Cu2ZnSnS4 (CZTS) thin films with fine control over composition and pure phase were fabricated by sulfurization of co-electroplated Cu–Zn–Sn–S precursors. We have systematically investigated that the concentration of Cu(II) ions can influence the properties of CZTS absorber layers and the photovoltaic performance of the resulting solar cell devices. The results indicate that an increase in Cu(II) concentration almost linearly increases the Cu content in the final CZTS thin films, greatly enhances the (112) preferred orientation, significantly improves the crystallinity of the absorber layer, remarkably reduces the ZnS secondary phase, and hence improves their photovoltaic performance. However, a further increase in the Cu(II) concentration degrades the crystal quality of the absorber layer, and forms the CuSx secondary phase, which is quite detrimental to the device photovoltaic performance. Here we introduce a novel sputtered CdS buffer layer for the CZTS solar cells. For the first time, co-electrodeposited CZTS solar cells exceed the 7% efficiency threshold. These findings offer new research directions for solving persistent challenges of chemical bath deposition of CdS in CZTS solar cells.

A simple and cost-effective co-electrodeposition process has been demonstrated to fabricate high-performance Cu2ZnSnS4 (CZTS) photovoltaic materials with composition tunability and phase controllability. Here we report a systematic investigation of the effects of the Zn(II) concentration on the properties of CZTS thin films and thus the performance of the as-resulted solar cells. These results indicate that increasing the concentration of Zn(II) linearly increases the Zn content in the final composition of CZTS thin films, significantly improves the grain size and morphology of the absorber layers, and consequently improves their photovoltaic properties, especially the response to the medium wavelength. In contrast, further increase of the Zn(II) concentration degrades the crystal quality of the absorber layer, and more ZnS phase appears on the surface of the CZTS thin film, forming a rather rough morphology, which is harmful to the photovoltaic performance of the device. When the concentration of Zn(II) is optimized to 30 mM, a power conversion efficiency of 7.23% is achieved, which, to the best of our knowledge, is the highest efficiency for a co-electrodeposited CZTS solar cell with a sputtered CdS buffer layer to date. Our findings offer a promising alternative approach towards the industrialization of CZTS solar cell modules.

Earth-abundant material, kesterite Cu2ZnSnS4 (CZTS), demonstrates the tremendous potential to serve as the absorber layer for the bifacial thin-film solar cell. The exploration of appropriate sulfurization conditions including annealing temperature is significant to gain insight into the growth mechanism based on the substrates using transparent conductive oxides (TCO) and improve device performance. The kesterite solar absorbers were fabricated on ITO substrates by sulfurizing co-electroplated Cu–Zn–Sn–S precursors in argon diluted H2S atmosphere at different temperatures (475–550 °C) for 30 min. Experimental proof, including cross-section scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, UV–vis–NIR transmission spectrum, and Raman and far-infrared spectroscopy, is presented for the crystallization of CZTS on an ITO substrate and the interfacial reaction between the ITO back contact and CZTS absorber. The complete conversion of precursor into CZTS requires at least 500 °C sulfurization temperature. The aggressive interfacial reaction leading to the out-diffusion of In into CZTS to a considerable extent, formation of tin sulfides, and electrically conductive degradation of ITO back contact occurs at the sulfurization temperatures higher than 500 °C. The bifacial devices obtained by 520 °C sulfurization exhibit the best conversion efficiencies and open circuit voltages. However, the presence of non-ohmic back contact (secondary diode), the short minority lifetime, and the high interfacial recombination rates negatively limit the open circuit voltage, fill factor, and efficiency, evidenced by illumination/temperature-dependent J–V, frequency-dependent capacitance–voltage (C–V–f), time-resolved PL (TRPL), and bias-dependent external quantum efficiency (EQE) measurements.Keywords: indium diffusion; interfacial reaction; ITO back contact; kesterite bifacial solar cell; sulfurization temperature; tin sulfides;

Implementing bifacial photovoltaic devices based on transparent conducting oxides (TCO) as the front and back contacts is highly appealing to improve the efficiency of kesterite solar cells. The p-type In substituted Cu2ZnSnS4 (CZTIS) thin-film solar cell absorber has been fabricated on ITO glass by sulfurizing coelectroplated Cu–Zn–Sn–S precursors in H2S (5 vol %) atmosphere at 520 °C for 30 min. Experimental proof, including X-ray diffraction, Raman spectroscopy, UV–vis–NIR transmission/reflection spectra, PL spectra, and electron microscopies, is presented for the interfacial reaction between the ITO back contact and CZTS absorber. This aggressive reaction due to thermal processing contributes to substitutional diffusion of In into CZTS, formation of secondary phases and electrically conductive degradation of ITO back contact. The structural, lattice vibrational, optical absorption, and defective properties of the CZTIS alloy absorber layer have been analyzed and discussed. The new dopant In is desirably capable of improving the open circuit voltage deficit of kesterite device. However, the nonohmic back contact in the bifacial device negatively limits the open circuit voltage and fill factor, evidencing by illumination-/temperature-dependent J–V and frequency-dependent capacitance–voltage (C–V–f) measurements. A 3.4% efficient solar cell is demonstrated under simultaneously bifacial illumination from both sides of TCO front and back contacts.Keywords: back contact; bifacial thin-film solar cell; H2S sulfurization; indium substituted CZTS; interfacial reaction

In this work, a Fe-based nanocrystalline microwire of 20 mm in length and 25 μm in diameter was placed in the center of a 316 stainless steel pipe. The pipe was 500 μm in diameter and a little shorter than the microwire. A series of voltages were applied on the pipe to study the influence of the electrical field on the Giant-Magneto-Impedance (GMI) effect of the microwire. Experimental results showed that the electronic field between the wire and the pipe reduced the hysteresis of the GMI effect. The results were explained based on equivalent circuit and eddy current consumptions analysis.

The results of an experimental study of quantum correction of electron–electron interaction (EEI) to the conductivity of two-dimensional electron gas (2DEG) in an undoped Al0.26Ga0.74N/AlN/GaN heterostructure are reported. A small but significant decrease of the Hall slope with the increase of temperature was discovered. This is not due to the increase of electron concentration as temperature increases but to the EEI effect. Both diffusion and ballistic contributions of EEI to the conductivity of 2DEG were observed. As the temperature increases, the negative diffusion EEI correction to the conductivity increases in an absolute value while the ballistic EEI correction reduces to a renormalization of the transport mobility.Highlights► The electron–electron interactions are studied by magneto-transport measurements. ► The Hall slope decreases with the increase of temperature. ► The ballistic EEI correction reduces to a renormalization of the mobility. ► The diffusion EEI correction increases in absolute value with the temperature.

We have observed the weak antilocalization (WAL) and beating SdH oscillation through magnetotransport measurements performed on a heavily δδ-doped In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As single quantum well in an applied magnetic field up to 13 T and a temperature at 1.5 K. Both effects are caused by the strong Rashba spin–orbit (SO) coupling due to high structure inversion asymmetry (SIA). The Rashba SO coupling constant αα and zerofield spin splitting Δ0 are estimated and the obtained values are consistent from different analysis for this sample.

Magneto-transport measurements have been carried out on double/single-barrier-doped In0.52Al0.48As/ In0.53Ga0.47As/ In0.52Al0.48As quantum well samples from 1.5 to 60 K in an applied magnetic field up to 13 T. Beating Shubnikov–de Haas oscillation is observed for the symmetrically double-barrier-doped sample and demonstrated due to a symmetric state and an antisymmetric state confined in two coupled self-consistent potential wells in the single quantum well. The energy separation between the symmetric and the antisymmetric states for the double-barrier-doped sample is extracted from experimental data, which is consistent with calculation. For the single-barrier-doped sample, only beating related to magneto-intersubband scattering shows up. The pesudospin property of the symmetrically double-barrier-doped single quantum well shows that it is a good candidate for fabricating quantum transistors.

Magneto-transport measurements have been carried out on double/single-barrier-doped In0.52Al0.48As/ In0.53Ga0.47As/ In0.52Al0.48As quantum well samples from 1.5 to 60 K in an applied magnetic field up to 13 T. Beating Shubnikov–de Haas oscillation is observed for the symmetrically double-barrier-doped sample and demonstrated due to a symmetric state and an antisymmetric state confined in two coupled self-consistent potential wells in the single quantum well. The energy separation between the symmetric and the antisymmetric states for the double-barrier-doped sample is extracted from experimental data, which is consistent with calculation. For the single-barrier-doped sample, only beating related to magneto-intersubband scattering shows up. The pesudospin property of the symmetrically double-barrier-doped single quantum well shows that it is a good candidate for fabricating quantum transistors.

A simple and cost-effective co-electrodeposition process has been demonstrated to fabricate high-performance Cu2ZnSnS4 (CZTS) photovoltaic materials with composition tunability and phase controllability. Here we report a systematic investigation of the effects of the Zn(II) concentration on the properties of CZTS thin films and thus the performance of the as-resulted solar cells. These results indicate that increasing the concentration of Zn(II) linearly increases the Zn content in the final composition of CZTS thin films, significantly improves the grain size and morphology of the absorber layers, and consequently improves their photovoltaic properties, especially the response to the medium wavelength. In contrast, further increase of the Zn(II) concentration degrades the crystal quality of the absorber layer, and more ZnS phase appears on the surface of the CZTS thin film, forming a rather rough morphology, which is harmful to the photovoltaic performance of the device. When the concentration of Zn(II) is optimized to 30 mM, a power conversion efficiency of 7.23% is achieved, which, to the best of our knowledge, is the highest efficiency for a co-electrodeposited CZTS solar cell with a sputtered CdS buffer layer to date. Our findings offer a promising alternative approach towards the industrialization of CZTS solar cell modules.