We report here the first efficient p-type Si-based semiconductor-liquid junction system. p-Type Si photocathodes have been previously reported to yield open circuit photovoltages, Voc, of 0.38-0.40 V with several redox systems1-8. Photocurrent-voltage studies of p-Si cathodes in CH 3CN solvent have demonstrated 2.5% efficiency for conversion of 632.8-nm light to electricity with the N,N′-dimethyl-4,4′- bipyridinium2+/+ redox system1, and 0.5-2.4% with other macrocyclic complexes7,8. Such modest energy conversion efficiencies for small band gap semiconductors have been attributed to surface states which pin the semiconductor Fermi level6-9 and promote recombination processes10. However, we find that p-type Si/CH3CN interfaces can yield solar conversion efficiencies in excess of 10%, and can display open circuit photovoltages within 0.08 V of the theoretical limit for an ideal junction.
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