Thickness reduction can be a key element in the quest for cheaper and more efficient solar cells. Making solar cells at least 10 times thinner than commercial ones would save material, reduce manufacturing costs, and enable new applications due to their greater flexibility. In a review on ultrathin solar cells published in Nature Energy on November 2nd, researchers from CNRS (C2N, IPVF and LAAS) highlight the very high potential of ultrathin solar cells, the challenges to overcome to get closer to the theoretical limits, and the most promising research directions.
The issue of sustainable energy production is a major societal challenge. Among the sources of renewable energy, solar photovoltaics – conversion of solar energy into electricity – has experienced a strong growth for more than 10 years. This growth must accelerate in order to fulfil the goals set for the energy transition. In the sustainable development scenarios of the International Energy Agency (IEA), the share of photovoltaics in electricity generation is expected to increase from 6% in 2017 to more than 21% in 2030. In order to reach this target, it is necessary to continue increasing the conversion efficiency of solar cells but also to reduce their cost. Most of solar modules on the market use silicon as a material that absorbs sunlight, achieving an average conversion efficiency of about 20% with thicknesses of more than 150 µm. However, reducing the thickness by a factor of 10 to 50 is a goal within reach.
In a review article published in Nature Energy, researchers from CNRS (C2N, IPVF and LAAS) highlight the dynamism and richness of the research work in the field of ultrathin solar cells. Upon its emergence about ten years ago, light trapping was the initial focus of researches: texturing at the sub-micrometer scale allows increasing the optical path, and thus the absorption in very thin layers. However, this review reveals that this optical approach is not sufficient: reducing the thickness of the absorber material challenges the complete architecture of the solar cell. Exploiting the full potential of ultrathin solar cells requires encompassing the aspects of photogeneration but also carrier collection, in particular surface passivation and contact selectivity. The crossover study of the industrially mature technologies (silicon, gallium arsenide, chalcogenides) allows identifying the most promising strategies to overcome the main technological obstacles.
The use of ultrathin layers opens up new prospects: their greater flexibility will facilitate the integration of photovoltaics into buildings, electric vehicles and aircrafts, and their higher tolerance to radiation exposure will increase the lifetime of modules in space. Current experimental performances are still far from the theoretical limits, but the research directions outlined in this review show that promising solutions are within reach.