Researchers from Shanghai Jiao Tong University and Shandong Normal University recently reported a co-deposition strategy that simultaneously boosts efficiency and stability in inverted perovskite solar cells by tailoring both the self-assembled monolayer (SAM) and the perovskite grain boundaries. Co-deposited perovskite architectures are attractive because they simplify fabrication, but a key drawback has been the excessive aggregation of planar SAM molecules during crystallization, which weakens interfacial adhesion and leads to incomplete coverage at the buried bottom interface, ultimately limiting device performance and operational stability.
To overcome this, the team designed an asymmetric SAM, PhBr-4PACz, incorporating steric hindrance around the conjugated core to suppress face-to-face π–π stacking. By disrupting the tendency of the planar carbazole-based units to aggregate, PhBr-4PACz enriches the presence of co-deposited SAMs at the bottom interface and yields a more conformal, well-adhered interlayer. At the electronic level, the bromine substituent deepens the SAM energy level and induces a p-type doping effect, which enhances band alignment for hole extraction while helping to suppress non-radiative recombination at the perovskite/SAM interface.
The researchers further addressed bulk and grain-boundary instability by introducing 1-allyl-3-vinylimidazolium chloride into the perovskite. This ionic species undergoes in-situ crosslinking, effectively sealing the grain boundaries and relieving residual mechanical stress within the film. A crucial benefit of this crosslinked network is the suppression of upward SAM diffusion under thermal stress, which is a known degradation pathway in co-deposited inverted stacks operated at elevated temperatures. The result is a more stable buried interface and a perovskite film with both mechanically and chemically robust grain boundaries.
With this synergistic strategy that combines asymmetric, sterically engineered PhBr-4PACz at the bottom interface and crosslinked 1-allyl-3-vinylimidazolium chloride in the bulk - the optimized inverted devices reach a certified power conversion efficiency of 27.03%. Under continuous illumination at the maximum power point tracking condition (65 °C, ISOS-L-2), the cells retain over 96% of their initial efficiency after 2,000 hours, underscoring that the interfacial and grain-boundary engineering effectively mitigates thermally driven degradation and SAM migration.
Notably, the same co-deposition process is compatible with different substrates: small-area flexible devices achieve a certified PCE of 24.49%, demonstrating that the interfacial adhesion, energy-level alignment, and grain-boundary sealing strategy can be translated to flexible platforms without sacrificing high efficiency.
