PTAA-Based Perovskite Photovoltaics Catching up: Ionic Liquid Engineering-Assisted Crystallization Through Sequential Deposition

PTAA as a widely studied polymeric hole transporting material, has garnered significant attention due to its outstanding thermal and chemical stability. However, the performance of PTAA-based p-i-n devices is shown to lag behind counterpart utilizing oxides or SAMs. In this study, the ionic liquid, 1-ethyl-3-methylimidazolium formate (EMIMCOOH), is innovatively introduced into the lead iodide (PbI₂) precursor solution, resulting in a more pronounced mesoporous PbI₂ film with expended pore-size and denser pores. This enhancement is attributed to the coordination bond between the ─C═O group in EMIMCOOH and Pb²⁺. This intensified mesoporous morphology not only facilities the reaction between PbI₂ and the organic layer, but also promotes the PbI₂ conversion into perovskite material. Importantly, the incorporation of EMIMCOOH slows down the perovskite conversion process, increasing perovskite domain size and suppressed Pb⁰ trap density, resulting in a uniform perovskite layer with enhanced charge transport properties, as evidenced by the conducting atomic force microscope (c-AFM) results. As a result, the incorporation of EMIMCOOH yields a power conversion efficiency (PCE) of 24.10% and a high fill factor exceeding 85%. Notably, the PCE of the EMIMCOOH-modified device can still maintain 86% of the initial value after 1500 h at 25 °C in an N₂ atmosphere.