In this work, we employ vacuum deposited Au nanoparticles (∼4 nm) to control the defect density on the surface of hydrothermally synthesized ZnO nanorod arrays (ZnO-NR), which are of interest for electron-transport layers in perovskite solar cells. Using a combination of photoluminescence spectroscopy, X-ray photoelectron spectroscopy, and ultraviolet photoelectron spectroscopy, we show that the Au particles reduce the presence of defects in the ZnO-NR. We discuss this in terms of trap filling due to band bending at the ZnO-NR surface. As a proof-of-concept, we apply the Au-decorated ZnO-NR as electron-transport layers in mixed-cation and mixed-halide lead perovskite solar cells (Cs0.15FA0.85PbI2.75Br0.25). Devices prepared with the Au-decorated ZnO-NR electron-transport layers demonstrate higher open-circuit voltages and fill factors compared to solar cells prepared with pristine ZnO-NR, resulting in an increase in the power-conversion efficiency from 11.7 to 13.7%. However, the operational stability of the solar cells is not improved by the Au nanoparticles, indicating that bulk properties of the perovskite may limit device lifetime.

A poly(biphenylene−pyrazinylene) (PPz, E g opt = 3.10 eV) and a head-to-tail regioregular polypyridine (rr-P4Py, E g opt = 3.25 eV) equipped with 1-alkenyl side chains have been prepared and postfunctionalized by hydroboration with different hydroboranes (9H-BBN, (C 6 F 5) 2 B-H (BPF-H), Cl 2 B-H) to give the corresponding ladder polymers featuring intramolecular coordinative N → B bonds. Characterization of the optical and electrochemical properties of the postfunctionalized polymers shows that the borylation strongly increases their electron affinity and lowers the optical gaps. Electron affinities between −3.75 eV (PPzBBN, E g opt = 2.16 eV) and −4.35 eV (PPzBPF, E g opt = 2.07 eV) can be reached for hydroborated PPz, while rr-P4Py-derivatives reach LUMO levels of −3.45 eV (P4PyBBN, E g opt = 2.88 eV), −3.85 eV (P4PyBPF, E g opt = 2.95 eV), and −4.15 eV (P4PyBCl 2 , E g opt = 2.95 eV). The potential of this class of compounds as electron acceptors is demonstrated by the investigation of the semiconducting properties of PPzBBN and PPzBPF, which showed ambipolar charge transport with hole and electron mobilities in order of 2 × 10 −5 cm 2 V −1 s −1. The polymers were tested as acceptors in all-polymer solar cells, which yielded functioning devices, with open-circuit voltages that directly reflect the electron affinity of the employed acceptor.

We report on the simple fabrication of Ag NP films via thermal evaporation and subsequent annealing. The NPs are formed on indium tin oxide electrodes, coated with PEDOT:PSS and implemented into PCPDTBT:PC70BM solar cells. Scanning electron microscopy and atomic force microscopy are used to determine the size distributions and surface coverage of the NP film. We apply finite‐difference time‐domain techniques to model the optical properties of different nanoparticle films and compare this with the absorption properties of the organic active layer. The simulations demonstrate that the absorption and scattering efficiency of the particles are very sensitive to particle geometry. Solar cells prepared with window electrodes containing NP layers with less surface coverage, show a 14.8% improvement in efficiency. We discuss variations in the external quantum efficiency of the devices in terms of forward scattering and parasitic absorption losses induced by the NP layer. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

The influence of ZnO seed layer thickness in Squaraine (SQ) is investigated: PC71BM bulk heterojunction solar cells that incorporate ZnO nanorods. The thickness of the ZnO seed layer varies between 16–249 nm by changing the concentration of the precursor solution. With atomic force microscopy (AFM), X‐Ray Diffraction (XRD), and Scanning Electron Microscopy (SEM) studies, it is shown that this approach allows to systematically tune the thickness of the ZnO seed layer without influencing seed layer grain size, or the morphology of the ZnO nanorods that are deposited on top of the seed layer. The proof‐of‐concept is demonstrated in SQ:PC71BM solar cells. It is found that seed layers with 55 nm thickness yield the highest short circuit current densities, resulting in power conversion efficiencies of 2.5 ± 0.1%. These results are compared to SQ:PC71BM solar cells prepared in planar architectures, and it is observed that both device architectures yield comparable results. The optimized nanostructured ZnO electrode enables the fabrication of BHJ devices with thick active layers without the loss in solar cell performance.

The single-atom transistor represents a quantum electronic device at room temperature, allowing the switching of an electric current by the controlled and reversible relocation of one single atom within a metallic quantum point contact. So far, the device operates by applying a small voltage to a control electrode or "gate" within the aqueous electrolyte. Here, the operation of the atomic device in the quasi-solid state is demonstrated. Gelation of pyrogenic silica transforms the electrolyte into the quasi-solid state, exhibiting the cohesive properties of a solid and the diffusive properties of a liquid, preventing the leakage problem and avoiding the handling of a liquid system. The electrolyte is characterized by cyclic voltammetry, conductivity measurements, and rotation viscometry. Thus, a first demonstration of the single-atom transistor operating in the quasi-solid-state is given. The silver single-atom and atomic-scale transistors in the quasi-solid-state allow bistable switching between zero and quantized conductance levels, which are integer multiples of the conductance quantum G = 2e /h. Source-drain currents ranging from 1 to 8 µA are applied in these experiments. Any obvious influence of the gelation of the aqueous electrolyte on the electron transport within the quantum point contact is not observed.