| Energy is essential to human survival,with the consumption of fossil fuels,changing the energy structure and develop new energy sources is becoming increasingly important.Solar energy as a clean and renewable energywill become increasingly important.Sulphur Copper-Zinc-Tin(Cu2ZnSnS4,abbreviation CZTS)thin-film solar cells with high conversion efficiency,stability as well as good,are considered to be the most promising type of solar cell.The preparation method is mainly divided into vacuum and non-vacuum two-class,vacuum due to high energy consumption,low material utilization and are therefore not suitable for large-area industrialization.Non-vacuum low energy consumption,simple operation,high utilization of materials suitable for large area industrial.Electro-deposition of CZTS is in a vacuum,with simple operation,low energy consumption,low cost,there are two main steps:preparation of precursor films deposited,annealing and recrystallization to form CZTS crystals.Current research focuses on testing and debugging phase,however,means it is difficult to reveal the electrodeposition of thin film growth and internal mechanisms of crystal growth of recrystallization annealing.In experiment research in the main is through adjustment electric deposition parameter to get different of film morphology,and for film internal defects of control mechanism,particles between mutual role potential of effect lack in-depth of research,on preparation film process in the of film growth mechanism of understanding not clear,film rough morphology formed of mechanism awareness not in-depth,these internal mechanism of awareness insufficient led to test in the hard control film of thickness,structure and morphology eventually led to bad of optical performance.Annealing again crystal of research also main is regulation different of experiment parameter to get different of crystal structure,and for high temperature annealing process in the CZTS crystal of formed growth mechanism understanding not clear,Crystal of shaped nuclear characteristics,growth characteristics research is enough in-depth,these problem of research insufficient makes in test hard control crystal of components and the miscellaneous phase of produced,serious effect has CZTS crystal of structure and components,serious effect has battery eventually of conversion efficiency.Paper launched a series of studies and discussion of these issues.This thesis is divided into three parts:(1)A three-dimensional(3D)Kinetic Monte Carlo(KMC)coupled with embedded-atom method(EAM)(KMC-EAM)has been developed to simulate film growth and morphology evolution of copper layer in Cu2ZnSnS4(CZTS)precursor during electrodeposition.KMC simulation is an effective tool for researching the growth mechanism,surface micro-construction and film morphology.Themulti-body EAM potential,which was based on density functional theory,was employed to calculate the interactions among themetal atoms.As the first electrodeposition stacking layer of the precursor,the structure and morphology of the copper layer isdominant,which directly or indirectly influences the absorber property and solar cell performance.Hence,the influences of thedeposition factors,including electrolyte concentration,temperature and electrode potential,on the surface and cross-section morphologywere studied.The results demonstrate that the electrolyte temperature and potential have a more significant impact onthe film growth compared with the concentration.The lowest roughness with smoother morphology was obtained at the optimalparameters(temperature 338 K,applied potential-0.9 V and concentration 0.5 mol/L).The texture parameters,such as cluster size,and the transformation behavior were selected to describe the film growth evolution during the copper electrodeposition.The clustersize distribution was compared between optimal and original parameters,showing that optimal conditions induce the formation of asmoother film with low roughness,fewer voids,and larger clusters.The comparison between deposition events and diffusion eventsindicates that the diffusion behavior has a dominant position 'in controlling the crystal micro structure and film morphology.The filmmorphology evolution was visualized using a 3D configuration with increasing atoms,and a competing mechanism between layergrowth and island growth was proposed.(2)An Atomistic Kinetic Monte Carlo coupled with Embedded-Atom Method(AKMC-EAM)is employed to simulate film growth and morphology evolution of a Cu-Zn-Sn precursor of Cu2ZnSnS4 solar cells by single-step electrodeposition.The deposition and diffusion events of three different metallic atoms are described by the simulation.Moreover,the multi-body Cu-Zn-Sn potential is used to calculate diffusion barrier energy.The effects of process factors,including temperature and electrode potential,on the cross-section morphology and surface roughness are explored,while keeping the elemental composition ratios constant.The lowest roughness with the smoothest morphology is obtained at the optimal parameters.The distribution and transformation behavior of cluster sizes is investigated in order to describe the alloy film growth process.Furthermore,the comparison between deposition events and diffusion events reveal that deposition events depend primarily on individual deposition rates of different metallic atoms,but diffusion events are mainly dependent on the interaction of metallic atoms.The film morphology evolution is visualized by three-dimensional configuration with increasing numbers of atoms,which suggests a competing mechanism between nucleation and growth of the thin film alloy.(3):CZTS films annealing recrystallization process using Monte Carlo methods to build corresponding mathematical models for simulating the process of recrystallization.Model considering the nucleation of recrystallization process and establish the corresponding module.Simulates six different temperatures,recrystallization rate changes with time.At the same temperature and crystallization rate changes with time basic was s-shaped trend,consistent with the experimental results.In the initial phase(recrystallization rate was 0.7 before)recrystallization rates under different temperature changes little;rate of recrystallization in 07-0.95 between different temperature recrystallization difference maximum,which 1300K most recrystallization(0.89),550K rate of recrystallization(0.79);But the rate of recrystallization exceeds 0.95,recrystallization rates changed little at different temperatures.Recrystallization kinetics at six different temperatures are investigated,recrystallization kinetics curves under different temperature changes little,the temperature does not affect the dynamics of recrystallization in agreement with theoretical analysis.Recrystallization kinetics of different temperatures can be divided into three stages,the slope of the three stages respectively,1.6,0.4 and 0.5 per cent,after two stages of the dynamical process are basically the same.Simulation of slope range in the theoretical value of 2 per cent range.Simulated changes in average grain size at different temperatures,increases as the temperature increases the average grain diameter.Analysis under different temperature recrystallization microstructure evolution of grain at the same temperature as time increases,at the initial stage is a small grain,grain growing with increasing time,topography appears in large Crystal block.At the same time,the higher the temperature of grain size increases,indicating high temperature and can promote the growth of grain. |
PDF Full Text Request