Perovskite Solar Cells: The Future of Energy Production

A solar cell is an electronic device that absorbs photons of light energy and converts them into electrical energy via the photovoltaic (PV) effect. Solar energy production corresponds to 6% of global energy production, with silicon solar cells contributing to 97% of this production. While silicon currently dominates the solar energy market, it is not infallible, offering other technologies, notably perovskite cells, an opportunity to attract a sizeable market share.

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A cell’s efficiency is optimised by maximising photon absorption whilst minimising thermal energy loss. This is dictated by a material’s band gap – which is tuned to absorb photons of a broad range of energies, capturing the highest possible proportion of the visible spectrum. The maximum silicon cell efficiency is 25.8%, with most commercial units hovering around 20%. Silicon, found as silica, SiO_2, is the second most abundant element in the Earth’s crust after oxygen. Extraction and purification processes are hugely energy-intensive and often pollute nearby water sources. While silicon is non-toxic and easy to work with, silica dust can cause lung cancer and pulmonary diseases. Thus, the production of silicon solar cells is limited by silicon production as opposed to the availability of the raw minerals. Currently, China produces 80% of the global silicon and boasts the 10 largest solar PV manufacturers, with 15% of units globally produced in a single facility in Xinjiang. These drawbacks inhibit the suitability of silicon solar cells, with researchers confident that perovskite cells can address these.

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Perovskite is a crystal structure with the general formula ABX₃ modelled on the mineral CaTiO₃. Perovskite structures typically incorporate lead and halide atoms into a cubic lattice with some utilising organic molecules too. These crystals boast large band gaps and high absorption coefficients enabling them to absorb light in a wide range of the visible spectrum. The first perovskite cell developed in 2009 displayed a meagre efficiency of 3.8%, yet progress has been rapid with Chinese firm Longi recently achieving a record efficiency of 34.6%. Perovskite cells are expected to be significantly cheaper than silicon equivalents as their components are readily available and do not require the costly process of silicon extraction. Furthermore, the manufacturing process will likely involve the printing of perovskite structures onto rolls which is easily scalable and requires low capital expenditure.

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However, the commercial feasibility of perovskite cells has been limited by the degradation of perovskite structures in the presence of moisture and oxygen. Early cells were only able to sustain high efficiencies for several minutes, rendering them unfeasible. With silicon cells demonstrating lifespans over 25 years, it is reckoned that perovskite cells must exhibit an efficiency of 25% for 20 years to compete with silicon units. Additionally, most record efficiencies have been achieved using test cells in a lab which are only 1 cm³. When these structures are scaled up to a commercial-sized cell there are significant performance drop-offs. While perovskite structures show promise materials researchers must overcome these hurdles to present the commercial feasibility of this next-generation technology.

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Upon cell degradation lead atoms react to form lead iodide, PbI₂, a highly carcinogenic substance. Thus, many studies have been done to substitute lead atoms with bismuth and tin indicating early success. While many of these studies have improved the safety and durability of perovskite cells it has proven difficult to replicate the high efficiency that lead-based units provide.

Oxford PV has developed the world’s first volume manufacturing line for perovskite-on-silicon tandem solar cells in Germany. Tandem cells incorporate regions of both structures and provide a compromise between the stability of silicon and the efficiency of perovskite structures, with Oxford PV’s cell exceeding 30% efficiency. Oxford PV achieved their first commercial sale in September 2024, heralding a new era for solar technology.

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Perovskites can be manufactured as thin, flexible cells, making them suited for rural applications where large silicon units may be unsuitable. The implementation of these cells can help to facilitate decentralised energy systems allowing remote areas to become self-sufficient, reducing the reliance on a central grid.

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While silicon solar cells have demonstrated their potential to support the energy transition, cheaper and more efficient devices are crucial for increasing the adoption of solar energy. Perovskite cells have demonstrated impressive properties, yet more research will be necessary to bolster the commercial viability of these devices.

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