ILGAR-ZnO Window Extension Layer:: An adequate substitution of the conventional CBD-CdS buffer in Cu(In,Ga) (S,Se)2-based solar cells with superior device performance

A novel Window Extension Layer (WEL) concept for chalcopyrite-based thin-film solar cell devices has been developed The optimization of its deposition is presented. WEL means the replacement of the conventional buffer layer by a layer consisting of the same material as the window, i.e., a part of the window is directly deposited onto the absorber by a soft process, such as ILGAR (Ion Layer Gas Reaction). This sequential cyclic technique has been applied to Cu(In,Ga)(SSe)(2) absorber substrates. The ILGAR procedure was optimized with respect to the efficiency of the resulting Mo/Cu(In,Ga)(S,Se)(2)/WEL/ZnO solar cells. The devices were characterized by J-V (under AM 1.5 and without illumination) as well as by quantum efficiency measurements. Devices with ZnO WEL yield total area (0.5 cm(2)) efficiencies of 14.6% (best cell) without any anti-reflecting coating. The efficiencies are superior to those of the corresponding devices with CBD (Chemical Bath Deposition)-CdS buffer (14.1%, best cell). Thus, in contrast to other ZnO buffers, ILGAR-ZnO achieves record efficiencies exceeding those of CBD-CdS buffered reference cells. Copyright (C) 2001 John Wiley Sons, Ltd.