Next Generation Perovskite Solar Cell Structures

With the UK government's target to reduce carbon emissions by 80 % by 2050, there is more demand than ever for renewable energy. Solar photovoltaics can directly harness the power of the sun (our most abundant source of renewable energy) by turning light into electricity. Photovoltaics are one of the most attractive sources of renewable energy because they can provide clean electricity on small or large scales with minimal impact on the local environment. The main form of photovoltaic cells used commercially are silicon solar cells.

Perovskite solar cells (PSCs) are an exciting new class of solar cell which have the potential to be flexible, thinner, and cheaper than silicon solar cells while achieving a similar efficiency with a lower energy cost of manufacture. I aim to improve the potential of PSCs even further by altering their design to a "back-contact" structure that could increase their performance whilst reducing material costs and making it easier to optimise their operation. A PSC is made from 3 key parts - an absorber for turning light into electricity, and two contacts for extracting the charge. In a normal solar cell these layers are stacked on top of each other like a sandwich, with the absorber in the middle. This means that light has to pass through the top layer of the sandwich in order to reach the absorber, meaning some of it is lost unless the top layer is made from very expensive materials which are both transparent and conductive. A back-contact cell overcomes this by having both contacts on the bottom of the absorber in a honeycomb pattern, or as a set of fingers interwoven with each other. This leaves the top of the absorber free to absorb light with no other layers getting in the way.

The back-contact structure has lots of advantages over the standard way of making PSCs, but it has not been studied in detail so far because it is harder to make than the standard structure. The interlocking metal fingers in a back-contact PSC must be thinner than a hundredth of the width of a human hair, whilst covering areas in the order of square meters. Because of this, nobody has been able to do this in a cost effective or scalable way so far. Perovskite lasers are frequently made diffraction gratings, which have very similar structures to the patterns needed in a back-contact solar cell, using a process called nanoimprint lithography. This involves making a stamp in the desired pattern and then physically pressing the features into the material. This is a cheap process which can make patterns quickly over large areas, and in this project I will adapt this technique for perovskite solar cells instead of diffraction gratings. This will enable efficient back-contact PSCs on large areas using a technique that could easily be scaled industrially.

Enabling the easy production of back-contact PSCs could help make PSCs with higher efficiency than the sandwich structure, whilst simultaneously reducing their material costs and removing several design constraints. A back-contact cell also enables studies of the physics of the absorber materials which are impossible in the sandwich structure. These experiments will greatly enhance our understanding of how PSCs work, and will speed up research to help find new and improved materials which achieve even higher efficiency. This could help solar power compete with or even become cheaper than fossil fuels, thus paving the way for a new revolution in green energy.

This project aims to provide a simple way to produce nanoscale back-contact perovskite solar cells (BC-PSCs). This design of solar cell is already widely used in commercial silicon solar cells, and it is now beginning to see increased interest in the PSC community due to its potential for higher efficiency, lower material cost, and easier testing. Until now however, researchers have been unable to produce BC-PSCs with contacts with fine enough features to achieve high efficiency. As such, this project will have a major impact on the scientific research in this field by providing a viable way of producing efficient BC-PSCs at low cost. The work will be disseminated to the global community through publications in high-impact journals and through presentations at international conferences. I will also investigate the feasibility of setting up a small company producing re-useable solar cell substrates for research groups. In addition to the economic benefits of starting a company, the work shall also benefit research groups streamlining testing and reducing the need for expensive equipment such as evaporators.

Outside of academia, there is great potential for this project to have long-term impacts on both the economy and the environment. Crucially, the need for a transparent contact is a major limiting factor on the cost and efficiency with most forms of solution-processed solar cells, and this project has the potential to eliminate this issue entirely. This could help increase the efficiency of solution-processed solar cells such as PSCs whilst also reducing their material costs. This could enable them to compete with fossil fuels as a low-cost way of generating energy. Solar energy is a renewable energy source that enjoys widespread public support due to its low impact on the local environment, but it remains hampered by its high cost. By further enhancing the potential of PSCs through production lower costs and higher efficiency, this project will help PSCs reach commercial viability, thus enabling British industry to lead the world in cutting carbon emissions and producing cheap, green energy.

Finally, this project will aim to influence government policy through its publicity and outreach program. I already have experience in presenting science to politicians and the general public through science advocacy programs, and I will apply this experience further to developing new demonstrations for presenting science at events. The aim will be to inspire the next generation of scientists whilst also educating policymakers on the importance of science in the UK.