Researchers at Sungkyunkwan University, University of Science and Technology of China, Hefei University of Technology and Shaanxi Normal University have developed an interface engineering approach for perovskite solar cells that controls electron and hole transport by swapping a single heteroatom in an organic interlayer cation, rather than relying on chemical doping. The approach reached a power conversion efficiency of 27.61%, certified at a steady-state 27.19%, together with strong operational stability and scalability to large-area modules.
Carrier-selective interfaces, the layers that determine how efficiently electrons and holes are extracted toward their respective electrodes, are typically tuned in perovskite solar cells through extrinsic chemical doping. That approach has a known weakness: dopant species can migrate from their intended positions or react with surrounding materials over a device's operating lifetime, degrading the very carrier-selectivity they were added to create, and contributing to the shorter operational lifetimes that have held perovskite solar cells back relative to silicon.
The research team's alternative works at the structural level instead. They used two closely related imidazoline-based organic cations that differ by only a single heteroatom, nitrogen in one and sulfur in the other, to form one-dimensional organic-lead-triiodide phases at the perovskite interface. Single-crystal analysis combined with theoretical calculations showed that this one-atom difference drives distinct octahedral-sharing patterns in the lead-iodide framework, a nitrogen-containing cation producing a single-chain connectivity and a sulfur-containing cation producing a double-chain connectivity. That change in connectivity reshapes orbital coupling, shifting the work function and absolute band-edge positions enough to produce complementary carrier-selective behavior, one interface favoring electron transport and the other favoring hole transport, without introducing any extrinsic dopant.
Applying the nitrogen-based cation at the electron-transport interface and the sulfur-based cation at the hole-transport interface produced complementary charge-selective contacts on both sides of the device. The resulting solar cells reached 27.61% power conversion efficiency (27.19% certified steady-state), scaled to 22.26% efficiency in 655-cm2 large-area modules, and retained 97.8% of their initial performance after 2,000 hours of continuous illumination.
"This study is the first in the world to demonstrate that the flow of electrons and holes can be perfectly controlled solely through changes in the crystal connection structure via single-atom substitution, without any artificial chemical doping," said Sungkyunkwan University's Nam-Gyu Park, adding that the team expects the approach "will greatly accelerate the commercialization of high-efficiency, high-stability perovskite solar cells in the future."
The authors define structurally driven interface reconfiguration as a dopant-free alternative to conventional chemical doping for engineering carrier-selective contacts in perovskite solar cells, offering a route to simultaneously improve efficiency and operational stability without the long-term reliability risks that extrinsic dopants can introduce, and one they argue is generalizable to other interface-engineering challenges in the field.
