Abstract
For the sake of energy shortage, renewable and clean energy substitution is a considerable point for the next generation. CIGS is the best thin film solar cell among the second generation solar cells owing to its various outstanding behaviors, such as the highest absorption coefficient, the easiest integration with Si-based technology and the highest efficiency in thin film solar cell. Therefore, it has already attracted tremendous attention in academic and industrial fields. Up to date, the highest efficiency of ~21.7% has been demonstrated by ZSW in Germany. Plasma application on solar cell has been researched by many groups. It has been found that Se vapor is easily formed as Sen, which is ring or train structure (2<n<8).These structures have low reactant energy, resulting in the problem of incomplete selenization. In this thesis, a progressing non-toxic plasma-enhanced solid Se vapor selenization process (PESVS) technique, compared with hydrogen-assisted Se vapor selenization (HASVS) to achieve a large-area (40x30 cm2) Cu(In,Ga)Se2 (CIGS) solar panel with enhanced efficiencies from 10.8 % to 13.2 % (14.7 % for active area), was demonstrated. The bonding of Se was partially broken by ICP plasma treatment and these Se radicals are helpful to enhance reaction activity for following selenization process at an extremely low temperature of 330 ˚C. The effects of plasma steps, plasma power, selenization temperature and optimized conditions were thoroughly studied in detail. The remarkable enhancement of the efficiency is ascribed to the better crystallinity, enlarged grain size, less Se vacancy and uniform depth distribution of Ga. From reaction kinetics point of view, PESVS provides extra energy to crack Se, resulting in the decrease in reaction activation energy. The PESVS methodology was also applied to low temperature (450 ˚C) selenized CIGS thin film solar panel with uniform conversion efficiency more than ~10 %. Furthermore, a large-area flexible stainless steel substrate with remarkable conversion efficiency of ~6.8 % without Na addition was demonstrated. We believed that this work can provide a facile approach of low temperature selenization on flexible substrate applications or fast selenization for throughput consideration, thus stimulating the mass-production in large scale CIGS PV industry.