The three-year project (2000-2002) described in this report was concerned with specific issues that have to be addressed in order to ensure Industrialization of the “micromorph” (microcrystalline/amorphous) thin-film silicon solar cell concept introduced in 1994 by IMT Neuchâtel: 1) Increase of microcrystalline silicon deposition rate, with corresponding fabrication of entire solar cells; here, novel compact VHF (Very High Frequency), electrodes were introduced in a part of our deposition systems, ensuring, thereby, higher deposition rates, as well as greater compatibility with the “plasmabox”-type electrodes used in the KAItype industrial production systems of UNAXIS; furthermore, first results were obtained on high-rate deposition in the so-called HPD (high-pressure depletion) regime. 2) Improvement of the performances of nip-type single-junction microcrystalline silicon solar cells; a record (stable) efficiency value of 9.2 % could be obtained for such a smallsize solar cell. 3) Investigation of the microstructure of microcrystalline silicon solar cells; establishment of a relationship between cell microstructure, as seen by TEM (transmission electron microscopy) and, also, by Raman spectroscopy, on one hand and the open-circuit voltage value of entire solar cells, on the other hand. This relationship is valid for both nip-type and pin-type solar cells. Furthermore, insight was gained into the complex growth mechanisms of microcrystalline layers and cells on various substrates. 4) Improvement of pin- and nip-type amorphous silicon solar cells. Here, pin-type single-junction amorphous silicon solar cells with a stabilised efficiency of over 9% could be obtained, thanks to the excellent light trapping obtained with our inhouse LP-CVD (low-pressure chemical vapour deposition) zinc oxide. In the case of nip-type solar cells, the accent has been on 2 separate issues: a) Improvement of stabilized efficiency AND of optical absorption thanks to the use of “moderately high temperatures” (300 to 350 degrees) for the plasma deposition of the intrinsic layer; b) Deposition of amorphous silicon layers at lower temperatures (190 degrees) on very low-cost substrates, like PET. These particular investigations on nip-solar cells are not yet completed. 5) Specific studies on transparent conductive oxides (TCOs), and on light trapping (solar cell current enhancement) obtained with various TCOs and, in general with various types of back reflectors and various substrate materials. Here, the main accent has been on the development of LP-CVD ZnO on transparent glass substrates, for pin-type solar cells, and on the preparation of a larger area (30cm x 30cm) deposition system for the same. A further accent was on the development of rough silver layers, useable as textured back reflectors, on opaque substrates, in the case of nip-type solar cells. 6) Basic considerations on the necessary spectral ranges for light trapping, both for amorphous silicon and for microcrystalline silicon solar cells of typical thickness were carried out. It was shown that the spectral ranges involved in the 2 cases are far from being the same. 7) Implementation of entire micromorph tandem solar cells, both in the pin- and in the nipconfiguration, as well as realization of pin-type micromorph minimodules with monolithic series connections. Schemes to improve the efficiency, such as the use of an intermediate reflector between the top cell and the bottom cell were studied. The problem of current matching of micromorph tandem solar cells was addressed.
