PhD Studentship: Atomic layer deposition of transparent conducting electrodes for silicon-based tandem 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. Atomic layer deposition (ALD) is a thin film deposition method used for surface passivation and is used in >50% of solar cells manufactured today.

A step change in cell efficiency progression can be achieved by the successful implementation of a tandem configuration, whereby a wider bandgap semiconductor is combined with a base cell, enabling more of the solar spectrum to be captured. To be implemented into mass production, it is highly likely that the base cell will be silicon given its maturity and manufacturing dominance. Potential top-cells include thin-film solar absorbers with a perovskite structure. To produce a tandem solar cell, it is necessary to engineer the interface between the two semiconductors. Specifically, a nanoscale interfacial layer which is both transparent to light and sufficiently conductive for charge carriers is required. The interfacial layer needs also to be compatible with the sensitivity limitations of potential top-cell materials.

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://www.birmingham.ac.uk/staff/profiles/mechanical/pain-sophie). Laboratory-based projects are available to develop new surface passivation and tandem-compatible transparent conductive oxides schemes by state-of-the-art ALD. The student will use the School of Engineering Cleanroom facility which is being upgraded to include state-of-the-art atomic layer deposition.

The objective of this PhD project is to develop an interfacial layer between the silicon device and a wider bandgap absorber, which is configured with appropriate hole and electron transport layers. The interfacial layer will be a transparent conducting electrode (TCE) deposited using atomic layer deposition (ALD). ALD, widely adopted across the photovoltaics industry, allows for deposition of uniform, conformal films with atomic layer control over film properties. This project will explore the ALD parameter space, including precursor and co-reactant selection, process conditions and doped/multilayer structures to develop films with the desired optical and conductivity properties. The objective will be to develop a fundamental understanding of material properties at the atomic scale and how these processes can be manipulated to develop transparent conductive materials. The student will be expected to fabricate test samples in the Cleanroom using chemical cleaning and etching processes, ALD and post-deposition annealing, for which full training will be given. The student will gain experience with cleanroom processing, silicon-specific analytical techniques (including minority carrier lifetime measurements and photoluminescence imaging) and materials characterisation, including spectroscopy and advanced microscopy (SEM/TEM).

Additional Funding Information

Funding is available for Home students, covering fees and providing a stipend at UKRI rates (current stipend: £20,780 p.a.) for 42 months. The PhD project would suit a candidate with an undergraduate degree (2:1 minimum) in materials science, physics, chemistry, electronic or chemical engineering

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