| Person in charge of the project: |
Use of negatively charged dielectrics for back surface passivation of silicon solar cells.|
Use of negative charged dielectrics for back surface passivation of solar cells In the evolution towards thinner and thinner solar cells, a good back surface passivation of bulk crystalline Si solar cells becomes more important. The standard screenprinted Aluminum Back Surface Field (Al-BSF) cannot be used anymore, because on one hand the resulting surface recombination velocity is simply too high and on the other hand, wafer bending becomes a serious problem as wafer thickness decreases below 200μm. The science behind the Al-BSF is the formation of a p+ layer in the base by creating a highly Al-doped region through an alloying process of Si with Al. Such an accumulation layer can also be obtained by field-effect through the deposition of a dielectric with fixed negative charges. Among the few dielectrics that show negative charges, Al2O3 is a promising candidate. It was found in the past that Al2O3 deposited via Atomic Layer Deposition (ALD) can provide excellent effective surface recombination velocities (SRV). The potential impact in cell processing and technology of negative charge dielectrics is enormous. Beside their low surface recombination velocity, which makes them ideal candidates for passivation of thin (<200μm) solar cells, these materials present significant advantages for e.g. local contact structures. In contrast to dielectrics with a high positive charge (e.g. standard SiNx:H), where field passivation is due to an inversion layer which needs to be floating and is very sensitive to parasitic shunting, no contact separation is needed, and firing through the layers with commercial screen-printed pastes is possible.
Faculty of Engineering
Doctoral Programme in Engineering
Duration of the project:
10.01.2008 - 10.01.2012