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

Both area selective atomic layer deposition (ALD) and area selective molecular layer deposition (MLD) are demonstrated on Cu/SiO 2 patterns using octadecylphosphonic acid (ODPA) self-assembled monolayers as a resist layer. X-ray photoelectron spectroscopy and Auger electron spectroscopy confirm that during a metal oxide ALD process, no growth occurs on ODPA-protected Cu, whereas the metal oxide grows on SiO 2 regions of the substrate, for up to 36 nm of metal oxide. The results also show that ODPA blocks the Cu surface from MLD, preventing polyurea deposition for up to 6 nm of film thickness.

We report here the utilization of atomic layer deposition to passivate surface trap states in mesoporous TiO 2 nanoparticles for solid-state dye-sensitized solar cells based on 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD). By depositing ZrO 2 films with angstrom-level precision, coating the mesoporous TiO 2 produces over a two-fold enhancement in short-circuit current density, as compared to a control device. Impedance spectroscopy measurements provide evidence that the ZrO 2 coating reduces recombination losses at the TiO 2 /spiro-OMeTAD interface and passivates localized surface states. Lowfrequency negative capacitances, frequently observed in nanocomposite solar cells, have been associated with the surface-state mediated charge transfer from TiO 2 to the spiro-OMeTAD.

Ultrathin films of TiO2, ZrO2, and Al2O3 were conformally created on SnO2 and TiO2 photoelectrodes via atomic layer deposition (ALD) to examine their influence upon electron transfer (ET) from the electrodes to a representative molecular receptor, I3(-). Films thicker than 2 Å engender an exponential decrease in ET time with increasing film thickness, consistent with tunneling theory. Increasing the height of the barrier, as measured by the energy difference between the transferring electron and the bottom of the conduction band of the barrier material, results in steeper exponential drops in tunneling rate or probability. The variations are quantitatively consistent with a simple model of quantum tunneling of electrons through square barriers (i.e., barriers of individually uniform energy height) that are characterized by individually uniform physical thickness. The findings demonstrate that ALD is a remarkably uniform and precise method for modifying electrode surfaces and imply that standard tunneling theory can be used as a quantitative guide to intentionally and predictively modulating rates of ET between molecules and electrodes.