Researchers from Tokyo City University in Japan claim to have achieved a world record power conversion efficiency for a tandem solar cell based on a top perovskite device and a bottom cell based on copper, indium, gallium and selenium (CIGS).
The tandem device has a two-terminal (2T) configuration, an active area of 1 cm2, and an certified efficiency of 25.14%. The result was verified by Japan's National Institute of Advanced Industrial Science and Technology (AIST).
The previous world record of 24.6% was achieved by German research institute HZB in Febuary 2025. “Since then, improvement research has been conducted around the world, but the 25% barrier had not been broken,” the Japanese team stated.
The scientists explained that the cell is based on bottom CIGS device developed by AIST itself and top perovskite cell with an improved perovskite absorber with higher cristallinity, which was achieved via a new barrier layer placed between the two cells.
The layer promotes better crystallinity of the perovskite film by providing a more suitable growth surface. At the same time, it reduces interfacial recombination losses that would otherwise lower device efficiency. It also prevents unwanted chemical reactions between the CIGS layer and perovskite precursors.
Image: Tokyo City University
The top cell was built with a substrate made of indium tin oxide (ITO), a self-assembled monolayer (SAM) known as MeO-2PACz, the perovskite absorber, an electron transport layer (ETL) relying on buckminsterfullerene (C60) and tin dioxide layer deposited via atomic layer deposition (ALD-SnO2), another ITO layer, an antireflective coating made of magnesium fluoride (MgF2), and silver metal contact.
The CIGS cell was made with a soda-lime glass (SLG) substrate, a molybdenum (Mo) back contact, a CIGS absorber, a cadmium sulfide (CdS) buffer layer, and a zinc oxide (ZnO) window layer.
Tested under standard illumination conditions, the tandem cell achieved an efficiency of 25.14%, an open-circuit voltage of 1.845 V, a short-circuit current density of 16.25 mA/cm2, and a fill factor of 83.5.%.
The researchers said further efficiency improvements can be expected by optimizing the cell configuration to improve the short-circuit current. In addition, they aim to accelerate research and development toward practical application through improvements in additives and passivation technology, with no further technical details of the new cell design being revealed.
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