Optical tracking is often combined with conventional flat panel solar cells to maximize electrical power generation over the course of a day. However, conventional trackers are complex and often ...require costly and cumbersome structural components to support system weight. Here we use kirigami (the art of paper cutting) to realize novel solar cells where tracking is integral to the structure at the substrate level. Specifically, an elegant cut pattern is made in thin-film gallium arsenide solar cells, which are then stretched to produce an array of tilted surface elements which can be controlled to within ±1°. We analyze the combined optical and mechanical properties of the tracking system, and demonstrate a mechanically robust system with optical tracking efficiencies matching conventional trackers. This design suggests a pathway towards enabling new applications for solar tracking, as well as inspiring a broader range of optoelectronic and mechanical devices.
Efforts to impart elasticity and multifunctionality in nanocomposites focus mainly on integrating polymeric and nanoscale components. Yet owing to the stochastic emergence and distribution of ...strain-concentrating defects and to the stiffening of nanoscale components at high strains, such composites often possess unpredictable strain-property relationships. Here, by taking inspiration from kirigami—the Japanese art of paper cutting—we show that a network of notches made in rigid nanocomposite and other composite sheets by top-down patterning techniques prevents unpredictable local failure and increases the ultimate strain of the sheets from 4 to 370%. We also show that the sheets' tensile behaviour can be accurately predicted through finite-element modelling. Moreover, in marked contrast to other stretchable conductors, the electrical conductance of the stretchable kirigami sheets is maintained over the entire strain regime, and we demonstrate their use to tune plasma-discharge phenomena. The unique properties of kirigami nanocomposites as plasma electrodes open up a wide range of novel technological solutions for stretchable electronics and optoelectronic devices, among other application possibilities.
The power conversion efficiency of organic photovoltaic cells has increased with the introduction of the donor-acceptor heterojunction that serves to dissociate strongly bound photogenerated ...excitons. Further efficiency increases have been achieved in both polymer and small-molecular-mass organic photovoltaic cells through the use of the bulk heterojunction (BHJ), where the distance an exciton must diffuse from its generation to its dissociation site is reduced in an interpenetrating network of the donor and acceptor materials. However, the random distribution of donor and acceptor materials in such structures can lead to charge trapping at bottlenecks and cul-de-sacs in the conducting pathways to the electrodes. Here, we present a method for growing crystalline organic films into a controlled bulk heterojunction; that is, the positions and orientations of donor and acceptor materials are determined during growth by organic vapour-phase deposition (OVPD), eliminating contorted and resistive conducting pathways while maximizing the interface area. This results in a substantial increase in power conversion efficiency compared with the best values obtained by 'random' small-molecular-weight BHJ solar cells formed by high-temperature annealing, or planar double heterojunction photovoltaic cells using the same archetypal materials systems.
In this work, bis-(triisopropylsilylethynyl) pentacene (TIPS pentacene) films were fabricated with a newly designed system for controlled solution casting with adjustable nitrogen flow and deposition ...temperature, which consequently enabled a systematic examination of crystal orientation-dependent mobilities in single crystal and single-crystal textured TIPS pentacene transistors. One of the two
π–
π stacking directions in TIPS pentacene films was found to be close to 2
1
0 (or the long axis of needle-shaped TIPS pentacene films), with frequent twinning observed between crystalline domains across the
(
1
2
¯
0
)
planes that are the lateral facets for individual crystallites. The 2
1
0 axes of crystalline TIPS pentacene thin films ran across source–drain channels at different angles, showing a ten-fold hole mobility increase as the 2
1
0 crystallographic axis became parallel to the channel direction. Our results also suggest that the controlled solution casting may be a promising method in fabricating solution-processible small-molecule organic semiconductors with varied morphologies.
Photoinduced charge-transfer (CT) processes play a key role in many systems, particularly those relevant to organic photovoltaics and photosynthesis. Advancing the understanding of CT processes calls ...for comparing their rates measured via state-of-the-art time-resolved interface-specific spectroscopic techniques with theoretical predictions based on first-principles molecular models. We measure charge-transfer rates across a boron subphthalocyanine chloride (SubPc)/C60 heterojunction, commonly used in organic photovoltaics, via heterodyne-detected time-resolved second-harmonic generation. We compare these results to theoretical predictions based on a Fermi’s golden rule approach, with input parameters obtained using first-principles calculations for two different equilibrium geometries of a molecular donor–acceptor in a dielectric continuum model. The calculated rates (∼2 ps–1) overestimate the measured rates (∼0.1 ps–1), which is consistent with the expectation that the calculated rates represent an upper bound over the experimental ones. The comparison provides valuable understanding of how the structure of the electron donor–acceptor interface affects the CT kinetics in organic photovoltaic systems.
There is growing need to develop efficient methods for early-stage drug discovery, continuous manufacturing of drug delivery vehicles, and ultra-precise dosing of high potency drugs. Here we ...demonstrate the use of solvent-free organic vapor jet printing to deposit nanostructured films of small molecular pharmaceutical ingredients, including caffeine, paracetamol, ibuprofen, tamoxifen, BAY 11-7082 and fluorescein, with accuracy on the scale of micrograms per square centimeter, onto glass, Tegaderm, Listerine tabs, and stainless steel microneedles. The printed films exhibit similar crystallographic order and chemistry as the original powders; controlled, order-of-magnitude enhancements of dissolution rate are observed relative to powder-form particles. In vitro treatment of breast and ovarian cancer cell cultures in aqueous media by tamoxifen and BAY 11-7082 films shows similar behavior to drugs pre-dissolved in dimethyl sulfoxide. The demonstrated precise printing of medicines as films, without the use of solvents, can accelerate drug screening and enable continuous manufacturing, while enhancing dosage accuracy.Traditional approaches used in the pharmaceutical industry are not precise or versatile enough for customized medicine formulation and manufacture. Here the authors produce a method to form coatings, with accurate dosages, as well as a means of closely controlling dissolution kinetics.
UV−visible diffuse reflectance spectroscopy was used to probe the electronic structure and domain size of tungsten oxide species in crystalline isopolytungstates, monoclinic WO3, and dispersed WO x ...species on ZrO2 surfaces. UV−visible absorption edge analysis, CO2 chemisorption, and Raman spectroscopic results show that three distinct regions of WO x coverage on ZrO2 supports appear with increasing WO x surface density: submonolayer region (0−4 W nm-2), polytungstate growth region (4−8 W nm-2), and polytungstate/crystalline WO3 coexistence region (>8 W nm-2). The structure and catalytic activity of WO x species on ZrO2 is controlled only by WO x surface density (W nm-2), irrespective of the WO x concentration, oxidation temperature, and ZrO2 surface area used to obtain a particular density. The submonolayer region is characterized by distorted octahedral WO x species that are well dispersed on the ZrO2 surface. These species show a constant absorption edge energy, they are difficult to reduce, and contain few acid sites where o-xylene isomerization can occur at 523 K. At intermediate WO x surface densities, the absorption edge energy decreases, WO x domain size increases, WO x species become easier to reduce, and o-xylene isomerization turnover rates (per W atom) increase with increasing WO x surface density. At high WO x surface densities, a polytungstate monolayer coexists with monoclinic WO3 crystallites. The growth of monoclinic WO3 crystallites results in lower o-xylene isomerization turnover rates because WO x species become inaccessible to reactants. In the presence of H2 at typical catalytic reaction temperatures (∼523 K), strong acid sites form on WO x −ZrO2 catalysts with polytungstate domains by a slight reduction of the cluster and delocalization of an electron from an H atom resulting in H+δ (Brønsted acid site).
A substantial broadband increase in the external quantum efficiency (EQE) of thin‐film organic photovoltaic (OPV) devices using near‐field coupling to surface plasmons is reported, significantly ...enhancing absorption at surface plasmon resonance (SPR). The devices tested consist of an archetypal boron subpthalocyanine chloride/fullerene (SubPc/C60) donor/acceptor heterojunction embedded within a planar semitransparent metallic nanocavity. The absorption and EQE are modeled in detail and probed by attenuated total internal reflection spectroscopy with excellent agreement. At SPR, the EQE can be enhanced fourfold relative to normal incidence, due to simulated ninefold enhancement in active layer absorption efficiency. The response at SPR is thickness‐independent, down to a few monolayers, suggesting the ability to excite monolayer‐scale junctions with an EQE of ≈6% and a 16‐fold absorption enhancement over normal incidence. These results potentially impact the future design of plasmonically enhanced thin‐film photovoltaics and photodetectors and enable the direct analysis of the dynamics of photocurrent production at OPV heterojunctions.
The process of broadband plasmonic photocurrent enhancement is studied using planar organic photovoltaics composed of archetypal boron subpthalocyanine chloride/fullerene (SubPc/C60) heterojunctions embedded within semitransparent silver nanocavities. External quantum efficiency enhancement factors of 4.3×/2.8× over normal incidence are demonstrated for inverted/conventional devices on resonance. The absorption efficiency is shown to be nearly identical between devices at surface plasmon resonance, while a higher internal quantum efficiency is exhibited in inverted structures.
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