High efficiency silicon solar cells with PECVD dielectric rear surafce passivation - HIGHPOINT

The project aim is to develop an industrial production process for a new design of monocrystalline silicon solar cells with an efficiency above 20% on a cell area of 150 cm2 which can be manufactured cost effectively in high volume. The solar cell structure will comprise the high efficiency front contact laser grooved buried contact process together with state of the art plasma enhanced chemical vapour deposition (PECVD) of low temperature dielectric films in the amorphous silicon dioxide/carbide/nitride family producing a passified rear surface. The metal contacts will be formed by a self-aligning plating process. The improvements will be demonstrated at an industrial scale and the potential for a 20% reduction in cost at the PV system level will be verified. The thin films we will be investigating for achieving good surface passivation of silicon (Si) wafers are based on hydrogenated amorphous silicon (a-Si:H) and its alloys with carbon (a-SiC:H) and nitrogen (a-SiN:H). A-SiN:H coatings are now standard in the PV industry for a wide range of solar cells / ranging from lower-efficiency devices fabricated from multicrystalline silicon wafers to the very high-efficiency (> 22%) solar cells manufactured by SunPower Corp. (CA, USA) and Sanyo (Japan). In addition, a-Si:H layers are used in novel high-efficiency heterojunction solar cell designs such as the Sanyo HIT cell. Films of a-SiC:H have received significantly less attention for wafer-based Si devices, being used more commonly in thin-film PV modules. This clearly indicates the compatibility of a-Si:H alloys for enhancing the performance of a wide variety of PV devices. NaREC's current laser-groove buried-grid (LGBG) technology is resulting in solar cells that exhibit a poorer performance than they are capable of, and they are LGBG solar cells are losing the competitive advantage they once held over the field. NaREC have carefully optimised the front side of the LGBG solar cell, however it is the rear-side of the device that is letting it down / particularly in its response to near-infrared light. Therefore, in the HIGHPOINT R&D project we aim to capitalise on the ability of a-Si:H thin film alloys to enhance the surface passivation at the rear of the LGBG solar cell. Furthermore, what is novel is that we will also engineer the HIGHPOINT solar cells to be compatible with NaREC's electroless metal plating method (for simultaneously forming selective metal contacts on both the front and rear) while not destroying the passivating properties of the a-Si:H films. If successful, this will enable the HIGHPOINT solar cells to achieve a conversion efficiency of 20% (absolute), while maintaining a simple solar cell structure that is compatible with high-volume manufacturing.