Simultaneous bulk hydrogen passivation and selective emitter formation assisted by ECR-plasma applied to industrial mc-Si solar cells

The authors present a new way of realising a selective emitter, using the simultaneous etching and hydrogenation properties of the ECR-H ₂ plasma (electron cyclotron resonance hydrogen plasma). The impact of the H₂-plasma on multicrystalline silicon (POLIX ^TM) is studied in terms of bulk lifetime. It is shown that during the hydrogenation step, the ECR-plasma etches back the emitter surface at a rate of about 100 nm/hour. Besides, on sheet resistance mappings, they have observed that the etch rate depends on grain orientation. The etch-back is used to form the selective emitter during the hydrogenation process. Solar cells were realised using the screen-printed contacts as a mask against the plasma effect. The short circuit current can gain more than 1 mA/cm₂, the gain coming from the whole spectral range, this due to the less recombinating surface and the hydrogenated bulk material