A simultaneously diffused, textured, in situ oxide AR-coated solar cell process (STAR process) for high-efficiency silicon solar cells
- Georgia Inst. of Tech., Atlanta, GA (United States). Dept. of Electrical and Computer Engineering
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 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 (SiO{sub 2}) 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 {Omega}-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{sub oe}. It is found that the in situ oxide provides very good front surface passivation, producing J{sub oe} values as low as 29.2 fA/cm{sup 2} for a 76 {Omega}/{open_square} emitter. The boron BSF obtained by this approach gives an effective back surface recombination velocity (S{sub 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{sup 2} in J{sub sc} over an equivalent structure without a BSR. 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.
- Sponsoring Organization:
- Sandia National Labs., Albuquerque, NM (United States)
- OSTI ID:
- 599837
- Journal Information:
- IEEE Transactions on Electron Devices, Vol. 45, Issue 1; Other Information: PBD: Jan 1998
- Country of Publication:
- United States
- Language:
- English
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