Effect Of Liquid Phase On Grain Size Of Copper Indium Gallium Selenium Via Sputtering Quaternary Ceramic Target

Copper Indium Gallium Selenium(CIGS)is a polycrystalline photovoltaic material with merit of stable,environmentally friendly and low-cost,and the champion photoelectric conversion efficiency has reached 23.35%in the world.Sputtering quaternary ceramic target has a important result on improving repeatability,but small grain has always been a disadvantage of this method,small grain will lead to more grain boundary which will increase more scattering of carrier,and it is easy to form more defects in the grain boundary.So in this paper,we use liquid phase to promote the grain growth and increase the grain size,so then to improve the photoelectric conversion efficiency of the device.Ag-doped could promote grain growth of CIGS.It was found that Ag doping had no effect on the phase composition,but increase the grain size and the carrier mobility significantly,so the open-circuit voltage and the filling factor increased.After Ag doped into the CIGS,Ag would occupy lattice,and then reduced melting point of the material,because the component of thin film would change towards?-rich which would be instrumental in formation of liquid phase contained Ag,the size of grain increased.Photoelectric conversion efficiency was improved from 9.25%to 12.64%with open-circuit voltage increased 100 mV.Annealing temperature had a great influence on open-circuit voltage,with increasing annealing temperature,grain size further increased.Open-circuit voltage increased more than 100 mV and we got champion photoelectric conversion efficiency of 14.33%.We used Bi to increased grain size.Bi-added could increase grain size and improve densification,meanwhile increase carrier concentration and mobility.Because Bi would not change the structure of the material,the increasing in the grain size of the thin film benefited from the formation of low-melting point compounds.Open-circuit voltage and filling factor increased and photoelectric conversion efficiency was improved from 9.52%to 11.79%with increased V_OC of 100 mV.By contrasting the effect of Na or Bi in the CIGS,we draw a conclusion that Bi had reliablelly improvement on carrier concentration and mobility,and Na and Bi would also increase grain size and improve open-circuit voltage and the filling factor.When we added Na and Bi into CIGS,the grain size of thin film was largest,open-circuit voltage and filling factor were highest,and their distribution was more uniform.Ag doping and Bi addition were increase grain size of CIGS.Taking Bi addition experiment as the main research object,we found that Cu₁Bi₃Se₅ low-melting point compound appeared during annealing,and with disappear of Cu₁Bi₃Se₅ the grain size increased dramatically.Therefore,it was proved that the migration of grain boundary was increased during the decomposition of Cu₁Bi₃Se₅ low-melting point compound,which promoted the growth of grain and increased the grain size.