Perovskite Solar Cells vs Silicon Solar Cells
Silicon is the most commonly used material in photovoltaic (PV) technology. In recent times perovskites have generated much excitement in the field of solar cell research. Here we discuss the pros and cons of each in addition to their use in conjunction with one another.
Silicon vs Perovskites
Silicon is the most common semiconductor material used in the production of solar cells and is also, in fact, the second most abundant element on Earth (after O2). Silicon solar cells can be based on amorphous or crystallised silicon. The crystallised form is preferrable and most commonly used, as this material has demonstrated the highest power conversion efficiency (PCE). That said, the material has to be extremely pure and devoid of structural defects to work efficiently and this drives up production costs.
The upper limit of efficiency for silicon has hovered at around 29%. Perovskite is much better at absorbing light than crystalline silicon and can even be ‘tuned’ to use regions of the solar spectrum largely inaccessible to silicon photovoltaics.
Perovskite holds a much better tolerance for defects and can function well with impurities and imperfections. This wonder material has thus drawn the attention of researchers around the globe and holds promise as a cost-effective means for future power generation. This stands in contrast to silicon PV fabricated at high temperatures and under vacuum conditions, making them comparatively expensive to produce. Perovskites meanwhile can be produced more easily and more flexibly. Flexibility is the operative word here too because perovskites are rollable and even printable, unlike the rigid silicon cell that, in aggregate form, also consume large amounts of space too (think solar panelled rooftops).
Silicon remains the dominant material in the solar energy market because it is known and trusted, and perovskites alone are yet to meet the standards in performance set by this material. Perovskites need to be ultrathin to enhance performance but at the same time retain stability — something of a problem for a material susceptible to temperature and humidity. Another drawback is the fact perovskites generate toxic lead during processing. Consequently, researchers around the world have been “racing to find new, more stable perovskite materials” and experimenting with different ways of optimising perovskites and their architecture in the creation of solar energy.
All of this is not to say research efforts focused upon silicon solar cells has stagnated; research remains vibrant, and this is of no surprise given the dominance of this material in the solar energy sphere. Even so, the allure of perovskites presents a serious challenge to the longstanding and sturdy position silicon has retained in the solar energy market thus far. To this end then Mártil (2022) posed the key question: will perovskite eventually replace silicon or complement it?
The Tandem Solar Cell: Perovskite on Silicon
For the present time one option for improving upon efficiency solar cells is to use stacked structures comprising different semiconductor materials — known as tandem photovoltaics. Researchers realised that combining silicon and perovskite was a good way to go. In Germany, Oxford PV have analysed the environmental impacts of manufacturing solar modules.
Oxford PV found less of an impact with the production of perovskite on silicon modules (i.e., a tandem photovoltaic cell) than with silicon only. With this in mind, in addition to the benefits in efficiency, the company has scaled up the commercial production of perovskite–silicon tandem solar cells (see Figure 1). The advantages of the perovskite-on-silicon cell have been described by (Mártil, 2022) who maintains that the with the “synergy of the two cells, the whole can overcome the 30% efficiency barrier, obtaining ‘the best of both worlds.’”
Researchers Break the 30% Efficiency Barrier
In July 2022, a new record in solar power generation was set when researchers at the Swiss Center for Electronics and Microtechnology (CSEM) and the École polytechnique fédérale de Lausanne (EPFL) achieved a power conversion efficiency exceeding 30% for a 1 cm2 tandem perovskite-silicon solar cell. The breakthrough was confirmed by the US National Renewable Energy Laboratory (NREL).
Since the Lausanne lab breakthrough, researchers around the globe have concentrated their efforts on surmounting the 30% barrier. According to Stefaan De Wolf and Erkan Aydin (2023), “overcoming this threshold provides confidence that high-performance, low-cost PVs can be brought to the market.”
Experts say perovskite-silicon tandems could theoretically reach efficiencies of around 45%. The optimal perovskite band gap (i.e., wavelength that can be absorbed relative to that which the solar cell can efficiently utilize) is limited by the thickness of the perovskite material and by parasitic energy absorption. This results in lost power, rather than the desired conversion of solar energy to electricity directly.
Just this week (correct as of 7 July 2023) two separate international research teams reported differing strategies for the development of perovskite-on-silicon tandem solar cells with a PCE exceeding the 30% threshold. Chin and a team of scientists achieved success in breaking the barrier using a technique to prevent energy losses. Meanwhile, Mariotti and colleagues have sought ways to improve upon the stability and efficiency of the tandem cell.
Tandem solar cells look set to decrease the levelized cost of electricity (a measure used to compare the cost of generating electricity over the lifetime of the solar cell when compared to other methods of generation) and researchers are now well on the way to realising the potential of this PV technology. Ignacio Mártil, who is Professor of Electronics at the Complutense University of Madrid, maintains that photovoltaic energy “is the fastest growing renewable source of all the power generation technologies” and undoubtedly then the perovskite-on-silicon tandem solar cell has much to contribute to the ongoing discussion over clean energy and climate change.
AAAS (2023) Two studies report: Perovskite-silicon tandem cells that break the 30% efficiency threshold. Science., 381, (6653). DOI: 10.1126/science.adg0091
Anon. (2023) Perovskites, a ‘dirt cheap’ alternative to silicon, just got a lot more efficient’ University of Rochester News Center, February 16th, 2023. Online here.
Bellini, E. (2022) CSEM, EPFL achieve 31.25% efficiency for tandem perovskite-silicon solar cell. PV Magazine. Online here.
Chin, X. et al. (2023) Interface passivation for 31.25%-efficient perovskite/silicon tandem solar cells. Science, 381, (6653), 59–63.
De Wolf, S. and E. Aydin (2023) Tandems have the power: perovskite-silicon tandem solar cells break the 30% efficiency threshold. Science, 381, (6653), 30–31.
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Professional Science Writer