The conversion efficiency of tandem solar cells to beyond the limits of today’s commercial photovoltaic (PV) modules has been pushed further. For the first time four-terminal perovskite/silicon tandem devices with a certified top cell, have passed the barrier of 30%. Such high efficiency enables more power per square meters and less cost per kWh.
The result has been presented during the 8th World Conference on Photovoltaic Energy Conversion (WCPEC-8) in Milan and was achieved by combining the emerging perovskite solar cell with conventional silicon solar cell technologies. The perovskite cell that features transparent contacts and is part of the tandem stack has been independently certified.
Additionally, achieving high-power density will create more opportunities to integrate these solar cells into construction and building elements, so that more existing surface area can be covered with PV modules. Breaking the 30% barrier is therefore a big step in accelerating the energy transition and improving energy security by reducing the dependency on fossil fuels.
Tandem devices can reach higher efficiencies than single junction solar cells because of a better utilization of the solar spectrum. The currently emerging tandems combine commercial silicon technology for the bottom device with perovskite technology: the latter featuring highly efficient conversion of ultraviolet and visible light and excellent transparency to near infrared light. In four-terminal (4T) tandem devices the top and bottom cells operate independently of each other which makes it possible to apply different bottom cells in this kind of devices.
Commercial PERC technology as well as premium technologies like heterojunction or TOPCon or thin-film technology such as CIGS can be implemented in a 4T tandem device with hardly any modifications to the solar cells. Furthermore, the four-terminal architecture makes it straight forward to implement bifacial tandems to further boost the energy yield.
Researchers from the Netherlands and Belgium have successfully improved the efficiency of the semi-transparent perovskite cells up to 19.7% with an area of 3×3 mm2 as certified by ESTI (Italy). “This type of solar cell features a highly transparent back contact that allows over 93% of the near infrared light to reach the bottom device. This performance was achieved by optimizing all layers of the semi-transparent perovskite solar cells using advanced optical and electrical simulations as a guide for the experimental work in the lab.” says Dr. Mehrdad Najafi of The Netherlands Organization for Applied Scientific Research (TNO).
Combined, 30.1% is the conversion efficiency of this non-area matched 4T tandem devices operating independently. This world’s best efficiency is measured according to generally accepted procedures.