Improvements in P/Al High Efficiency Technology, AlSi

Abstract

Objective of this work was to get softly doped and deep emitters in single thermal step. Due to high temperature diffusion, dead layer (electrically inactive) is formed which produces recombination centers and increases saturation current density (Joe). For appropriate choice of selective emitter in order to decrease emitter saturation current density (Joe), it is necessary to have a passivated emitters, i.e. with silicon nitride. We have presented a process which combines with standard technology used for selective emitter formation in a single thermal step which leads to lowly doped and deep emitters. This process is feasible for industrial fabrication of P/Al solar cells. In this process the gettering is higher than conventional process. Surface concentration value ranging from 3.6x1019 cm-3 to 7.2x1019 cm-3 and depth junction values from 0.52 to 0.71 µm for sheet resistance ~100 ¿/¿ has obtained. By deposition of SiNx layer, further improved emitters quality by passivating the surface and we have obtained Joe value as low as 40 fA/cm2. The estimated saturation current density (Joe) is around 30-35fA/cm2 with optimization. First experiment has given Sun-Voc 624 mV, which corresponds to Joe 6.45E-13 A/cm2. This Joe is due to rear emitters (Al-BSF), it can be further improved and theoretically expected is around 650 mV. Process which is used to fabricate selective emitter is feasible to apply for industrial fabrication P/Al silicon solar cells with expected high efficiency.