Post-Treatment-Free Dual-Interface Passivation via Facile 1D/3D Perovskite Heterojunction Construction

For achieving high-efficiency perovskite solar cells, it is almost always necessary to substantially passivate defects and protect the perovskite structure at its interfaces with charge transport layers. Such a modification generally involves the post-treatment of the deposited perovskite film by spin coating, which cannot meet the technical demands of scaling up the production of perovskite photovoltaics. In this work, we demonstrate one-step construction of buried and capped double 1D/3D heterojunctions without the need for any post-treatment, which is achieved through facile tetraethylammonium trifluoroacetate (TEATFA) prefunctionalization on the SnO₂ substrate. The functional TEATFA salt is first deposited onto the SnO₂ substrate and reacts on this buried interface. Once the FAPbI₃ perovskite precursor solution is dripped, a portion of the TEA⁺ cations spontaneously diffuse to the top surface over film crystallization. The TEATFA-based water-resistant 1D/3D TEAPbI₃/FAPbI₃ heterojunctions at both the buried and capped interfaces lead to much better photovoltaic performance and higher operational stability. Since this approach saves the need for any postsynthesis passivation, its feasibility for the fabrication of large-area perovskite photovoltaics is also showcased. Compared to ∼15% for a pristine 5 cm × 5 cm FAPbI₃ mini-module without postsynthesis passivation, over 20% efficiency is achieved following the proposed route, demonstrating its great potential for larger-scale fabrication with fewer processing steps.