The electrical transport in amorphous titanium dioxide (a-TiO 2 ) thin films deposited by atomic-layer deposition (ALD), and across heterojunctions of p + -Si|a-TiO 2 |metal substrates that had various top metal contacts, has been characterized by AC conductivity, temperaturedependent DC conductivity, space-charge-limited current (SCLC) spectroscopy, electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), and current density versus voltage (J-V) characteristics. Amorphous TiO 2 films were fabricated using either tetrakis(dimethylamido)-titanium (TDMAT) with a substrate temperature of 150 °C or TiCl 4 with a substrate temperature of 50, 100, or 150 °C. EPR spectroscopy of the films showed that the Ti 3+ concentration varied with the deposition conditions, and increases in the concentration of Ti 3+ in the films correlated with increases in film conductivity. Valence-band spectra for the a-TiO 2 films exhibited a defect-state peak below the conduction-band minimum (CBM), and increases in the intensity of this peak correlated with increases in the Ti 3+ concentration measured by EPR as well as with increases in film conductivity. The temperature dependent conduction data showed Arrhenius behavior at room temperature with an activation energy that decreased with decreasing temperature, suggesting that conduction did not occur primarily through either the valence or conduction bands. The data from all of the measurements are consistent with a Ti 3+ defect-mediated transport mode involving a hopping mechanism with a

We report the photophysical properties of the dicarboxylated diphenylisobenzofuran dye (1) bound to nanocrystalline metal oxide surfaces. With increased surface loading of 1, emission from the films is significantly quenched but with a small amount of excimer emission at maximum surface loadings. Long-lived triplets were observed by ns TA spectroscopy that are consistent with singlet fission occurring on mesoporous ZrO2. The evolution of these triplets, however, could not be convincingly resolved by our subnanosecond TA spectroscopy. Dye-sensitized devices composed of 1 on a TiO2|Al2O3 core–shell structure exhibited an unusual decrease, increase, and then decrease in J sc with respect to the thickness of Al2O3. In these films the Al2O3 acts as a tunneling barrier to slow electron injection from the singlet excited state such that singlet fission, and electron injection from the triplet state becomes competitive. Proof-of-principle self-assembled bilayer films that exhibit efficient triplet energy transfer from a low energy absorbing dye to 1 is demonstrated as another step toward a SF-based DSSC that can circumvent the Shockley–Queisser limit.

Fast and earth-abundant-element polyoxometalates (POMs) have been heavily studied recently as water oxidation catalysts (WOCs) in homogeneous solution. However, POM WOCs can be quite unstable when supported on electrode or photoelectrode surfaces under applied potential. This article reports for the first time that a nanoscale oxide coating (AlO) applied by the atomic layer deposition (ALD) aids immobilization and greatly stabilizes this now large family of molecular WOCs when on electrode surfaces. In this study, [{Ru(OH)(HO)}(γ-SiWO)] (RuSi) is supported on hematite photoelectrodes and then protected by ALD AlO; this ternary system was characterized before and after photoelectrocatalytic water oxidation by Fourier transform infrared, X-ray photoelectron spectroscopy, energy-dispersive X-ray, and voltammetry. All these studies indicate that RuSi remains intact with AlO ALD protection, but not without. The thickness of the AlO layer significantly affects the catalytic performance of the system: a 4 nm thick AlO layer provides optimal performance with nearly 100% faradaic efficiency for oxygen generation under visible-light illumination. AlO layers thicker than 6.5 nm appear to completely bury the RuSi catalyst, removing all of the catalytic activity, whereas thinner layers are insufficient to maintain a long-term attachment of the catalytic POM.

Plasmon induced hot carrier transfer is a promising novel approach for solar energy conversion, but its practical application is often hindered by its low efficiency. This work demonstrates an unprecedented quantum efficiency of plasmonic hot-electron transfer of up to 53 ± 2% from 1.7 nm silver nanoparticles to anatase nanoporous TiO2 films at 400 nm excitation. This efficient hot-electron transfer consists of contributions of both hot electrons generated by plasmon decay through exciting Ag intraband transitions and Ag-to-TiO2 interfacial charge-transfer transitions. The efficiencies of both pathways increase at smaller Ag particle sizes from 5.9 to 1.7 nm, suggesting that decreasing particle sizes is a promising way toward efficient plasmonic hot-carrier extraction.

A simple, extensible control software scheme for sequential deposition applications including atomic layer deposition, molecular beam epitaxy, and layer-by-layer deposition is presented. While single-component loops are easily programmed, nested loop architectures needed for complex multilayer thin films or compositionally graded structures are cumbersome to implement with only “For-loop” coding. Software code based on a generic tree architecture is introduced to achieve multilevel or compound sequencing. This architecture makes it possible to write many different deposition sequences without modifying the underlying software. The tree can be easily traversed using recursive techniques, simplifying the programmer's task and opening up novel material combinations and sequences to thin film researchers. A labview software implementation consisting of a few simple functions is presented, as well as a sampling of the potential complex deposition schemes facilitated by this architecture.

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Refractive index, density, and optical polarizabilities as a function of atomic layer deposition (ALD) growth temperature for titanium dioxide (TiO2) thin films are reported for the first time between 38 and 150 °C using the titanium tetrachloride-water reaction. Consistent with prior reports, Raman spectroscopy and x-ray diffraction indicate that the films are amorphous below 150 °C and form the crystalline anatase phase at deposition temperatures at or above 150 °C. Despite this change in atomic structure, mass densities of the TiO2 films are found to increase smoothly between 38 and 125 °C (3.25–3.68 g cm−3), as measured by both x-ray reflectometry (XRR) and optical ellipsometry. Molecular polarizabilities were calculated from the XRR mass densities, and ellipsometric refractive indices and were found to vary from 5.26–5.83 × 10−24 cm−3, which is consistent with prior reports of chemical vapor deposition of amorphous TiO2 thin films. Here, the authors demonstrate that the greater precision of ALD provides better control over the atomic structure and molecular polarizability of amorphous TiO2 thin films than other growth approaches, providing new opportunities for precisely studying the structure of amorphous oxides.

CsPbI3 perovskite quantum dot (QD) solar cells are a promising device platform for further development due to their improved stability compared to bulk materials. The fabrication of these devices often involves postsynthetic washing of colloidal QDs to remove surface ligands. Herein, we investigate how this postsynthetic treatment affects the charge separation (CS) and charge recombination (CR) processes at the interface of CsPbI3 QDs and the TiO2 electron extraction layer. The CS time constant at QD/TiO2 interface decrease from 457 ± 4 ps for QDs directly deposited on TiO2 to 288 ± 1 ps for QDs that were washed twice by methyl acetate, increasing the ET efficiency from 89.9 ± 0.3% to 98.3 ± 0.01%. Interestingly, this treatment also lengthens the average charge recombination time constants from 346 ± 18 ns to 1180 ± 60 ns, which is also beneficial for reducing charge recombination loss. This result demonstrates the pronounced effect of QD washing by methyl acetate (MeOAc) on interfacial charge transfer processes, suggesting the important effect of postsynthesis modification of colloidal perovskite QDs on solar cell efficiencies.