Introduction: A new study in France highlights the potential of ultrathin photovoltaic cells, but the road to commercial production will be fraught with challenges. Researchers have proposed a series of novel cellular structures that integrate photonic and electronic elements.
A team of scientists at the French National Centre for Scientific Research (CNRS) conducted a study to assess the potential and limitations of ultrathin solar cells based on crystalline silicon, gallium arsenide (GaAs), and copper indium gallium selenide (CIGS).
In a recent article published in *Nature Energy*, titled "Advances and Prospects for Ultrathin Solar Cells," scientists claim that producing solar cells that are at least ten times thinner than commercial solar cells would be significantly cheaper due to a substantial reduction in the amount of material required. The reduced deposition time associated with thinner cell layers would also lead to higher production throughput and lower investment costs.
Researcher Stephan Collin stated, "We believe the application of ultrathin solar cells will be limitless in the future. Once the technical challenges are overcome, they could offer cost advantages and material savings without any drawbacks."
Currently, solar cells use too many materials, but once fully developed and industrialized, ultrathin solar cells may have the same performance.
Collin said, "For crystalline silicon, the trend is to reduce the thickness of solar cells, and this research will stimulate that trend. We may expect silicon solar cells to become thinner to about 50 µm within a few years, but to become thinner will require significant changes in the manufacturing process."
The research team stated that the optical methods currently used in developing such batteries are insufficient because excessively reducing the thickness of the absorber material could damage the overall structure of the solar cell.
The group stated, "Overall, the problems of carrier photogeneration and collection are closely linked, and the thinning of the absorbent further limits the realization of selective contacts and passivation layers."
Strategies for enhancing light absorption in crystalline solar cells are more complex. Scientists say that industrially viable ultrathin solar cells can be achieved by “applying bottom-up growth methods and scalable patterning techniques to process silicon cells as thin as 10 μm to achieve efficiencies of over 15%.”
Gallium arsenide-based ultrathin batteries are considered model devices for exploring novel light-harvesting strategies that can be applied to other materials.
Collin said, "For III-V, ultrathin solar cells have a clear advantage in space applications due to their longer lifespan, so we expect to work hard in this direction and hope to see them used in the medium term."
The first commercial products may be CIGS and cadmium telluride (CdTe) batteries.
Collin added, "These technologies can benefit from reduced thickness without requiring major changes to the battery structure or manufacturing process."
The main technical challenge is to develop a back contact that can maintain a high CIGS deposition temperature of approximately 500°C while providing high light reflectivity, forming an ohmic contact with CIGS, and exhibiting low surface recombination rate.
The researchers added that multi-junction ultrathin cells also hold promise for applications, but challenges remain regarding efficient light capture across the overall broadband spectrum and current matching between subcells. However, Colin believes that ultrathin solar cells can be used in building-integrated photovoltaics (BIPV).
