Fast Growth of Microcrystalline Silicon Solar Cells on Lp-cvd Zno in Industrial Kai Pecvd Reactors

We report in this paper on the latest research results of microcrystalline (μc-Si:H) silicon solar cells fabricated in a commercial Oerlikon Solar (former UNAXIS) KAI-S single-chamber PECVD reactor (substrate size up to 35 cm x 45 cm) driven at an excitation frequency of 40.68 MHz. The cell structure consists of a stack of glass/ front-TCO / p-i-n μc-Si:H solar cell / back-contact. Our “in-house” boron-doped ZnO (zinc oxide), prepared by LPCVD (low-pressure chemical vapour deposition) is implemented for the front and the back-side transparent conductive contacts (TCO) of the devices. Homogeneous solar-grade films can be deposited at a rate up to 18Å/sec The Raman crystallinity of these films is of 62% in the center as well as on the border of the whole substrate area (35x45cm). By suitable optimisation of the device fabrication process we are able to make μc-Si:H solar cells with conversion efficiencies of 8.4% in a 'true' single-chamber process. The i-layer is 1.5μm thick and is deposited at 0.7 nm/sec on LP-CVD ZnO. The back ZnO contact is coated with white paint. Finally, we show that μc-Si:H solar cells with 6% efficiency can be grown, using so called 'low-flow' silane plasma in a depletion regime at a rate of 1 nm/s.