RF sputter deposition of the high-quality intrinsic and n-type ZnO window layers for Cu(In,Ga)Se-2-based solar cell applications

Transparent ZnO films were prepared by rf magnetron sputtering, and their e lectrical, optical, and structural properties were investigated under vario us sputtering conditions. Aluminum-doped n-type(n-ZnO) and undoped intrinsi c-ZnO (i-ZnO) layers were deposited on a glass substrate by incorporating d ifferent targets in the same reaction chamber. The n-ZnO films were strongl y affected by argon ambient pressure and substrate temperature, and films d eposited at 2 mTorr and 100 degrees C showed superior properties in resisti vity, transmission, and figure of merit (FOM). The sheet resistance of ZnO film was less dependent on film thickness when the substrate was heated dur ing deposition. These positive effects of elevated substrate temperature ar e presumably attributed to the rearrangement of the sputtered atoms by the heat energy. Also, the films are electrically uniform through the 5 cm x 5 cm substrate. The maximum deviation in sheet resistance is less than 10%. A ll of the films showed strong (0 0 2) diffraction peak near 28 = 34 degrees . The undoped i-ZnO films deposited in the mixture of argon and oxygen gase s showed high transmission properties in the visible range, independent of the Ar/O-2 ratio, while resistivity rose with increased oxygen partial pres sure. The Cu(In,Ga)Se-2 solar cells, incorporating bi-layer ZnO films (n-Zn O/i-ZnO) as window layer, were finally fabricated. The fabricated solar cel ls showed 14.48% solar efficiency under AM 1.5 conditions (100 mW/cm(2)). ( C) 2000 Elsevier Science B.V. All rights reserved.