Advances in surface passivation schemes for high efficiency c-silicon solar cells

Effective surface passivation is one of the most important prerequisites for high efficiency crystalline silicon (c-Si) solar cells fabricated on thin wafers. To obtain, a good quality SiO² films and SiO₂/Si interfaces low temperature post oxidation annealing was carried out. Surface recombination velocity of 62 cm/s, a low interface trap density of 3 × 10¹¹ states/cm²/eV and fixed charge density was reduced to 1 × 10¹¹/cm² due to the annealing at 500°C. Similarly we analyzed and compared the optical and passivation properties of Al₂O₃/SiN_x and Al₂O₃/SiON_x stack layer. Silicon oxynitride (SiON_x) has been used to improve antireflection and passivation properties since SiON_x provides an excellent optical reflection than the conventional SiN_x. Dielectric stack passivation layer of Al₂O₃/SiON_x is preferred for high efficiency solar cell since SiN_x is not suitable for p-type c-Si passivation due to the formation of an inversion layer. The effective lifetime of the Al₂O₃/SiON_x stack has resulted in 0.85 ms after firing. The reference cell with Al₂O₃/SiN_x stack shows an efficiency of 18.61% with V_oc of 614 mV. With optimized layer parameters, cells having Al₂O₃/SiON_x stack shows an efficiency of 19.45% with V_oc of 626 mV, J_sc of 40.53 mA/cm², and FF of 76.6%.