Graphene as non conventional transparent conductive electrode in silicon heterojunction solar cells

Chemical Vapor Deposited (CVD) graphene is an attractive candidate as transparent conductive electrode (TCE) for solar cells. Here it is proposed as TCE for silicon heterojunction solar cells (Si-HJSCs) and tested over devices with area up to 4 cm realized on n-type c-Si wafers with three different p-type emitters facing the dry-transferred graphene stack: amorphous silicon (a-Si:H), nanocrystalline silicon (nc-Si:H), and nanocrystalline silicon oxide (nc-SiO:H). A dependence of the cell performance on the material in contact with graphene has been observed with the most promising results in case of nc-Si:H and nc-SiO emitter. In particular, with respect to reference cells with standard TCE a short circuit current density gain of 1.4 mA/cm has been achieved when including an antireflection coating. The present work demonstrates the high quality of dry-transferred CVD-graphene over relatively large area and the feasibility of Si-HJSCs integrating graphene, where the fabrication sequence asks for a transfer process that guarantees a much better contact with the underlying functional layer with respect to more common designs where graphene is transferred onto a support substrate. This approach provides a possible pathway to Si-HJSCs free from conventional plasma-based TCEs and their deleterious effects due to plasma luminescence and ion bombardment, while offering an interesting platform for getting insights in the mechanisms at play at the interfaces with graphene within Si wafer-based devices.