Faceted growth of 1D perovskite layers via ionic liquid control for efficient and stable inverted perovskite solar cells

Abstract

One-dimensional (1D) perovskite capping layers present a promising pathway to improve the efficiency and stability of perovskite solar cells (PeSCs), though their integration into inverted architectures remains limited. In this study, we reveal how the dissociation behavior of ionic liquids (ILs) governs the morphology, surface termination, and optoelectronic characteristics of 1D perovskite (EMIMPbI3) layers. Highly dissociative 1-ethyl3-methylimidazolium (EMIM+)-based ILs enable the controlled growth of rod-shaped 1D EMIMPbI3 with preferred (200) facet orientation. Density functional theory calculations identify the (200) facet as a high electron-density surface that provides superior charge transport and interfacial contact compared to the (102) facet. However, excessive IL dissociation leads to an undesired 3D-to-1D phase transition, reducing device stability. To overcome this limitation, we employ a low-dissociation IL in combination with a strongly PbI2-coordinating solvent, which modulates PbI2 sites and allows low-dissociation ILs to replicate the benefits of highly dissociative ones. This approach enables the formation of rod-shaped 1D perovskites with dominant (200) facets while preserving long-term stability. Consequently, the optimized 1D/3D heterojunction PeSC achieves a power conversion efficiency of 25.40 % and exhibits excellent device stability under ISOS-D1 and ISOS-L testing. These results present a viable strategy for employing 1D perovskites as functional interfacial layers in stable, highefficiency photovoltaic devices.