energy, [4] large scale and portable energy storage becomes increasingly more important. Therefore, continued research into high-performing alternatives, which will meet the increased demand is imperative. A common way of evaluating potential alternatives for Li-based batteries involves calculating the theoretical specific capacity of potential candidates and comparing these results with other figures of merit. This reasoning leads to the conclusion that metals in the upper left corner of the periodic table are more interesting than the others. Table 1 shows these calculations together with some other parameters for common metal anodes.A second important parameter when searching for potential battery materials is the oxidation potential of the anode, where lower (less noble) is better. Comparing these parameters for the metals listed in Table 1 shows immediately that Li is one of the most promising candidates, but rare. The second most promising metal is aluminium (Al), which has a relatively high standard oxidation potential. Heavier metals and those in higher groups show much worse performance indicators. Nevertheless, this method of evaluation has to be considered with caution, because it is based on numerous assumptions. Such as, that the anode is oxidized during the charging/discharging process, which is not true for many practical systems.The literature on non-Li based intercalation batteries is clearly dominated by sodium (Na), [9,10] magnesium (Mg) [11,12] and Al [13] systems that are all more abundant natural elements than Li. There are few examples of potassium (K) [14] and (Ca), [15] which coincides clearly with the trend observed in Table 1 (as mentioned above, low performing "candidates" have been omitted in this table). Great efforts are aimed at these alternatives to improve capacity, power and cycles. Comparing Na-ion with Li-ion batteries, the common feature is a monovalent ion that can be inserted/extracted into/from the electrode material. Here, only one charge transfer takes place in contrast to Mg-ion, Ca-ion or Al-ion where two and three charges are involved in redox reactions respectively. As a result of multielectron reactions, higher specific capacity and energy density may be obtained. A key issue in order for multivalent ion insertion to be feasible is the electrode material that has to allow ion mobility.In this review, electrode materials for Al-ion batteries, namely different cathodes are discussed. Furthermore, their performance is compared highlighting drawbacks and advantages of every material.Over the last decade, optimizing energy storage has become significantly important in the field of energy conversion and sustainability. As a result of immense progress in the field, cost-effective and high performance batteries are imperative to meeting the future demand of sustainability. Currently, the best performing batteries are lithium-ion based, but limited lithium (Li) resources make research into alternatives essential. In recent years, the performance of aluminium-ion batteries ha...

1D semiconducting oxides are unique structures that have been widely used for photovoltaic (PV) devices due to their capability to provide a direct pathway for charge transport. In addition, carbon nanotubes (CNTs) have played multifunctional roles in a range of PV cells because of their fascinating properties. Herein, the influence of CNTs on the PV performance of 1D titanium dioxide nanofiber (TiO2 NF) photoelectrode perovskite solar cells (PSCs) is systematically explored. Among the different types of CNTs, single‐walled CNTs (SWCNTs) incorporated in the TiO2 NF photoelectrode PSCs show a significant enhancement (≈40%) in the power conversion efficiency (PCE) as compared to control cells. SWCNTs incorporated in TiO2 NFs provide a fast electron transfer within the photoelectrode, resulting in an increase in the short‐circuit current (J sc) value. On the basis of our theoretical calculations, the improved open‐circuit voltage (V oc) of the cells can be attributed to a shift in energy level of the photoelectrodes after the introduction of SWCNTs. Furthermore, it is found that the incorporation of SWCNTs into TiO2 NFs reduces the hysteresis effect and improves the stability of the PSC devices. In this study, the best performing PSC device constructed with SWCNT structures achieves a PCE of 14.03%.

The origin of performance enhancements in p‐i‐n perovskite solar cells (PSCs) when incorporating low concentrations of the bulky cation 1‐naphthylmethylamine (NMA) are discussed. A 0.25 vol % addition of NMA increases the open circuit voltage (Voc) of methylammonium lead iodide (MAPbI3) PSCs from 1.06 to 1.16 V and their power conversion efficiency (PCE) from 18.7% to 20.1%. X‐ray photoelectron spectroscopy and low energy ion scattering data show NMA is located at grain surfaces, not the bulk. Scanning electron microscopy shows combining NMA addition with solvent assisted annealing creates large grains that span the active layer. Steady state and transient photoluminescence data show NMA suppresses non‐radiative recombination resulting from charge trapping, consistent with passivation of grain surfaces. Increasing the NMA concentration reduces device short‐circuit current density and PCE, also suppressing photoluminescence quenching at charge transport layers. Both Voc and PCE enhancements are observed when bulky cations (phenyl(ethyl/methyl)ammonium) are incorporated, but not smaller cations (Cs/MA)—indicating size is a key parameter. Finally, it demonstrates that NMA also enhances mixed iodide/bromide wide bandgap PSCs (Voc of 1.22 V with a 1.68 eV bandgap). The results demonstrate a facile approach to maximizing Voc and provide insights into morphological control and charge carrier dynamics induced by bulky cations in PSCs.

A simple and fast “top‐down” protocol is introduced herein to prepare solution processable few‐layer phosphorene nanosheets using vortex fluidic mediated exfoliation under near‐infrared (NIR) pulsed laser irradiation. This novel shear‐exfoliation method requires short processing times and produces highly crystalline, atomically thin phosphorene nanosheets (4.3 ± 0.4 nm). The as‐prepared phosphorene nanosheets are used as an effective electron transporting material (ETM) for low‐temperature processed, planar n‐i‐p perovskite solar cells (PSCs). With the addition of phosphorene, the average power conversion efficiency (PCE) increases from 14.32% to 16.53% with a maximum PCE of 17.85% observed for the phosphorene incorporated PSCs which is comparable to the devices made using the traditional high‐temperature protocol. Experimental and theoretical (density‐functional theory) investigations reveal the PCE improvements are due to the high carrier mobility and suitable band energy alignment of the phosphorene. The work not only paves the way for novel synthesis of 2D materials, but also opens a new avenue in using phosphorene as an efficient ETM in photovoltaic devices.

All-optical ultrasound transducers are promising for imaging applications in minimally invasive surgery. In these devices, ultrasound is transmitted and received through laser modulation, and they can be readily miniaturized using optical fibers for light delivery. Here, we report optical ultrasound transmitters fabricated by electrospinning an absorbing polymer composite directly onto the end-face of optical fibers. The composite coating consisting of an aqueous dispersion of multi-walled carbon nanotubes (MWCNTs) in polyvinyl alcohol was directly electrospun onto the cleaved surface of a multimode optical fiber and subsequently dip-coated with polydimethylsiloxane (PDMS). This formed a uniform nanofibrous absorbing mesh over the optical fiber end-face wherein the constituent MWCNTs were aligned preferentially along individual nanofibers. Infiltration of the PDMS through this nanofibrous mesh onto the underlying substrate was observed and the resulting composites exhibited high optical absorption (>97%). Thickness control from 2.3 μm to 41.4 μm was obtained by varying the electrospinning time. Under laser excitation with 11 μJ pulse energy, ultrasound pressures of 1.59 MPa were achieved at 1.5 mm from the coatings. On comparing the electrospun ultrasound transmitters with a dip-coated reference fabricated using the same constituent materials and possessing identical optical absorption, a five-fold increase in the generated pressure and wider bandwidth was observed. The electrospun transmitters exhibited high optical absorption, good elastomer infiltration, and ultrasound generation capability in the range of pressures used for clinical pulse-echo imaging. All-optical ultrasound probes with such transmitters fabricated by electrospinning could be well-suited for incorporation into catheters and needles for diagnostics and therapeutic applications.