Industrially feasible casting-mono crystalline solar cells with PECVD AlOx/SiNx rear passivation stack towards 19.6% efficiency

Cost reduction and efficiency gain are the major goals of research and development in crystalline silicon solar cell technology. Casting-mono crystalline silicon produces higher cell efficiencies compared to multi-crystalline silicon material with the same average minority carrier lifetime and with a similarly low production cost. Aluminum oxide provides excellent passivation on crystalline solar cell and has received great research interests in recent years due to combination of chemical passivation and field-effect passivation provided by a large amount of fixed negative charges. In particular, deposition of AlO_x using ALD or PECVD in PERC structure has been well studied. PECVD is preferred for its fast deposition rate. Our research shows that PECVD AlO_x films indeed show good passivation quality on casting-mono wafers, which can achieve more than 200μs average lifetime, 700mV implied V_oc and with good stability. Combined with the laser ablation to realize the PERC structure, the PECVD-AlO_x contributes to a 12mV increase in V_oc compared to the Al-BSF cell. The final cell efficiency reached 19.4% in average with a batch size of 30 wafers and 19.6% for the best cell. Additionally, PECVD AlO_x can be easily integrated with the current industrial production line at no significant additional cost.