Mild vacuum selective solvent removal for wide-window vacuum-flash perovskite solar cells

The conventional DMSO/DMF system for vacuum‑flash perovskite fabrication requires ultrahigh vacuum (<10 Pa) to forcibly remove solvents, but often causes excessive desorption, intermediate‑phase disruption, and bottom‑interface voids, resulting in an extremely narrow processing window (<20 s). We address this by introducing an NMP/DMF solvent system, which exploits the large volatility difference between NMP and DMF. Under a moderate vacuum of 50–100 Pa, DMF is selectively and rapidly removed, while NMP is kinetically retained owing to its low volatility and strong coordination, yielding a stable, dense intermediate film. This extends the processing window to several minutes and markedly improves reproducibility. The optimized devices achieve 26.75% efficiency (Jsc = 26.51 mA cm⁻², Voc = 1.171 V, FF = 0.862) with negligible hysteresis, and mini‑modules (15 cm²) deliver 23.92% with a T90 lifetime >700 h under continuous illumination at 45 °C. This work provides a mild, scalable solvent‑engineering approach for fabricating high‑quality perovskite films with wide process tolerance.