PTAA-based perovskite photovoltaics catching up : ionic liquid engineering-assisted crystallization through sequential deposition

Abstract

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.