Department of Physics, University of Oxford Homepage

University of Oxford, Department of Physics

Semiconductors Group


* PhD projects to start in 2018

General PhD Projects open for applications:

1. Charge generation dynamics in novel materials for solar cells


Metal halide perovskites have emerged as an extremely promising photovoltaic (PV) technology due to their rapidly increasing power conversion efficiencies (PCEs) and low processing costs. Surprisingly, many of the fundamental mechanisms that underpin the remarkable performance of these materials are still poorly understood. Factors that influence the efficient operation of perovskite solar cells include electron-phonon coupling, charge-carrier mobility and recombination, light emission and re-absorption, and ion migration. During this project we will advance the efficiencies of perovskite solar cells by gaining an understanding of fundamental photon-to-charge conversion processes using a combination of ultra-fast optical techniques, e.g. photoluminescence upconversion and THz pump-probe spectroscopy. These studies feed directly into collaborative efforts aimed at addressing remaining challenges in the creation of commercially available perovskite solar cells, e.g. stability, band-gap tunability, lead-free perovskites, trap-free materials, material morphology control and alternative device structures. The project will be part of active collaboration with researchers working on solar cell fabrication within Oxford and the UK.


2. Transitions from quantum confined to fully delocalized electronic states in semiconductor nanocrystal assemblies

Semiconductor Nanocrystals

The last decade has seen rapid progress in the fabrication and assembly of nanocrystals into thin layers of semiconducting material. Such systems may allow facile deposition of high-quality inorganic semiconductor layers through simple and scalable protocols such as ink-jet printing. However, these procedures raise fundamental questions on the nature of charge transport through such layers. While in sufficiently small nanocrystals, quantum confinement leads to the formation of discrete electronic layers that may exhibit “atom-like”, energetically discrete states, increasing electronic coupling between nanocrystals may induce the formation of mini-bands or bulk-like continuum states. In this project, we will explore such transitions between fundamentally different regimes of electronic coupling and charge transport. We will spectroscopically investigate nanocrystal networks made of established lead chalcogenide inorganic semiconductors, but also explore more recently developed metal halide perovskite colloid materials. These studies will be interesting not only from a fundamental point of view, but also allow for development of such systems in light-emitting, photovoltaics or transistor devices.


3. Energy and charge transfer in biomimetic light-harvesting assemblies

Porphyrin Nanorings

Photosynthetic organisms use arrays of chlorophyll molecules to absorb sunlight and to transfer its energy to reaction centers, where it is converted into a charge gradient. These processes are remarkably fast and efficient, because the excited states are coherently delocalized over several chlorophyll units. For natural scientists striving to create new molecular light-harvesting materials for applications such as photovoltaics, the designs nature has invented for us are fantastic templates to learn from. This project will explore energy transfer within and between large porphyrin nanorings that directly mimic natural light-harvesting chlorophyl ring assemblies. By creating interfaces with electron-accepting molecules we aim to create light-harvesting layers that rival their natural counterparts in photon conversion efficiency. This project offers exciting possibilities for work in a new interdisciplinary area of research in collaboration with Prof Harry Anderson at the Universities of Oxford.


These projects allow the exploration of physical phenomena in the increasingly popular area of solution-processed and nanostructured semiconductors, and offer a high degree of training in the elegant and versatile techniques of femtosecond optical spectroscopy.

Applications for these projects can be submitted through the University's Postgraduate Admissions Programme to the Department of Condensed Matter Physics - see the official Graduate Application Guide for more information. Informal inquiries may be directed by email to Prof. Laura Herz at Some useful information on funding for International Postgraduate Students may be found here.

Current PhD Project vacancies with Centres for Doctoral Training:

EPSRC CDT in Plastic Electronics

The programme was established to train PhD students in the area of plastic electronics. The field is a growth area, with the emerging industries in organic photovoltaics and lighting having enormous potential in the context of environmentally friendly low-carbon electricity and energy efficiency. The subject is inherently interdisciplinary, encompassing basic physics, optoelectronics, physical and materials chemistry, device engineering and modelling, as well as the design, synthesis and processing of molecular electronic materials. Students accepted into the CDT program will be admitted to and register for their first year with Imperial College London, who will award an MRes degree upon successful completion of a course that includes both formally taught elements and a nine-month research project. For acceptance into the course based on this Oxford-led project, the student will spend this nine-month project with the indicated supervisors at the University of Oxford. Subject to successful completion of the MRes, the student will then be enrolled for a DPhil (Phd) program at the University of Oxford for a further three years, during which they will carry out the research project chosen at admissions point. Successful completion of this part of the CDT program will result in the award of a DPhil (PhD) degree from the University of Oxford.

University of Oxford Graduate Entry
CDT Web Pages

Pump-push-probe spectroscopy for identification and elimination of trap states in hybrid perovskites

Hybrid metal halide perovskites are promising semiconductors for next-generation solar cells now achieving power conversion efficiencies in excess of 22%. However, perovskite cells currently still suffer from sub-bandgap trap states that can act as non-radiative recombination centres, reducing device efficiencies. While the presence of traps in these materials has been inferred from charge-carrier recombination kinetics, their causes and nature are still largely unknown. Computational simulations have predicted the energies of specific point defects, however, matching experimental evidence for specific trap depths is more elusive. This project will address this issue by implementing a new spectroscopic technique, optical-pump-THz-probe-IR-push transient photoconductivity spectroscopy, to monitor de-trapping processes that are stimulated by a short laser pulse whose photon energy is matched to the trap depth. Standard optical-pump-THz-probe techniques already in operation will be extended by a third pulse of tunable photon energy that is used to “push” charges from trap states back into the conduction or valence bands. We will build on the resulting trap identification to develop processing protocols to remove specific hurdles to the adoption of perovskite as photovoltaic light-harvesters. We will target lead-free tin perovskites that currently exhibit dominant defect-related charge recombination, and mixed-halide perovskites for silicon tandems that suffer from trap-mediated halide segregation under illumination.

This project is supervised by Prof Laura Herz and Prof Michael Johnston in association with the EPSRC Centre for Doctoral Training in Plastic Electronics for start in October 2018.