Researchers at the Ulsan National Institute of Science and Technology (UNIST), led by corresponding authors Professor Changduk Yang, Professor Seung-Jae Shin and Professor Myoung Hoon Song, have developed a self-assembled monolayer (SAM) hole-selective contact for inverted perovskite solar cells that keeps working through repeated thermal cycling between −100°C and +100°C. The material, named LY-m, isolates the effect of molecular linker position on interfacial packing and pushed cell efficiency to 26.39% (certified 26.37%) with a record-high open-circuit voltage of 1.231 V.
In inverted (p-i-n) perovskite solar cells, SAMs form a molecule-thin hole-selective layer between the transparent electrode (ITO) and the perovskite absorber, and their performance is highly sensitive to incomplete surface coverage, molecular aggregation, and interfacial heterogeneity, particularly under heat and large temperature swings. While SAM chemistry has been widely explored, how the molecular topology of the linker itself governs packing and device durability had remained poorly understood. To isolate that variable, the UNIST team synthesized three isomeric SAMs, LY-ortho (LY-o), LY-meta (LY-m), and LY-para (LY-p), that share an identical carbazole head group and differ only in where the linker attaches to the ring.
Among the three, LY-m adopted a favorable tilted geometry on the ITO substrate, forming a dense, uniform, and defect-suppressive interfacial layer with the strongest binding energy of the series and improved energy-level alignment with the perovskite. Devices built with LY-m reached 26.39% efficiency (23.25% in a 1 cm² cell and 21.20% in a 3×1 cm² mini-module), and, notably, survived repeated extreme thermal cycling between −100°C and +100°C with only about 9% efficiency loss, far outperforming state-of-the-art commercial SAMs under the same conditions. The devices also retained more than 80% of their initial performance after roughly 2,000 hours at 85°C.
"The performance of a solar cell is greatly influenced not only by the light-absorbing material but also by how perfectly each interface between layers is formed," said Yang. "This study demonstrates that efficiency and stability can be simultaneously enhanced through precise molecular-level design, and it increases the prospects for applying solar cells in environments such as space and aviation, where extreme temperature fluctuations are expected."
The findings establish molecular linker topology as a distinct design lever for SAM engineering, separate from head-group chemistry or anchoring group choice, offering a rational framework for building perovskite photovoltaics intended for extreme-environment deployment, such as satellites, high-altitude platforms, and other aerospace applications where large diurnal temperature swings are routine.
