A collaborative team of researchers in China has demonstrated that deliberately polarizing the solvent environment with fluorinated polymers can tightly regulate the intermediate phase during perovskite crystallization, enabling both record efficiency and greatly improved operational stability in inverted perovskite solar cells. Their work shows that embedding polar polymers to stabilize these fragile intermediate states gives device engineers a new, polarization-based handle over film formation and defect suppression, pushing perovskites closer to industrially relevant processing windows.
Dynamic solution processing of perovskite absorbers typically involves rapid solvent evaporation and uncontrolled intermediate‑phase formation, which can lead to non‑uniform nucleation, high defect densities, and instability under continuous illumination. This sensitivity severely limits process latitude for scalable coating methods such as blade coating or slot‑die, where even modest changes in local solvent composition or drying rate can translate into significant efficiency loss and poor reproducibility. Conventional solvent engineering - for example, tuning Lewis base additives - improves film formation but does not directly stabilize the solvent‑rich intermediate structures that govern final crystal quality.
To address this, the team introduced polar polymers, most prominently poly(pentafluorostyrene) (PPFS), into the precursor ink to actively tune the effective solvent polarity and evaporation kinetics during film formation. The highly polarized, densely populated C–F groups in PPFS were designed to interact strongly with the coordinating solvent molecules, stabilizing a well‑defined, solvent‑containing intermediate phase rather than allowing it to collapse rapidly into a defective perovskite network.
By combining scanning transmission electron microscopy with in situ optical measurements, they directly imaged this stabilized intermediate and correlated its evolution with the emergence of highly compact, pinhole‑free perovskite layers in inverted device architectures.
Using this polarized‑solvent strategy, inverted perovskite solar cells reached a power conversion efficiency of 26.4%, placing them among the highest reported for this device geometry. Under continuous 1‑sun equivalent illumination, the cells retained 92% of their initial efficiency after 1000 hours, indicating substantially mitigated light‑induced degradation pathways. The resultant films exhibited a more uniform surface morphology and reduced nonradiative recombination, as evidenced by enhanced photoluminescence and narrowed device‑to‑device performance spread compared with control samples processed without the polar polymer additive.
Mechanistically, the polar polymer acts as a dynamic regulator of the solvent–solute microenvironment: its strong dipoles partially lock solvent molecules into the intermediate adduct, slowing their exfoliation and extending the time window for orderly crystal growth. This controlled release of solvent promotes gradual, defect‑suppressing nucleation and growth, yielding larger, better‑oriented grains and fewer deep traps that would otherwise facilitate nonradiative recombination and ion migration. At the same time, the altered polarity landscape influences local electric fields and can reduce uncontrolled internal polarization, helping to stabilize the perovskite lattice under bias and illumination without sacrificing charge transport.
This work highlights polarization - implemented through tailored polar polymers and solvent engineering - as a powerful new design parameter for scaling perovskite solar cells while preserving efficiency and lifetime. If such polarized‑solvent formulations can be transferred to roll‑to‑roll and large‑area coating lines, they could substantially accelerate the commercialization of high‑efficiency, stable perovskite modules compatible with industrial manufacturing conditions.
