Evaluating the impact of thermal annealing on c-Si/Al2O3 interface: Correlating electronic properties to infrared absorption

Al2O3 is the standard for the passivation of p-type PERC (Passivated Emitter Rear Contact) solar cells. It is well established that the thin interfacial silicon oxide layer in between Al2O3 and c-Si plays a key role in its surface passivation mechanism. In this work, we investigate the interface properties of c-Si/Al2O3 by non-destructive methods. We show that Brewster angle Fourier transform infrared spectroscopy has a remarkable sensitivity to the interfacial silicon oxide layer by exploiting the large cross-section of the longitudinal-optic mode. These measurements show that the interfacial SiOx layer increases in atomic density for higher annealing temperatures which coincide with an increase in negative fixed charge density (Qf) determined from contactless capacitance-voltage measurements. X-ray photoelectron spectroscopy results show a decrease of [OH] at higher annealing temperatures which could be correlated to denser SiOx increasing Qf. This work provides insight into the impact of thermal annealing on the Al2O3/c-Si interface.