Progress in screen printed front side metallization schemes for CSiTF solar cells

The Buried Base Contact (BBC) concept represents a simple industrially feasible scheme for metallizing crystalline silicon thin film (CSiTF) solar cells on insulating substrates and further allows metallization by screen printing. However, cells suffered from fill factors of ~50% due to Rs and Rp losses. By evaluating Al and AgAl pastes for base contacts, Rs is reduced below 1.5 Ohm cm2. Improved definition of base regions and improved alignment results in shunt resistances > 1k Ohm cm2. The interdigitated cells processed on Cz-Si wafers show fill factors up to 73% and efficiencies of 11,5%. Implementation of a firing through SiNx sequence is difficult due to the formation of inversion channels between emitter and the base grid and Rs problems. An extended BBC process scheme is proposed which allows an integrated interconnection of CSiTF cells on one substrate. However, the application to CSiTF leads to significant difficulties due to surface roughness of the substrates.