Amorphous silicon carbide hetero-emitters for high efficiency silicon solar cells

We investigated different amorphous SixC1-x:H layers for their applicability as hetero-emitter materials. The deposition with Plasma Enhanced Chemical Vapour Deposition (PECVD) in a preliminary industrial stage plasma reactor was done without any wet-chemical pre-cleaning directly before the deposition. In a first step the single layers were characterised optically with Spectral Ellipsometry (SE) which showed an enhanced transparency of a-SixC1-x:H layers with a very low carbon content below 10 % compared to a-Si:H. On both sides passivated Si float zone wafers we measured minority carrier lifetimes with the Quasi Steady-State Photoconductance (QSS-PC) method which showed excellent passivation performance for 70 nm thick layers and a detrimental performance loss for thicknesses below 10 nm. With the Constant Photocurrent Method (CPM) we found a significant increase of the Urbach energy when incorporating phosphorous into the layer network. The solar cell had a hetero-junction on the front-side and a passivated rear-side (SiO2) with local contacts (PERC). The first cell batches were strongly influenced by technological problems such as material inhomogeneities over the cell area, contaminations on the surface and a poor grid finger/ITO adhesion behaviour. Nevertheless, we could achieve an excellent open circuit voltage of 674 mV.