Ultra thin Al₂O₃ passivation for hetero-junction Si solar cell

This work focuses on ultra thin (≤ 1nm) Al₂O₃ passivation for silicon hetero-junction solar cell. We developed a post annealing process compatible with the hetero-junction structure. We accomplished effective minority lifetime over 3 ms and implied open circuit voltages over 700 mV using a 10 nm thick Al₂O₃. To promote carrier transportation across the Al₂O₃ layer we had to reduce the layer thickness by a factor of 10. The 1 nm thin layer alone provides very poor passivation as demonstrated by the low effective minority carrier lifetime (50μs) and low implied open circuit (590mV). To improve both passivation and carrier transportation, a ultra thin stack of SiO₂-Al₂O₃ (1.7 nm/1 nm) was developed successfully and effective minority carrier lifetimes up to 350 μs and implied open circuit voltage up to 648mV were demonstrated without post annealing optimization.