Desenvolvimento de células solares bifaciais PERT base P com junção flutuante e análise da passivação

Abstract

The bifacial solar cell converts the solar energy incident on both sides into electrical energy. The expectation is that in the coming years the technology of bifacial modules will be used more than that of monofacial modules. The objective of this work was to develop PERT p-type bifacial solar cells, with reduction of thermal steps. In process α, the patent granted BR 10 2012 030606-9 B1 was used and two thermal steps in the diffusion of dopants were reduced. In the process β, patent application BR 10 2018 0085760, three thermal steps were reduced in relation to the standard process and the diffusion of boron and phosphorus was carried out in the same thermal step. The emitter, the back surface field (BSF) and the firing process of the metallization pastes were optimized. The minority charge carrier lifetime and the SiO2 passivation were also analyzed and methods to form the floating junction in the BSF and in the emitter were developed. The higher electrical parameters of solar cells produced with the process α and β were obtained with the same temperature and time to form both the emitter and the BSF. The minority charge carrier lifetime after thermal steps is higher than the initial one and better results were obtained with the process β. The higher efficiency () was obtained with SiO2 passivation and the floating junction did not improve the electrical parameters. In the process α, the higher efficiency was obtained with the oxidation temperature (TOXI) of 800 °C and 830 °C and time of 45 and 30 minutes, respectively. With the TOXI of 800 °C the efficiency of 16.9 % was obtained with irradiance in the emitter. However, high open circuit voltage value of 605.9 mV was obtained with the TOXI of 830 °C. With the process β, the higher values of the electrical parameters were obtained with a TOXI of 800 °C and time of 45 minutes, resulting in a ηemitter of 16.6 % and ηBSF of 12.7 %. The efficiency obtained is a little lower than the efficiency of a commercial bifacial module (ηemitter = 20.5 % and ηBSF = 14.4%), but the production process has fewer steps and, consequently, there is a reduction in production cost.