Reader in Energy Materials & Devices
In our drive towards net-zero, solar cells are a vital part of the renewable energy offering. Dr Joe Briscoe and his team are exploring innovative manufacturing techniques to make perovskite solar cells more efficient and stable. This will offer extraordinary possibilities for cheap, flexible solar cells in a range of applications.
Currently, over 90% of solar cells are made of silicon. We are close to reaching the limits of power conversion efficiency (PCE) with this technology, so researchers are exploring the potential of other materials. Dr Briscoe has been working with perovskite solar cells, which are made of a material normally containing lead, a halide (normally iodide or bromide) and an organic molecule, such as methylammonium lead triiodide (MAPbI3), formamidinium lead triiodide (FAPbI3), or mixtures of those and other compositions. Unlike silicon, which has to be melted at over 1000 degrees C perovskites have a crystalline structure which can be formed from a chemical solution and then annealing at a much lower temperature (around 100-150 degrees C). They are thus much cheaper to produce.
Perovskite solar cells were initially much less efficient than silicon, but with development, they have shown great improvements. They can now convert around 25% of solar energy into electricity, which is very close to silicon. However, the perovskite cells are not without drawbacks. These challenges need to be addressed so perovskites can become a competitive commercial technology.
The crystalline structure means that perovskites often show a high number of flaws after the manufacturing process. They can also decompose when they react with moisture and oxygen. These flaws greatly reduce efficiency, especially when the material is used over large areas.
Dr Briscoe has investigated a new method called aerosol-assisted solvent treatment. This technique passes an aerosol over a surface in a controlled manner. The aerosolised solution passes from a misting bottle through a reactor, containing the heated perovskite sample. This takes no more than five minutes and can also facilitate processing at a lower temperature (100 degrees C) compared to direct thermal annealing.
Dr Briscoe’s team experimented with several different methods of making this aerosol solution. They tried a dimethylformamide (DMF) solution – an organic, colourless, water-soluble solvent. In further tests, they added methylammonium chloride (MACI). This method showed the most dramatic results.
Perovskite cells treated with this process show substantial grain growth. Local defects are almost completely eliminated, and the cell shows an overall improvement in uniformity. In tests, the researchers have seen an increase in efficiency and stability across a wide range of perovskite compositions, device structures and areas.
This process was also applied to photodetectors made from the same perovskite materials. The detectors also show a large improvement in low light photoresponse, making them almost twice as efficient in conditions of low light – a development which also applies to solar cells. This will make all the difference in countries such as the UK, where many months offer limited hours of weak sunlight, or for new applications such as solar cells powered from indoor light.
One of the issues with silicon is that it’s close to its maximum efficiency ... and so we need new technology to try and overcome these challenges.— Dr Joe Briscoe
Further tests will be undertaken to establish the longevity of the new process. Can efficiency improvements be maintained over long timescales? The researchers will also need to see if the process can be expanded and used on commercial-scale samples. They aim to develop and optimise the process in a large-area reactor (23x23 cm2).
So far, the process has shown promising results. Dr Briscoe predicts the aerosol can improve perovskite material that is printed onto sheets of plastic, which will mean they can develop cheap, flexible/ lightweight solar cells.
These could potentially be used in many innovative ways, including indoor locations, self-powered consumer electronics, on car ports and on the sides of buildings. They could even be integrated into electric vehicles.
It will also be possible to use perovskites in tandem with existing silicon solar technology. This could be done at little extra cost, boosting the overall efficiency of these cells.
Dr Briscoe’s team is launching a spinout company, AeroSolar, which has been awarded £50,000 by Innovate UK to build a large-scale reactor. The company is already actively engaging with perovskite solar cell manufacturers who could be potential customers for their process and products, and other investors have shown interest in the project.
The perovskite solar cell market is predicted to grow to US$1.2 billion by 2033. The development of low cost, efficient solar energy offers great hope for the future. It is exciting to see Queen Mary’s researchers shedding new light on our journey to net-zero.
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