Shinichi Shimakawa

Cu(In,Ga)Se2 solar cells on stainless steel substrates covered with insulating layers

Abstract We have developed the flexible Cu(In,Ga)Se 2 (CIGS) solar cells on the stainless steel substrates with the insulating layer for the fabrication of the integrated module. The CIGS films have strong adhesion to the Mo films with insulating layers. An efficiency of 12.3% was achieved by the flexible CIGS solar cell with a structure of ITO/ZnO/CdS/CIGS/Mo/SiO 2 /stainless steel. The insertion of the SiO 2 insulating layer did not have an influence on the formation of the CIGS film and solar cell performances.

Large-area CIGS absorbers prepared by physical vapor deposition

Abstract An in-line process for deposition of Cu(In,Ga)Se 2 (CIGS) films on 10×10xa0cm 2 substrates has been developed in order to fabricate high-efficiency CIGS modules. At the first step, CIGS solar cells with a small area were fabricated by the in-line evaporation. The cells on different positions in 10×10xa0cm 2 area showed almost the same efficiency of over 14%. Twelve cells on a substrate of 5×10xa0cm 2 size showed an average efficiency of about 13%. Device-quality CIGS films can be prepared by the in-line evaporation. Furthermore, interconnected CIGS submodules were fabricated on 10×10xa0cm 2 size substrates. The CIGS submodule has achieved an efficiency of 10.5%. The segmental cells in the submodule showed an average open-circuit voltage higher than 0.6xa0V, comparable to that of a high-efficiency cell with a laboratory size.

Production technology for CIGS thin film solar cells

Abstract Composition ratios such as Cu/(In+Ga) and Ga/In have a great influence not only on performances but on yields of Cu(In,Ga)Se 2 (CIGS) solar modules. We demonstrated on a composition monitoring of a Cu/(In+Ga) ratio and control of a Ga/In profile in the CIGS films using a Cu rich composition in Cu rich growth stage. A composition monitoring method based on emissivity of CIGS films is proposed and developed for the preparation of large area CIGS films. The substrate temperature cooling rate immediately after the deposition increases with increasing the Cu/(In+Ga) ratio in Cu-rich films, while Cu poor films have almost the same cooling rate. Measurement of the temperature cooling rate therefore enables the determination of whether the deposited film has Cu rich or poor composition. In and Ga depth profiles in completed CIGS films depend on the Cu/(In+Ga) ratios in Cu rich growth stage. Smooth gradient profile near the surface was formed in the CIGS film prepared from a heavily Cu rich film due to the fast diffusion rate of Ga into an excess Cu x Se layer. The bandgap profile, induced by the Ga/In depth profile, can be controlled by the Cu rich composition in Cu rich growth stage to improve performance of solar cells.

Preparation of Cu(In,Ga)Se2 thin films from Cu–Se/In–Ga–Se precursors for high-efficiency solar cells

Improved preparation process of a device quality Cu(In,Ga)Se 2 (CIGS) thin film was proposed for production of CIGS solar cells. In-Ga-Se layer were deposited on Mo-coated soda-lime glass, and then the layer was exposed to Cu and Se fluxes to form Cu-Se/In-Ga-Se precursor film at substrate temperature of over 200°C. The precursor film was annealed in Se flux at substrate temperature of over 500°C to obtain high-quality CIGS film. The solar cell with a MgF2/ITO/ZnO/CdS/CIGS/Mo/glass structure showed an efficiency of 17.5% (V oc = 0.634 V, J sc = 36.4 mA/cm 2 , FF = 0.756).