Silicon materials for high-efficiency photovoltaics

The capacity of photovoltaic (PV) installations now exceeds 1.5 TW peak worldwide due to the success of silicon-based solar cell technologies which account for >95% of production. Advances in silicon-based cells and modules will have a real-world impact on climate change mitigation and improving energy supply security. Silicon-based cell designs have continued to evolve with current tunnel oxide passivated contact (TOPCon) cells becoming the industrial standard. Record-breaking cells have efficiencies >26%, with advances in cell technologies rapidly driving efficiency towards the theoretical maximum of ~29%.

Advances in silicon solar cell efficiencies have been driven by improvements in the silicon wafers, as well as improvements in surface passivation and cell designs. Ten years ago, most solar cells were made from p-type boron doped silicon wafers, but recent advances in crystal growth have enabled p-type gallium doped wafers and even n-type wafers doped with antimony. Charge carrier lifetimes in silicon wafers start at close to the fundamental limit, but under cell operating conditions the lifetime can degrade and hence reduce cell efficiencies. Surface passivation is now routinely performed with techniques such as atomic layer deposition (ALD).

The University of Birmingham is starting a new research activity in silicon-based photovoltaics, led by Prof. John Murphy (https://www.birmingham.ac.uk/staff/profiles/eese/murphy-john) and Dr Sophie Pain (https://raeng.org.uk/programmes-and-prizes/programmes/uk-grants-and-prizes/support-for-research/research-awardees/research-fellowships-awardees/2024-2029/dr-sophie-pain/). Laboratory-based projects are available in several research areas including:

• Understanding light- and elevated temperature-induced degradation in the latest wafer types (e.g. Sb doped Si for TOPCon cells).

• Development of new surface passivation schemes by state-of-the-art ALD methods.

• Advanced characterisation of wafers and cells using techniques such as photoluminescence imaging, transmission electron microscopy and/ or beamline-based techniques (e.g. photo-µSR or ToF-ERDA).

• Fabrication of tandem-compatible transparent conductive oxides on silicon by ALD.

• Development of solar cell contacts less reliant on critical materials such as silver.

The student will use the School of Engineering Cleanroom facility which is being upgraded to include state-of-the-art atomic layer deposition. The student will be expected to fabricate test samples in the Cleanroom using chemical process and ALD processes, for which full training will be given. The project will provide opportunities for collaboration with leading industrial and academic partners in the UK and internationally.