电沉积法制备铜锌锡硫薄膜概述

Cu_2ZnSnS_4(CZTS)为锡黄锡矿结构的四元化合物,其禁带宽度为1.45 e V,与半导体太阳能电池所要求的最佳禁带宽度(1.5 eV)十分接近;该材料与目前在薄膜太阳能电池领域表现出色的黄铜矿结构的CIGS(铜铟镓硒)材料具有相似的晶体结构,且CZTS有着很好的光电性能,组成元素在地球上含量丰富,安全无毒和环境友好,因而成为太阳能电池吸收层的最佳候选材料之一。介绍了Cu_2ZnSnS_4(CZTS)薄膜材料的结构特性和光学特性,总结了电化学沉积方法制备CZTS的研究现状。最后对CZTS目前存在的挑战和今后的研究重点进行总结并展望了将来可能的突破方向。     

A review on growth optimization of spray pyrolyzed Cu2ZnSnS4 chalcogenide absorber thin film

The progress of solar cell technology in the development of clean and economic quaternary compound copper zinc tin sulfide (CZTS)‐based absorber thin films using the spray pyrolysis technique are presented in this review. CZTS (Cu₂ZnSnS₄) is the only potential competitor for the existing solar thin film absorbing materials owing to its environment‐friendly Earth abundant constituents. Even though different nonvacuum thin film technologies have been developed for the large area fabrication of this nontoxic absorber material, spray pyrolysis technique offers more versatility in changing the process parameters which has a direct impact on the cell efficiency. It can be used for depositing a wide variety of materials even with complex composition with good crystallinity, and the method has the advantage of being flexible and straightforward to design and can be quickly adopted for extensive area deposition. A survey on the effects of experimental conditions as well as the nature of precursors on the structural, morphological, electrical, and optical properties on the spray pyrolyzed CZTS thin films is discussed in detail. This analysis certainly could provide a potential to obtain new insights in the fabrication of high‐efficiency CZTS‐based solar cells and to launch it into the commercial market to satisfy the ever‐growing future energy demand.     

Surface modification of semiconductor photoelectrode for improved solar cell performance

The investigation is focused on the synthesis of nanostructured TiO₂–CuO admixed photoelectrode and its use as a photoelectrode of high-efficiency PEC solar cells for hydrogen production. TiO₂, in the nanostructured form, has been prepared by hydrolysis of titanium(IV) isopropoxide solution. An improvement in the nanostructured TiO₂ photoelectrode carried out in the present work corresponds to admixing CuO to improve the spectral response. In the present study, photo-electrochemical (PEC) and hydrogen evolution characteristics of new types of ns-TiO₂–CuO admixed/Ti septum-based semiconductor septum photo-electrochemical (SC-SEP PEC) solar cell has been studied. The CuO admixed ns-TiO₂ exhibited a high photocurrent and photovoltage of 18.6 mA/cm² and 680 mV, respectively. The ns-TiO₂–CuO electrode exhibited a higher hydrogen gas evolution rate of 14.00 l/h m².     

Phase transformation of solution‐based p‐type Cu2ZnSnS4 thin film: applicable for solar cell

In this present work, quaternary Cu₂ZnSnS₄ thin films were deposited on commercial glass substrates at room temperature by a novel solution growth dip coating technique. The influence of annealing temperature of the films at 300 °C in a hot air furnace without the presence of any inert gas, on structural, optical, and electrical properties was investigated and discussed. The structural analyses were analyzed by X‐ray diffraction and Raman spectroscopy, whereas optical and electrical properties were analyzed by means of ultra violet infrared (UV‐ViS/IR). The results analyzed showed that there exists a phase formation from orthorhombic to kesterite crystal structure with an increase in optical bandgap and an optical conductivity, with an increase in annealing temperature. The electrical conductivity was observed of the order of 10^?6 ohm cm^?1. Copyright © 2015 John Wiley & Sons, Ltd.     

An efficient tandem photoelectrochemical cell composed of FeOOH/TiO2/BiVO4 and Cu2O for self-driven solar water splitting

An integrated solar water splitting tandem cell without external bias was designed using a FeOOH modified TiO₂/BiVO₄ photoanode as a photoanode and p-Cu₂O as a photocathode in this study. An apparent photocurrent (0.37 mA/cm² at operating voltage of +0.36 V_RHE) for the tandem cell without applied bias was measured, which is corresponding to a photoconversion efficiency of 0.46%. Besides, the photocurrent of FeOOH modified TiO₂/BiVO₄–Cu₂O is much higher than the operating point given by pure BiVO₄ and Cu₂O photocathode (∼0.07 mA/cm² at +0.42 V_RHE). Then we established a FeOOH modified TiO₂/BiVO₄–Cu₂O two-electrode system and measured the current density-voltage curves under AM 1.5G illumination. The unassisted photocurrent density is 0.12 mA/cm⁻² and the corresponding amounts of hydrogen and oxygen evolved by the tandem PEC cell without bias are 2.36 μmol/cm² and 1.09 μmol/cm² after testing for 2.5 h. The photoelectrochemical (PEC) properties of the FeOOH modified TiO₂/BiVO₄ photoanode were further studied to demonstrate the electrons transport process of solar water splitting. This aspect provides a fundamental challenge to establish an unbiased and stabilized photoelectrochemical (PEC) solar water splitting tandem cell with higher solar-to-hydrogen efficiency.     

Rapid microwave synthesis of Cu2ZnSnS4 nanocrystals for photovoltaic junctions

Copper zinc tin sulfide ( CZTS) nanocrystal (NC) ink was prepared using thiourea as sulphur source by microwave assisted process. Thin films fabricated by doctor blading technique were then used to analyze the structure and morphology of the CZTS NCs. Variation in the properties of the NCs with varying Zn content in the precursor solution was studied. A Zn/Sn ratio of 1.4 with a Cu/(Sn + Zn) ratio of 0.8 in the starting solution was identified as an optimum compositional ratio to get good optoelectronic properties. Synthesis of CZTS NCs was done in ethylene glycol solvent and in a solvent which is a 1:1 mixture of isopropanol and poly ethylene glycol. The films developed from the latter ink showed better morphological and optoelectronic properties. CZTS thin films show absorption coefficient of the order of 10⁴ cm^?1 and optical band gap of 1.5 eV. The electrical resistivity was found to be 2.5 × 10² Ω/cm and hole mobility 0.051 cm²/ (Vs). Glass/FTO/CdS/CZTS multilayer structures were fabricated to form P‐N junctions. A knee voltage of 0.8 V from the I‐V characteristics of the PN junction indicates that a good V_oc can be expected from a solar cell constructed with CZTS ink as absorber layer.     

Enhancement of photoconversion efficiency and light harvesting ability of TiO2 nanotube-arrays with Cu2ZnSnS4

We report an underpotential deposition (UPD) route of Cu₂ZnSnS₄/TiO₂ nanotube arrays (TiO₂-NTAs) in which the Kesterite (Cu₂ZnSnS₄) was employed as a sensitizer to enhance the photoconversion efficiency of the TiO₂-NTAs. Cu₂ZnSnS₄ was simultaneously coated on TiO₂-NTAs by depositing its constituent metals from the precursor ions via electrochemical atomic layer deposition (EC-ALD) and subsequent annealing. The detailed synthesis process, the surface morphology, crystalline structure, photoelectrochemical properties and hydrogen production rate of the as-prepared Cu₂ZnSnS₄/TiO₂-NTAs were discussed. Thickened TiO₂ nanotubes were observed, suggesting that the Cu₂ZnSnS₄ coating was about 5 ± 0.5 nm. The results showed that the light harvesting of TiO₂-NTAs has an obvious improvement after sensitizing them with Cu₂ZnSnS₄. In comparison with pure TiO₂-NTAs, a two-fold increment in photoconversion efficiency was achieved using the composite of Cu₂ZnSnS₄/TiO₂-NTAs. The novel photoanode of CZTS/TiO₂ NTAs achieved a maximum hydrogen generation rate of 49 ml h^?1 cm^?2.     

Progress in chalcopyrite compound semiconductor research for photovoltaic applications and transfer of results into actual solar cell production

This paper gives an overview of the main research directions in chalcopyrite material research and the application of results for the improvement and fabrication of solar cells. So far the copper indium gallium sulphur selenide material family is the base for the highest efficiency thin-film solar cells and the most advanced in terms of actual commercialisation. The transfer of research results into actual production from its early stage and the development of the chalcopyrite thin-film solar cell industry are sketched. The last part of the review shortly describes a number of current industrial players involved in the manufacturing of chalcopyrite solar cells.     

Fabrication of Cu2ZnSnS4 films by sulfurization of Cu/ZnSn/Cu precursor layers in sulfur atmosphere for solar cells

Cu₂ZnSnS₄ (CZTS) absorbers were grown by sulfurization of Cu/ZnSn/Cu precursors in sulfur atmosphere. The reaction mechanism of CZTS formation from the precursor was analyzed using XRD and Raman spectroscopy. The films with a single phase CZTS were formed at 560 and 580 °C by sulfurization for 30 min. The film grown at 560 °C showed bi-layer morphology with grooved large grains on the top and dense small grains near the bottom of the film. On the other hand, the film grown at 580 °C showed large grains with grooves that are extended from surface top to bottom of the film. The solar cell fabricated with the CZTS film grown at 560 °C showed the best conversion efficiency of 4.59% for 0.44 cm² with V_oc=0.545 V, J_sc=15.44 mA/cm², and FF=54.6. We found that further improvement of the microstructure of CZTS films can increase the efficiency of CZTS solar cells.     

Advanced buried contact solar cell structure

This paper discusses the feasibility of overcoming the recombination losses associated with the rear metal contact of buried contact solar cells. The buried contact locally diffused rear (BCLD) structure has been proposed as one of the structures that will limit the rear surface recombination and improve on cell efficiency. The one-dimensional (1D) modeling, using PC-1D has given an energy conversion efficiency of close to 21% with all the possible losses taken into account. This means that by proper optimization of the processing steps energy conversion efficiency in excess of 19% would be achieved on large-area cells.     

Template synthesis of porous hierarchical Cu2ZnSnS4 nanostructures for photoelectrochemical water splitting

Environmentally friendly and low-cost Cu₂ZnSnS₄ (CZTS) is a promising light absorber for photoelectrochemical (PEC) hydrogen production from water splitting due to the earth-abundant elements, high absorption coefficient, and narrow bandgap. Herein, the hierarchical CZTS film with porous nanostructures was successfully synthesized by a template method. The hierarchical CZTS film was composed of flower-like particles, which were assembled with thin CZTS nanosheets. Macropores were generated owing to the aggregation of flower-like spheres, and mesopores were formed from the stacking of CZTS nanosheets. Compared to the dense CZTS film, the porous hierarchical CZTS film showed a much higher PEC property for water splitting. The improved performance could be attributed to three merits of the porous hierarchical morphology: enhanced light absorption, improved charge separation and transfer, and enlarged electrochemically active surface area. This study provides a useful idea to design efficient semiconductor photoelectrodes for water splitting with delicately controlled morphology.     

Technical note An approximation to solar cell equation for determination of solar cell parameters

An approximation was applied to a solar cell equation to eliminate reverse saturation current. I–U curves obtained from the approximated equation were fitted to experimentally measured data by using the iteration technique. All instrumentation errors were taken into account in the fitting procedure. The Filling Factor (FF) and the series resistance (R_s) appeared to be important for fitting accuracy. The fitting procedure was repeated for different illuminations and solar cell temperatures.     

Modeling and simulation of solar cells quantum well based on SiGe/Si

In recent years, the development of quantum well solar cells QWSCs (Quantum Well Solar Cells) has generated a great deal of interest. These configurations have shown good promise to optimize the low conversion efficiency of conventional solar cells because of the high rate of absorption losses present in them. In this work, we are interested in modeling and simulation of two different structures of solar cells, a simple solar cell based on silicon Si and a quantum well solar cell SiGe/Si. When a solar cell is compared to 80 quantum well layers of Si_0.8Ge_0.2with a pin solar cell based on Si. The short circuit current J_sc increases from 23.55 to 37.48 mA/cm² with a relative increase of 59.15% found. In addition, the limit of the absorption band of the lower energy photons extends from 1100 nm to 2000 nm.     

Simple size-controlled fabrication of Zn2SnO4 nanostructures and study of their behavior in dye sensitized solar cells

Zn₂SnO₄ nanostructures were obtained via facile and rapid co-precipitation approach in presence of amines with different long chain as a novel basic and capping agents. The effect of different amines such as NH₃, ethylenediamine, triethylenetetramine, tetraethylenepentamine on the size of Zn₂SnO₄ nanostructures were investigated. The results demonstrated that applying the appropriate amount of organic amine could be effective in particle size control. The obtained nanostructure products were specified by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectra, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX) and ultraviolet–visible (UV–vis) spectroscopy. Dye sensitized solar cells (DSSC) were created by the constructed electrodes as working electrode and then were studied by current density–voltage (J–V) curve. It was found that incorporating of TiO₂ nanoparticles to optimized Zn₂SnO₄ nanostructures has significant role on the constructed DSSCs photovoltaic properties.     

12.6% efficient CdS/Cu(In,Ga)S2-based solar cell with an open circuit voltage of 879 mV prepared by a rapid thermal process

A Cu(In,Ga)S₂-based solar cell with a confirmed efficiency of 12.6% together with an open circuit voltage of 879 mV, prepared from sputtered metals subsequently sulfurized using rapid thermal processing in sulfur vapor, is reported. The performance of the new cell is superior to those obtained previously with multi-source evaporated absorbers. We show that by carefully adjusting the temperature profile, good absorber properties could be transferred from a long process to a rapid thermal process. The improved efficiency is due to an appropriate degree of gallium diffusion toward the surface, which could be achieved despite the short sulfurization time. Absorber and solar cell characteristics are presented.     

Low temperature polycrystalline silicon: a review on deposition, physical properties and solar cell applications

This review article gives a comprehensive compilation of recent developments in low temperature deposited poly Si films, also known as microcrystalline silicon. Important aspects such as the effect of ions and the frequency of the plasma ignition are discussed in relation to a high deposition rate and the desired crystallinity and structure. The development of various ion energy suppression techniques for plasma enhanced chemical vapour deposition and ion-less depositions such as HWCVD and expanding thermal plasma, and their effect on the material and solar cell efficiencies are described. The recent understanding of several important physical properties, such as the type of electronic defects, structural effects on enhanced optical absorption, electronic transport and impurity incorporation are discussed. For optimum solar cell efficiency, structural considerations and predictions using computer modelling are analysed. A correlation between efficiency and the two most important process parameters, i.e., growth rate and process temperature is carried out. Finally, the application of these poly Si cells in multijunction cell structures and the best efficiencies worldwide by various deposition techniques are discussed.     

Effect of thermal conductivity on the efficiency of single crystal silicon solar cell coated with an anti-reflective thin film

This paper presents the working of a single crystal silicon solar cell coated with a zinc oxide thin film. Single crystalline silicon is the absorber of incident solar radiation, while the zinc oxide film - an optically black film, offers optical improvement. Thermal conductivity measurements were made using the transient line heat source (TLHS) method, where the heat source is placed against the inner and outer surfaces of the solar cell to provide heating and to sense the temperature changes at the same time. In the temperature range 297-360 K, values of thermal conductivities for the silicon material, zinc oxide and the surrounding air at atmospheric pressure were found to be 0.884-1.26 × 10³ Wm⁻¹ K⁻¹. By comparing the calculation results for the highest and lowest values of thermal conductivities, against the solar cell output, the value of collection efficiency for photo-generated carriers in the cell is seen to be varied. At moderate values of thermal conductivity - corresponding to mid temperatures, the cell output power and hence efficiency is observed to be high.     

Investigation of influence of redox species on the interfacial energetics of a dye-sensitized nanoporous TiO2 solar cell

The photoelectrochemical behaviours of dye-sensitized nanoporous TiO₂ solar cells are studied under influences of light intensity, redox couple concentration, temperature, different cations and water in the nonaqueous solution. The value of the ideality factor of dyed nanoporous TiO₂ film is determined to be 1.08. The diode behaviour of the dyed nanoporous TiO₂ film approaches an ideal rectification characteristic. The rate of the reaction of I₃⁻ with the electron at the surface of the dyed TiO₂ electrode is of first order, like the reduction of I₃⁻ at the Pt electrode. By analysis of the relationship of the photovoltage with temperature, the activation energies of the back-reaction for dyed nanoporous TiO₂ electrodes in different solutions are obtained. Cations of different kinds and water are found to modify the interfacial properties of the dyed TiO₂ electrode. Finally, a quantitative relationship between the short-circuit photocurrent and the light intensity, the I₃⁻ concentration is obtained and used to explain the diffusion-controlled photocurrent. The corrected diffusion coefficient of I₃⁻ is 5.4–6.2×10⁻⁶ cm²/s in a CH₃OCH₂CN solution.     

a-C:H absorber layer for solar cells matched to solar spectrum

An a-C:H-based absorber layer for photovoltaic application was fabricated by a DC PECVD. The stepped voltage biasing of the deposition process makes it possible to tailor the bandgap of the manufactured layers and match them to the solar spectrum. Such system can be used as intrinsic layer in p–i–n solar cells as well as in converter solar cells.     

Optimization of fabrication process of high-efficiency and low-cost crystalline silicon solar cell for industrial applications

The process conditions for a high-efficiency and low cost crystalline silicon solar cell were optimized. Novel approaches such as wafer cleaning and saw -damage removal using 0.5 wt% of 2,4,6-trichloro-1,3,5-triazine, silicon surface texturing with optimized pyramid heights (∼5 μm), and a third step of drive-in after phosphosilicate glass (PSG) removal followed by oxide removal were investigated. A simple method of chemical etching adopted for edge isolation was optimized with edge etching of 5-10 μm, without any penetration of chemicals between the stacked wafers. The conversion efficiency, open-circuit voltage, short-circuit current, and fill factor of the cell fabricated with the optimized process were a maximum of 17.12%, 618.4 mV, 5.32 A, and 77% under AM1.5 conditions, respectively.