selenization process. The fitting to the Arrhenius plot and the stretched tail at the long-wavelength side of PL spectrum obtained at 10 K indicated a high concentration of zinc on copper (Cu Zn) point defects. The dispersive-photon-energy-dependent TRPL at 10 K exhibited non-exponential stretched PL decay at all photon energies and, in particular, revealed the highly fluctuating potential of CZTSe that caused carrier localization. This effect was observed to be caused by [2Cu Zn − + Sn Zn 2+] defect clusters, which produce a significant conduction/valence band-edge shift in their vicinity in CZTSe and can cause shunt leakage and an increase in series resistance. This systematic investigation presents the experimental characterization of [2Cu Zn − + Sn Zn 2+] defect clusters and provides perspective to help clarify the performance deterioration of CZTSe solar cells. [ABSTRACT FROM AUTHOR]

• Multi-stacked metallic layer precursors were used to suppress the formation of secondary phase defects. • SnSex losses were correlated with the structure (stacking number) of the multi-stacked metallic layer precursors. • Environmentally-benign process without toxic H2Se. • The bifacial properties of CZTSe films were improved. In this study, Cu 2 ZnSnSe 4 (CZTSe) films were prepared via evaporation and selenization. Metallic precursors were first deposited upon a fluorine-doped tin oxide (FTO) substrate via evaporation, followed by selenization in a selenium–argon atmosphere at a maximum temperature of 500 °C for a duration of 30 min. Selenization is always accompanied by interdiffusion between the metallic precursor layers. However, in conventional stacked precursor structures, various secondary phases are formed in the film owing to insufficient interdiffusion between the precursor metals. To address this problem, we constructed CZTSe films using multi-stacked metallic layer precursors (without changing the total thickness of each type of metal or using metal selenides as precursors). Consequently, the secondary phase formation was effectively suppressed, the quality of the CZTSe film was improved, and its performance as a bifacial photovoltaic device was enhanced. The optimal efficiency with front illumination was 4.23 %; bifacial illumination further increased the efficiency to 4.45 %. [ABSTRACT FROM AUTHOR]

• Substrates significantly affect the diffusion behavior the photovoltaic performance. • CZTSe solar cell on FTO substrate has better heterojunction rectifying character. • CZTSe solar cell on FTO substrate shows highly resistive to damp heat weathering. This paper presents a thorough investigation over characteristics and device performance of Cu 2 ZnSnSe 4 (CZTSe) thin films and CZTSe solar cells prepared on Mo substrate, and on transparent oxide layers including SnO 2 :F (FTO) layer, and In 2 O 3 :Sn (ITO) layer. The resultant CZTSe thin film is characterized by X-ray diffraction (XRD), secondary ion mass spectroscopy (SIMS), field emission scanning electron microscope (FESEM), and photoluminescence (PL), and is subsequently fabricated into CZTSe solar cell. The characterization measurements have unveiled that, different substrate material can affect the diffusion of sodium and zinc, hence alters the distribution of ZnSe, surface morphology and crystalline structure of the CZTSe thin film. In comparison, FTO shows superior stability among Mo substrate and ITO substrate during high temperature fabrication process for CZTSe thin film solar cells. For weatherability test of the three CZTSe solar cells with different substrates, all of the three devices have also been exposed to damp heat damage. Test results shows the least efficiency decline on the CZTSe solar cell with FTO substrate after damp heat damage, suggesting that the CZTSe solar cell with FTO substrate is the most resistive to damp heat weathering. The CZTSe solar cell with Mo substrate can be deteriorated at Mo substrate layer and shows more drastic efficiency decrease. The comparison reflects a high potential in CZTSe solar cell for the next generation photovoltaic applications, such as see-through solar cells and building-integrated photovoltaic (BIPV). [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we report the studies on the hetero-epitaxial growth of wurtzite indium nitride (InN) thin films on oxide buffer layer by RF metal-organic molecular beam epitaxy (RF-MOMBE) system. Oxide buffer layer was pre-sputtered using RF sputtering technique. The structural properties and surface morphology were investigated by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). We also investigated the optical properties by temperature-dependence photoluminescence (PL). Near-infrared emission peak centered at 0.75eV was observed from PL measurement. The irregular and asymmetric PL line shape was caused by absorbed moisture and surface electron accumulation in InN films. According to the fitting results of PL spectra measured at 20K, we could estimate the bandgap and Fermi level is 0.65eV and 113meV, which confirm to previous reports. Our results reveal that the oxide thin film could be a suitable buffer layer for engineering the growth of InN on sapphire wafer, and it might be also applicable for other lattice-mismatched III-V hetero-epitaxial systems. [Copyright &y& Elsevier]

Abstract: We have investigated the effects of III/V ratio on the properties of InN films grown on sapphire substrates with oxide buffer by metalorganic molecular-beam epitaxy. The structural, optical and electrical properties of the InN films were investigated by X-ray diffraction, scanning electron microscopy, Hall-effect and temperature-dependent photoluminescence (PL) measurements. Near-infrared emission peaks between 0.74 and 0.78eV were observed. On increasing the III/V flux ratio, the PL emission peak red-shifted that is related to the reduction in carrier concentration. In addition, the PL spectra show an abnormal behavior with increase in temperature. The temperature-dependence PL spectra exhibit blue-shift as the temperature increased up to 150K and then red-shift, reflecting a competition between the blue-shift induced by thermal screening and the red-shift induced by electron–phonon interaction. [Copyright &y& Elsevier]

The thermochromic properties of vanadium dioxide (VO 2) hold great promise for applications in smart glass windows. VO 2 films exhibit a high phase transition temperature (T c), low visible transmission (T lum), and low solar modulating ability (ΔT sol), making them inadequate for the requirements of smart glass windows. While some improvement in VO 2 film performance can be achieved through single-element doping, these limited enhancements still fall short of ideal results. Therefore, there is a pressing need for the improvement of VO 2 films. In this study, we utilized the sol-gel method to prepare VO 2 samples simultaneously doped with three elements: W, Sn, and Zr. Microscopic characterization confirmed the successful incorporation of these elements. Optical measurements, including ultraviolet–visible–near-infrared spectroscopy, were conducted to assess the optical properties of the films. Ultimately, outstanding T lum (69%) and ΔT sol (14%) were achieved, along with an appropriate T c (27.6 °C). Energy consumption simulations were performed using the EnergyPlus model with experimental data, revealing that compared to conventional glass, VO 2 glass reduces total cooling energy consumption by 9.8%. In comparison to previous work, the multi-element-doped films push the performance limits of VO 2 films, offering a viable approach for fabricating superior VO 2 smart glass windows. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: In this study, we discussed the effects of growth parameters on the structural and optical properties of Al-doped zinc oxide (AZO) deposited at room temperature by radio-frequency magnetron sputtering. The AZO films have been characterized in detail using X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, Hall-effect measurement system and UV–visible spectrophotometer. It was found that the morphological, structural, electrical and optical properties of AZO films are greatly dependent on sputtering power. Collision between sputter species and surface morphology play important roles in optoelectrical properties of AZO films. According to our experimental results, the AZO films can be used in versatile devices to meet various requirements. [Copyright &y& Elsevier]

Abstract: This work reports on the heteroepitaxial growth of wurtzite indium nitride (InN) thin films on highly orientated n-ZnO buffer layer by RF metal-organic molecular beam epitaxy (RF-MOMBE) system. Highly orientated n-ZnO buffer layers were pre-sputtered using RF co-sputtering. We investigated the surface morphology and crystal structure properties by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), respectively. XRD pattern shows InN films were hexagonal wurtzite structure with preferential c-axis orientation. Electrical properties such as carrier concentration and mobility were performed by Hall measurement at room temperature. Particularly, the InN has high growth rate of 1.5μm/h. SEM images also reveal the InN surface become rough as increasing the flow rate of trimethylindium (TMI) vapor. Meanwhile, the carrier mobility decrease at higher TMI flow rate. The phenomena probably originate from surface imperfection by excess In incorporation in the films. These results indicate that the high-quality buffer layer is essential for engineering the growth of InN on silicon wafer, and it might be also applicable for other lattice-mismatched III–V heteroepitaxial systems. [Copyright &y& Elsevier]