Damp-heat degradation and repair of oxide-passivated silicon

• Published in: Physica status solidi. A, Applications and materials science Applications and materials science, 2011-08, Vol.208 (8), p.1931-1936
• Main Authors: McIntosh, Keith R., Dai, Xi
• Format: Article
• Language: English
• Subjects: Applied sciences; degradation; Energy; Exact sciences and technology; humidity; Natural energy; passivation; Photovoltaic conversion; silicon; SiO2; Solar cells. Photoelectrochemical cells; Solar energy
• ISSN: 1862-6300; 1862-6319
• DOI: 10.1002/pssa.201026492

SiO2‐passivated Si degrades when exposed to a ‘damp‐heat’ atmosphere of 85% relative humidity and 85 °C. We find the effective surface recombination velocity at the SiO2/Si interface of phosphorus‐diffused (111) Si to increase from 2200 to 11 000 cm/s after 7 days of damp‐heat exposure. This degradation is of concern to many high‐efficiency solar cells, which are manufactured from SiO2‐passivated Si with phosphorus‐diffused (111) facets at the front surface, and which must withstand 1000 h of damp‐heat exposure during reliability testing. Our experiments indicate that the damp‐heat exposure causes (i) absorption of H2O into the SiO2, (ii) an increase in the concentration of H at the SiO2/Si interface, (iii) a latent source of degradation that continues after samples are returned to room conditions, and (iv) SiO2/Si interface damage that can be repaired by a short anneal at 300 °C in N2. The results of these experiments are discussed in relation to the various mechanisms that might underlie damp‐heat degradation of SiO2/Si interfaces.