Rear surface passivation of ultra-thin CIGS solar cells using atomic layer deposited HfO<sub>x</sub>
Gizem Birant, Jorge Mafalda, Romain Scaffidi, Jessica de Wild, Dilara G. Buldu, Thierry Kohl, Guy Brammertz, Marc Meuris, Jef Poortmans, Bart Vermang
Abstract
In this work, hafnium oxide layer is investigated as rear surface passivation layer for ultra-thin (550 nm) CIGS solar cells. Point contact openings in the passivation layer are realized by spin-coating potassium fluoride prior to absorber layer growth. Contacts are formed during absorber layer growth and visualized with scanning electron microscopy (SEM). To assess the passivating qualities, HfO x was applied in a metal-insulator-semiconductor (MIS) structure, and it demonstrates a low interface trap density in combination with a negative density of charges. Since we used ultra-thin devices that are ideal to probe improvements at the rear, solar cell results indicated improvements in all cell parameters by the addition of 2 nm thick HfO x passivation layer with contact openings.