| In contemporary society, the application of solar energy technology for tackling energy shortage and optimizing energy structure has attracted a lot of attention in all countries. The key point of solar energy technology lies in the photovoltaic (PV) cell technology. Among the new generations of PV cells, CuInSe2(CISe) solar cells have become hot topics in the areas of materials science, chemistry and energy science, due to their advantages of adjustable band gap, high absorption coefficient, excellent PV conversion efficiency, good performance stability, and so on. However, in the aspects of fabricating CISe absorber layers, vacuum methods, such as sputtering and co-evaporation, are usually adopted, which have several disadvantages like high-cost and bad repeatability. Recently, it is reported that the non-vacuum methods, such as electro-deposition and screen printing, can both reduce the cost and maintain the high quality. Therefore, it is meaningful to focus on the beneficial soft chemistry method.According to the "powders-slurry-films" soft chemistry route, CISe powders were firstly fabricated by solvothermal method, then the effect of PVP-assisting, Ga-doping, S-doping on the phase, morphology and properties of CISe powders were studied. Furthermore, the CISe slurry and films were also fabricated in the present dissertation. Some new and important results were achieved and listed as follows.Synthesis of CISe and PVP/CISe powders was carried out by a simple and convenient solvothermal method, where ethylenediamine was used as the solvents. The influence of reaction temperature and PVP content on samples was also studied. The experimental results reveal that chalcopyrite CISe powders with novel "hexagonal flake cluster" morphologies are successfully fabricated at180℃, and their band gaps are accordingly broadened to1.30eV as a result of the quantum size effect. After increasing the temperature to210℃, samples with "hexagonal sphere cluster" morphologies are obtained, while the band gaps are decreased to1.24eV due to the weakened quantum size effect. Adding PVP does not cause any significant changes to the phase of CISe powders. However, with the increase of PVP content, the morphologies of PVP/CISe powders evolve from "hexagonal flake cluster" to "micro-cuboid". And this in turn causes a red shift of the absorption edge of the samples, the band gaps are gradually reduced to1.08eV when the PVP content is1.0g(64%w/w). Additionally, a possible "nucleation-growth" mechanism of the novel morphologies is preliminarily proposed in the present dissertation. Based on the synthesis of CISe powders, the effects of Ga-doping and S-doping on the phase, morphology and properties of CISe powders were further studied. It is found that the stoichimetric ratios of each component could be accurately controlled from the starting composition of the precursors. Ga-doping does not change the chalcopyrite structure of CISe powders, while S-doping results in the samples’phase being transferred to the wurtzite structure. With the increase of dopant amount, the morphologies of CIGSe powders evolve to flake cluster, nano-sphere and sheet respectively, while the CISeS powders severally develop to sheet and sphere structure. As to the optical absorption properties, both CIGSe and CISeS powders exhibit a blue shift of the absorption edge, their band gaps are also gradually increased to1.58eV and1.40eV, respectively. In addition, chalcopyrite CIS powders were also prepared in ethanol-thiourea system. It is proposed that the chalcopyrite structure may be regarded as a superstructure of the wurtzite type. When the Cu+and In3+ion of wurtzite structure ordering in the cation positions, the wurtzite structure can revert to chalcopyrite structure, and this enhances the samples’band gap to1.48eV.The preparation process of well dispersive CISe slurry was studied by single-factor experimental method. The results demonstrate that the best dispersion process is:the volume ratio of glycerin to ethanol ranges between0.4and0.5, the mass ratio of PVP to CISe powders also ranges between0.4and0.5, and before sheering the mixture at3000-4000r/min for3-4hours, ultrasound dispersing for15-20minutes is very crucial. By then, the as-prepared CISe slurry can stabilize for60days without obvious settlement. Finally, after adding proper amount of additives into the as-prepared slurry, the CISe paste suitable for dip-coating is prepared.CISe precursor coatings were successfully deposited on glass substrate by dip-coating method, and the precursor coatings were subjected to selenization process to obtain the chalcopyrite CISe films. It is found that the CISe precursor coatings coated at10mm/min and dried at70℃for1h possess good quality, where the adhesive force reaches0-level and the thickness is about105.26μm. After selenized at500℃for1h with Se vapor effused at350℃, the obtained chalcopyrite CISe films show good mechanical and optical properties with the value of band gap1.14eV, which demonstrates a promising applicability in CISe solar cells. |
PDF Full Text Request