| Due to the development of technology and human life,the need for natural energy increases steadily.Traditional coal,oil and other non-renewable resources can not meet the demand.Electrical energy is gradually becoming the choice of the world’s energy in the 21st century as a kind of renewable clean energy.The electric-car industry also is prompting the need for innovation of electricity generation.Solar power generation is an environment-friendly method.Since the last century,scientists have been looking for new semiconductor materials to replace silicon-based solar cells to improve solar-electricity conversion efficiency.Since the 1970s,cuprous oxide has been regarded by researchers as a direct bandgap semiconductor material,which is non-toxic,abundant and possesses low preparation cost with 20%theoretical photoelectric conversion efficiency.Thus cuprous oxide is the best choice for solar photovoltaic devices from both theoretical and practical viewpoint.Magnetron sputtering,thermal oxidation,electrochemical deposition and high temperature sintering can be used to produce stable cuprous oxide films.Cuprous oxide thin films prepared by magnetron sputtering have the advantages of uniform density and simple processing,which have attracted increasing attentions.However,currently,the limiting factor for the application of cuprous oxide thin-film solar cells is the low heterojunction photoelectric conversion efficiency.It is necessary for high efficiency cuprous oxide solar cell to effectively control the cuprous oxide film composition and crystal orientation,improve the cuprous oxide thin film optical and electrical properties,and thus improve the photoelectric conversion efficiency of photovoltaic devices.In this work,the P-type cuprous oxide thin films were prepared by radio frequency reactive magnetron sputtering method,and the deposited thin films were then treated by annealing and doping.XRD,SEM,XPS,Raman,light transmittance and absorption as well as Hall-effect measurement were used to analyze the thin film composition,crystal structure,surface morphology,optical and electrical properties of thin films.The main results are as follows:1、The P type Cu2O thin films were prepared by using pure copper target and oxygen gas in radio frequency（rf）magnetron sputtering system.The stoichiometric P type Cu2O films were deposited through controlling the deposition temperature、oxygen gas flow、target power。It is concluded that the optimal deposition parameters were 120W（target Power）,7.5%（oxygen rate）,400℃（substrate temperature）with a preferential orientation of（111）.The experiment results showed that increasing deposition temperature would lower the deposition rate and therefore the film thickness was reduced.Increase in deposition temperature would also increase the grain size of the films,but the requirement for oxygen rate was not changed.The films deposited in this work were confirmed to be P type with an optical band gap value of 2.15eV,which agrees well with the theoretical optical band gap of cuprous oxide.2.On the basis of the aforementioned deposition process,the vacuum annealing treatment at 600℃ with different durations were performed to improve the structural and electrical properties of cuprous oxide films.It is shown that the growth direction of Cu2O films changed from（111）to（200）after annealing treatment,and that the film surface morphology became more compact and grain size grew larger.Simultaneously,the Hall mobility of Cu2O films was increased from 5 cm2/vs to 14 cm2/vs after vacuum annealing.3.Two different doping methods,high temperature diffusion and co-sputtering,were used to investigate the influence of Na-doping on Cu2O films composition,surface morphology and electrical properties.The introduction of NaF changed the film growth direction from（200）to multiple directions.The distribution of Na was thought to be non-uniform across the film thickness in the case of Na-doping by high temperature diffusion.Nevertheless,the co-sputtering method could achieve a uniform doping with better performance.The introduction of NaF could reduce the O vacancy in the films and improve the hole density.As Na content was increased,the carrier density increased from 1.78×1015cm-3 to 1.12×1017cm-3,and the resistivity decreased from 673Ωcm to 114Ωcm. |
