Rapid Thermal Processing of Next Generation Silicon Solar Cells

摘要

Rapid and potentially low-cost process techniques are analyzed and successfully applied towards the fabrication of high-efficiency mono- and multicrystalline Si solar cells. First, a novel dielectric passivation scheme (formed by stacking a plasma silicon nitride film on top of a rapid thermal oxide layer) is developed that serves as antireflection coating and reduces the surface recombination velocity (S_(eff)) of the 1 centre dot 3 #OMEGA#-cm p-Si surface to approximately 10 cm/s. The essential feature of the stack passivation scheme is its ability to withstand short 700-850 deg C anneal treatments used to fire screen printed (SP) contacts, without degradation in S_(eff). The stack also lowers the emitter saturation current density (J_(oe)) of 40 and 90 #OMEGA#/ square emitters by a factor of three and 10, respectively, compared to no passivation. Next, rapid emitter formation is accomplished by diffusion under tungsten halogen lamps in both belt line and rapid thermal processing (RTP) systems (instead of in a conventional infrared furnace). Third, a combination of SP aluminium and RTP is used to form an excellent back surface field (BSF) in 2 min to achieve an effective back surface recombination velocity (S_(eff)) of 200 cm/s on 2 centre dot 3 #OMEGA#-cm Si. Finally, the above individual processes are integrated to achieve: (1) >19 percent efficient solar cells with emitter and Al-BSF formed by RTP and contacts formed by vacuum evaporation and photolithography, (2) 17 percent efficient manufacturable cells with emitter and Al-BSF formed in a belt line furnace and contacts formed by SP.