Desenvolvimento e análise da passivação com dióxido de silício de células solares com campo retrodifusor seletivo

Abstract

The passivation of silicon solar cell surfaces is important for reducing the recombination rate of electron-hole pairs and, consequently, for improving efficiency. The goal of this work was to analyze the passivation quality obtained with thermal oxidation of solar grade silicon wafers and of solar cells with type p base and selective back surface field, producing thin films of SiO2. First, the dependence of minority carrier lifetime on oxidation time and temperature with and without the addition of chlorine was analyzed. I-V curves and spectral response measurements were conducted to determine the influence of oxidation parameters on the solar cells electrical characteristics. The results related to the oxidation furnace cleaning showed that introducing chlorine during oxidation it was possible to avoid the decline of minority carrier lifetime for silicon of Czochralski type and temperatures higher than 1000 °C. As regarded to the oxide passivation, it was observed that the effective minority carrier lifetime increases for thicker oxides. The oxidation time and temperature that resulted in the highest efficiencies were 45 min and 800 °C, resulting in oxide thicknesses on the front and back surfaces of 53 nm and 10 nm, respectively. The best solar cell with selective back surface field and SiO2 passivation presented Jsc = 36.0 mA/cm2, Voc = 598.6 mV and FF = 0.777, corresponding to an efficiency of 16.8 %.