Imidazolium Ionic Liquid as Organic Spacer for Tuning the Excitonic Structure of 2D Perovskite Materials

Abstract

Even though two-dimensional (2D) perovskites have outstanding atmospheric durability, the quantum well (QW) structure of the materials considerably limit their photovoltaic efficiencies far below the three-dimensional (3D) analogues. Herein in this work, we adopt the ionic liquid (IL) 1butyl-3-methylimidazolium iodide (BMI) as an organic spacer in 2D perovskite to fundamentally alter the QW structures. In comparison to the traditional Ruddlesden−Popper (RP) type perovskites, the new RP-2D perovskite shows drastically decreased interlayer distance to 3.5 Å, which endows stronger interactions between the inorganic slabs and a weaker quantum confinement effect of the material. We further unveil that the combination of BM + and BA + cations enables a facile regulation of the excitonic structures and optical p r o p e r t i e s o f 2 D p e r o v s k i t e . B y t h i s d e s i g n , t h e h y b r i d (BM) 2−x (BA) x MA n−1 Pb n I 3n+1 based PSCs achieve an optimized PCE of 17.3%, which is among the highest reported values for 2D PSCs to date. Due to the outstanding heat resilience of IL, the PSCs also demonstrate extraordinary thermal stability under aging at 85 °C.

Charge‐Carrier Transport in Quasi‐2D Ruddlesden–Popper Perovskite Solar Cells

“…[30] Interestingly, Liu et al proposed the use of ionic liquid 1-butyl-3-methylimidazolium iodide as the spacer, and through the hydrogen bond with the inorganic layer (Figure 2e), the imidazole rings of the two layers were arranged coplanarly, which dramatically reduced the interlayer spacing and weakened the quantum confinement, leading to a smooth charge through the organic ammonium molecules. [31] It can be concluded that introducing aromatic spacer cations to produce intermolecular or intramolecular interactions can improve the energy arrangement with the inorganic layer and effectively increase the out-of-plane conductivity, thereby greatly promoting carrier transport.…”

“…The CB, VB, LUMO, and HOMO are conduction band, valence band, the lowest unoccupied molecular orbital, and the highest occupied molecular orbital and bandgap values. Reproduced with permission [31]. Copyright 2020, American Chemical Society.…”

Targeted Distribution of Passivator for Polycrystalline Perovskite Light-Emitting Diodes with High Efficiency

“…Thus, the perovskite films show a similar crystal structure, indicating that BMIMBF 4 modification does not induce obvious crystallographic orientation. In addition, the GIWAXS images show no reflections centered on q < 10 nm –1 , which otherwise can result from the BMIM + ions layered low dimensional perovskites . It is indicated that the BMIM + ions do not enter the perovskite lattices, which is possibly due to the low concentration addition.…”

“…In addition, the GIWAXS images show no reflections centered on q < 10 nm −1 , which otherwise can result from the BMIM + ions layered low dimensional perovskites. 37 It is indicated that the BMIM + ions do not enter the perovskite lattices, which is possibly due to the low concentration addition. On the above results, it is reasonable to infer that the BMIM + ions mainly are targeted to primarily interact to the film surface and the crystal surface of the polycrystalline perovskite films, facilitating the sufficient Pb-related defect passivation for the polycrystalline perovskite layers.…”

Strategies for high‐performance perovskite solar cells from materials, film engineering to carrier dynamics and photon management

“…(B) Performance comparison for 2D, 3D, and 2D/3D perovskite films and HPSCs. Reproduced with permission 118 . Copyright 2020 American Chemical Society.…”