Análise da bifacialidade e da influência da concentração de oxigênio e nitrogênio na passivação de células solares bifaciais PERT base P

Abstract

The objective of this work was to analyze the influence of boron diffusion temperature (TB) on the bifaciality, the output power in the bifacial mode and internal quantum efficiency of p-type PERT bifacial solar cells, as well as the passivation on the emitter and back surface field (BSF) produced by the silicon oxide layer grown with different oxygen flow rates and nitrogen presence. The diffusion of dopants, boron and phosphorus, was implemented in the same thermal step, based on the patent request BR1020180085760. The highest bifacial power, 1.13 W, was obtained with the boron diffusion process at a temperature of 950 °C, resulting in the sheet resistance of 68 Ω/□ and 59 Ω/□ for the emitter and BSF, respectively. In this solar cell, the bifaciality was 0.63 and the increase in the output power with the bifacial illumination mode was 12.6%. Regarding the passivation analysis, three dry thermal oxidation processes were implemented: 1) with standard O2 flow rate, 2) with reduced O2 flow rate, and 3) with reduced O2 flow rate and addition of N2. The thickness of silicon oxide in the emitter and back surface field and the minority carrier lifetime were analyzed. In the boron back surface field, the highest thickness was observed with the reduction of O2 flow rate and addition of N2 (22 nm). However, on the emitter side, the highest thickness was obtained with the reduction of O2 flow rate (34 nm). The minority carrier lifetime was similar for the standard process and with the reduction of O2 (~250 μs). The presence of N2 tended to decrease the minority carrier lifetime in the bulk after the growth of the silicon oxide layer. Therefore, it was proven that it is possible to reduce the O2 flow rate without compromising the quality of passivation and allowing the reduction of production costs of PERT p-type bifacial solar cells