Effects Of Sulfurization Heat Treatment On Absorbing Layer Of Cu₂ZnSnS₄ Thin Film Solar Cells

As a renewable energy source,solar energy is one of the important ways to solve the energy crisis.Cu₂ZnSnS₄?CZTS?thin film solar cells have been attracted wide attention,because its constituent elements are abundant in the earth's crust and environmental friendly.It become the most promising material in the new generation of solar cells.In this thesis,the absorption layer of CZTS thin film solar cells was taken as the research object.The precursor Cu-Sn-Zn film was prepared by magnetron sputtering deposition on the soda lime glass coated with molybdenum layer,and then it was sulfurized at ten different temperatures?230?,250?,290?,310?,350?,400?,450?,500?,550?,600??to form CZTS thin film.The microstructure and chemical composition of the film and the interface between the film and molybdenum layer were studied by XRD,SEM,TEM,HAADF and EDS.It was discussed that the formation process of CZTS thin film during the sulfurization process.The main results are as follows:?1?The precursor Cu-Sn-Zn film has different phases after sulfurization process.Binary phase and ternary phase are formed in the sulfurized thin films below 400?.The CZTS phase is formed at 400?,and which is the main constituent phase.The CZTS phase is stable at 400?to 550?.and is decomposed at 600?.The CZTS grains are twinned in films sulfurized at temperatures above 400?.With the temperature increasing,the size of the CZTS twin crystal grains increases.?2?The surface of the films are uneven and granular at different temperatures.The size of the grains is small in near-molybdenum layer,while that of the surface grains is large.There is a layer of MoS₂ between the near molybdenum layer and the molybdenum layer.With the temperature increasing,the CZTS phase gradually forms,the crystal grains continue to grow,and the crystallinity increases.The thickness of the film increases slightly with the temperature increasing,especially at 550?.?3?The element distribution of Cu,Zn and Sn is uneven at low temperatures.It become uniform with the increasing of sulfurization temperature.The ratios of?Cu+Zn+Sn?/S are between 0.83 and 0.99,and are mostly above 0.9 close to 1.The Cu/?Zn+Sn?ratios are large at low temperatures and around 1 at temperatures above400?,as well as it rises to nearly 2 at 600?.The Zn/Sn ratios in the film increase as the sulfurization temperature increases.?4?The formation of CZTS films involve four stages in the sulfurization process of the Cu-Sn-Zn films:alloying of precursor and diffusion of alloying elements;alloying elements combining with S to form sulfides?binary or ternary sulfides?;nucleation and growth of CZTS grains;decomposition of CZTS grains at high temperature.