Atomic Layer Deposition of Highly Transparent Platinum Counter Electrodes for Metal/Polymer Flexible Dye‐Sensitized Solar Cells

Atomic layer deposition (ALD) is used to deposit Pt nanoparticles at low temperature (25–150 °C) to fabricate highly transparent counter electrodes (CEs) for flexible dye‐sensitized solar cells (DSCs). The Pt nanoparticles (NPs) are deposited for different number of ALD cycles on indium tin oxide (ITO)/polyethylene naphthalate (PEN) substrates. Rutherford backscattering spectroscopy (RBS) and transmission electron microscopy (TEM) are used to assess the Pt NP loading, density, and size. There is a trade‐off between transparency and catalytic activity of the CE, and the best cell performances of back‐side‐illuminated DSCs (≈3.7% efficiency) are achieved for Pt ALD at temperatures in the range of 100–150 °C, even though deposition at 25 °C is also viable. The best cell produced with ALD platinized CE (100 cycles at 100 °C) outperforms the reference cells fabricated with electrodeposited and sputtered Pt CEs, with relative improvements in efficiency of 19% and 29%, respectively. In addition, these parameters are used to fabricate a large area CE for a sub‐module (active area of 17.6 cm²), resulting in an efficiency of 3.1%, which demonstrates the scalability of the process.     

Flexible Supercapacitors Based on Bacterial Cellulose Paper Electrodes

Supercapacitors based on freestanding and flexible electrodes that can be fabricated with bacterial cellulose (BC), multiwalled carbon nanotubes (MWCNTs), and polyaniline (PANI) are reported. Due to the porous structure and electrolyte absorption properties of the BC paper, the flexible BC‐MWCNTs‐PANI hybrid electrode exhibits appreciable specific capacitance (656 F g^?1 at a discharge current density of 1 A g^?1) and remarkable cycling stability with capacitance degradation less than 0.5% after 1000 charge–discharge cycles at a current density of 10 A g^?1. The facile and low‐cost of this binder‐free paper electrode may have great potential in development of flexible energy‐storage devices.     

Achieving High Rate Performance in Layered Hydroxide Supercapacitor Electrodes

Layered hydroxides (LHs) are promising supercapacitor electrode materials with high specific capacitances. However, they generally exhibit poor energy storage ability at high current densities due to their insulating nature. Nickel‐cobalt‐aluminum LHs are synthesized and chemically treated to form LHs with enhanced conductivity that results in greatly enhanced rate performances. The key role of chemical treatment is to enable the partial conversion of Co²⁺ to a more conductive Co³⁺ state that stimulates charge transfers. Simultaneously, the defects on the LHs caused by the selective etching of Al promoted the electrolyte diffusion within LHs. As a result, the LHs show a high specific capacitance of 738 F g^?1 at 30 A g^?1, which is 57.2% of 1289 F g^?1 at 1 A g^?1. The strategy provides a facile and effective method to achieve high performance LHs for supercapacitor electrode materials.     

High‐Performance Lithium‐Iodine Flow Battery

A cathode‐flow lithium‐iodine (Li–I) battery is proposed operating by the triiodide/iodide (I₃^?/I^?) redox couple in aqueous solution. The aqueous Li–I battery has noticeably high energy density (≈0.28 kWh kg^?1_cell) because of the considerable solubility of LiI in aqueous solution (≈8.2 m ) and reasonably high power density (≈130 mW cm^?2 at a current rate of 60 mA cm^?2, 328 K). In the operation of cathode‐flow mode, the Li–I battery attains high storage capacity (≈90% of the theoretical capacity), Coulombic efficiency (100% ± 1% in 2–20 cycles) and cyclic performance (>99% capacity retention for 20 cycles) up to total capacity of 100 mAh.     

Unexpected Improved Performance of ALD Coated LiCoO2/Graphite Li‐Ion Batteries

The performance of Al₂O₃ atomic layer deposition (ALD) coatings for LiCoO₂/natural graphite (LCO/NG) batteries is investigated, where various permutations of the electrodes are coated in a full battery. Coating both electrodes with ～1 nm of alumina as well as coating only the LCO (positive electrode) enables improved performance when cycling at high voltage, where the LCO is known to degrade. However, we found that coating only the NG (negative electrode) also improves the performance of the whole battery when cycling at high voltage. Under these conditions, the uncoated LCO (positive electrode) should degrade quickly, and the NG should be unaffected. A variety of characterization techniques show the surface reactions that occur on the negative electrode and positive electrode are related, resulting in the enhanced performance of the uncoated LCO.     

Improvement of Transparent Metal Top Electrodes for Organic Solar Cells by Introducing a High Surface Energy Seed Layer

We present highly transparent and conductive silver thin films in a thermally evaporated dielectric/metal/dielectric (DMD) multilayer architecture as top electrode for efficient small molecule organic solar cells. DMD electrodes are frequently used for optoelectronic devices and exhibit excellent optical and electrical properties. Here, we show that ultrathin seed layers such as calcium, aluminum, and gold of only 1 nm thickness strongly influence the morphology of the subsequently deposited silver layer used as electrode. The wetting of silver on the substrate is significantly improved with increasing surface energy of the seed material resulting in enhanced optical and electrical properties. Typically thermally evaporated silver on a dielectric material forms rough and granular layers which are not closed and not conductive below thicknesses of 10 nm. With gold acting as seed layer, the silver electrode forms a continuous, smooth, conductive layer down to a silver thickness of 3 nm. At 7 nm silver thickness such an electrode exhibits a sheet resistance of 19 Ω/□ and a peak transmittance of 83% at 580 nm wavelength, both superior compared to silver electrodes without seed layer and even to indium tin oxide (ITO). Top‐illuminated solar cells using gold/silver double layer electrodes achieve power conversion efficiencies of 4.7%, which is equal to 4.6% observed in bottom‐illuminated reference devices employing conventional ITO. The top electrodes investigated here exhibit promising properties for semitransparent solar cells or devices fabricated on opaque substrates.