Two advances that address the main challenges of all-perovskite two-terminal tandem solar cell fabrication are reported. First, a nucleation layer is used to enable high-quality atomic layer deposition-based recombination layers that reduce electronic losses. Second, cation tuning is used for wide-band-gap perovskite solar cells that produce high, stable voltages. Combining these advances allows us to fabricate tandem perovskite solar cells on both rigid and flexible plastic substrates that have high efficiency and promising stability.

Extrinsic ions (e.g., Li+) migrate across perovskite solar cells and modify the TiO2 layer, affecting device performance and hysteresis.

We modify the fundamental electronic properties of metallic (1T phase) nanosheets of molybdenum disulfide (MoS) through covalent chemical functionalization, and thereby directly influence the kinetics of the hydrogen evolution reaction (HER), surface energetics, and stability. Chemically exfoliated, metallic MoS nanosheets are functionalized with organic phenyl rings containing electron donating or withdrawing groups. We find that MoS functionalized with the most electron donating functional group (p-(CHCH)NPh-MoS) is the most efficient catalyst for HER in this series, with initial activity that is slightly worse compared to the pristine metallic phase of MoS. The p-(CHCH)NPh-MoS is more stable than unfunctionalized metallic MoS and outperforms unfunctionalized metallic MoS for continuous H evolution within 10 min under the same conditions. With regards to the entire studied series, the overpotential and Tafel slope for catalytic HER are both directly correlated with the electron donating strength of the functional group. The results are consistent with a mechanism involving ground-state electron donation or withdrawal to/from the MoS nanosheets, which modifies the electron transfer kinetics and catalytic activity of the MoS nanosheet. The functional groups preserve the metallic nature of the MoS nanosheets, inhibiting conversion to the thermodynamically stable semiconducting state (2H) when mildly annealed in a nitrogen atmosphere. We propose that the electron density and, therefore, reactivity of the MoS nanosheets are controlled by the attached functional groups. Functionalizing nanosheets of MoS and other transition metal dichalcogenides provides a synthetic chemical route for controlling the electronic properties and stability within the traditionally thermally unstable metallic state.

Organometal–halide perovskite solar cells have greatly improved in just a few years to a power conversion efficiency exceeding 20%. This technology shows unprecedented promise for terawatt-scale deployment of solar energy because of its low-cost, solution-based processing and earth-abundant materials. We have studied charge separation and transport in perovskite solar cells—which are the fundamental mechanisms of device operation and critical factors for power output—by determining the junction structure across the device using the nanoelectrical characterization technique of Kelvin probe force microscopy. The distribution of electrical potential across both planar and porous devices demonstrates p–n junction structure at the TiO2/perovskite interfaces and minority-carrier diffusion/drift operation of the devices, rather than the operation mechanism of either an excitonic cell or a p-i-n structure. Combining the potential profiling results with solar cell performance parameters measured on optimized and thickened devices, we find that carrier mobility is a main factor that needs to be improved for further gains in efficiency of the perovskite solar cells.

An earlier paper (Zatsarinny O and Froese Fischer C 2002 J. Phys. B: At. Mol. Opt. Phys. 35 4669) presented oscillator strengths for transitions from the 2p 2 3P term to high-lying excited states of carbon. The emphasis was on the accurate prediction of energy levels relative to the ionization limit and allowed transition data from the ground state. The present paper reports some refined transition probability calculations for transitions from 2p 2 3 P, 1 D, and 1 S to all odd levels up to 2p3d 3 P o . Particular attention is given to intercombination lines where relativistic effects are most important. 1 The customary unit cm −1 used here is related to the SI units of energy (joules) by 1 cm −1 = 1.986 445 61(34)× 10 −21 J [5].

Metal nanoparticles (NPs) respond to electromagnetic waves by creating surface plasmons (SPs), which are localized, collective oscillations of conduction electrons on the NP surface. When interparticle distances are small, SPs generated in neighboring NPs can couple to one another, creating intense fields. The coupled particles can then act as optical antennae capturing and refocusing light between them. Furthermore, a molecule linking such NPs can be affected by these interactions as well. Here, we show that by using an appropriate, highly conjugated multiporphyrin chromophoric wire to couple gold NP arrays, plasmons can be used to control electrical properties. In particular, we demonstrate that the magnitude of the observed photoconductivity of covalently interconnected plasmon-coupled NPs can be tuned independently of the optical characteristics of the moleculea result that has significant implications for future nanoscale optoelectronic devices.

We demonstrate a ferroelectric response in MAPbI3 single crystals that can modulate the electronic response and increase stability.

We have simultaneously imaged the chemically bound head groups and exposed tail groups in bicomponent alkanethiolate self-assembled monolayers on Au{111} with molecular resolution. This has enabled us to resolve the controversy of scanning tunneling microscopy image interpretation and to measure the molecular polar tilt and azimuthal angles. Our local measurements demonstrate that ordered domains with different superstructures also have varied buried sulfur head group structures.