A conductive polymer (poly(p-phenylenevinylene), PPV) was covalently modified with Ru
complexes to develop an all-polymer photocathode as a conceptual alternative to dye-sensitized NiO, which is the ...current state-of-the-art photocathode in solar fuels research. Photocathodes require efficient light-induced charge-transfer processes and we investigated these processes within our photocathodes using spectroscopic and spectro-electrochemical techniques. Ultrafast hole-injection dynamics in the polymer were investigated by transient absorption spectroscopy and charge transfer at the electrode-electrolyte interface was examined with chopped-light chronoamperometry. Light-induced hole injection from the photosensitizers into the PPV backbone was observed within 10 ps and the resulting charge-separated state (CSS) recombined within ~ 5 ns. This is comparable to CSS lifetimes of conventional NiO-photocathodes. Chopped-light chronoamperometry indicates enhanced charge-transfer at the electrode-electrolyte interface upon sensitization of the PPV with the Ru
complexes and p-type behavior of the photocathode. The results presented here show that the polymer backbone behaves like classical molecularly sensitized NiO photocathodes and operates as a hole accepting semiconductor. This in turn demonstrates the feasibility of all-polymer photocathodes for application in solar energy conversion.
Historically, the field of plasmonics has been relying on the framework of classical electrodynamics, with the local-response approximation of material response being applied even when dealing with ...nanoscale metallic structures. However, when the confinement of electromagnetic radiation approaches atomic scales, mesoscopic effects are anticipated to become observable, e.g., those associated with the nonlocal electrodynamic surface response of the electron gas. Here, we investigate nonlocal effects in propagating gap surface plasmon modes in ultrathin metal-dielectric-metal planar waveguides, exploiting monocrystalline gold flakes separated by atomic-layer-deposited aluminum oxide. We use scanning near-field optical microscopy to directly access the near-field of such confined gap plasmon modes and measure their dispersion relation via their complex-valued propagation constants. We compare our experimental findings with the predictions of the generalized nonlocal optical response theory to unveil signatures of nonlocal damping, which becomes appreciable for few-nanometer-sized dielectric gaps.
Highlights
The electrical transport of the metallized vein networks is mimicked from the material transport function of the leaf vein networks.
The vein-like transparent conducting electrodes show ...ultralow sheet resistance < 0.1 Ω □
−1
, broadband optical transparency > 80%, and high current density transport capability > 6000 A cm
−2
.
The metal consumption for the metallization of the leaf veins can be as low as 4 g m
−2
.
In this contribution, inspired by the excellent resource management and material transport function of leaf veins, the electrical transport function of metallized leaf veins is mimicked from the material transport function of the vein networks. By electroless copper plating on real leaf vein networks with copper thickness of only several hundred nanometre up to several micrometre, certain leaf veins can be converted to transparent conductive electrodes with an ultralow sheet resistance 100 times lower than that of state-of-the-art indium tin oxide thin films, combined with a broadband optical transmission of above 80% in the UV–VIS–IR range. Additionally, the resource efficiency of the vein-like electrode is characterized by the small amount of material needed to build up the networks and the low copper consumption during metallization. In particular, the high current density transport capability of the electrode of > 6000 A cm
−2
was demonstrated. These superior properties of the vein-like structures inspire the design of high-performance transparent conductive electrodes without using critical materials and may significantly reduce the Ag consumption down to < 10% of the current level for mass production of solar cells and will contribute greatly to the electrode for high power density concentrator solar cells, high power density Li-ion batteries, and supercapacitors.
In this work, a double self‐assembly (DSA) process is demonstrated based on the surface interaction between graphene flakes (GFs) and surfactant molecules at water/air interface, leading to the ...formation of a stable and dense monolayer of graphene flakes (MGFs) floating on water surface. The thus prepared MGFs can be easily transferred onto various substrates almost independent of their surface wettability. During deposition both the GFs and excess surfactant molecules rearrange themselves in a self‐assembled way, so that optimal compression of the MGFs is ensured. Consequently, high performance deposition of MGFs can be easily achieved. The here‐reported process combines a fast, reliable, equipment‐free large‐area (>75 cm2 in this work) high performance MGFs deposition onto most substrates irrespective to their wettability. Moreover, the DSA process enables an excellent conformal coating of MGFs on 3D structures. Thus, this technology has the potential to pave the way to many large‐scale affordable applications of low‐cost graphene feedstocks.
A double self‐assembly process is disclosed based on surface interaction between graphene flakes and surfactant molecules at water/air interface. It enables formation of high‐performance monolayer of graphene flakes and allows a fast, reliable, and equipment‐free transferring of the formed monolayer on various substrates almost independent of their surface wettability. A conformal coating on complex 3D structures can be achieved.
We have developed an efficient, low temperature, synthetic route for ZnO nanoflowers (NFs) as photoanode material. This alternative route yields small flowerlike nanostructures, built from densely ...self-assembled tip-ended rod structures. The obtained ZnO NFs possess a large bandgap of 3.27 - 3.39 eV, enabling the generation of an average open current voltage of 0.56 V. Additionally, they show a high internal light harvesting of 14.6•10
A-mol
. The growth mechanism and self-assembly of ZnO NFs were studied in detail by joint spectroscopic-TEM investigations. It is shown that the ZnO crystallite size increases with increasing annealing temperatures and that the stress and the improved crystallinity are induced by annealing and reduce the lattice strain and the dislocation density. The bandgaps of ZnO are affected by the lattice strain revealing an optimal region of lattice strain to gain high bandgap energies. The properties of the synthesized ZnO NFs are compared with other morphologies,
. ZnO spherical aggregates (SPs) and ZnO nanorods (NRs), and are tested as electrode materials in dye-sensitized solar cells.
Herein, a process for the large‐area passivating and contacting of nanowire‐based solar cells is demonstrated. The nanowire‐based solar cells are prepared on layered laser crystallization (LLC) ...polycrystalline silicon (pc‐Si) thin films with thickness less than 2 μm. It is demonstrated that the space between the nanowires can be filled with a passivating dielectrics Al2O3 layer, and the nanowire tips can be exposed by a self‐regulating selective etching of the Al2O3 deposited on the tips and that on the sidewalls. The exposed tips of the nanowires can be connected by a transparent conducting aluminum‐doped zinc oxide (Al:ZnO or AZO) layer deposited by atomic layer deposition (ALD). The laser beam‐induced current mapping (LBIC) demonstrates that the current density can increase up to 63% at 633 nm due to light trapping and the superior passivation of the nanowires with an thin pc‐Si film of only 1.73 μm.
Nanowire‐based axial junction solar cells are prepared on laser‐crystallized polycrystalline silicon thin films with thickness less than 2 μm. The space between the nanowires is filled with a passivating dielectrics Al2O3 layer. The nanowire tips are exposed by a self‐regulating selective etching and are connected by a transparent conducting aluminum‐doped zinc oxide layer deposited by atomic layer deposition.
Layers of aligned dyes are key to photo‐driven charge separation in dye sensitized solar cells, but cannot be exploited as rectifying membranes in photocatalysis to separate half‐cells because they ...are not sufficiently stable. While impressive work on the fabrication of stable noncovalent membranes has been recently demonstrated, these membranes are inherently suffering from non‐uniform orientation of the constituting dyes. To stabilize layers made from uniformly assembled and aligned dyes, they can be covalently cross‐linked via functional groups or via chromophores at the expense of their optical properties. Here stable membranes from established dyes are reported that do not need to be elaborately functionalized nor do their chromophores need to be destroyed. These membranes are free‐standing, although being only non‐covalently linked. To enable uniform dye‐alignment, Langmuir layers made from linear, water‐insoluble dyes are used. That water‐soluble charge transfer dyes adsorb onto and intercalate into the Langmuir layer from the aqueous subphase, thus yielding free‐standing, molecularly thin membranes are demonstrated. The developed bifacial layers consist almost entirely of π‐conjugated units and thus can conduct charges and can be further engineered for optoelectronic and photocatalytic applications.
The use of template layers for extension of Langmuir‐Blodgett and related techniques to utilize water‐soluble dyes for the synthesis of quasi‐two‐dimensional molecular layers at the water‐air interface is . Bilayers and intercalated layers stable enough to span 25 µm × 25 µm meshes, although not covalently bonded, are demonstrated. Scalable fabrication of these broadly absorbing pi‐conjugated films is realized via a modified roll‐to‐roll process.
A new method of diode laser treatment of passivating contacts for solar cells application based on electron beam evaporated highly doped amorphous silicon (a‐Si) layers deposited on solar‐grade ...Czochralski wafers with SiOx tunneling layers is investigated. In a first step, an interface oxide is grown and a highly doped n‐type a‐Si layer is deposited on both sides by electron beam evaporation. In a next step, the laser treatment is applied. Two different scanning speeds of 15 and 20 mm s−1 are used. Electron backscattering diffraction and quasi‐steady‐state photo conductance measurements indicate that the a‐Si layer can be crystallized without breaking up the thin oxide layer. To determine the best parameters, the lifetime and the implied open‐circuit voltage for each laser power are measured. The first results show a fitted lifetime of 4.06 ms and an implied open‐circuit voltage up to 711 mV after a passivation step.
A new method of laser treatment of passivated contacts for wafer solar cell application was investigated. The Czochralski wafer samples were deposited with highly doped amorphous silicon layers on both sides. The samples are scanned with two different speeds and the corresponding power densities. A fitted lifetime above 4.06 ms and an implied open‐circuit voltage of 711 mV were achieved.
We describe the preparation and properties of bilayers of graphene‐ and multi‐walled carbon nanotubes (MWCNTs) as an alternative to conventionally used platinum‐based counter electrode for ...dye‐sensitized solar cells (DSSC). The counter electrodes were prepared by a simple and easy‐to‐implement double self‐assembly process. The preparation allows for controlling the surface roughness of electrode in a layer‐by‐layer deposition. Annealing under N2 atmosphere improves the electrode's conductivity and the catalytic activity of graphene and MWCNTs to reduce the I3− species within the electrolyte of the DSSC. The performance of different counter‐electrodes is compared for ZnO photoanode‐based DSSCs. Bilayer electrodes show higher power conversion efficiencies than monolayer graphene electrodes or monolayer MWCNTs electrodes. The bilayer graphene (bottom)/MWCNTs (top) counter electrode‐based DSSC exhibits a maximum power conversion efficiency of 4.1 % exceeding the efficiency of a reference DSSC with a thin film platinum counter electrode (efficiency of 3.4 %). In addition, the double self‐assembled counter electrodes are mechanically stable, which enables their recycling for DSSCs fabrication without significant loss of the solar cell performance.
The straightforward, low‐temperature, and cheap production of metal‐free counter electrodes for dye‐sensitized solar cells (DSSCs) is presented. The self‐assembly of carbon materials such as graphene flakes and multi‐walled carbon nanotubes (MWCNTs) leads to high‐performing counter electrodes. Recycling of counter electrodes in DSSCs is demonstrated and compared for different electrolyte compositions.
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