Preparation And Properties Of The Key Layers Of Cu₂ZnSnS₄ Thin Film Solar Cell

Cu2ZnSnS4(CZTS)semiconductor has been confirmed as a promising material for the absorption layer of thin film solar cells.CZTS is the ?2-?-?-?4 quarternary compound semiconductor by substituting the Se with S,the rare metal In,Ga with Zn and Sn in Cu(In,Ga)Se2(CIGS)compound.Due to its abundant component elements in earth,nontoxic and environmentally friendly,CZTS thin film is one of the best candidate materials for solar absorbing layer.This work is focused on the CZTS thin film solar cell prepared by pulsed DC magnetron sputtering.The preparation and properties of the absorbing layer CZTS materials and the window layer ZnO-based films were studied.The effects of deposition parameters on the porperties of the CZTS films and ZnO-based films deposited by one-step pulsed DC magnetron sputtering were systematically investigated.Detailed research contents are shown as follows:(1)Based on hydrothermal and mechanochemical process,the synthesis mechanism and sintering properties of the CZTS powder were investigated.The results show that with increasing the ball milling time or the rotational speed,the CZTS powders can be directly formed from Cu,Zn,Sn,and S elemental materials by the mechanochemical process.The relative density value of the CZTS sinters is the highest when the sintering temperature reaches to 700 ?.The quaternary compounds CZTS ceramic target was prepared under these conditions.(2)CZTS films were deposited by one-step pulsed DC magnetron sputtering from a single quaternary target without sulfurization process.The effect of substrate temperature,working pressure,sputtering power and pulsed frequency on the properties of CZTS films vere systematically investigated.The results show that,when the substrate temperature is less than 500 ?,the deposited CZTS films are single kesterite structure and show a preferential orientation along(112)plane.In addition,when the substrate is at room temperature,the difference of working pressure can change the preferential orientation of the CZTS thin films.Namely,when the working pressure is 0.4 Pa,the CZTS film shows a preferential orientation along(220)plane,and the CZTS film shows a preferential orientation along(112)plane when the pressure is up to 0.6 Pa.The CZTS films deposited at suitable substrate temperature(350 ? to 400 ?),working pressure(less than 0.8 Pa)and sputtering power(not less than 200 W)show better photoelectric performance,which is suitable for the absorption layer of CZTS thin film solar cell.(3)Based on sol-gel and magnetron sputtering method,the preparation and porperties of ZnO-based films were systematically studied.Firstly,the effects of boron concentration and pyrolysis temperature on the porperties of B-doped ZnO(BZO)films prepared by sol-gel method were disscussed.The results show that,the boron concentration and pyrolysis temperature are the critical factors for determining the crystallization behavior of the BZO films.When the concentration of doped boron is 0.5 at.%and the pyrolysis temperature is 500 ?;the BZO film shows the lowest resistivity.Secondly,the effect of boron concentration,substrate temperature and sputtering power on the properties of BZO films deposited by one-step pulsed DC magnetron sputtering were investigated.The results show that,the BZO films deposited at the substrate temperature of 400 ? and sputtering power of 100 W with 1.0 at.%BZO target show better photoelectric performance.Lastly,the effect of substrate temperature and O2/O2+Ar flow ratio on the properties of ZnO films deposited by pulsed DC magnetron sputtering were disscussed.The results show that,the increasing of the substrate temperature can enhance the crystallization of ZnO thin films,and the O2 can reduce the carrier concentration of the ZnO films,which is suitable for the i-ZnO layer of CZTS thin film solar cell.(4)The preparation of CZTS thin film solar cells by magnetron sputtering.The solar cells with the structure glass/Mo/CZTS/i-ZnO/BZO/Cu were obtained.The current-voltage curve demonstrates that the efficiency of 0.02%is achieved at the area of 0.5cm2 with open circuit voltage of 15.5 mV,short current density of 5.6 mA/cm2 and the fill factor of 23.8%.The reasons for the loss of solar cell efficiency have been analyzed.