| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2002: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 2001: ¥2,900,000 (Direct Cost: ¥2,900,000)
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| Research Abstract |
Aiming to develop the solar cells free from the environmental contaminants, promising solar cell of a thin film type could be produced by using Cu_2ZnSnS_4 (CZTS) film as the absorber. The CZTS film possesses promising characteristic optical properties ; band-gap energy of about 1.5 eV and large absorption coefficient in the order of 10^4 cm^<-1>, which means large possibility of commercial production of the most suitable absorber by using the CZTS film. Also as the CZTS film contains neither rare metals nor toxic materials, combining this film with Cd-free buffer layer we can expect coming solar cells with non-toxic thin films in the near future.
CZTS thin films were able to be produced successfully in our previous work by vapor phase sulfurization of the stacked precursors that were prepared by sequential vacuum evaporation of Cu, Sn and ZnS. The best conversion efficiency with the heterojunction of ZnO : AI/CdS and CZTS was 5.45 %, which showed the possibility of a very low cost solar cell. It has been, however, quite difficult to prepare CZTS film with high reproducibility.
This study showed the photovoltaic properties of CZTS-based thin film solar cells fabricated by using 3 types of precursors; (1) the conventional precursor with stacked layers of Cu/Sn/ZnS, (2) the modified precursor with the stacking order of Sn/Cu/ZnS, (3) the precursor with 5 periods of Cu/SnS_2/ZnS, which was produced to increase the amount of S and to enhance the interdiffusion in precursor. By optimizing the compositions of CZTS absorber, the order of stacked layer in precursor and the sulfurization condition, the present study could achieve the maximum conversion efficiency of 4.53 %. By using the multi-periods precursors that were annealed in high vacuum, the highest fill factor of 0.66 was achieved. Compared with the conventional stacked precursors of the other CZTS films, the surface morphology was much improved in this study.
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