Researchers from Nanjing University, University of Oxford and Hong Kong University of Science and Technology have developed a stable and scalable perovskite ink that enables record‑level efficiencies in solar cells and mini‑modules processed in air. The main idea is to redesign the ink so that the perovskites stay well-dissolved and well-dispersed for a long time, while still crystallizing into a high‑quality film during large‑area coating.
In the commonly used 2‑ME/DMSO inks, one of the solvents (DMSO) binds too strongly to lead, which causes small crystals and aggregates to form in the liquid within minutes. This short “shelf life” (less than about 15 minutes) makes the ink unstable for real production lines and leads to films with pinholes, internal strain and compositional inhomogeneity that all hurt performance. The team systematically tuned the solvent chemistry and showed that using a mixture of DMF and NMP - with NMP binding less strongly to lead and DMF helping dissolve the complexes - creates a more balanced environment where the ink remains clear and stable for over 10 000 minutes in air.
With this new DMF/NMP ink, the perovskite does not crystallize too quickly or too unevenly during blade coating. Instead, crystal formation is slower and more uniform across the wet film, yielding dense layers with large grains, lower defect density and more uniform composition through the thickness. Optical measurements like photoluminescence confirm that these films lose less energy through nonradiative recombination, which is exactly what is needed for high‑efficiency solar cells.
When the researchers used the old 2‑ME/DMSO ink in inverted perovskite cells coated in air, they reached around 21.9% power conversion efficiency, in line with previous scalable work. With the DMF/NMP ink, otherwise similar cells (6.84 mm² aperture) surpass 26% efficiency, with high voltage, strong current and a very high fill factor, and an independent lab confirms a stabilized efficiency of about 26.05% with negligible hysteresis. Electrical probes of defects and light emission show fewer traps and better interfaces, explaining why voltage losses and nonradiative losses are so low in the new devices.
The stability results are particularly important for commercialization. Under a standard ISOS‑L‑2 test at 65 °C in air with continuous illumination and maximum power point tracking, encapsulated cells made from the DMF/NMP ink retain about 99% of their initial efficiency after 1700 hours, whereas reference cells from the 2‑ME/DMSO ink drop to roughly 43% after 500 hours. Even at 85 °C, DMF/NMP devices with a more stable protection layer keep around 96.9% of their initial performance after 1300 hours.
Using the same ink and blade‑coating process, the team also fabricates larger mini‑modules (10–60 cm² aperture) with very narrow “dead” regions between series‑connected sub‑cells, achieving a high geometry fill factor of 96.1%. A 12.6 cm² module reaches 23.5% aperture efficiency (about 24.5% on an active‑area basis), and an independent calibration confirms a stabilized aperture efficiency of 22.84%, with over 90% of 45 modules exceeding 21% efficiency. Together, these results show that carefully controlling solvent - lead interactions in the ink can unlock both high efficiency and high stability in scalable, air‑processed perovskite photovoltaics.
