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The enhancement of long wavelength (>600 nm) light absorption by light scattering can result in a significant increase in the short circuit current density of a-Si:H-based solar cells. A model of absorption enhancement is presented and used to predict both light absorption in the active i layer and the total reflectance of single-junction a-Si:H p-i-n solar cells. These results are compared with the corresponding measurements performed on actual solar cells. It is found that the texture imparted to the metallic interface may result in a significant decrease in the reflectance of the rear contact, and in certain of the rear contacts considered, the reflectance is also reduced by interface formation phenomena. These mechanisms reduce the reflectance of the aluminum rear contact to less than 50% in the solar cells studied. In these cells and others where large light absorption occurs in the rear contact, incomplete light randomization is not found to be an important enhancement limiting effect. A thin layer of indium-tin-oxide inserted between the a-Si:H n layer and the contact metal results in critical trapping of scattered light and so reduces light absorption in the rear contact.

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This contribution is a summary of a workshop convened to discuss the characterization and modeling of thin‐film CuInSe2(CIS)‐based solar cells, 17‐19 October 1993, in Estes Park, Colorado. the participants of the workshop are the authors of this paper. the subject matter was examined along four lines: device modeling, characterization, processing, and manufacturing issues. Fundamental numerical modeling has successfully guided device design efforts, including the design of variable band‐gap absorbers. Quantitative analysis, however, has been compromised by incomplete data on fundamental material properties. Phenomenological modeling and device characterization have sucessfully contributed to the understanding of the device physics. Although classified as a heterojunction device, the forward‐current recombination of the ZnO/CdS/CIS occurs almost exclusively in the space‐charge with diode quality factors ranging from 1.2 to 1.7 for good devices. the next generation of device modeling must incorporate two‐ and three‐dimensional effects. Recent fabrication work has focused on improving the CIS absorber and adding Ga and S to the matrix to increase its band‐gap. A better understanding of the ternary's fundamental properties is required to support the modeling efforts. Control of Ga and S introduction and the resulting absorber band‐gap profiles will facilitate the realization of optimized device designs. Inadequate understanding of fundamental device operation and process control at the laboratory level are amplified in the manufacturing environment. Modeling and characterization can identifv areas where corrective actions will result in improved performance and yield at the module level.

Materials issues central to the application of microcrystalline silicon (μc-Si) doped layers in a-Si:H based solar cells are discussed, which include: (1) characterization of ultra-thin layers to be incorporated in the device, and (2) methods to promote nucleation of μc-Si on desired substrates within a thickness on the order of ∼100Å. Successful application of (μc-Si) in multijunction a-Si:H based solar cells are demonstrated.