Solar Energy Materials and Solar Cells, Vol.160, 470-475, 2017
Organic passivation of silicon through multifunctional polymeric interfaces
In this work, we demonstrate a solvent-free, low temperature (< 25-170 degrees C) approach using chemical vapor deposition (CVD) grafting and polymerization processes to passivate the unpaired electrons or "dangling" bonds on the surface of silicon. The multifunctional (dielectric and electronically conducting) passivating layers described here achieved several orders of magnitude improvement in minority carrier lifetime ( > 2 ms) compared to bare silicon (similar to 30 mu s), and remained stable in air for over 200 h. These values approach that of SiNx films deposited at significantly higher temperatures. The polymer passivation processes and materials are shown to significantly reduce surface recombination rates: chemically by reducing density of surface states and electrostatically by altering band bending at the silicon interface. Passivation quality also improved on grafting using aliphatic monomers compared to aromatic ones suggesting a reduction in steric effects in the former, helping us posit design rules for polymer based surface passivation of silicon. Finally, the ability to use an electrically conducting polymer for passivation creates a direct interface between traditional silicon microelectronics and organic electronics. Beyond microelectronics and photovoltaics, these processes can enable the fabrication of hybrid or: multifunctional devices, such as biosensors and light emitting diodes.