Role of incorporated sulfur into the surface of Cu(InGa)Se2 thin-film absorber

High-performance Cu(InGa)Se₂ (CIGS) thin-film absorbers with an intentionally graded band-gap structure have been fabricated by a simple two-stage method using In/Cu–Ga/Mo stacked precursors and H₂Se gas. Additional sulfurization step to form a thin Cu(InGa)(SeS)₂ (CIGSS) surface layer on the absorber is necesarry to improve the device performance. In order to understand the role of S incorporated into CIGS absorber, approaches with S are discussed. One approach is carried out by changing the condition of our absorber formation process. It is verified to be possible to incorporate more S into the CIGS absorber, but difficult to improve the device performance with higher S contained CIGS absorbers because of decrease in FF. The incorporated S is concluded to be effective to improve the pn heterojunction quality due to the passivation of surface and grain boundary of CIGS absorber through the formation of a thin CIGSS surface layer.     

Yield issues on the fabrication of 30 cm×30 cm-sized Cu(In,Ga)Se2-based thin-film modules

The approaches to establish a more robust and reproducible baseline process for 30cm×30 cm-sized CIGS-based thin-film circuits with a Zn(O,S,OH)_x buffer layer are reported, which also lead to an achievement of 12.93% efficiency on an aperture area of 864 cm². Monitoring the transparency or transmittance (%T) of dip solution as a process control parameter in the chemical bath deposition (CBD)-buffer deposition step and setting the end point of dipping the CIGS-based absorbers in the solution as the %T of 60% remarkably contribute to make our CBD-buffer deposition process more reproducible. By considering carefully the growth process of metal-organic chemical vapor deposition (MOCVD)-ZnO:B window, a thin layer of high-resistivity, intrinsic ZnO is deposited on the Zn(O,S,OH)_x buffer layer to simulate the film structure of MOCVD-ZnO:B window in the case of sputtered-5.7 GZO window. Achievement of the reproducibility of 85% for the CIGS-based thin-film circuits with a sputtered-5.7 GZO window confirms that the yield goal of 85% is surely attainable independent of window-layer deposition techniques, such as MOCVD and sputtering. In this study, it is emphasized how important to eliminate unknown factors in the fabrication process for CIGS-based thin-film modules to improve both reproducibility and efficiency.     

Progress in large-area Cu(InGa)Se2-based thin-film modules with a Zn(O,S,OH)x buffer layer

Applying basically the same innovative and robust fabrication technologies which, for the first time, led to the achievement of remarkably high efficiency of 14.2% at an aperture area of 51.7 cm² with a Zn(O,S,OH)_x buffer layer, the following goals have been targeted: (1) 13% efficiency on a 30 cm×30 cm module and (2) establishment of the fabrication technologies to attain 140 yen/W_p in the annual production capacity of 100 MW_p/a. The main focus is currently on the technology development (1) to increase the V_oc related to the CIGS absorber and (2) to improve the J_sc related to the DC-sputtered ZnO window layer with a multilayered structure. This contribution well explains the status and strategy of Showa Shell Sekiyu K.K. on the R&D of CIGS-based thin-film modules to achieve the above two goals by the end of FY2000.