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 I₃^-/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 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 bandedge shifts and tunneling based blocking behavior playing only secondary roles.