No abstract

Leading edge p-i-n type halide perovskite solar cells (PSCs) severely underperform n-i-p PSCs. p-i-n type PSCs that use PEDOT:PSS hole transport layers (HTLs) struggle to generate open-circuit photovoltage values higher than 1 V. NiO HTLs have shown greater promise in achieving high V oc values albeit inconsistently. In this report, a NiO nanomesh with Ni3+ defect grown by the hydrothermal method was used to obtain PSCs with V oc values that consistently exceeded 1.10 V (champion V oc = 1.14 V). A champion device photoconversion efficiency of 17.75% was observed. Density functional theory modeling was used to understand the interfacial properties of the NiO/perovskite interface. The PCE of PSCs constructed using the Ni3+-doped NiO nanomesh HTL was ∼34% higher than that of conventional compact NiO-based perovskite solar cells. A suite of characterization techniques such as transmission electron microscopy, field emission scanning electron microscopy, intensity-modulated photocurrent spectroscopy, intensity-modulated photovoltage spectroscopy, time-resolved photoluminescence, steady-state photoluminescence, and Kelvin probe force microscopy provided evidence of better film quality, enhanced charge transfer, and suppressed charge recombination in PSCs based on hydrothermally grown NiO nanostructures.

is a well-known photocatalyst for the photocatalytic transformation of CO 2 into methane. The formation of C 2+ products such as ethane and ethanol rather than methane is more interesting due to their higher energy density and economic value, but the formation of C−C bonds is currently a major challenge in CO 2 photoreduction. In this context, we report the dominant formation of a C 2 product, namely, ethane, from the gas-phase photoreduction of CO 2 using TiO 2 nanotube arrays (TNTAs) decorated with large-sized (80−200 nm) Ag and Cu nanoparticles without the use of a sacrificial agent or hole scavenger. Isotope-labeled mass spectrometry was used to verify the origin and identity of the reaction products. Under 2 h AM1.5G 1-sun illumination, the total rate of hydrocarbon production (methane + ethane) was highest for AgCu-TNTA with a total C x H 2x+2 rate of 23.88 μmol g −1 h −1 . Under identical conditions, the C x H 2x+2 production rates for Ag-TNTA and Cu-TNTA were 6.54 and 1.39 μmol g −1 h −1 , respectively. The ethane selectivity was the highest for AgCu-TNTA with 60.7%, while the ethane selectivity was found to be 15.9 and 10% for the Ag-TNTA and Cu-TNTA, respectively. Adjacent adsorption sites in our photocatalyst develop an asymmetric charge distribution due to quadrupole resonances in large metal nanoparticles and multipole resonances in Ag−Cu heterodimers. Such an asymmetric charge distribution decreases adsorbate−adsorbate repulsion and facilitates C−C coupling of reaction intermediates, which otherwise occurs poorly in TNTAs decorated with small metal nanoparticles.

The harvesting of hot carriers produced by plasmon decay to generate electricity or drive a chemical reaction enables the reduction of the thermalization losses associated with supra-band gap photons in semiconductor photoelectrochemical (PEC) cells. Through the broadband harvesting of light, hot-carrier PEC devices also produce a sensitizing effect in heterojunctions with wide-band gap metal oxide semiconductors possessing good photostability and catalytic activity but poor absorption of visible wavelength photons. There are several reports of hot electrons in Au injected over the Schottky barrier into crystalline TiO2 and subsequently utilized to drive a chemical reaction but very few reports of hot hole harvesting. In this work, we demonstrate the efficient harvesting of hot holes in Au nanoparticles (Au NPs) covered with a thin layer of amorphous TiO2 (a-TiO2). Under AM1.5G 1 sun illumination, photoanodes consisting of a single layer of ∼50 nm diameter Au NPs coated with a 10 nm shell of a-TiO2 (Au@a-TiO2) generated 2.5 mA cm–2 of photocurrent in 1 M KOH under 0.6 V external bias, rising to 3.7 mA cm–2 in the presence of a hole scavenger (methanol). The quantum yield for hot-carrier-mediated photocurrent generation was estimated to be close to unity for high-energy photons (λ < 420 nm). Au@a-TiO2 photoelectrodes produced a small positive photocurrent of 0.1 mA cm–2 even at a bias of −0.6 V indicating extraction of hot holes even at a strong negative bias. These results together with density functional theory modeling and scanning Kelvin probe force microscope data indicate fast injection of hot holes from Au NPs into a-TiO2 and light harvesting performed near-exclusively by Au NPs. For comparison, Au NPs coated with a 10 nm shell of Al2O3 (Au@Al2O3) generated 0.02 mA cm–2 of photocurrent in 1 M KOH under 0.6 V external bias. These results underscore the critical role played by a-TiO2 in the extraction of holes in Au@a-TiO2 photoanodes, which is not replicated by an ordinary dielectric shell. It is also demonstrated here that an ultrathin photoanode (<100 nm in maximum thickness) can efficiently drive sunlight-driven water splitting.

Anodically formed TiO 2 nanotube arrays (TNTAs) constitute an optoelectronic platform that is being studied for use as a photoanode in photoelectrocatalytic cells, as an electron transport layer (ETL) in solar cells and photodetectors, and as an active layer for chemiresistive and microwave sensors. For optimal transport of charge carriers in these one-dimensional polycrystalline ordered structures, it is desirable to introduce a preferential texture with the grains constituting the nanotube walls aligned along the transport direction. Through x-ray diffraction analysis, we demonstrate that choosing the right water content in the anodization electrolyte and the use of a post-anodization zinc ion treatment can introduce a preferential texture in sub-micron length transparent TNTAs formed on non-native substrates. The incorporation of 1.5 atom% of Zn in TiO 2 nanotubes prior to annealing, was found to consistently result in the strongest preferential orientation along the [001] direction.[001] oriented TNTAs exhibited a responsivity of 523 A W −1 at a bias of 2 V for 365 nm photons, which is among the highest reported performance values for ultraviolet photodetection using titania nanotubes. Furthermore, the textured nanotubes without a Zn 2+ treatment showed a significantly enhanced performance in halide perovskite solar cells that used TNTAs as the ETL.