Electrochemical Preparation And Performance Optimization Of Flexible Double-Sided CZTSe Solar Cell

Solar energy is regarded as an important representative of clean and renewable energy because of its inexhaustible and green advantages.Solar cells based on semiconductor materials can directly convert solar energy into electricity,which is an important way to solve energy crisis and environmental problems.Flexible double-sided solar cells can be produced on a large scale through roll-to-roll process,and have the advantages of thin film solar cells and high power to mass ratio.They have great development potential in the fields of communication,aerospace,civil facilities and so on.At the same time,double-sided solar cells can absorb multi-directional light sources,and improve the utilization rate of light per unit area,with goog economic benefits.Among many thin film solar cells,Cu₂ZnSn Se₄（CZTSe）is regarded as a new generation of photovoltaic materials with great development potential due to its abundant components,environmental friendliness,good stability,high light absorption coefficient,and high theoretical conversion efficiency.At present,the flexible two-sided Cu₂ZnSn（S,Se）₄thin-film solar cells constructed by solution method have made a great breakthrough,and the efficiency of the two-sided cells is above 9.0%.However,the solution method has the disadvantages of complicated preparation process and low safety factor.In addition,it is far from the theoretical efficiency.The main factors limiting its efficiency are serious open-circuit voltage loss and low filling factor.This is due to the inherent defects brought by the flexible substrate and the narrow phase stability region of material,which is easy to produce heterophase/adverse defects,and the secondary phase and excessively thick molybdenum selenide are easy to produce at the back interface in the process of high temperature selenization,forming a valence band barrier and inducing severe back interface recombination.Therefore,the exploration of simple and green preparation technology and the suppression of bad defects/heterophase are the key to the construction of efficient flexible double-sided CZTSe solar cells.In this paper,a new technology of efficient preparation of flexible double-sided CZTSe solar cells was developed by using simple green electrochemical deposition technology in view of the disadvantages caused by the conventional solution method for the preparation of double-sided absorption layer and the uniform ion diffusion/adsorption mechanism and the conductive characteristics of molybdenum foil.To inhibit the undesirable defects/heterophases,a step prealloy method is proposed to effectively suppress the undesirable defects/clusters,optimize the back interface,and further improve the performance of flexible double-sided devices.Specific research contents are as follows:1.Flexible double-sided CZTSe thin film solar cells were prepared by electrodepositionIn view of our previous experience on electrodeposition and inspired by the research idea of solution processed double-sided absorption layer,we put forward a simple and green electrodeposition process to prepare high-quality flexible double-sided absorption layer in one step.Firstly,molybdenum foil was treated by electropolishing and regia king etching to remove oxides/impurities on the surface of molybdenum foil,and its effects on surface roughness and electrical properties of molybdenum foil were studied.Secondly,the two-sided Cu/Sn/Znprefabricated layer was prepared by stacked electrodeposition,and the influence of different heating time on the morphology,composition and phase structure of the absorption layer film was explored.By optimizing and exploring a series of experimental parameters,the efficiency of the flexible double-sided CZTSe solar cell was successfully increased to more than 6.0%.At the same time,it is found that the two-sided device constructed in this paper has good flexibility and two-sided optical response characteristics,which provides more possibilities for its wider applications.2.Cu/Sn prealloying optimizes device performanceIn order to improve the quality of the absorption layer,reduce the formation of undesirable defects and optimize the back interface,a Cu/Sn prealloying process was proposed to further improve the efficiency of flexible double-sided CZTSe devices.The effects of different Cu/Sn prealloy temperature and holding time on the morphology,elemental composition,phase structure,crystal growth,defect suppression and device performance of the double-sided thin film were investigated,and the mechanism of photoelectric performance improvement of the flexible double-sided CZTSe was revealed,and the photoelectric performance optimization of the double-sided absorption layer was realized.The results show that after Cu/Sn prealloying,the absorption layer is flat and compact,the grain penetration is inhibited,the concentration of interfacial defects and bulk defects is reduced effectively,and the charge transport is significantly improved,and the efficiency of the double-sided device is successfully increased to more than8.0%.Based on the current research status and existing key issues of flexible double-sided CZTSe solar cells,this paper proposes a scheme of one-step construction of high-quality flexible double-sided CZTSe absorption layer by electrodeposition,and designs a pre-alloying strategy to improve the photoelectric performance of flexible double-sided CZTSe solar cells,so as to realize the construction and performance optimization of flexible double-sided CZTSe solar cells.This paper provides effective technical guidance and experimental reference for the efficient development and application of new flexible double-sided CZTSe and other double-sided materials prepared by green electrodeposition,which has important scientific significance and application value.