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This study utilized a postdeposition sulfurization method to produce thin films of the Cu2SnSnS4 (CZTS) absorber layer. Initially, metal precursors were deposited onto a tin oxide‐coated substrate through thermal evaporation. Subsequently, sulfurization occurred in a mixed environment of sulfur vapor and argon gas. The sulfurization temperature was set at 500°C for a duration of 30 min. During the sulfurization process, the facile evaporation of tin compounds could lead to a deviation in the atomic ratio within the absorber layer and potentially result in the attachment of secondary phases to the surface of the absorber layer. Therefore, this study employed a multilayered metal precursor structure (with a constant total thickness for each metal and nonmetal sulfides as precursors) for sulfurization. This method effectively suppressed the formation of secondary phases, including ZnS within the absorber layer and SnS2 on the surface. From the quantification results, the ratio of ZnS to CZTS signal intensity decreased from 0.52 to 0, while the ratio of SnS2 to CZTS signal intensity dropped from 1.2 to 0. Additionally, the efficiency increased to 2.79%. In summary, this research introduced a novel preparation method to enhance the quality of CZTS films. The modification to a multilayered metal precursor structure reduced the evaporation of tin compounds, consequently minimizing the generation of secondary phases. [ABSTRACT FROM AUTHOR]

In Cu2ZnSnS4 (CZTS) solar cells, it is crucial to suppress the generation of and remove the SnS2 secondary phase to improve the solar cell characteristics, as the SnS2 secondary phase affects the barrier for carrier collection and diode characteristics of the device. In this study, the nano-metallic precursor was modified to effectively suppress the generation of the SnS2 secondary phase on the surface and simultaneously improve the uniformity and quality of the thin film. The CZTS bifacial solar cells prepared via the proposed method exhibited significantly improved junction-rectifying characteristics, as the efficiency was improved to 1.59%. The proposed method to figurremove SnS2 is effective, simple, and environmentally friendly. [ABSTRACT FROM AUTHOR]

We found the dependence of luminescence efficiency on Er[sup 3+] concentration and sintering temperature in the Er-doped Ba[sub 0.7]Sr[sub 0.3]TiO[sub 3] (BST) thin films is governed by crystallinity and ion-ion interaction. X-ray diffraction and Raman studies of the sol-gel prepared samples show that the BST polycrystalline phase occurred when the sintering temperature reaches 700°C, whereas, it becomes worse for temperature above 700°C resulting from phase separation and the Er[sup 3+] concentration exceeding 3 mol % due to charge compensation mechanism. The observed green emission reaches maximum at sintering temperature 700°C and 3 mol % Er[sup 3+] ions concentration. We also showed the Er dopant does not affect the dielectric property of BST thin films in C-V measurement and the Ba[sub 0.7]Sr[sub 0.3]TiO[sub 3]films doped with Er[sup 3+] ions may have potential use for electroluminescence devices. [ABSTRACT FROM AUTHOR]

In this work, aiming at developing a rapid and environmental-friendly process for fabricating CuInGaSe (CIGS) solar cells, we demonstrated the one-step selenization process by using selenium vapor as the atmospheric gas instead of the commonly used HSe gas. The photoluminescence (PL) characteristics indicate that there exists an optimal location with superior crystalline quality in the CIGS thin films obtained by one-step selenization. The energy dispersive spectroscopy (EDS) reveals that the Ga lateral distribution in the one-step selenized CIGS thin film is intimately correlated to the blue-shifted PL spectra. The surface morphologies examined by scanning electron microscope (SEM) further suggested that voids and binary phase commonly existing in CIGS films could be successfully eliminated by the present one-step selenization process. The agglomeration phenomenon attributable to the formation of MoSe layer was also observed. Due to the significant microstructural improvement, the current-voltage ( J- V) characteristics and external quantum efficiency (EQE) of the devices made of the present CIGS films have exhibited the remarkable carrier transportation characteristics and photon utilization at the optimal location, resulting in a high conversion efficiency of 11.28%. Correlations between the defect states and device performance of the one-step selenized CIGS thin film were convincingly delineated by femtosecond pump-probe spectroscopy. [ABSTRACT FROM AUTHOR]

A novel scheme for hybridizing inkjet-printed thin film Cu(In,Ga)Se2 (CIGS) solar cells with self-assembled clusters of nanocrystal quantum dots (NQDs), which provides a 10.9% relative enhancement of the photon conversion efficiency (PCE), is demonstrated. A non-uniform layer of NQD aggregates is deposited between the transparent conductive oxide and a CdS/CIGS p-n junction using low cost pulsed-spray deposition. Hybridization significantly improves the external quantum efficiency of the hybrid devices in the absorption range of the NQDs and in the red to near-IR parts of the spectrum. The low wavelength response enhancement is found to be induced by luminescent down-shifting (LDS) from the NQD layer, while the increase at longer wavelengths is attributed to internal scattering from NQD aggregates. LDS is demonstrated using time-resolved spectroscopy, and the morphology of the NQD layer is investigated in fluorescence microscopy and cross-sectional transmission electron microscopy. The influence of the NQD dose on the PCE of the hybrid devices is investigated and an optimum value is obtained. The low costs and limited material consumptions associated with pulsed-spray deposition make these flexible hybrid devices promising candidates to help push thin-film photovoltaic technology towards grid parity. [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]

Wurtzite InN films were prepared on a 6H-SiC substrate by a self-designed plasma-assisted metal-organic molecular-beam epitaxy system without a buffer layer. In this article, the authors investigate the structural and optical properties of InN films grown on a 6H-SiC substrate. The crystallinity and microstructure of the thin film were further characterized by x-ray diffraction (XRD), field-emission scanning-electron microscopy, and transmission-electron microscopy. Electrical and optical properties were evaluated by Hall and photoluminescence (PL) measurements. XRD results indicate that InN film grown at 500 °C is epitaxially grown along the c-axis orientation. The two-dimensional growth mode is clearly shown in scanning-electron microscope images. Room-temperature PL spectra show that the emission peak is located at ∼0.83 eV due to the Burstein-Moss effect. In addition, the crystalline InN samples crack and peel away from the substrate at elevated growth temperature. This phenomenon may be attributed to lattice mismatch and grain coalescence while increasing the growth temperature. The narrow window of the growth temperature plays an important role in engineering the InN epitaxial growth. [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]

Abstract: Highly preferential -axis orientation ZnO thin films on Si(100) and quartz substrates have been achieved by the sol–gel method. Structural investigation including surface morphology and microstructure was carried out by XRD, SEM and AFM measurements. Also, optical properties were determined by photoluminescence, ellipsometry and UV–VIS spectrum analyses. XRD results indicated that an extremely sharp (002) peak will dominate under optimum annealing-treatment condition. Moreover, thin film quality and the morphology were improved by annealing treatment. The SEM images show that the grain sizes increased with increasing annealing temperature up to 750 ∘C, where the particle size was about 50 nm. Photoluminescence spectra revealed two main peaks centered at about 380 nm and 520 nm, corresponding to the band-edge and defect-related emission. The variation in UV emission intensity was attributed to the competition between the excitonic and nonradiative recombination. It was proposed that annealing temperature plays a key role in the formation of defects, which is strongly related to the nonradiative recombination centers. In addition, optical transmittance spectra demonstrated that these films are very transparent (∼90%) in the range of 380–800 nm wavelength, and optical band-gap was determined accordingly. The impact of the thermal treatment on the structural and optical properties was discussed in detail. [Copyright &y& Elsevier]

In this study, a radio-frequency magnetron sputter system was used to deposit Al2O3 doped ZnO (AZO) thin films at room temperature, and the soda lime glass (SLG) substrates were placed at different zones relative to the center of the sample holder under the target. The samples were then analyzed using an X-ray diffractometer, Hall-effect measurement system, UV-visible spectrophotometer, and X-ray photoelectron spectroscopy. It was found that the electrical, structural, and optical properties of AZO films strongly depend on the target racetrack. The AZO thin film grown at a location outside the racetrack not only has the most suitable figure of merit for transparent conductive films, but also retains the least residual stress, which makes it the most suitable candidate for use as a CZTSe transparent conductive layer. When applied to CZTSe solar cells, the photoelectric efficiency is 3.56%. [ABSTRACT FROM AUTHOR]

• 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]

The influence of annealing on the AgGaS2 films grown by pulsed laser deposition has been investigated. The X-ray diffraction results show the AgGaS2 films were found with preferential orientation (1 1 2) normal to the surface and silver droplets were diminished after the post-annealing. Photoluminescence (PL) measurements reveled the exciton energy is slightly red shifted that is possibly due to the thermal strain effect. The binding energy of the shallow donors is ∼28 meV determined from temperature dependent PL spectra. In addition, the A-exciton and the B/C-exciton could be observed in the transmittance spectra at room temperature. [Copyright &y& Elsevier]

• 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]