The Green Chemical Preparations And Photovoltaic Device Performaces Of Cu₂ZnSnS₄ And CdS Thin Films

Cu₂ZnSnS₄?CZTS?is a direct-bandgap semiconductor material which has high light absorption coefficient?>104 cm-1?and suitable bandgap?c.a.1.50 eV?matching the solar radioation,and is composed by earth-abundant and non-toxic elements.Due to these excellent properties,CZTS is considered as one of the most promising absorber layer materials in the field of solar cells.Currently,research on CZTS solar cell mainly focus on the preparation method of absorber layer and buffer layer with low cost and low energy consumption.While vacuum process requires rigorous equipment with complex process and unremarkable cost advantage,non-vacuum process is less strict in equipment and can be easily turned into mass production.Among those methods,the solution-processed method,as a low cost non-vacuum technology,has gradually been applied in the industrialized production of semiconductor thin film.And in the preparation of CZTS solar cells,hydrazine and chemical bath deposition method,based on the solution method,has made great progress on preparation of CZTS absorber layer and cadmium sulfide?CdS?buffer layer.However,the hydrazine solvent the former uses is high-toxic and subsequent processing the latter is costly.Therefore,looking for a more environmatally-friendly chemical methods to prepare CZTS absorption layer and CdS buffer layer is of important significance to the industrialization of CZTS solar cell devices.In this dissertation,we have discussed the spin-coating preparation of CZTS micro-films and the effects of its process conditions on the device performance of the cell.Besides,we have studied the photochemical deposition of CdS nano-films,the influence of preparation conditions on the film morphology and the growth mechanism of thin film.In addition,we have investigated the photochemical deposition of CdS buffer layer on CIGS absorber layer,which is analogous to CZTS absorber layer,to discuss the performance distinction of CIGS solar cells when CdS buffer layer was respectively prepared by photochemical deposition?PCD?and chemical bath deposition?CBD?,the main work is as follows:?1?Spin-coating preparation of kesterite CZTS micro-film and its process optimization as well as cell performance testing.We used low-toxic Ethanedithiol-ethylenediamine mixture?EDT-EN?and metal chalcogenide to prepare precursor solution,and examined how the volume ratio of EDT/EN in the precursor solution,heat treatment temperature of precursor film,selenization conditions of film and the added amount of selenium in precursor solution influenced the phase,morphology and electrical device performance of films.Results showed that precursor had excellent spin-coating performance when the volume ratio of EDT/EN was 1:4.The optimal heat treatment temperature of precursor film was 300 oC.The resistence of films increased first and then decreased with the increase of selenium amount for selenization.The grain size,resistance and device efficiency of the selenized film increased as the amount of selenium added increased in precursor solution.And the cell efficiency reached 1.96% when 3 mmol amount of selenium was added in the precursor solution.?2?The preparation of CdS nano-film with PCD method and its process optimization as well as growth mechanism of film.We studied the phase and optical properties of the PCD-processed CdS thin film,and how the growth site number,deposition time,light intensity,and pH value,cadmium ion?Cd2+?concentration,thiosulfate ion?S2O32-?concentration of deposition solution during the deposition process influenced the morphology and element composition of CdS thin film.Besides,we discussed the growth mechanism of the films according to those varieties of influence.Results shows that PCD-processed CdS film was grown in hexagonal with a small amount of S2O32-ion impurities.The adsorbing amount of Cd2+ on surface of the ITO substrate directly affected the compactness of CdS film grown on substrate.The concentration of charged sulfur particles around the substract directly affected the CdS grain growth rate.When pH value was 3.50,Cd2+ ion concentration was 2 mM,S2O32-ion concentration was 100 mM,light intensity was 1 mW/cm2 and deposition time was between 60 min and 65 min,the preparation conditions for CdS nano-film reached the optimum.?3?Optimization of PCD-processed CdS buffer layer in preparation of CIGS solar cell and investigation on difference between PCD-processed and CBD-process CdS buffer layer for CIGS solar cell.We have discessed the influence of pH value of deposition solution on morphology of CdS thin film corresponding cell performance.And then we compared the PCD-processed in optimal condition with the CBD-processed one.Results show that the coverage and adherent particle number of CdS thin film as well as the corresponding CIGS cell efficiency decreased as pH rises.The CIGS cell with PCD-processed CdS buffer layer performed a slightly lower efficiency than with the CBD-processed one.The reason is that PCD-processed CdS buffer layer had a poorer uniformity and adhesion,which had increased the recombination site of carrier CdS in the interface between CIGS and CdS.