Study On The Doping Characteristics Of Cu₂Zn_x?_1-xSnS₄??=Cd,Ba? Thin Film Solar Cells

Cu₂ZnSnS₄?CZTS?thin film has the advantages of earth-abundant,non-toxic,low cost and high absorption coefficient,which has attracted extensive attention in the field of thin film solar cells.The magnetron sputtering is a suitable method for the large area growth of multi-component compounds.It is found that sputtering CZTS film will makes thin films has crack and even fall off,due to the large stress after annealing.Now,CZTS solar cell has reported power conversion efficiencies?PCE?of more than 12%.However,both Cu Zn and Zn Cu of CZTS reverse defects can lead to serious potential fluctuations and tail-band states,which can reduce the optoelectronic performance of devices.In this year,more and more people pay attention to the preparation of CZTS-based thin film solar cell by cationic substitution method.In the position of group II metals,atoms with large size deviation from Cu,such as Cd and Ba,are adopted for displacement doping.This method can effectively solve the problem of cation disorder in the Kesterite crystal and reduce the loss of open circuit voltage.Therefore,CZTS thin film was grown by magnetron sputtering firstly,studying the influence of ZnS sputtering power on the adhesion of CZTS film.Then,the Cu₂?Zn,II?SnS₄??= Cd,Ba?thin films doped with Cd and Ba displacements were prepared by magnetron sputtering and chemical spin coating.Details as following:?1?The stacking precursors SLG/Mo/ZnS/SnS/Cu were sputtered ZnS,SnS and Cu target in sequence on soda-lime glass?SLG?substrates in which the sputtering power of ZnS changed from 50 W to 140 W.Then Cu₂ZnSnS₄?CZTS?thin films were obtained by annealing.The effects of ZnS sputtering powers on the morphology,microstructure and adhesion in ZnS thin films and followed CZTS thin films were investigated.The results showed that the ZnS thin films with different power sputtering were hexagonal wurtzite with?008?preferred orientation.The poor crystallization in ZnS thin film was found at low sputtering power.The compressive stress in ZnS thin film increased by an order of magnitude with sputtering power from 50 W to 140 W.When sputtering power of ZnS was lower than 80 W or higher than 110 W,the crack and even falling off phenomenon were observed in the annealed CZTS thin films.From 80 W to 110 W,the surface of CZTS thin film was even but more holes and secondary phases appeared at higher power of 110 W.The CZTS solar cell was prepared with ZnS thin films sputtered at 80 W,which showed open circuit voltage of 572 m V,short circuit current density of 14.23 m A/cm2 and photoelectric conversion efficiency of 3.34 %.?2?By magnetron sputtering,Cd was doped with CZTS to prepare Cu₂(Zn_1-xCd_x)SnS₄?x = 0⁰.5?film.It was found that the doping of a small amount of Cd element could play a role in facilitating melting of thin films,increasing grain size,improving film uniformity,and inhibiting formation of the hole and small grains.With the increase of the concentration of Cd element,the Cu₂?Zn1-x Cdx?SnS₄?x = 0-0.5?of the I4_Kesterite ore structure transferred to the I42 m wurtzite structure gradually.In addition,the increase of doping concentration of cadmium can promoting the carrier concentration of CZCTS thin film solar cell.However,as the film surface of magnetron sputtering is denser,the small grains and holes are still observed in the film surface and cross section.In addition,the grains of CZCTS thin films prepared by magnetron sputtering were small and holes,which observed in the surface and cross section of thin films.?3?The Cu₂Zn_0.3?_0.7SnS₄??=Cd,Ba?thin films with the same stoichiometric ratio were prepared by chemical spin coating.The results show that the binding energy of each element doped with Cd and Ba is consistent with the CZTS thin film,and there is no impurity phase.Compared with magnetron sputtering,the Cu₂(Zn_1-xCd_x)SnS₄ thin films with spin coating method were more uniform.The cross section shows columnar growth and the inhibition of local clusters reduces the pores and fine grains.The CZCTS solar cell with the doping of Cd/?Cd+Zn?=0.3 had the best performance.The Open Circuit Voltage?Voc?,Short Circuit Density?Jsc?,Filling Coefficient?FF?and Photoelectric Conversion Efficiency?PCE?were 585 m V,14.86 m A/cm2,46.2% and 3.65%,respectively.And the PCE was 50% higher than before doping CZTS.However,the PCE of Ba doped CZBTS was only 1.4% because of the poor film forming quality.