Facile nanometer thick native oxide based passivation of silicon for high efficiency photovoltaics

Fabrication of low cost solar cells using ultra-thin (approximately 20 μm) silicon wafers is a viable route given the significant potential of reduced material cost and its versatility to a range of portable and terrestrial applications. Low temperature processing is a compelling opportunity for the synthesis of high-efficiency ultra-thin silicon wafers. Further, excellent surface passivation attainable through facile low temperature processing techniques is an essential enabler for effective manufacturing of ultra-thin silicon solar cells, and thus paving the way for high-efficiency low-cost silicon foil photovoltaics. This article presents a novel low temperature passivation scheme using approximately 1 nm thick facile native oxide and 75 nm PECVD SiN_x. A maximum lifetime of 1.7 ms has been obtained for the passivation scheme. Moreover, the passivated wafers were also used to fabricate Back Amorphous-Crystalline Silicon Heterojunction (BACH) cells using double side polished n-type FZ wafers. A maximum cell efficiency of 16.7% is obtained for facile native oxide -PECVD SiN_x bilayer passivated cells having V_OC of 641 mV, J_SC of 33.7 mA/cm² and fill-factor of 0.77 for a 1 cm² untextured cell (all measurements having been performed under AM 1.5 global spectrum illumination).