• Energy Research

AbstractNew hybrid materials consisting of ZnO nanorods sensitized with three different biomass‐derived carbon quantum dots (CQDs) were synthesized, characterized, and used for the first time to build solid‐state nanostructured solar cells. The performance of the devices was dependent on the functional groups found on the CQDs. The highest efficiency was obtained using a layer‐by‐layer coating of two different types of CQDs.

AbstractThe integration of piezoelectric materials onto carbon fiber (CF) can add energy harvesting and self‐power sensing capabilities enabling great potential for “Internet of Things” (IoT) applications in motion tracking, environmental sensing, and personal portable electronics. Herein, a CF‐based smart composite is developed by integrating piezoelectric poly(3,4‐ethylenedioxythiophene) (PEDOT)/CuSCN‐coated ZnO nanorods onto the CF surfaces with no detrimental effect on the mechanical properties of the composite, forming composites using two different polymer matrices: highly flexible polydimethylsiloxane (PDMS) and more rigid epoxy. The PDMS‐coated piezoelectric smart composite can serve as an energy harvester and a self‐powered sensor for detecting variations in impact acceleration with increasing output voltage from 1.4 to 7.6 V under impact acceleration from 0.1 to 0.4 m s−2. Using epoxy as the matrix for a CF‐reinforced plastic (CFRP) device with sensing and detection functions produces a voltage varying from 0.27 to 3.53 V when impacted at acceleration from 0.1 to 0.4 m s−2, with a lower output compared to the PDMS‐coated device attributed to the greater stiffness of the matrix. Finally, spatially sensitive detection is demonstrated by positioning two piezoelectric structures at different locations, which can identify the location as well as the level of the impacting force from the fabricated device.

The functional biomass additive TBA-Alg simultaneously improves the PCE, stability and lead immobility of lead halide perovskite solar cells.

Electromechanical energy harvesting converts mechanical energy from the environment, such as vibration or human activity, into electrical energy that can be used to power a low power electronic device. Nanostructured piezoelectric energy harvesting devices, often termed nanogenerators, have rapidly increased in measured output over recent years. With these improvements nanogenerators have the potential to compete with more traditional micro- or macroscopic energy harvesting devices based on piezoelectric ceramics such as lead zirconate titanate (PZT), polymers such as polyvinylidene fluoride (PVDF) or electrostatic, electret or electromagnetic kinetic energy harvesters. Power output from a nanogenerator is most commonly measured through open-circuit voltage and/or short-circuit current, where power may be estimated from the product of these values. Here we show that such measures do not provide a complete picture of the output of these devices, and can be misleading when attempting to compare alternative designs. In order to compare the power output from a nanogenerator, techniques must be improved in line with those used for more established technologies. We compare ZnO nanorod/poly(methyl methacrylate) (PMMA) and ZnO nanorod/poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) devices, and show that despite an open-circuit voltage nearly three times lower the ZnO/PEDOT:PSS device generates 150 times more power on an optimum load. In addition, it is shown that the peak voltage and current output can be increased by straining the device more rapidly and therefore time-averaged power, or time-integrated measures of output such as total energy or total charge should be calculated. Finally, the internal impedance of the devices is characterised to develop an understanding of their behaviour and shows a much higher internal resistance but lower capacitive impedance for the ZnO/PMMA device. It is hoped that by following more rigorous testing procedures the performance of nanostructured piezoelectric devices can be compared more realistically to other energy harvesting technologies and improvements can be rapidly driven by a more complete understanding of their behaviour.

AbstractFerroelectric semiconductors can exhibit extraordinarily long charge carrier lifetimes following photoexcitation. However, it remains unclear whether these long‐lived charge carriers are available to participate in the necessary solar water splitting redox reactions. Presented here are coupled transient optical and photoelectrochemical measurements that demonstrate the correlation between photo‐generated hole lifetimes, photocurrent density, and the energetic driving force associated with enhanced performance in ferroelectric BaTiO3 porous photoanodes with induced polarization states. For the first time, a three‐fold increase in photocurrent density following water‐oxidation‐preferential poling is correlated with a three orders of magnitude increase in hole lifetime in comparison to an un‐poled film. Transient absorption and photocurrent measurements demonstrate the polarized films benefit from reduced charge carrier recombination, enhanced charge carrier separation, increased hole population, and more efficient electron extraction over the water oxidation relevant timescales of µs to tens of seconds. Photoelectron spectroscopy and Kelvin probe measurements elucidate the effect of the presence and polarity of a ferroelectric polarization on core and band‐edge positions and work function values, ultimately revealing energy level differences of 300–400 meV that are found to be the driving force behind the associated lifetime and photocurrent gain.

AbstractIt has recently been shown that waste biomass can be converted into a wide range of functional materials, including those with desirable optical and electronic properties, offering the opportunity to find new uses for these renewable resources. Photovoltaics is one area in which finding the combination of abundant, low‐cost and non‐toxic materials with the necessary functionality can be challenging. In this paper the performance of carbon nanodots derived from a wide range of biomaterials obtained from different biomass sources as sensitisers for TiO2‐based nanostructured solar cells was compared; polysaccharides (chitosan and chitin), monosaccharide (d‐glucose), amino acids (l‐arginine and l‐cysteine) and raw lobster shells were used to produce carbon nanodots through hydrothermal carbonisation. The highest solar power conversion efficiency (PCE) of 0.36 % was obtained by using l‐arginine carbon nanodots as sensitisers, whereas lobster shells, as a model source of chitin from actual food waste, showed a PCE of 0.22 %. By comparing this wide range of materials, the performance of the solar cells was correlated with the materials characteristics by carefully investigating the structural and optical properties of each family of carbon nanodots, and it was shown that the combination of amine and carboxylic acid functionalisation is particularly beneficial for the solar‐cell performance.

ZnO nanorod-based piezoelectric devices have gained wide attention in energy harvesting systems as they can be processed at low temperatures onto flexible plastic substrates, giving a good potential for low cost. However, the vacuum-evaporated, precious metal contacts remain a high-cost element of the devices. This paper discusses the use of transparent conductive adhesives (TCAs) as an alternative top contact that is free from both vacuum-evaporation and precious metals. TCA films of various thicknesses were tape-cast onto nickel microgrid on PET substrates and adhered using low-pressure cold-lamination to bond the adhesive component of the TCA to piezoelectric generators with the final device structure of PET/ITO/ZnO-seed/ZnO-nanorods/CuSCN/PEDOT:PSS/TCA. The piezoelectric performances of the devices were compared by measuring output voltage in open-circuit and maximum power output across a range of resistive loads. The voltage output was observed to rise with increasing TCA thickness, reaching a maximum value of 0.72 V generated with 110 mu m of TCA as top contact. However, the higher resistance due to increased TCA thickness led to decreased power output; a maximum calculated power of 0.25 mu W was obtained from the device with the thinnest TCA layer of 22 mu m. Finally, the performance of piezoelectric nanogenerators with TCA contacts were compared to a control device with an evaporated gold contact.

Aligning dipoles in ferroelectric BaTiO3 (BTO) nanoparticles enhances Li–S cathode performance by improving polysulfide adsorption.

We developed a carbon underlayer from low-cost carbon dots between FTO and hematite photoanodes. The bulk and interfacial charge transfer dynamics of hematite are greatly improved, leading to a remarkable enhancement in the photocurrent response.