Scientists at Nanjing University in China have developed an all-perovskite tandem solar cell that demonstrates reduced interfacial non-radiative recombination and enhanced charge extraction. These all-perovskite tandem cells, consisting of two different perovskite cells stacked together, potentially offer efficiency levels similar to tandem perovskite-silicon devices, surpassing 30%, while providing greater flexibility, reduced weight, and lower environmental impact compared to silicon wafer-based technologies.

Hairen Tan, the lead author of the research, stated that all-perovskite tandem solar cells made from wide/narrow bandgap perovskite cells possess high efficiency and low cost, making them an essential development in next-generation photovoltaic technology. The all-perovskite tandem solar cells can be applied in various areas such as power station generation, rooftop photovoltaics, water catalytic decomposition, carbon dioxide catalytic decomposition, and even space applications due to their high open circuit voltage and efficiency.

Previously, all-perovskite tandem devices faced challenges like low open-circuit voltage and fill factor due to high defect density on the surface of narrow bandgap perovskite films composed of lead and tin (Pb-Sn). This caused the loss of non-radiation recombination at the interface between the perovskite absorber and the buckminsterfullerene (C60) electron transport layer. Tan's team addressed these issues by designing a unique 3D/3D double-layer perovskite heterostructure.

The researchers utilized both vacuum evaporation and solution processing to develop a 3D pure lead wide-bandgap perovskite film on a Pb-Sn mixed narrow bandgap perovskite film. Tan explained that the 3D pure lead wide-bandgap perovskite formed a Type-II heterojunction structure with a narrow bandgap perovskite, which enhanced charge carrier extraction and significantly improved the solar cells' open-circuit voltage, fill factor, and efficiency.

The solar cell demonstrated a power conversion efficiency of 28.5%, an open-circuit voltage of 2.112 V, a short-circuit current of 6.5 mA cm-2, and a fill factor of 81.9%. The Japan Electrical Safety and Environment Technology Laboratories certified its stabilized efficiency at 28.0%. The researchers reported that the encapsulated tandem devices maintained over 90% of their initial performance after 600 hours of continuous operation under simulated one-sun illumination.

Additionally, the Chinese team produced a cell with a large area of 1.05 cm2 and achieved 26.9% efficiency. The researchers published their findings in the paper "All-perovskite tandem solar cells with 3D/3D bilayer perovskite heterojunction" in Nature. Moving forward, the team plans to investigate electrical and optical losses to fully harness the potential of all-perovskite tandem solar cells. Possible solutions include reducing optical reflection via light management, utilizing more transparent front electrodes and hole transport materials, and exploring thicker narrow-bandgap perovskite absorber layers. Recently, other researchers at Nanjing University developed an all-perovskite tandem solar cell with a 24.2% efficiency.