Application of SiO2 passivation technique in mass production of silicon solar cells

Abstract

Effective surface passivation is one of the primary prerequisites for high-efficiency silicon solar cells. In this paper, high-quality silicon dioxide (SiO2) films with excellent surface passivation abilities have been realized by thermal oxidation and plasma-enhanced chemical vapor deposition, respectively. By employing SiO2 capped with hydrogenated silicon nitride (SiNx:H) (SiO2/SiNx:H stacks) as the front passivation layers, the emitter saturation current density has been reduced from 90.5 fA/cm2 to 62.3 fA/cm2. We have successfully mass-produced thermal-oxidized p-type Czochralski-Si (CZ-Si) solar cells with high conversion efficiency (η) of 20.1%, which is 0.2% absolutely higher than that of the conventional Al back surface field (Al-BSF) solar cells. With a rational design of process integration, we have further presented a cost-effective way to fabricate high-efficiency SiO2 passivated emitter and rear cells (PERCs) at an existing production line. The introduction of SiO2/SiNx:H stacks on the rear surface can effectively increase the long wavelength response and the rear surface recombination is also suppressed with a rather low surface recombination velocity of 26 cm/s achieved after a post-annealing process. The industrial SiO2 passivated p-type CZ-Si PERCs possess outstanding performances with the average η of 21.3% and the highest η of over 21.9%, absolute 1.3% increment in average η compared with the conventional Al-BSF solar cells. Moreover, we have demonstrated that the relative low illumination response (below 50 W/m2) loss of our SiO2 PERCs over a day is extremely limited to be less than 0.2%.