Technology And Co-deposition Behavior Of Electrodeposition Of CIGS Thin Films In [BMIm][BF₄]-EtOH System

The prominent adventages of Cu In_1-x-x Ga_x Se₂?CIGS?thin film solar cell are high efficiency,adjustable band gap,good stability,strong anti-radiation.Comparing with other solar cells,CIGS thin film solar cell also possesses the adventages of low cost,good performance,and material saving.It will become an important direction for the development of solar cells in the future.At present,high energy consumption and high cost of preparation methods of CIGS thin film are prominent bottleneck for limiting its large-scale application.Therefore,it is of great theoretical significance and practical application value to develop low energy consumption and low cost preparation methods for CIGS thin film.In this thesis,a special[BMIm][BF₄]-Et OH system has been adopted to prepare CIGS thin films by electrodeposition.The research contents include the properties of[BMIm][BF₄]-Et OH system,the influence of Et OH content in electrolytes on the properties of deposited CIGS thin films,the electrodeposition process of CIGS thin film in[BMIm][BF₄]-Et OH system,and the electrodeposition process of three-dimensionally ordered macropores?3DOM?CIGS thin films.The effect of Et OH in electrolytes on the co-deposition mechanism of CIGS and the effect of polystyrene microsphere?PS?template on the electrochemical behaviors of CIGS were discussed.After[BMIm][BF₄]mixed with Et OH,the electrochemical window of mixtures becomes narrower and negative shifted comparing to that of[BMIm][BF₄].Electrochemical stability of the mixture which containing 25 vol.%Et OH was the best.The results of a combined quantum chemical calculations and FTIR study suggested that hydrogen bonds has been formed between ethanol molecules and the anions and cations of ionic liquids,which can reduce the energy of the mixed system in a certain range.Quantum chemical calculations and molecular dynamic?MD?simulations show that[BMIm][BF₄]-Et OH has the smallest?E and shows stronger chemical adsorption on Mo?110?than ethanol and[BMIm][BF₄].[BMIm][BF₄]-Et OH system is the best choice for stable adsorption on Mo?110?surface,it is more suitable for one-step galvanostatic electrodeposition of CIGS thin films than[BMIm][BF₄].The effect of Et OH content on electrochemical behaviors of unitary systems?Cu,In,Ga,Se?and multicomponent systems?Cu-Se,Cu-In-Se,Cu-In-Ga-Se?were investigated by cyclic voltammetry.Et OH in mixtures promotes the reduction of Cu²⁺and Se⁴⁺,but inhibits the reduction of In³⁺and Ga³⁺.Therefore,the content of In and Ga in deposited layers prepared by mixtures with high ethanol content are insufficient.Layers prepared by electrodeposition is mixture of metals and alloys,the process begins with Se and Cu-In alloys,Cu-Se alloys,In-Se alloys,and then Cu-In-Se alloys,finally metallic Ga.Deposited layers undergoes annealing and a continuous transformation of the alloy phase,finnally become CIGS thin films.The properties of CIGS thin film were further characterized by using multiple techniques as a function of ethonal content.The results further confirmed the hypothesis in CV that high ethanol content can break the balance of elemental distribution.The electrolyte composition of galvanostatic electrodeposition CIGS thin film in mixture containing 25 vol.%Et OH after optimization was c?Cu Cl₂?=10mmol·L^-1,c?In Cl₃?=25 mmol·L^-1,c?Ga Cl₃?=50 mmol·L^-1,c?Se Cl₄?=20 mmol·L^-1,deposition technology:current density 3 m A·cm^-2,deposition temperature 40°C,deposition time 30 min,stirring speed 550 r·min^-1.After annealing,CIGS thin film is a Ga-rich,well-crystallized p-type semiconductor with a chalcopyrite structure,its bandgap is 1.41 e V and photocurrent density is 0.019 m A·cm^-2.3DOM CIGS thin films were prepared in[BMIm][BF₄]-Et OH system by PS template assisted one-step galvanostatic electrodeposition.Optimized electrolyte composition and deposition technology are:c?Cu Cl₂?=10 mmol·L^-1,c?In Cl₃?=10mmol·L^-1,c?Ga Cl₃?=50 mmol·L^-1,c?Se Cl₄?=20 mmol·L^-1,current density 3 m A·cm^-2,deposition temperature 40°C,deposition time 10 min,stirring speed 550 r·min^-1.The Ga content in the CIGS thin films decreases with the increase of the diameter of PS microspheres,so that the bandgap of the thin films decreases.3DOM CIGS thin films are all Ga-rich and well-crystallized chalcopyrite structures.Bandgap of PS template with apertures 500 nm is 1.69 e V,its photocurrent density is 0.020 m A·cm^-2.Cyclic voltammetry was used to study the effect of PS templates on electrochemical behaviors of unitary systems?Cu,In,Ga,Se?and multicomponent systems?Cu-Se,Cu-In-Se,Cu-In-Ga?in mixtures.It was found that the existence of PS templates caused the change of the reduction path of In³⁺,the underpotential deposition of Ga³⁺,and the loss of the reduction step of Se⁴⁺,which directly led to the change of the composition of deposited 3DOM CIGS thin film.