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 presente d, which incorporates a Simultaneously diffused emitter and Back Surfa ce Field (BSF), on a Textured silicon wafer, with an in situ thermal o xide for surface passivation and Anti-Reflection coating, In a single high-temperature step, the STAR process provides four important qualit y-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 l ight trapping, The STAR process is implemented using a novel diffusion technique which can simultaneously form boron and phosphorus diffusio ns and grow an in situ thermal oxide in a conventional diffusion furna ce, without the deleterious effects of cross doping, Conversion effici encies as high as 20.1% have been obtained for this structure on 2.0 O hm.cm Boat zone silicon. This paper presents a detailed characterizati on of the impact of each of the above quality enhancement features, us ing a combination of an extended IQE analysis, minority carrier lifeti me measurements, and measurements of the emitter saturation current de nsity J(oe). It is found that the in situ oxide provides very good fro nt surface passivation, producing J(oe) values as low as 29.2 fA/cm(2) for a 76 Ohm/square emitter, The boron BSF obtained by this approach gives an effective back surface recombination velocity (S-eff) of 390 cm/s, while the in situ back oxide BSR greatly enhances the absorption of long wavelength radiation, providing an additional 1.3 mA/cm(2) in J(sc) over an equivalent structure without a BSR, Computer simulation s are used to improve the understanding of STAR cells and show that th e STAR process is capable of producing device efficiencies over 19% on thin, relatively modest quality, solar grade silicon materials.