Congratulations to Helen on the publication of her first (joint) first author paper, which is a review of recent progress understanding how layered semiconducting perovskites can be designed and used in photovoltaic applications.
D. Sirbu, F. H. Balogun, R. L. Milot and P. Docampo
Advanced Energy Materials (May 2021)
Layered hybrid perovskites (LPKs) have emerged as a viable solution to address perovskite stability concerns and enable their implementation in wide-scale energy harvesting. Yet, although more stable, the performance of devices incorporating LPKs still lags behind that of state-of-the-art, multi-cation perovskite materials. This is typically assigned to their poor charge transport, currently caused by the choice of cations used within the organic layer. On balance, a compromise between efficiency and stability is sought, involving careful control of phase purity and distribution, interfaces and energy/charge transfer processes. Further progress is hindered by the difficulty in identifying the fundamental optoelectronic processes in these materials. Here, the high exciton binding energy of LPKs lead to the formation of multiple photoexcited species, which greatly complicate measurement interpretation. In this light, this review gives an overview of how complementary measurement techniques must be used to separate the contributions from the different species in order to identify device bottlenecks, and become a useful tool to narrow down the limitless list of organic cations. A move away from making compromises to mitigate the impact of poor charge transport is required. The root of the problem must be addressed instead through rational design of the interlayer cations.
2D sheets of atomically-thin materials have been intensively studied over the last few years, and have been found to bind together via van der Waals forces to create composites with unique optical and electronic properties. Here we report a study of the atomic structure and optoelectronic properties of some of the first examples of radial van der Waals heterostructures, where cylindrical sheets of different semiconductors (nanotubes) encase other materials. As described in our paper in Nano Letters, we found that BN overgrowth around carbon nanotube bundles created a good template for the creation of high-quality MoS2 nanotubes. This outer semiconducting wall had good electrical properties and strong optical absorption (including from the K-point excitons of MoS2), while the inner carbon nanotubes retained their excellent conductivity. This new class of composite may be suitable for unique functional optoelectronic devices on the nanoscale, such as 1D radial p-n junctions or transistors, for instance where the inner carbon nanotubes electrically control the outer semiconductor's conductivity.
Congratulations to Hannah on her first paper
Hannah's first paper presents "A Robust Protocol for In Vivo THz Skin Measurements" and has just appeared in J. Infrared MM THz - check it out here!
Congratulations to Maria on the publication of her first paper from her PhD! Her work on the negative terahertz photoconductivity of controllably doped carbon nanotubes has just appeared in ACS Photonics - click here for more.
A joint collaboration between the Chinese University of Hong Kong and the University of Warwick has developed an efficient and broadband modulator of THz radiation. By reflecting THz radiation from a conductive, gated graphene layer the team have shown that the amplitude of THz radiation pulses can be modulated by more than 99%. Further, phase modulation was acheived by working above Brewster's angle. The findings are described in a recent article in Nature Communications, and are described in an article in Physics World.
Congratulations to Sarah on the publication of her work on the vibrational properties of methylammonium lead halide perovskites, which you can read more about in J. Phys. Chem. C. In this work thin-film total internal reflection (TF-TIR) spectroscopy is shown to have an enhanced sensitivity to the vibrational properties of thin films in comparison to standard THz transmission spectroscopy. This increased sensitivity was used to track photoinduced modifications in the strengths of phonon modes under illumination.
Our work on the conductivity of double-walled carbon nanotubes wrapped in xylan, a type of hemicellulose, has recently been published in Nanotechnology. Importantly the tubes were efficiently dispersed in water, and had excellent conductive properties. The hemicellulose was shown to not seriously interfere with the inter-tube conductance. This work was led by our collaborators in Finland at Jyvaskyla. Thanks to Maria & Connor for their efforts on our FTIR and THz-TDS results.
Congratulations to Connor on the publication of his recent work in a special issue of J. Phys. D: Applied Physics devoted to the applications of ultrafast spectroscopy. In this work we demonstrate that terahertz electromagnons can be used to directly probe the nature of a phase transition between magnetically ordered phases in the improper ferroelectric CuO.