Terawatt (TW) deployment of renewable energy is critical for the world to achieve net-zero emissions. Solar power is one of the most promising technologies for renewable electricity generation and has the largest available resource for exploitation. To boost solar electricity to TW levels, we must accelerate the development of new technologies enabling ever higher efficiencies. At present, the dominant silicon technology is close to reaching its practical efficiency limit. For higher performance to be unlocked, other semiconductor absorbers must be adopted in what is known as a tandem architecture: where two or more light absorbers are integrated on top of each other to make better use of high energy visible photons, reduce thermalisation losses and convert a higher fraction of the solar energy into electrical energy. Among such new absorbers, mixed organic-inorganic metal halide perovskite semiconductors have recently witnessed unprecedented progress and are the most promising technology to integrate into a tandem device. Significant advances have already been made integrating perovskites with silicon to make high efficiency tandems, but efforts so far have almost ubiquitously employed high-end silicon heterojunction rear cells, which do not represent the main-stream mass-produced Si PV technology. In this project, we will tackle the development of perovskite-on-silicon tandem solar cells based on the lowest cost "PERC" and "TOPCon" silicon cells. Our goal is to deliver a novel tandem technology with the potential to scale up to TW levels, due to moving away from the use of rare materials, and employing fully-scalable manufacturing methodologies, for both the silicon and perovskite cells. Enabling the vast installed capacity for silicon cell production to "upgrade" to perovskite tandem technology will accelerate deployment of perovskite-on-silicon tandems in a way that it is not yet possible with current designs. Most importantly, a shift towards scalable tandems will produce a step change in energy capture per metre square as high as 45%rel (from 24% to 35%abs), at a marginal extra cost. Because half the CO2 emissions of PV manufacturing come from silicon production, tandem higher efficiencies greatly reduce the carbon footprint per unit energy generated, potentially to the lowest level of any electricity generating technology to date.

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.