Almost any sort of mechanical or chemical process is more efficient than plants. Photosynthesis is only 3% efficient; by the time the energy enters the plant, you've lost 97% of it. Then you figure various biological pathways, and you're down to maybe 1-2% efficiency for the best plants.

This, among other reasons, is why grain ethanol was such a scam.

The worst mechanical processes, by contrast, usually get at least 10-15% efficiency. That's what photovoltaics can do, for example. Gasoline engines have a thermal efficiency of about 30%, diesel about 45%. Granted, you lose energy in the extraction/refining/transportation steps, but it's still an order of magnitude more efficient than photosynthesis.