Simultaneous formation of emitter and passivation layer in a single rapid thermal cycle [solar cells]

In this paper, the authors investigate the simultaneous processing of the emitter junction and the emitter surface passivation by rapid thermal annealing (RTA) from a doped spin-on glass (SOG). Test structures and solar cells of different emitter profiles and surface concentrations were made by diluting two different doped spin-on glass liquids with methanol. By this procedure, oxide thickness and doping can be controlled. RTA was performed in an argon atmosphere in the temperature range of 850°C-1000°C for 5-60 sec. The results show that emitter surface doping concentration between 1*10¹⁹ cm ^-3 and 3*10²⁰ cm^-3 and junction depth from 0.1 μm could be obtained. Sheet resistances lower than 150 Ω/□ could be easily reached. External quantum efficiency measurements from solar cells, made from CZ and FZ p-type silicon wafers, demonstrate the passivation effect of the remaining SOG-film. The highest efficiency obtained with this ohmic back contacted cells, which had an oxide thickness of about 70 nm, are 12.8%