Preparation And Characteristic Modulation Of Light Absorption Layers In Intermediate Band Solar Cells With Doped Transition Metal Sulfides

In recent years,the thin film solar cells with intermediate bands have attracted much attention due to their high theoretical photoelectric conversion efficiency.The key semiconductors in this kind of thin film cells are the intermediate band optical absorption layers,which can absorb not only the high-energy photons in the visible region but also the low-energy photons in the infrared region,to promote the efficency of light transformation.In this thesis,alternate magnetron sputtering and ball milling methods were adopted to prepare the intermediate band absorption layers doped by transition metals.The host semiconductors with suitable optical bandgaps were chosen,including chalcopyrite CuGaS₂,spinel structure Cdln₂S₄ and In₂S₃,ZnS with mixed structures of sphalerite and wurtzite.The dopant materials Cr₂S₃ and TiS₂ were selected.The main research results are as follows:1.Thin films of Ti-CuGaS₂ and Cr-CuGaS₂ with the pure chalcopyrite structure were prepared by sputtering method.The results showed that the photoelectrical properties of the films were improved when the substrates were kept at 100℃.For Ti-CuGaS₂ thin films,it was observed in the UV-vis-NIR light absorption spectra that the light absorption was enhanced with increase of Ti content,and additional subband edge responses appeared at 1.45,1.13 and 0.87 eV,indicating the formation of multiple intermediate bands.For Cr-CuGaS₂ thin films,two additional subband edge responses were observed to show the formation of a half-filled intermediate band.With increase of Cr content,the light absorption was enhanced,and the subband edge position was shifted to the direction of low energy.The results of transient photocurrent response test showed that the photogenerated carriers increased by doping and the photogenerated electron-hole pair recombination reduced,which furtherly verified the formation of intermediate bands.2.Ti-Cdln₂S₄ thin films with a pure spinel structure were prepared by sputtering method.The results showed that rapid annealing for 20minutes was the best.The UV-vis-NIR light absorption spectra revealed that two additional optical absorption bands with subband gaps appeared at about 760 and 1150 nm,in addition to the corresponding light absorption band edge response for CdIn₂S₄,the optical band gap being2.32 eV,indicating the formation of partially filled intermediate bands.The response test results of transient photocurrent once again proved the existence of the intermediate band.3.Cr-ZnS thin films with mixed phase structures of sphalerite and wurtzite were prepared by sputtering method.The results showed that the absorption coefficient increased in the UV-vis-NIR light absorption spectra,and two additional absorption peaks were found near 650 and459 nm,indicating the formation of intermediate bands in the original band structure,which was proved furtherly by the transient photocurrent response spectra.4.Light obsorption materials of semiconductor Cr-In₂S₃ with the spinel structure were prepared by ball milling method.By studying their spectrograms of UV-vis-NIR diffuse reflection and therelation curves of（αhν）² versus hν,it was found that doping Cr element could greatly reduce the intensity of light reflection.Combined with the results of transient photocurrent response test,it was revealed that the light absorption was enhanced and the light carriers increased.