Introduction Silicon solar cells are currently of high interest in the quest for sustainable energy sources. To be independent of solar light availability, solar fuels such as hydrogen can be produced. As known from literature, the electricity output of silicon solar cells can be improved using a silicon nitride passivation layer, for example. On the other hand, hydrogen evolution catalysts can be coupled to surfaces by electrodepositing particles. However, combining both functions into a passivation layer with the catalyst on top disables electronic transport from silicon to the catalyst due to the thickness of the passivation layer. Therefore we use monolayers of organic molecules to passivate silicon solar cells. These monolayers are short enough to enable electrical transport to a coupled catalyst, but also passivate silicon surfaces. Experimental Silicon solar cells were fabricated by doping 2D substrates and 3D micropillars with flat and radial junctions, respectively. Monolayers of organic molecules were coupled to these substrates via a thermal hydrosilylation method in which chemical compounds with unsaturated end groups are grafted onto silicon in an oxide-free way. J-V measurements were recorded to study the influence of monolayers on the solar cell output. Results and Discussion The monolayer blocks dangling bonds at the silicon surface, so that less electron-hole recombination can occur. This increased the photovoltaic efficiency of pillared p/n solar cells from 8.6 to 9.7% (Figure 1). A 56% improvement in shunt resistance proved the electrical passivation effect of the monolayer. Conclusion In conclusion, molecular monolayers show electrical passivation of silicon solar cells, as shown by a 56% improvement in shunt resistance. Subsequent catalyst coupling would be possible at the monolayer head groups to make the devices suitable for solar-to-fuel purposes.

Molecular monolayers as electrical passivation for silicon solar cells

251st National Meeting (2016)

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