Atomically Thin Photovoltaics

Atomically Thin Solar Cells:
Sustainability is a predominant idea in the energy sector to protect the planet going forward, with many countries including the U.K. setting "net-zero" carbon emission targets by 2050. Renewables are methods of energy generation which do not directly emit carbon-based greenhouse gases, these include: wind, hydropower, and solar power. The sun's energy can be harvested at no direct cost to the planet using a solar panel. This is a device which converts the energy from the sun's light to electricity. Solar cells, alternatively called photovoltaic (PV) cells are the units which make up solar panels. The efficiency of a PV cell quantifies how effective it converts energy from the light to electricity - current commercial solar panels based on silicon (Si) achieve ~25% efficiency, which is the industry's standard. Alternative materials to Si are explored so that they can be used where silicon's properties may restrict the applications of devices based upon them. For example, traditional PV cells suffer decreasing efficiency as they become thinner, typically not reduced below 0.1-0.4mm. These are made from Si and metals, rendering them heavy, non-flexible, and visible to the eye, restricting their applications. The alternative materials investigated in this project may be scaled down to just a few atoms in thickness (hence are called atomically thin), rendering them light, flexible, invisible to the eye and ~100,000 times thinner than Si devices. Imagine placing PV in new places like clothing, your phone, or coating buildings. Unfortunately, the best achieved efficiencies from atomically thin PV cells are comparably worse than Si at ~5-10%, but this may not be the ultimate factor for viability if they can be placed in new locations.
PV cells only function under solar illumination which is not always available due to time of day or weather on Earth, therefore, they have always been explored for extra-terrestrial use to circumvent this. An important consideration for space applications is spacecraft launch costs, mainly depending on mass and volume. Atomically thin materials have several main advantages here due to their low mass and volume. They have been proven to withstand the harsh radiation found in space, and their flexibility would allow electricity generation on the body of the spacecraft. This could supplement the craft's existing solar panels, without increasing its volume. This may lead to high suitability for use in space.

Aims:
This project aims to increase the efficiency of atomically thin PV cells through the novel application of highly reflective mirrors to increase photon absorption, optimum material choices, and sizing of the cells. The feasibility of these devices for concentrator solar cells will be investigated which will bring another element of novelty. These are cells where the intensity of light is increased by focusing it upon the cell to achieve higher efficiency. This increased intensity may damage the cells, akin to fire starting due to light through a magnifying glass, therefore it must be shown that they are undamaged for to demonstrate their suitability.

Methodology:
The PV cells will be produced by cleaving apart the layers of materials known as transition metal dichalcogenides, and black phosphorus. This can be done until they are only one atomic layer thick because these materials' layers are only bound weakly. Layers of different materials can then be stacked on each other however you choose, analogous to how one stacks Lego, to produce new materials with specific properties. These devices can then have their thickness characterised by atomic force microscopy, and their chemical composition by Raman spectroscopy. Their efficiency is determined by measuring electrical current generated when the devices are illuminated by a solar light simulator, however a laser can be used to determine the response when specific positions on the device are illuminated.

ReNU's enhanced doctoral training programme delivered by three uniquely co-located major UK universities, Northumbria (UNN), Durham (DU) and Newcastle (NU), addresses clear skills needs in small-to-medium scale renewable energy (RE) and sustainable distributed energy (DE). It was co-designed by a range of companies and is supported by a balanced portfolio of 27 industrial partners (e.g. Airbus, Siemens and Shell) of which 12 are small or medium size enterprises (SMEs) (e.g. Enocell, Equiwatt and Power Roll). A further 9 partners include Government, not-for-profit and key network organisations. Together these provide a powerful, direct and integrated pathway to a range of impacts that span whole energy systems.

Industrial partners will interact with ReNU in three main ways: (1) through the Strategic Advisory Board; (2) by providing external input to individual doctoral candidate's projects; and (3) by setting Industrial Challenge Mini-Projects. These interactions will directly benefit companies by enabling them to focus ReNU's training programme on particular needs, allowing transfer of best practice in training and state-of-the-art techniques, solution approaches to R&D challenges and generation of intellectual property. Access to ReNU for new industrial partners that may wish to benefit from ReNU is enabled by the involvement of key networks and organisations such as the North East Automotive Alliance, the Engineering Employer Federation, and Knowledge Transfer Network (Energy).

In addition to industrial partners, ReNU includes Government organisations and not for-profit-organisations. These partners provide pathways to create impact via policy and public engagement. Similarly, significant academic impact will be achieved through collaborations with project partners in Singapore, Canada and China. This impact will result in research excellence disseminated through prestigious academic journals and international conferences to the benefit of the global community working on advanced energy materials.