Surface Passivation of Nanoporous TiO₂ via Atomic Layer Deposition of ZrO₂ for Solid-State Dye-Sensitized Solar Cell Applications

Abstract

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.

Surface engineered angstrom thick ZnO-sheathed TiO2 nanowires as photoanodes for performance enhanced dye-sensitized solar cells

“…Several studies show that high band-gap metal-oxide materials such as In 2 O 3 , ZrO 2 , Al 2 O 3 , Nb 2 O 5 , Ga 2 O 3 and SiO 2 could reduce recombination in DSSCs by blocking the back-transfer of electrons and thus preventing the recombination of electrons with either oxidized dye molecules or the oxidized redox couple (the latter one is thought to be particularly dominant in device performance degradation) [17][18][19][20][21][22] or reducing the density of surface trap states on the TiO 2 surface. 18,23 In addition, some studies demonstrate that metal-oxides like Nb 2 O 5 , SrTiO 3 , ZrO 2 and Al 2 O 3 can contribute to device performance enhancement by inducing a surface dipole at the metal-oxide/dye interface, leading to a negative shi in the TiO 2 conduction band 24 and an enhancement in the injection yield of photo-induced electrons. 25 In addition to the improved electrodynamics at the interface, improvement in device performance has also been related to dye adsorption enhancement.…”

Improving the efficiency of dye-sensitized solar cells by photoanode surface modifications

“…Insulating materials with conduction bands higher than that of TiO2, such as Al2O3, SiO2, ZrO2, and SrO, have been coated onto TiO2 photoanodes to enhance the performance of DSSCs [31,32]. Palomares et al [31] deposited SiO2, Al2O3, and ZrO2 onto the surfaces of TiO2 electrodes by a dip-coating technique using an organic solution of their respective alkoxides.…”

“…The electron lifetime increased exponentially as the number of ALD cycles increased, but the photocurrent significantly decreased at the same time. Li et al [32] reported the utilization of ALD to passivate surface trap states in mesoporous TiO2 NPs for solid-state DSSCs. The mesoporous TiO2 was coated by depositing ZrO2 films with angstrom-level precision, producing a more than two-fold enhancement in short-circuit current density.…”

Enhanced Performance of Nanowire-Based All-TiO2 Solar Cells using Subnanometer-Thick Atomic Layer Deposited ZnO Embedded Layer

“…Controlling the impact of surface or interface-derived electronic states is, therefore, a prime goal in modern semiconductor processing. To this end, utilization of an interfacial semiconductor, typically a metal oxide with high energy band gap, layer is commonly employed [8,15,16]. However, the main drawback associated with such an interfacial layer is the fact that just a couple of nanometers of such a layer can significantly hamper injection efficiency.…”