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 Al 2 O 3 deposited via atomic layer deposition (ALD) on SnO 2 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 Al 2 O 3 increases the lifetimes of injected electrons by more than 2 orders of magnitude. The modified SnO 2 photoanode yields nearly a 2-fold improvement fill factor and a greater than 2-fold increase in open-circuit photovoltage, with a slight increase in short-circuit photocurrent. The overall energy conversion efficiency increases by roughly 5-fold. The effects appear to arise primarily from passivation of reactive, low-energy tin-oxide surface states, with band-edge shifts and tunneling based blocking behavior playing only secondary roles.