Naughty Paul

Single-layered MoS₂ doped with Re (n-type) and Au (p-type) are investigated by in situ scanning transmission electron microscopy. Re atoms substituting Mo sites enhance the local chemical affinity, evidenced by agglomeration of other dopant/impurity atoms. Au atoms exist as adatoms and show larger mobility under the electron beam. These behaviors are consistent with density functional theory calculations.

An inverted architecture of quantum dot solar cells is demonstrated by introducing a novel ZnO method on top of the PbS CQD film. Improvements in device characteristics stem from constructive optical interference from the ZnO layer that enhances absorption in the PbS CQD layer. Outstanding diode characteristics arising from a superior PbS/ZnO junction provide a further electronic advantage.

Colloidal quantum dot solar cells (CQDSCs) are attracting growing attention owing to significant improvements in efficiency. However, even the best depleted-heterojunction CQDSCs currently display open-circuit voltages (V_OCs) at least 0.5 V below the voltage corresponding to the bandgap. We find that the tail of states in the conduction band of the metal oxide layer can limit the achievable device efficiency. By continuously tuning the zinc oxide conduction band position via magnesium doping, we probe this critical loss pathway in ZnO–PbSe CQDSCs and optimize the energetic position of the tail of states, thereby increasing both the V_OC (from 408 mV to 608 mV) and the device efficiency.

A fundamental loss mechanism in depleted-heterojunction colloidal quantum dot solar cells (CQDSCs) is identified to arise from the metal oxide conduction band tail. This loss is studied in ZnO–PbSe CQDSCs and minimized by optimizing the ZnO–PbSe conduction band alignment via magnesium-doping of the ZnO. Significant improvements in open-circuit voltage and efficiency are achieved.

Semiconducting MoS_2(1-x)Se_2x mono­layers where x = 0–0.40 are successfully grown over large areas. A random arrangement of the S and Se atoms and a tunable bandgap photoluminescence are observed. Atomically thin, 2D semiconductor alloys with tunable bandgaps have potential applications in nano- and opto-electronics. Field-effect transistors fabricated with the monolayers exhibit high on/off ratios of >10⁵.

We fabricated a robust electrocatalyst by chemically depositing an ultrathin layer of amorphous molybdenum sulfide on the internal surface of dealloyed nanoporous gold. The catalyst exhibits superior electrocatalysis toward hydrogen evolution reaction in both acidic and neutral media with 2–6 times improvement in catalytic activies compared to other molybdenum sulfide based materials.

Two types of quantum nanostructures based on self-assembled GaAs quantumdots embedded into GaAs/AlGaAs hexagonal nanowire systems are reported, opening a new avenue to the fabrication of highly efficient single-photon sources, as well as the design of novel quantum optics experiments and robust quantum optoelectronic devices operating at higher temperature, which are required for practical quantum photonics applications.

Driven by the potential advantages and promising applications of organic solar cells, donor-acceptor (D-A) polymers have been intensively investigated in the past years. One of the strong electron-withdrawing groups that were widely used as acceptors for the construction of D-A polymers for applications in polymer solar cells and FETs is isoindigo. The isoindigo-based polymer solar cells have reached efficiencies up to ∼7% and hole mobilities as high as 3.62 cm² V⁻¹ s⁻¹ have been realized by FETs based on isoindigo polymers. Over one hundred isoindigo-based small molecules and polymers have been developed in only three years. This review is an attempt to summarize the structures and properties of the isoindigo-based polymers and small molecules that have been reported in the literature since their inception in 2010. Focus has been given only to the syntheses and device performances of those polymers and small molecules that were designed for use in solar cells and FETs. Attempt has been made to deduce structure-property relationships that would guide the design of isoindigo-based materials. It is expected that this review will present useful guidelines for the design of efficient isoindigo-based materials for applications in solar cells and FETs.

This review summarizes isoindigobased polymers and small molecules for bulk-heterojunction solar cells and field-effect transistors (FETs). The structure-property relationships are deduced based on results from the literature and density functional theory (DFT) calculations. Isoindigo-based materials are anticipated to play an important role in the development of solar cells and FETs due to their appropriate energy levels, high absorption coefficients, and mobility.

Assembly of single layers: Three-dimensional assembly of single-layered MoS₂ is achieved on a large scale via a solution method. The as-prepared tubular architectures have tunable size and mesopores in the shell, which are desirable for applications. As a example, they exhibit excellent lithium storage properties and are highly active for hydrodesulfurization of thiophene resulting from their structural advantages.

“My biggest motivation is curiosity. The most exciting thing about my research is not knowing what comes next. …” This and more about Alexander Eychmüller can be found on page 2028.