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Ultrafast & Terahertz Photonics Group


Warwick Centre for Ultrafast Spectroscopy

We are part of WCUS, a joint activity between the Physics and Chemistry Departments at the University of Warwick.

Warwick Centre for Ultrafast Spectroscopy

Recent news from WCUS

   

Recent publications from the group

Cs1−xRbxSnI3 light harvesting semiconductors for perovskite photovoltaics

K.P. Marshall, S. Tao, M. Walker, D.S. Cook, J. Lloyd-Hughes, S. Varagnolo, A. Wijesekara, D. Walker, R.I. Walton and R.A. Hatton
Materials Chemistry Frontiers 2:1515 (June 2018) [ pdf ] [ ref ]

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We show that films of the 3-dimensional perovskite Cs1−xRbxSnI3 can be prepared from room temperature N,N-dimethylformamide solutions of RbI, CsI and SnCl2 for x ≤ 0.5, and that for x ≤ 0.2 film stability is sufficient for utility as the light harvesting layer in inverted photovoltaic (PV) devices. Electronic absorption and photoluminescence spectroscopy measurements supported by computational simulation, show that increasing x increases the band gap, due to distortion of the lattice of SnI6 octahedra that occurs when Cs is substituted with Rb, although it also reduces the stability towards decomposition. When Cs0.8Rb0.2SnI3 perovskite is incorporated into the model inverted PV device structure; ITO|perovskite|C60|bathocuproine|Al, an ∼120 mV increase in open-circuit is achieved which is shown to correlate with an increase in perovskite ionisation potential. However, for this low Rb loading the increase in band gap is very small (∼30 meV) and so a significant increase in open circuit-voltage is achieved without reducing the range of wavelengths over which the perovskite can harvest light. The experimental findings presented are shown to agree well with the predictions of density functional theory (DFT) simulations of the stability and electronic structure, also performed as part of this study.

Wed 13 Jun 2018, 12:34 | Tags: 2018, photoluminescence, perovskites, Lloyd-Hughes

Conduction properties of thin films from a water soluble carbon nanotube/hemicellulose complex

D. Shao, P. Yotprayoonsak, V. Saunajoki, M. Ahlskog, J. Virtanen, V. Kangas, A. Volodin, C. Van Haesendonck, M. Burdanova, C. D. W. Mosley and J. Lloyd-Hughes
Nanotechnology 29 145203 (Feb 2018) [ pdf ] [ ref ]

Complex THz conductivity of a 130nm thick DWNT/xylan compositeWe have examined the conductive properties of a carbon nanotube (CNT) based thin film, which were prepared via dispersion in water by non-covalent functionalization of the nanotubes with xylan, a type of hemicellulose. Measurements of low temperature conductivity, Kelvin Probe Force Microscopy, and high frequency (THz) conductivity elucidated the intra-tube and inter-tube charge transport processes in this material. The measurements show excellent conductive properties of the as prepared thin films, with bulk conductivity up to 2000 S/cm. The transport results demonstrate that the hemicellulose does not seriously interfere with the inter-tube conductance.

Tue 06 Feb 2018, 13:50 | Tags: THz spectroscopy, 2018, nanomaterials, Lloyd-Hughes

Tracking a hysteretic and disorder-broadened phase transition via the electromagnon response in improper ferroelectrics

C. D. W. Mosley, D. Prabhakaran and J. Lloyd-Hughes
J. Phys. D: Applied Physics 51 084002 (Jan 2018) [ pdf ][ ref ]

We demonstrate that Hysteresis in the electromagnon oscillator strength in CuZnOelectromagnons can be used to directly probe the nature of a phase transition between magnetically ordered phases in an improper ferroelectric. The antiferromagnetic/paraelectric to antiferromagnet/ferroelectric phase transition in Cu1-xZnxO (x = 0, 0.05) alloys was tracked via the electromagnon response using terahertz time-domain spectroscopy, on heating and cooling through the phase transition. The transition was found to exhibit thermal hysteresis, confirming its first-order nature, and to broaden under the influence of spin-disorder upon Zn substitution. The energy of the electromagnon increases upon alloying, as a result of the non-magnetic ions modifying the magnetic interactions that give rise to the multiferroic phase and electromagnons. We describe our findings in the context of recent theoretical work that examined improper ferroelectricity and electromagnons in CuO from phenomenological and first-principles approaches.

Wed 17 Jan 2018, 08:02 | Tags: THz spectroscopy, 2018, Lloyd-Hughes

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