Department of Physics, University of Oxford Homepage

















University of Oxford, Department of Physics

Semiconductors Group


Vacancies

* PhD projects to start in 2017

Current PhD Project vacancies with Centres for Doctoral Training:

EPSRC CDT in New and Sustainable Photovoltaics

The aim of the Centre for Doctoral Training in New and Sustainable Photovoltaics is to meet the new challenges of growth, affordability and sustainability for future solar photovoltaic technologies. Students will apply for individual research projects at one of seven universities. For this Oxford-led project, the student will join the University of Oxford, which will, upon successful completion of the course, award the PhD degree. All students will be introduced to the project environment and tasks of their main research project from the outset. In addition to their research project all students in the CDT will participate in a taught course in photovoltaics during their first year. This will be taught in two week blocks hosted by each of the participating universities and will involve a mixture of lectures, group exercises, masterclasses and industrial lectures/visits. Students will therefore receive the benefit of the different facilities, expertise and approaches of the leading photovoltaics groups in the UK. In addition, students will form a network that will enhance their learning and research collaboration both now and in their future careers.

University of Oxford Graduate Entry
CDT Web Pages

Stability of Hybrid Perovskites for Tandem Solar Cells

Photovoltaics

Hybrid metal halide perovskites have emerged as an important new class of materials for photovoltaics. Their integration in tandem with other photovoltaic technologies such as silicon cells is highly desirable, allowing low-cost cells with efficiencies in excess of the Shockley-Queisser single-junction limit. Optimized photocurrent matching between top and bottom cells requires careful control over band-gap energy of the perovskite for which the development of stable, compositionally tuneable perovskites will be essential. In this project, we will explore emerging hybrid perovskites with a focus on developing our fundamental understanding of how structural properties in these relatively “soft” semiconductors are related to their thermodynamic stability and optoelectronic properties. The project will be based around a multi-facetted experimental investigation, involving structural probes e.g. through X-ray diffraction, and transient charge-carrier probes using THz conductivity and photoluminescence spectroscopy. Using these measurements, we will establish links between structural and electronic properties, which will allow us to reveal e.g. the mechanisms behind light- and electric-field-induced changes in these materials, and the causes of miscibility gaps. We will exploit the resulting insight to develop new perovskite compositions and material processing protocols to create thin-film perovskite absorbers with long term stability for tandem solar cells.

This project is supervised by Prof Laura Herz and Prof Paolo Radaelli in association with the EPSRC Centre for Doctoral Training in New and Sustainable Photovoltaics for start in October 2017.

 

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

Understanding and Enhancing the Stability of Sn based perovskites for all-perovskite tandem solar cells

Porphyrin Nanorings

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. Single junction perovskite devices have reached a certified 22% PCE, but the first commercial iterations of perovskite PVs will likely be as an “add-on” to silicon (Si) PV by making perovskite-on-silicon tandem cells with enhanced efficiency. However, an all-perovskite tandem cell could deliver lower fabrication costs, but requires band gaps that have not yet been realized. The highest efficiency tandem devices would require a rear cell with a band gap of 0.9 to 1.2 eV and a front cell with a band gap of 1.7 to 1.9eV. Although materials such as FA0.83Cs0.17 Pb(IxBr1-x)3 deliver appropriate band gaps for the front cell, Pb-based materials cannot be tuned to below 1.48 eV for the rear cell. Completely replacing Pb with Sn can shift the band gap to ~1.3eV (for MASnI3), but the tin-based materials are notoriously air-sensitive and difficult to process. We have very recently demonstrated a stable 15% efficient perovskite solar cell based on a 1.2eV bandgap FA0.75Cs0.25Pb0.5Sn0.5I3 absorber and integrated this into all perovskite tandem cells delivering over 20% efficiency. The key challenges now remaining are to; i) ensure that devices incorporating this new low band gap material will be stable enough to last for 25 years; ii) Push the efficiency of the combined tandem cell to above 25 and towards 30%, to deliver a thin film PV technology with far superior efficiency as compared to Si or GaAs. Within this PhD project, through a combination of electronic and spectroscopic fundamental investigations and through device construction and engineering, we will tackle these challenges and specifically aim to understand and control the mechanisms which are inducing degradation, and those responsible for influencing the electronic properties of the perovskite absorber layers.

This project is supervised by Prof Henry Snaith and Prof Laura Herz in association with the EPSRC Centre for Doctoral Training in Plastic Electronics for start in October 2017.

 

General PhD Projects open for applications:

1. Charge generation dynamics in novel materials for solar cells

Photovoltaics

Increasing world needs for electrical power have intensified research into materials suitable for cheap and efficient solar cells. Solution-processed semiconductors offer great benefits in this area, as they can be easily processed into devices allowing cheap production of large-scale solar panels. A number of exciting new materials systems have emerged, including dye-sensitized solar cells, hybrid metal-halide perovskite cells, and all-organic molecular photovoltaics, each of which now offer power conversion efficiencies exceeding 10%. Surprisingly, many of the fundamental mechanisms underlying both the process of charge-separation from photoexcitation and subsequent motion to electrodes are still barely understood. During this project we will advance the efficiencies of photovoltaic systems 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. This project will be part of active collaboration with researchers working on solar cell fabrication within Oxford and the UK.
See further details here.

 

2. 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 researchers at the Universities of Oxford (Harry Anderson) and Nottingham (Peter Beton).
See further details here.

 

Both 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 laura.herz@physics.ox.ac.uk. Some useful information on funding for International Postgraduate Students may be found here.