Cu(InGa)Se/sub 2/ thin films by elemental co-evaporation/sputtering and large area module results
We report process optimization and understanding resulting in high quality Cu(In,Ga)Se/sub 2/ (CIGS) films and high efficiency devices/modules using a hybrid process for CIGS formation. In the hybrid process, the Cu is supplied by magnetron sputtering, and the In, Ga, and Se are supplied by linear thermal sources. The advantages of the hybrid process include: i) the ease and precision of Cu thickness control; and ii) flexibility to adjust the Ga depth profile. The investigation was conducted in a large-area, pilot-line system. Among others, important parameters were found to be the Cu/(In+Ga) ratio of the Cu/(InGa)/sub 2/Se/sub 3/ precursor, selenization temperature, and timing of the Ga and In fluxes. Cell efficiencies of over 13.0% and module efficiencies of 7.5% (26 W, 0.35 m/sup 2/) were achieved. The film properties were investigated by XRD, SEM, and AES.
New technologies for CIGS photovoltaics
Abstract This paper describes a new process for forming Cu(In,Ga)Se 2 (CIGS) by vacuum processing. It is termed the hybrid process, and it involves thermal delivery of In, Ga, and Se and sputtering of Cu. The optimization of the process is described, followed by its successful application to large area processing of CIGS devices and modules. Other processing issues in module formation are also discussed and analyzed, including deposition of the buffer and window layers, and interconnect resistance. The paper also describes the application of a new sputtering process for compound film formation to the area of CIGS processing. This process is termed reactive environment sputtering, and is based on a hollow cathode discharge. The process is applied to the formation of transparent conducting oxides (TCO) such as ZnO:Al, ZnO:B, In 2 O 3 :Mo (IMO) and In 2 O 3 :Ti (ITiO), and to their use as window layers for CIGS devices.
Photoemission investigation of the electronic structure at poiycrystalline CullnSe, thin-film interfaces
The surface versus bulk composition and electronic structure of polycrystalline CuInSe2 thin‐film interfaces were studied by synchrotron radiation soft‐x‐ray photoemission spectroscopy. An n‐type In2Se3/CuIn3Se5 surface layer forms on enhanced‐grain polycrystalline thin‐film p‐type CuInSe2 during fabrication. Enhanced‐grain CuInSe2 films were sputter etched (500 V Ar) and analyzed in situ to determine core‐level binding energies and Fermi‐level positions for the n‐type surface and the p‐type CuInSe2 bulk within ±0.1 eV. The transition between the n‐type surface and the p‐type bulk was experimentally observed by noting the change in the position of the valence‐band maximum relative to the Fermi level EF. From these measurements, the valence‐band offset ΔEv between the layers was determined to be 0.50 eV. Measurement of the work functions φ was also completed and reveals φ=4.75 eV for the In2Se3 (CuIn3Se5) surface layer and φ=4.04 eV for the bulk CuInSe2. Combining these results allows construction of a sur...