A simultaneously diffused, textured, in situ oxide AR-coated solar cell process (STAR process) for high-efficiency silicon solar cells

A novel device fabrication process called the STAR process is presented, which incorporates a Simultaneously diffused emitter and Back Surface Field (BSF), on a textured silicon wafer, with an in situ thermal oxide for surface passivation and Anti-Reflection (AR) coating. In a single high-temperature step, the STAR process provides four important quality-enhancement features: (1) emitter oxide passivation, (2) back surface passivation via a boron back surface field, (3) a low reflectance (SiO₂) single layer AR coating, and (4) a back surface reflector (BSR) for light trapping. The STAR process is implemented using a novel diffusion technique which can simultaneously form boron and phosphorus diffusions and grow an in situ thermal oxide in a conventional diffusion furnace, without the deleterious effects of cross doping. Conversion efficiencies as high as 20.1% have been obtained for this structure on 2.0 Ω·cm float zone silicon. This paper presents a detailed characterization of the impact of each of the above quality enhancement features, using a combination of an extended IQE analysis, minority carrier lifetime measurements, and measurements of the emitter saturation current density J_oe. Computer simulations are used to improve the understanding of STAR cells and show that the STAR process is capable of producing device efficiencies over 19% on thin, relatively modest quality, solar grade silicon materials