Preparation And Photoelectric Properties Of The CdTe Thin Film Solar Cells With Superstrate Configuration

Cadmium telluride?CdTe?thin film solar cell is one of the key research in the world.The main problem at present is the lower photoelectric conversion efficiency,which causes its poor competitiveness compared with the conventional energy sources.Therefore,it is very significant to in-depth study the performance of the photoelectric conversion materials.In this thesis,the thin film PV devices were fabricated in FTO/CdS/CdTe/Cu/Au superstrate configuration by RF sputtering on ultra-white glass and flexible polyimide substrates.The films of CdS,CdTe,AZO,i-ZnO,and Mo were prepared by rf magnetron sputtering.In addition,the films were also prepared by chemical bath deposition?CBD?and close space sublimation?CSS?as compared.The films were prepared by CdCl₂ annealing and the properties were improved.The properties of thin films were characterized with XRD,SEM,AFM,UV-visible spectroscopy,Auger electron spectroscopy,etc.The main research contents and results are as follows:CdS films were prepared by different processes,e.g.,chemical bath?CBD?,near space sublimation?CSS?and magnetron sputtering?SPUT?,and on different substrates,e.g.,fluorine doped tin oxide?FTO?,indium tin oxide?ITO?and aluminum doped zinc oxide?AZO?,respectively.By studying the morphology,structure,transmission spectrum and short circuit current density of as-deposited and CdCl₂annealed CdS thin films,the results showed that:the properties of CdS thin films prepared by different processes and substrates were different,the crystal quality of CdS thin film was improved obviously after CdCl₂ annealing,with the higher spectral transmittance and less short-circuit current density losses.The effects of different Ar pressure and target power on the growth rate,morphology,microstructure,residual stress,sheet resistance and reflection spectra of sputtered Mo thin films were studied.The Mo thin films prepared by high Ar pressure and low target power exhibited residual compressive stress and had a strong adhesion with the substrate,however the surface resistance and spectral reflectance were lower.The Mo thin films prepared by low Ar pressure and high target power exhibited residual tensile stress and had a poor adhesion with the substrate,at the same time the surface resistance and spectral reflectance were high.With the increase of Ar pressure,the crystallinity,carrier concentration and mobility of the sputtered AZO films were decreased,and the resistivity was increased.In the ultraviolet region,the cut-off wavelength of transmission spectra was obviously shifted to the long wavelength.With the increase of target power and substrate temperature,the crystallinity,carrier concentration and mobility of the sputtered AZO films were increased,and the resistivity was decreased.In the ultraviolet region,the cut-off wavelength of transmission spectra was obviously shifted to the short wavelength.By inserting a i-ZnO layer between AZO and CdS films,the efficiency of CdTe thin film solar cell was improved.When the thickness of i-ZnO layer was 50 nm,the device efficiency reached the best values.The PV devices were prepared in TCO/i-Zn O/CdS/CdTe/Cu/Mo superstrate configuration by magnetron sputtering.The device efficiencies of 12%(V_oc=820mV?J_sc=22.4 mA/cm² and FF=70%)and 10%(V_oc=810 mV?J_sc=18.3 mA/cm²and FF=69%)were reached on glass and polyimide?Uplex12.5?substrates,respectively.For improving the efficiency of flexible CdTe thin film solar cell on polyimide substrate,the key was to improve the performance of pn junction,reduce the surface reflection and increase the transmittance of polyimide films.