Plasma Immersion Ion Implantation for the doping and texturization of silicon based solar cells

Cost reduction is the overall goal in the further development of solar cell technologies. In case of low quality mc-Si containing a relatively high concentration of metal impurities a low temperature process is desirable for solar cell fabrication. In order to avoid diffusion of metal impurities into the space charge region of the p-n junction the temperature of the mc-Si substrate should not exceed 400 oC. Although ion implantation doping got very recently distinct consideration for doping of monocrystalline solar material, efficient doping of multicrystalline solar material remains the main challenge to reduce costs. The influence of different annealing and implantation techniques on the optical and electrical properties of mc-Si solar cells was investigated. Flash Lamp Annealing in the ms-range combined with plasma immersion ion implantation (PIII) is demonstrated here as a very promising techniques for the emitter formation at an overally low thermal budget.
The flat silicon surface has a natural reflectivity in the range of 40 % with a strong spectral dependence. The minimization of the reflection loss is very important for high efficiency solar cells fabrication. In order to reduce the surface reflectivity wet chemical etching is the most widely used method in photovoltaic fabrication. Here we present a novel environment friendly method for silicon texturisation. As the reactive gases the mixture of SF6 and O2 with the ratio of 3:2 was used. After 10 min etching the black needle-like surface was obtained. The black silicon fabricated by PIII etching shows the average reflectance below 2% measured over the range from 200 nm to 1100 nm. Presented technology shows great promise to replace the conventional POCl3 –doping and wet chemical etching texturization for efficient silicon based solar cells fabrication.