BaZrS3 is a prototypical chalcogenide perovskite, an emerging class of unconventional semiconductor. Recent results on powder samples reveal that it is a material with a direct band gap of 1.7-1.8 eV, a very strong light-matter interaction, and a high chemical stability. Due to the lack of quality thin films, however, many fundamental properties of chalcogenide perovskites remain unknown, hindering their applications in optoelectronics. Here we report the fabrication of BaZrS3 thin films, by sulfurization of oxide films deposited by pulsed laser deposition. We show that these films are n-type with carrier densities in the range of 10 19 -10 20 cm -3 . Depending on the processing temperature, the Hall mobility ranges from 2.1 to 13.7 cm 2 /Vs. The absorption coefficient is > 10 5 cm -1 at photon energy > 1.97 eV. Temperature dependent conductivity measurements suggest shallow donor levels. By assuring that BaZrS3 is a promising candidate, these results potentially unleash the family of chalcogenide perovskites for optoelectronics such as photodetectors, photovoltaics, and light emitting diodes.

Tackling the complex challenge of harvesting solar energy to generate energy-dense fuels such as hydrogen requires the design of photocatalytic nanoarchitectures interfacing components that synergistically mediate a closely interlinked sequence of light-harvesting, charge separation, charge/mass transport, and catalytic processes. The design of such architectures requires careful consideration of both thermodynamic offsets and interfacial charge-transfer kinetics to ensure long-lived charge carriers that can be delivered at low overpotentials to the appropriate catalytic sites while mitigating parasitic reactions such as photocorrosion. Here we detail the theory-guided design and synthesis of nanowire/quantum dot heterostructures with interfacial electronic structure specifically tailored to promote light-induced charge separation and photocatalytic proton reduction. Topochemical synthesis yields a metastable β-Sn 0.23 V 2 O 5 compound exhibiting Sn 5s-derived midgap states ideally positioned to extract photogenerated holes from interfaced CdSe quantum dots. The existence of these midgap states near the upper edge of the valence band (VB) has been confirmed, and β-Sn 0.23 V 2 O 5 /CdSe heterostructures have been shown to exhibit a 0 eV midgap state-VB offset, which underpins ultrafast subpicosecond hole transfer. The β-Sn 0.23 V 2 O 5 /CdSe heterostructures are further shown to be viable photocatalytic architectures capable of efficacious hydrogen evolution. The results of this study underscore the criticality of precisely tailoring the electronic structure of semiconductor components to effect rapid charge separation necessary for photocatalysis.

Semiconductor heterostructures for solar energy conversion interface light-harvesting semiconductor nanoparticles with wide-band-gap semiconductors that serve as charge acceptors. In such heterostructures, the kinetics of charge separation depend on the thermodynamic driving force, which is dictated by energetic offsets across the interface. A recently developed promising platform interfaces semiconductor quantum dots (QDs) with ternary vanadium oxides that have characteristic midgap states situated between the valence and conduction bands. In this work, we have prepared CdS/β-Pb0.33V2O5 heterostructures by both linker-assisted assembly and surface precipitation and contrasted these materials with CdSe/β-Pb0.33V2O5 heterostructures prepared by the same methods. Increased valence-band (VB) edge onsets in X-ray photoelectron spectra for CdS/β-Pb0.33V2O5 heterostructures relative to CdSe/β-Pb0.33V2O5 heterostructures suggest a positive shift in the VB edge potential and, therefore, an increased driving force for the photoinduced transfer of holes to the midgap state of β-Pb0.33V2O5. This approach facilitates a ca. 0.40 eV decrease in the thermodynamic barrier for hole injection from the VB edge of QDs suggesting an important design parameter. Transient absorption spectroscopy experiments provide direct evidence of hole transfer from photoexcited CdS QDs to the midgap states of β-Pb0.33V2O5 NWs, along with electron transfer into the conduction band of the β-Pb0.33V2O5 NWs. Hole transfer is substantially faster and occurs at <1-ps time scales, whereas completion of electron transfer requires 530 ps depending on the nature of the interface. The differentiated time scales of electron and hole transfer, which are furthermore tunable as a function of the mode of attachment of QDs to NWs, provide a vital design tool for designing architectures for solar energy conversion. More generally, the approach developed here suggests that interfacing semiconductor QDs with transition-metal oxide NWs exhibiting intercalative midgap states yields a versatile platform wherein the thermodynamics and kinetics of charge transfer can be systematically modulated to improve the efficiency of charge separation across interfaces.

BaZrS 3 , a prototypical chalcogenide perovskite, has been shown to possess a direct band gap, an exceptionally strong near band edge light absorption, and good carrier transport. Coupled with its great stability, nontoxicity with earth-abundant elements, it is thus a promising candidate for thin film solar cells. However, its reported band gap in the range of 1.7–1.8 eV is larger than the optimal value required to reach the Shockley–Queisser limit of a single-junction solar cell. Here, we report the synthesis of Ba(Zr 1– x Ti x )S 3 perovskite compounds with a reduced band gap. It is found that Ti-alloying is extremely effective in band gap reduction of BaZrS 3 : a mere 4 atom % alloying decreases the band gap from 1.78 to 1.51 eV, resulting in a theoretical maximum power conversion efficiency of 32%. Higher Ti-alloying concentration is found to destabilize the distorted chalcogenide perovskite phase.

Conspectus The development of efficient solar energy conversion to augment other renewable energy approaches is one of the grand challenges of our time. Water splitting, or the disproportionation of H2O into energy-dense fuels, H2 and O2, is undoubtedly a promising strategy. Solar water splitting involves the concerted transfer of four electrons and four protons, which requires the synergistic operation of solar light harvesting, charge separation, mass and charge transport, and redox catalysis processes. It is unlikely that individual materials can mediate the entire sequence of charge and mass transport as well as energy conversion processes necessary for photocatalytic water splitting. An alternative approach, emulating the functioning of photosynthetic systems, involves the utilization of hybrid systems wherein different components perform the various functions required for solar water splitting. The design of such hybrid systems requires the multiple components to operate in lockstep with optimal thermodynamic driving forces and interfacial charge transfer kinetics. This Account describes a new class of nanoscale heterostructures comprising M x V2O5 nanowires, where M is a p-block cation with a (n – 1)d 10 ns 2 np 0 electronic configuration characterized by a stereoactive lone pair of electrons and x is its stoichiometry, interfaced with II–VI semiconductor quantum dots (QDs). Photocatalytic water splitting involves the transfer of excited-state holes from QDs to mid-gap states (derived from the stereoactive lone pairs of p-block cations) of nanowires, hole transport through nanowires, the reduction of protons at a QD-immobilized catalyst, and water oxidation at an anode. The M x V2O5/QD architectures provide a vast design space for evolutionary optimization of function with considerable tunability of composition and structure of the individual components as well as of the interfacial structure, thereby facilitating programmability of absorption spectra, energetic offsets, and charge-transfer reactivity. The available design space spans choice of the p-block cation M, its stoichiometry x, the composition and size of various QDs, and the nature of the nanowire/QD interface. This multivariate parameter space has been navigated by integrating first-principles modeling, diversified synthesis, spectroscopic measurements, and catalytic evaluation to facilitate the rational design of several generations of heterostructures and the systematic improvement of their photocatalytic performance. The electronic structures of the target heterostructures are predicted by DFT calculations in light of the revised lone pair model of stereoactive structural distortions and evaluated by hard X-ray photoelectron spectroscopy such as to systematically tune the interfacial band offsets. Central to this approach is the development of a topochemical “etch-a-sketch” intercalation approach that allows for facile installation of p-block cations in metastable polymorphs of V2O5. The interfacial charge transfer kinetics of M x V2O5/QD het...

Recent advances in the field of flexible electronics have garnered immense attention. Flexible pressure sensors with high sensitivity and the capability of being additively manufactured are becoming crucial for monitoring signals pertaining to various stimuli. Herein, we describe a conformal resistive pressure sensor by direct writing of metal nanowires onto flexible ceramics for impact sensing and pressure monitoring under extreme environments. The conformal pressure sensor shows a sensitivity of 1.45 kPa −1 for static pressures as low as 49 Pa to 4905 Pa, a fast response time of 70 ms, and high cyclic stability and reliability (>1000 cycles). It can also be utilized for wireless detection of impacts and pressure impacts as a consequence of laser shockwaves with resulting dynamic pressures ranging from 0.17−0.29 MPa. The printed pressure sensor also displays the capability of detecting the pulse and providing vital information regarding the arterial physical situation in a noninvasive way. The findings shown here detail the capability of sensor electronics with the capability of additive manufacturing for next-generation flexible hybrid electronics.

Copper has attracted immense interest in advanced electronics attributed to its abundance and high electrical and thermal characteristics. However, the ease of oxidation when subjected to heat and humidity drastically limits its material reliability under extreme environments. Here, we utilize copper nanoplates as a building block to achieve a thermally stable (upwards of 1300 °C), antioxidation, and anticorrosion-printed conductor, with the capability of additively manufacturing on Corning flexible Alumina Ribbon Ceramic. We elucidate the printed copper nanoplates with a low sheet resistance of 4 mΩ/sq/mil by means of a surfacecoordinated formate that inculcates high oxidation and corrosion resistance on a molecular level. In addition, an in situ copper− graphene conversion leads to a hybridized conductor displaying stability at elevated temperatures up to 1300 °C with high ampacity. Further mechanistic studies reveal high-temperature stability from in situ graphene conversion for copper and graphene interfaces, and preferential stacking of copper nanoplates, distinctly suited for emerging high-temperature flexible electronics.

We synthesized a new class of heterostructures by depositing CdS, CdSe, or CdTe quantum dots (QDs) onto α-V2O5 nanowires (NWs) via either successive ionic layer adsorption and reaction (SILAR) or linker-assisted assembly (LAA). SILAR yielded the highest loadings of QDs per NW, whereas LAA enabled better control over the size and properties of QDs. Soft and hard x-ray photoelectron spectroscopy in conjunction with density functional theory calculations revealed that all α-V2O5/QD heterostructures exhibited Type-II band offset energetics, with a staggered gap where the conduction- and valence-band edges of α-V2O5 NWs lie at lower energies (relative to the vacuum level) than their QD counterparts. Transient absorption spectroscopy measurements revealed that the Type-II energetic offsets promoted the ultrafast (10−12–10−11 s) separation of photogenerated electrons and holes across the NW/QD interface to yield long-lived (10−6 s) charge-separated states. Charge-transfer dynamics and charge-recombination time scales varied subtly with the composition of heterostructures and the nature of the NW/QD interface, with both charge separation and recombination occurring more rapidly within SILAR-derived heterostructures. LAA-derived α-V2O5/CdSe heterostructures promoted the photocatalytic reduction of aqueous protons to H2 with a 20-fold or greater enhancement relative to isolated colloidal CdSe QDs or dispersed α-V2O5 NWs. The separation of photoexcited electrons and holes across the NW/QD interface could thus be exploited in redox photocatalysis. In light of their programmable compositions and properties and their Type-II energetics that drive ultrafast charge separation, the α-V2O5/QD heterostructures are a promising new class of photocatalyst architectures ripe for continued exploration.