Researchers at the University of Tokyo have developed an all-perovskite tandem solar cell using FAPbI3 nanoparticles, achieving 30.2% efficiency by combining a wide-bandgap top cell and a narrow-bandgap bottom cell. FAPbI3 is known for its high efficiency in solar cells but can transform into a non-functional phase, limiting performance. The researchers used a two-step method to fabricate the perovskite layers, stabilizing the material and improving durability. The four-terminal spectral splitting architecture of the device minimizes losses and efficiently utilizes the solar spectrum across both cells. The study suggests that carefully chosen spectral splitting wavelengths can lead to high efficiencies in both four-terminal and two-terminal perovskite solar cell architectures, with practical deployment options including outdoor photovoltaic systems and integration with concentrator photovoltaics.