High-efficiency Cu(In,Ga)Se2 thin-film solar cells with a novel In(OH)3:Zn buffer layer

We propose the inclusion of a novel In(OH)₃:Zn²⁺ buffer layer for fabricating high-efficiency CIGS solar cells. This buffer layer was deposited using a solution consisting of ZnCl₂, InCl₃·4H₂O, and thiourea. The In(OH)₃:Zn²⁺ films showed high resistivities of 2.1×10⁸ Ω cm and transmittance of above 95% in the visible range. We expected two effects due to this new buffer layer: first is the formation of a passivation layer on the CIGS surface and the second is Zn-doping into CIGS layer, resulting in the formation of a buried junction. A cell efficiency of 14.0% (V_oc: 0.575 V, J_sc: 32.1 mA/cm², FF: 0.758) was achieved by using an In(OH)₃:Zn²⁺ buffer layer, without the light soaking effect.     

Electrophoretic behavior of solvothermal synthesized anion replaced Cu2ZnSn(SxSe1-x)4 films for photoelectrochemical water splitting

Quaternary Cu₂ZnSn(S_xSe_1-x)₄ (CZT(S_xSe_1-x)₄) compounds have drawn a great deal of attention for being used in the fabrication of optoelectronic devices such as solar cells, photocatalysts, and photoelectrochemical water splitting. However, one major challenge facing the utilization of this material is to reduce the production cost of synthesis and fabrication of high quality CZT(S_xSe_1-x)₄ films. In the present study, a facile and beneficial solvothermal route has been reported for synthesis of CZT(S_xSe_1-x)₄ compounds. The process of electrophoretic deposition (EPD) of synthesized CZT(S_xSe_1-x)₄ nanoparticles, is systematically compared with each other in order to obtain high quality films with appropriate porosity. The XRD patterns, EDS and Raman spectra confirm the formation of CZT(S_xSe_1-x)₄ phases with no trace of impurities and appreciable crystallinity and also with near stoichiometry composition in all the samples. The obtained particle size for CZTS, CZTSSe and CZTSe samples was in the range of 50–100 nm and also for some agglomerate particles was in the range of 500 nm to 2 μm. Based on the obtained results for thin films prepared using EPD in the present study, the best EPD parameters for each CZTS, CZTSe and CZTSSe samples with 120 V and 5 min as applied voltage and deposition time were reported as the best samples. The obtained photocurrent-potential and current-time curves of CZT(S_xSe_1-x)₄ thin film samples demonstrate that the photocurrents of each CZTS, CZTSe, CZTSSe thin films, are different in the range of ?2.1 to ?6 mA/cm² and also the CZTS and CZTSe samples show a detectable current under the exposure of sunlight that can have an appropriate stability for 3000 s but the CZTSSe sample showed a stable photocurrent just for 2000 s. According to the mentioned results in this study, the CZTS and CZTSe samples can potentially be suitable candidates for further applications.     

High-temperature electrochemical performance of Al-α-nickel hydroxides modified by metallic cobalt or Y(OH)3

Al-α-Ni(OH)₂ microspheres are modified with metallic Co and Y(OH)₃, respectively, in order to improve the high-temperature electrochemical performance. The microstructure, morphology, and surface chemical state of the as-prepared and the modified Al-α-Ni(OH)₂ microspheres are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), respectively. Metallic cobalt nanoparticles are distributed on the nanosheets of the microsphere edges. The existence of metallic Co and Y(OH)₃ can be further verified from ICP and XPS results. The effect of metallic Co or Y(OH)₃ on high-temperature performance of the Al-α-Ni(OH)₂ microspheres is measured by galvanostatic charge–discharge experiments and cyclic voltammetric (CV) measurements. The discharge capacities of the Al-α-Ni(OH)₂ microspheres, with optimized 5 wt% Co and 1 wt% Y(OH)₃, are 283.5 mAh g⁻¹ and 315 mAh g⁻¹, respectively, much higher than that of the as-prepared Al-α-Ni(OH)₂ (226.8 mAh g⁻¹) at 0.2 C and 60 °C. Furthermore, the high-rate discharge capability at high temperature can be also improved for both the modified samples.     

Electronic structure and water splitting under visible-light irradiation of Zn and Ag co-doped In(OH)ySz photocatalysts

Zinc and silver co-doped In(OH)_yS_z with nanocubic blocks morphology were prepared by a one-step hydrothermal method and their photocatalytic activities were investigated. The as-synthesized products were characterized by transmission electron microscopy (TEM), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), inductively coupled plasma (ICP) and UV–visible spectroscopy. The electron microscope observations revealed that the particle sizes of Zn-doped In(OH)_yS_z crystals were smaller than that of the non-doped In(OH)_yS_z, which accords with BET results. While Zn–Ag co-doped In(OH)_yS_z showed the nanocubic blocks with different particle sizes. The UV–vis spectra indicate that the single Zn ions doping leads to the absorbance band shifts toward lower wavelength upon increasing the Zn doping. Consequently, the band gap of In(OH)_yS_z also increases gradually with increasing the Zn doping. In contrast, an obvious red-shift is observed for Zn–Ag co-doped In(OH)_yS_z solid solution, which mainly attributed to the transition from Ag 4d + S 3p orbitals to Zn 4s + In 5s orbitals. The sample doped with 4 mol% Ag and Zn was found to have the highest activity, which is 20 times that of the In(OH)_yS_z.     

Analysis of heterointerface recombination by Zn1−xMgxO for window layer of Cu(In,Ga)Se2 solar cells

An adjustment of a conduction band offset (CBO) of a window/absorber heterointerface is important for high efficiency Cu(In,Ga)Se₂ (CIGS) solar cells. In this study, the heterointerface recombination was characterized by the reduction of the thickness of a CdS layer and the adjustment of a CBO value by a Zn_1−xMg_xO (ZMO) layer. In ZnO/CdS/CIGS solar cells, open-circuit voltage (V_oc) and shunt resistance (R_sh) decreased with reducing the CdS thickness. In constant, significant reductions of V_oc and R_sh were not observed in ZMO/CdS/CIGS solar cells. With decreasing the CdS thickness, the CBO of (ZnO or ZMO)/CIGS become dominant for recombination. Also, the dominant mechanisms of recombination of the CIGS solar cells are discussed by the estimation of an activation energy obtained from temperature-dependent current-voltage measurements.