Researchers from Nankai University, Beijing Institute of Technology, Princess Nourah Bint Abdulrahman University, University of Copenhagen, Hebei University, King Saud University and ULVAC-PHI Instruments Co. have reported a new strategy to overcome a long-standing efficiency bottleneck in conventional n-i-p perovskite solar cells, achieving a certified steady-state power conversion efficiency (PCE) of 27.17%.
Despite the robustness and scalability of the n-i-p architecture, its steady-state efficiency has remained stalled at around 26%, trailing behind competing device designs. The researchers attribute this limitation to non-radiative recombination losses at the buried interface between the textured electron transport layer (ETL) and the perovskite absorber.
“Previous research had struggled to identify the physical mechanisms driving these losses,” the research team explained. “With our work, we showed that energy-band misalignment and electron accumulation at the buried interface act together to accelerate carrier trapping and interfacial recombination, ultimately limiting device efficiency.”
By focusing on SnO₂-based ETLs, the team showed that lattice mismatch and electron accumulation reinforce each other, increasing recombination at the interface. This dual mechanism creates both an energetic barrier (band offset) and a local buildup of charge carriers, which enhances recombination pathways and reduces device performance.
To address these coupled effects, the researchers developed a continuously graded n⁺/n-doped SnO₂ electron transport layer using a ligand-competitive binding strategy. This approach enables precise spatial control of doping across the ETL thickness.
The resulting structure transitions from a lightly doped region near the perovskite interface to a heavily doped region farther away. This gradient creates an internal electric field that serves two key functions:
- Reduces band misalignment at the interface, lowering the energetic barrier for electron transfer.
- Accelerates electron extraction away from the interface, limiting electron accumulation.
“This graded architecture simultaneously minimizes band offset and accelerates electron extraction, thereby effectively suppressing the cross-interface recombination,” the academics explained.
The team also linked the formation of this graded structure to the chemistry of the SnO₂ deposition process, showing how ligand interactions influence oxygen vacancy concentration and, in turn, the material’s energy band structure.
Solar cells incorporating the graded ETL achieved a certified steady-state PCE of 27.17%, with a reverse-scan efficiency of 27.50%, representing the highest reported performance for n–i–p perovskite solar cells to date.
Beyond small-area devices, the approach demonstrated:
- 25.79% efficiency for a 1 cm² device.
- 23.33% efficiency for a module with a 16.02 cm² aperture area.
These results indicate that the interfacial engineering strategy remains effective when transitioning from lab-scale cells to larger-area modules.
“Our research has dispelled the longstanding ‘performance fog' surrounding formal structural devices at the mechanistic level, opening a universal and effective new pathway for the rational design of electron transport layers in inverted perovskite devices,” the team concluded. “This development is expected to provide technical support for the high stability and scalable production of perovskite photovoltaic modules.”
Overall, the work establishes a broader framework for energy-band engineering in metal-oxide transport layers, addressing a fundamental recombination pathway and enabling further efficiency gains in perovskite photovoltaics.
