Influences Of The Heat Treatment Temperature And Na Doping Concentration On The Structures And Properties Of CIGS Thin Film

Thin film solar cells have developed rapidly in recent years.Due to the matched band gap to the solar spectrum and high absorption coefficient,Chalcopyrite semiconductors are promising materials for high efficiency and low cost solar cells,and Copper indium gallium selenide?CIGS?is the most representative one.However,the device efficiency is still much lower than the theoretical value.To investigate the correlations between film fabrication parameters,microstructures and properties/cell performance,CuIn_x Ga_1-x-x Se₂?CIGS?films were deposited on soda-lime glass by magnetron sputtering with followed selenization and magenetron sputtering using CIGS quaternary target in this work.Using X-ray diffraction?XRD?,Raman spectra,scanning electron microscope?SEM?,high resolution transmission microscopy?HR-TEM?,high-angle annular dark field method in scanning transmission electron microscope mode?STEM-HAADF?and X-ray energy dispersive spectrum?EDS?mapping,as well as Current-voltage curve?J-V?measurements,the influence of preparation conditions on the characters of CIGS was studied.The main conclusions are as the following:?1?CIGS films were deposited on soda-lime glass by magnetron sputtering and selenization heat treatments.The influence of selenization temperature on the characters of CIGS/Mo interface was studied.It was found that CIGS/Mo interface was sharp when the selenization temperature was 400?.A MoSe₂ thin layer and Na-riched second phase nanoparticles were detected at CIGS/Mo interface at 500?.The MoSe₂ layer became thicker and the Na-riched nanoparticles grew into a curved band at 600?,the CIGS/Mo interface therefore developed into a multilayered structure of CIGS/Na-riched second phase/MoSe₂/Mo.In addition,the orientations of MoSe₂ grains depends on the selenization temperature,and may effect on the formation of second phases.There is no preferred orientations of MoSe₂ grain when the selenization temperature was 500?.The c-axis of the MoSe₂ grain is perpendicular to the colunmar grain growth direction of Mo at 600?.This orientation facilitates the diffusion of Se,Na,etc.elements between the Mo layer and the CIGS layer.?2?CIGS films were deposited by magnetron sputtering using CIGS quaternary target.The thin films were annealed at different temperatures.It was found that,the film was more compacted and elements distributions were more homogenous when the annealing temperature was 500?.?3?Na was doped into Mo back contact layer to modify the structure and properties of CIGS film.It was found that the density of the thin film is increased with the doped Na.Formation of Na₂Se might suppress the diffusion of Se atoms,inducing the thickness of MoSe₂ decreased.Therefore,the series resistance reduced and fill factor?FF?increased.The increase of Ga concentration in the back region of the absorber layer was also due to the increase of the doped Na.In such case,the forbidden band width of the back surface increased and the electric field intensity enhanced,forming a strong back electric field which facilitated carrier transport and collection,improved short circuit current(J_SC),as well as battery performance.