Ultrafast optical techniques provide powerful probes of different states of matter, using light pulses that have femtosecond duration. In Warwick our activities span a number of areas:
studying the dynamics of the light-matter interaction in novel compounds and nanomaterials via terahertz spectroscopy and pump-probe methods,
performing terahertz medical imaging and spectroscopy,
developing methods and components for terahertz imaging and terahertz spectroscopy.
Group facilities
The Group has labs across the campus, in the main Physics building, Materials and Analytical Sciences, and Millburn House. Read more about our experimental capabilities in terahertz science and technology. We also run the Research Technology Platform.
We make use of a wide range of Warwick's excellent materials analysis equipment, including , Raman spectroscopy, and .
Join the group!
PhD positions are available for UK students and potentially for exceptional international students. Please get in touch if you are interested in PhD or MSc by Research topics in the group. We also support postdoctoral researchers to apply for independent fellowship schemes - let us know if that appeals.
Group, Theses & Photos
Contact details for our current and our photo gallery. For recent theses from the group, please see here.
Research areas
Nanomaterials
We use pump/probe spectroscopy to study how light and matter interact on femtosecond to nanosecond timescales. Using visible probes we can track electronic processes, while infrared radiation lets us study vibrational states of molecules and atomic-scale defects in semiconductors.
Performing in vivo studies of the THz properties of skin is a major initiative in the group, supported by the EPSRC Terabotics Programme GrantLink opens in a new window. We develop robust measurement protocols and test them on a statistically significant number of patients, cross-checking with other methods.
A major strand of our research is to improve our knowledge of the fundamental science underpinning new semiconductor materials, such as metal-halide perovskites, which are often attractive for photovoltaic applications.
We develop new THz devices and integrate them into novel systems designs that can perform THz imaging and THz spectroscopy faster, and with increased capabilities (e.g. polarisation control; robot-controlled probes).
Jake D. Hutchinson, Marcin Giza, Nathaniel P. Gallop, Benjamin Vella, Edward Butler-Caddle, Shaoyang Wang, James Lloyd-Hughes, Pablo Docampo and Rebecca L Milot
Adv. Optical Materials 13 e02011 (Dec 2025)
The incorporation of Ruddlesden–Popper (RP)/3D perovskite heterostructures into photovoltaic cells has been shown to increase both the efficiency and stability of the devices. Here, a series of methylammonium lead triiodide (MAPbI3) thin films treated with varying 2-phenylethylammonium (PEA) concentrations are investigated with static and ultrafast spectroscopic techniques to reveal the mechanisms of the observed performance benefits. Transient absorption spectroscopy is employed to elucidate the effect of a surface RP layer on the excited state of the MAPbI3 films and reveal that several different RP structures are formed and participate in the charge-carrier dynamics. The passivation effects of PEA are investigated with optical pump–terahertz probe (OPTP) experiments using a variety of excitation conditions to simultaneously probe the surface and bulk recombination dynamics. Fitting models to the OPTP data for each excitation scheme allows the material parameters that govern the ultrafast dynamics to be quantified. It is found that as the PEA concentration increases, the surface recombination velocity exhibits a monotonic decrease, suggesting the RP layer is effective at passivating surface traps. Furthermore, the bulk monomolecular recombination rate is also found to decrease with the addition of PEA, indicating that the benefits of this passivation approach are not limited to the upper surface of the MAPbI3 films.
A. Ali, V. Cascos, F.G. Pritchard, J.R.R. Verlet, N.R. Sutherland, J. Woolley, J. Lloyd-Hughes, M. Avdeev, A. Beeny, S.J. Clark and E.E. McCabe J. Mater. Chem. A 13 23073 (Apr 2025)
The Dion–Jacobson phases are increasingly gaining attention for their photoactivity and potential applications as photocatalysts and sensors, in addition to their polar structures. The structure – composition – property relationships for the n = 3 phases (of general formula A鈥睞2B3O10e.g., A鈥� = Rb, Cs; A = Ca, Sr, Ba; B = Nb, Ta) are not well understood because of the lack of reliable structural models for this series. Our combined experimental and computational study addresses this by determining and explaining the complex structural chemistry of these materials, and provides a guide to allow structures and properties of new materials to be predicted and understood. We find that both A鈥� and A cations determine the tilts of BO6 octahedra and hence small A2+ ions tend to give materials with larger band gaps. The polar structures observed for A = Ca phases result from 鈥減roper鈥� mechanisms and the role of the second-order Jahn–Teller effect of the B = Nb, Ta cations is discussed.
E. Butler-Caddle, K.D.G.I. Jayawardena, A. Wijesekara, R.L. Milot and J. Lloyd-Hughes Phys. Rev. Applied 22024103 (Aug 2024)
In perovskite solar cells, photovoltaic action is created by charge transport layers (CTLs) either side of the light-absorbing metal halide perovskite semiconductor. Hence, the rates for desirable charge extraction and unwanted interfacial recombination at the perovskite-CTL interfaces play a critical role for device efficiency. Here, the electrical properties of perovskite-CTL bilayer heterostructures are obtained using ultrafast terahertz and optical studies of the charge carrier dynamics after pulsed photoexcitation, combined with a physical model of charge carrier transport that includes the prominent Coulombic forces that arise after selective charge extraction into a CTL, and cross-interfacial recombination. The charge extraction velocity at the interface and the ambipolar diffusion coefficient within the perovskite are determined from the experimental decay profiles for heterostructures with three of the highest-performing CTLs, namely C60, PCBM and Spiro-OMeTAD. Definitive targets for the further improvement of devices are deduced: fullerenes deliver fast electron extraction, but suffer from a large rate constant for cross-interface recombination or hole extraction. Conversely, Spiro-OMeTAD exhibits slow hole extraction but does not increase the perovskite鈥檚 surface recombination rate, likely contributing to its success in solar cell devices.
Justas Deveikis, Marcin Giza, David Walker, Jie Liu, Claire Wilson, Nathaniel P. Gallop, Pablo Docampo, James Lloyd-Hughes and Rebecca L. Milot J. Phys. Chem. C 128 13108(July 2024)
Improved knowledge of the influence of temperature upon layered perovskites is essential to enable perovskite-based devices to operate over a broad temperature range and to elucidate the impact of structural changes upon the optoelectronic properties. We examined the Ruddlesden–Popper layered perovskite 2-thiophenemethylammonium lead iodide (ThMA2PbI4) and observed a structural phase transition between a high- and a low-temperature phase at 220 K using temperature-dependent X-ray diffraction, UV–visible absorption, and photoluminescence (PL) spectroscopy. The structural phase transition altered the tilt pattern of the inorganic octahedra layer, modifying the absorption and PL spectra. Further, we found a narrow and intense additional PL peak in the low-temperature phase, which we assigned to radiative emission from a defect-bound exciton state. In both phases we determined the thermal expansion coefficient and found values similar to those of cubic 3D perovskites, i.e., larger than those of typical substrates such as glass. These results demonstrate that the organic spacer plays a critical role in controlling the temperature-dependent structural and optoelectronic properties of layered perovskites and suggests more widely that strain management strategies may be needed to fully utilize layered perovskites in device applications.
