Surface Modification of SnO2 Photoelectrodes in Dye-Sensitized Solar Cells: Significant Improvements in Photovoltage via Al2O3 Atomic Layer Deposition

We report here the exploitation of ultrathin layers of Al2O3 deposited via atomic layer deposition (ALD) on SnO2 photoanodes used in dye-sensitized solar cells featuring the I-3(-)/I- couple as the redox electrolyte. We find that a single ALD cycle of Al2O3 increases the lifetimes of injected electrons by more than 2 orders of magnitude. The modified SnO2 photoanode yields nearly a 2-fold improvement fill factor and a greater than 2-fold increase in open circuit photo voltage, with a slight increase in short-circuit photocurrent. The overall energy conversion efficiency increases by roughly 5-fold. The effects appear to arise primarly from passivation of reactive, low-energy tin oxide surface states, with band edge shifts and tunneling based blocking behavior playing only secondary roles.