Interface control to enhance the fill factor over 0.70 in a large-area CIS-based thin-film PV technology

To improve the fill factor (FF) over 0.7, the following research has been performed, such as 1) our sulfurization after selenization (SAS) process condition for the Cu(InGa)(SeS)(2) (CIS)-based absorber formation is fixed to attain the open-circuit voltage (V(oc)) of over 0.630 V/cell, 2) thickness of a double buffer structure with both Zn(O,S,OH)(x) deposited by a chemical-bath deposition (CBD) technique and intrinsic ZnO deposited by a metal-organic chemical vapor deposition (MOCVD) technique is adjusted by optimizing the series resistance (R(s)) and the shunt resistance (R(sh)), 3) post-deposition annealing in vacuum after CBD is applied to reduce the hydroxide (OH) concentration, and 4) narrower pattern-2 and -3 scribe lines contribute to make the interconnect width less than 200 mu m and to keep the short-circuit current density (J(sc)) over 34 mA/cm(2). As the result, for the first time a FF of over 0.7 has been achieved in our CIS research and development (R&D) since FY1993. This is the biggest contributor to achieve our FY2007 milestone of 15% efficiency with aperture area larger than 800 cm(2). We have achieved this milestone in the form of a laminated module. (C) 2008 Published by Elsevier B.V.