Thin films for silicon-based tandem photovoltaics

More than 90% of photovoltaic solar cells are made from crystalline silicon, and this market share is increasing as worldwide installations approach the terawatt level. The best single-junction silicon cells have efficiencies of up to 26.7%, and record cells are closing in on silicon’s maximum efficiency of 29.4%. This limit can be exceeded by depositing, or mounting a wider bandgap semiconductor on top of the silicon based solar cell to form a tandem configuration, which are capable of exceeding efficiencies of 35%. Such device architectures are very timely, and if successful will have significant impact on global energy production through renewable sources.

Much attention has focused on placing a variety of thin film semiconductors onto silicon (e.g. perovskites, CdTe, CIGS), but less attention has been paid on the interface with the silicon. The Electronic Materials and Interfaces Group in Warwick Engineering aims to address the fundamental science underpinning the interface between the silicon and the thin film semiconductor to accelerate the development of tandem cells. Much of our research is in close collaboration with industrial partners and we frequently collaborate with many of the world’s leading institutions in the silicon photovoltaics field.

The aim of this PhD project is to develop ultra-thin passivation films (< 1 nm) using atomic layer deposition (ALD), which exhibit excellent thermal and electrical stability when applied to semiconductor surfaces. Central to the project is Warwick’s new £400k ALD facility which was commissioned in the Science City Cleanroom in early 2018. The objective will be to develop a fundamental understanding of the passivation mechanism at the atomic scale and how processes can be manipulated in order to achieve optimal long-term thermal and electrical properties. The films developed will then be applied in a range of contexts; mainly silicon photovoltaics (with a focus on tandems), but also on other applications such lithium ion battery anodes. The student will gain experience with cleanroom processing, and cutting-edge materials characterisation by electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and nuclear magnetic resonance. In addition, the student will use silicon-specific analytical techniques including for minority carrier lifetime measurements, and photoluminescence imaging.

The project would suit someone with a physics, materials science, or electrical engineering background. Dr Murphy leads the multi-institution EPSRC SuperSilicon PV project (EP/M024911/1) and is part of the EPSRC Supergen Solar Network+ (EP/S000763/1) so there will be opportunities for collaboration with other universities in the UK. There are likely to be opportunities for visiting international laboratories for short periods, and for attendance at national and international conferences.

Potential applicants should send their CV to the supervisors by e-mail ([Email Address Removed] and [Email Address Removed]) or using the contact form below.