Charged oxide inversion layer (COIL) solar cells

Lead Research Organisation: University of Oxford
Department Name: Materials


Photovoltaic (PV) solar cells now generate a significant proportion of the world's electricity and have vast potential for further growth. PV is enormously important to the UK with >13.5 GW now installed here, and growth worldwide is forecast to be over tenfold in the next three decades. More than 90% of solar cells are produced from crystalline silicon, and costs have fallen to levels not previously thought possible (< 2.34 US cents/kWh). Other technologies have yet to gain industrial traction and commercial barriers to entry are becoming substantial. Silicon-based solar technology is hence likely to remain dominant and critical to the expansion of renewable energy in the coming decades. Its continuous advancement is essential to accelerate uptake of and impact from green electricity generation worldwide and for fulfilling the UK's obligations under the Paris Agreement.

The passivated emitter and rear cells (PERC) architecture is standard for today's silicon solar cells. The PERC technology will reach its practical limits in the next 10 years, with a top forecast commercial efficiency of ~24%. Overcoming this efficiency boundary requires cell architectures that circumvent the limitations of PERC. This project aims to develop a new cell technology to supersede PERC in which the drawbacks of high temperature processing are avoided, the efficiency potential of a single junction is fully exploited, and a route to implement tandem and bifacial architectures is directly possible. This programme brings together teams at the Universities of Oxford and Warwick with world-leading expertise in silicon surface passivation, carrier lifetime, and impurity management for the development of PV devices. The aim is to conduct fundamental work necessary to facilitate a step-reduction in the cost per Watt of PV electricity, thus producing a disruptive change in the advancement of this important renewable energy industry.

This project will develop a charged oxide inversion layer (COIL) solar cell by integrating advanced nanoscale thin-film materials to augment the PV potential of a silicon absorber. This novel cell architecture has the potential to overtake the current standard PERC devices, while providing a direct route to use in emerging selective contact, tandem, and bifacial designs. So far, the efficiency of an inversion layer architecture has been exploited only to a limited extent, e.g. in a 18% cell. The potential of the COIL cell extends well beyond this mark, and as high as 28% in a single-junction configuration could be achieved. This project will deliver the fundamental understanding necessary to unlock this potential, exploit the inversion layer concept by engineering highly charged dielectric thin-films, and use these films to produce a prototype cell device.


10 25 50
Description Marie Curie Postdoctoral Fellowship
Amount € 250,000 (EUR)
Organisation European Research Council (ERC) 
Sector Public
Country Belgium
Start 06/2023 
End 06/2025
Description The Philip Leverhulme Prize
Amount £100,000 (GBP)
Organisation The Leverhulme Trust 
Sector Charity/Non Profit
Country United Kingdom
Start 11/2023 
End 11/2025
Description AIST Japan project in passivating contacts 
Organisation National Institute of Advanced Industrial Science and Technology
Country Japan 
Sector Public 
PI Contribution Know-how and expertise in the area of silicon solar cell manufacturing and characterisation, specifically in the understanding of interface electronic phenomena.
Collaborator Contribution Provision of test specimens, expertise in solar cell manufacturing, scientific exchange, access to research facilities and data.
Impact Origin of the tunable carrier selectivity of atomic-layer-deposited TiOx nanolayers in crystalline silicon solar cells T Matsui, M Bivour, PF Ndione, RS Bonilla, M Hermle Solar Energy Materials and Solar Cells 209, 110461
Start Year 2020
Description EPFL collaboration on polysilicon passivating contacts 
Organisation Swiss Federal Institute of Technology in Lausanne (EPFL)
Country Switzerland 
Sector Public 
PI Contribution A new set of functional nanolayer materials are proposed and evaluated to be deployed as passivating contact structures on solar cell devices. Synthesis and characterisation of the nanolayers.
Collaborator Contribution Partners are in charge of manufacturing the devices.
Impact Collaboration resulted in joined publications, and it is of an interdisciplinary nature, with materials science, electrical engineering, and solar photovoltaic design all involved.
Start Year 2022
Description UNSW collaboration on silicon cell development 
Organisation University of New South Wales
Country Australia 
Sector Academic/University 
PI Contribution Know-how and expertise in the area of silicon solar cell manufacturing and characterisation, specifically in the understanding of interface electronic phenomena.
Collaborator Contribution Provision of test specimens, expertise in solar cell manufacturing, scientific exchange, access to research facilities and data.
Impact M. Yu, R. Zhou, P. Hamer, D. Chen, X. Zhang, P.P. Altermatt, P.R. Wilshaw, R.S. Bonilla, Imaging and quantifying carrier collection in silicon solar cells: A submicron study using electron beam induced current, Sol. Energy. 211 (2020) 1214-1222. R. Zhou, M. Yu, D. Tweddle, P. Hamer, D. Chen, B. Hallam, A. Ciesla, P.P. Altermatt, P.R. Wilshaw, R.S. Bonilla, Understanding and optimizing EBIC pn-junction characterization from modeling insights, J. Appl. Phys. 127 (2020) 024502. P. Hamer, B. Hallam, R.S.S. Bonilla, P.P.P. Altermatt, P. Wilshaw, S. Wenham, Modelling of hydrogen transport in silicon solar cell structures under equilibrium conditions, J. Appl. Phys. 123 (2018) 043108. P. Hamer, C. Chan, R.S.R.S. Bonilla, B. Hallam, G. Bourret-Sicotte, K.A.K.A. Collett, S. Wenham, P.R.P.R. Wilshaw, Hydrogen induced contact resistance in PERC solar cells, Sol. Energy Mater. Sol. Cells. 184 (2018) 91-97. C. Chan, P. Hamer, G. Bourret-Sicotte, R. Chen, A. Ciesla, B. Hallam, D. Payne, R.S. Bonilla, S. Wenham, Instability of Increased Contact Resistance in Silicon Solar Cells Following Post-Firing Thermal Processes, Sol. RRL. 1 (2017) 1700129. B.J. Hallam, P.G. Hamer, R.S. Bonilla, S.R. Wenham, P.R. Wilshaw, Method of Extracting Solar Cell Parameters From Derivatives of Dark I-V Curves, IEEE J. Photovoltaics. 7 (2017) 1304-1312. R.S. Bonilla, B. Hoex, P. Hamer, P.R. Wilshaw, Dielectric surface passivation for silicon solar cells: A review, Phys. Status Solidi. 214 (2017) 1700293.
Start Year 2016
Description STEM for Britain poster presentation 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Policymakers/politicians
Results and Impact STEM for BRITAIN is a major scientific poster competition and exhibition which has been held in Parliament since 1997, and is organised by the Parliamentary & Scientific Committee. Chaired by Stephen Metcalfe MP, its aim is to give members of both Houses of Parliament an insight into the outstanding research work being undertaken in UK universities by early-career researchers.
Year(s) Of Engagement Activity 2023