Excellent low temperature passivation scheme with reduced optical absorption for back amorphous-crystalline silicon heterojunction (BACH) photovoltaic device

Low temperature processing of silicon photovoltaic (PV) solar cells with excellent passivation quality enables the effective use of ultra-thin wafers for solar cell manufacturing, thus paving the way for high-efficiency low-cost silicon photovoltaics. This article presents Back Amorphous-Crystalline Silicon Heterojunction (BACH) cell performance using low temperature (<;= 400°C) facile native oxide-PECVD silicon nitride (SiN_x) dual layer passivation scheme. The cell performance is also compared with the BACH cells fabricated using intrinsic hydrogenated amorphous silicon (i-aSi:H) and PECVD SiN_x layer passivation. Reduced optical absorption in the native oxide-SiN_x passivation layer resulted in a higher short-circuit current, J_SC, compared to the i-aSi:H-SiN_x passivated cells. The fill-factor also improved for the native oxide-SiN_x passivated cells owing to the improved transport properties. The i-aSi:H-SiN_x passivated cells exhibited optimum cell performance of 10.9% efficiency with V_OC of 598.7 mV, J_SC of 34.3 mA/cm² and fill-factor of 0.531. In contrast, a maximum cell efficiency of 16% is obtained for native oxide-SiN_x passivated cells with V_OC of 651 mV, J_SC of 35.4 mA/cm² and fill-factor of 0.694 for a 1 cm² untextured cell (all measurements having been performed under AM 1.5 global spectrum illumination). The above untextured cell performance is a record efficiency for a back amorphous-crystalline silicon heterojunction PV device synthesized using all low temperature processes, exceeding the previously reported highest cell efficiency of ~15%.