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In this study, we established a core/shell (C/S) model that evaluates the surface coverage of an overlayer deposited on nanoparticles in terms of X-ray photoelectron spectroscopy signals of the nanoparticles. We used the model to estimate the coverage of Al 2 O 3 shell layers, which were deposited on the nanoporous TiO 2 electrodes of dye-sensitized solar cells (DSSCs) by atomic layer deposition (ALD), as a function of the number of ALD reaction cycles. The surface coverage increased with the average thickness of the Al 2 O 3 shell layers, indicating that the ALD Al 2 O 3 deposition on the nanoporous electrode was via the island growth mode. The power conversion efficiency of the DSSCs was highest after the first ALD reaction cycle for the Al 2 O 3 shell layers, which had a coverage of 0.25, according to the C/S model. The study shows that, to further improve the PCE, optimization of the ALD Al 2 O 3 deposition condition is required so that the surface coverage of the shell layer can be increased at the first ALD reaction cycle.

Low-temperature (approximately 150 degrees C), atomic-layer-deposited Al(2)O(3) films on nanoporous TiO2 electrodes of dye-sensitized solar cells (DSSCs) were investigated using electron spectroscopy. The power conversion efficiency (PCE) of the DSSCs was increased from 5.7% to 6.5%, an improvement of 14%, with one monolayer of Al(2)O(3) with a thickness of approximately 0.2 nm. The formation of Ti-O-Al(OH)(2) and interfacial dipole layers exhibited a strong influence on the work function of the Al(2)O(3) over-layers, while the thicker Al(2)O(3) over-layers caused the values of valence band maximum and band gap to approach the values associated with pure Al(2)O(3). A work function difference (Delta Phi(A-T)) of 0.4 eV and a recombination barrier height (epsilon(RB)) of 0.1 eV were associated with the highest PCE achieved by the first monolayer of the Al(2)O(3) layer. Thicker Al(2)O(3) over-layers, however, caused significant reduction of PCE with negative Delta Phi(T-A) and increased interfacial energy barrier height ((*)epsilon(IB)) between the N719 dyes and TiO2 electrodes. It was concluded that the PCE of the DSSCs may correlate with Delta Phi(A-T), epsilon(RB), and (*)epsilon(IB) resulting from various thicknesses of the Al(2)O(3) over-layers and that interfacial reactions, such as the formation of Ti-O-Al(OH)(2) and dipole layers, play an important role in determining the interfacial energy levels required to achieve optimal performance of dye-sensitized TiO2 solar cells.

NiO is an attractive hole-transporting material for polymer solar cells (PSCs) owing to its excellent stability and electrical/optical properties. This study demonstrates, for the first time, fabrication of uniform, defect-free, and conformal NiO ultra-thin films for use as hole-transporting layers (HTLs) in PSCs by atomic layer deposition (ALD) through optimization of the ALD processing parameters. The morphological, optical, and electrical properties of ALD NiO films were determined to be favorable for their HTL application. As a result, PSCs containing an ALD NiO HTL with an optimized thickness of 4 nm achieved a power conversion efficiency (PCE) of 3.4%, which was comparable to that of a control device with a poly(3,4-ethylenedioxy-thiophene):poly(styrene-sulfonate) HTL. The high quality and manufacturing scalability of ALD NiO films demonstrated here will facilitate the adoption of NiO HTLs in PSCs.

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