Researchers China's Nanjing University, University of Science and technology of China and Chinese Academy of Sciences (CAS) have fabricated an all-perovskite tandem solar cell that is said to show lower interfacial non-radiative recombination and improved charge extraction.
All-perovskite tandem cells could have efficiencies similar to those of tandem perovskite-silicon devices, but with better flexibility, lighter weight, and a lower environmental impact than technologies relying on silicon wafers. The research team explained that their all-perovskite tandem solar cells can be used in power station power generation, rooftop photovoltaic, water catalytic decomposition, carbon dioxide catalytic decomposition, and space applications due to their high open circuit voltage and high efficiency.
The scientists also explained that all-perovskite tandem devices tend to suffer from low open-circuit voltage and fill factor due to the high defect density on the surface of the mixed narrow bandgap perovskite films based on lead and tin (Pb-Sn), which causes cause serious non-radiation recombination loss at the interface between the perovskite absorber and the buckminsterfullerene (C60) electron transport layer (ETL). A common strategy is to reduce the interface recombination loss of perovskite cells by depositing a two-dimension (2D) perovskite layer on the perovskite surface through solution post-treatment to form 2D/3D heterojunction structure. However, the 2D perovskite obtained by solution post-treatment has poor uniformity (layer n value is difficult to control) and low conductivity, which is not conducive to the interface transport and extraction of carriers.
To solve these challenges, the team designed a novel 3D/3D double-layer perovskite heterostructure. Using a mixture of vacuum evaporation and solution processing, a 3D pure lead wide-bandgap perovskite film was grown on a Pb-Sn mixed narrow bandgap perovskite film.
The solar cell achieved 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%, with the Japan Electrical Safety and Environment Technology Laboratories certifying a stabilized efficiency of 28.0%. “The encapsulated tandem devices retain over 90% of their initial performance after 600 hours of continuous operation under simulated one-sun illumination,” the researchers stated.
The team also fabricated a cell with a large area of 1.05 cm2, and its efficiency reached 26.9%.
Looking forward, the scientists said some electrical and optical losses should be further investigated to leverage the full potential of all-perovskite tandem solar cells.
