Mechanism of Spectral Sensitization of ZnO Coadsorbing p-Type and n-Type Dyes

We systematically measured photocurrents in ZnO layers coadsorbing p- and n-type dye. On the basis of our results, the mechanism of the spectral sensitization arising from the combination of p- and n-type dyes is discussed. We found that the photocurrents are proportional to e - Δ E / k T , where Δ E is the difference in energy between the conduction bands of the p- and n-type dyes. Our results lead us to believe that the “sensitization with two dyes” induced by combining the p- and n-type dyes, is caused by the injection of electrons from the n-type dye layer into the ZnO layer via the p-type dye layer over the barrier of Δ E .