Supramolecular Modulation of Hybrid Perovskite Solar Cells via Bifunctional Halogen Bonding Revealed by Two-Dimensional ¹⁹F Solid-State NMR Spectroscopy

Abstract

There has been an ongoing effort to overcome the limitations associated with the stability of hybrid organic-inorganic perovskite solar cells by using different organic agents as additives to the perovskite formulations. The functionality of organic additives has been predominantly limited to exploiting hydrogen bonding interactions, with the relevant atomic-level binding modes remaining elusive. Herein, we introduce a new bifunctional supramolecular modulator, 1,2,4,5-tetrafluoro-3,6-diiodobenzene, which interacts with the surface of the triple-cation double-halide perovskite material via halogen bonding. We elucidate its binding mode using two-dimensional solid-state 19 F NMR spectroscopy in conjunction with DFT calculations. As a result, we demonstrate a stability enhancement of the perovskite solar cells upon supramolecular modulation, without compromising the high photovoltaic performances. Supporting Information Materials and Methods, DFT Energy and NMR Chemical Shift Calculations, Supplementary Data, and Transient Capacitance Measurements. The Supporting Information is available free of charge on the ACS Publications website.

Mixed Conductivity of Hybrid Halide Perovskites: Emerging Opportunities and Challenges

“…In the case of interfacial engineering, using molecular assemblies (Bai et al, 2019;Milić et al, 2019b;Zhang et al, 2019) and graphene composites (Arora et al, 2017;Milić et al, 2018) at the interface of charge selective transport layers was found to be particularly effective in stabilizing the perovskite devices (Ehrler and Hutter, 2020). This is often related to blocking the ions from the neighboring layers (Domanski et al, 2016), although very few systematic investigations demonstrate this particular mode of action (Merdasa et al, 2020;Ruiz-Preciado et al, 2020). Moreover, using appropriate selective charge-selective extraction layers can suppress the (photo)redox degradation pathways (Wei et al, 2020).…”

DFT Simulations as Valuable Tool to Support NMR Characterization of Halide Perovskites: the Case of Pure and Mixed Halide Perovskites

“…In spite of the number of important studies devoted to halide perovskites, however, the number of DFT simulations targeting NMR parameters is much more scarce. Just in the last years, few NMR investigations included estimates of the magnetic shielding tensor via DFT simulations, mainly exploiting the molecular approach from quantum‐chemistry [31,34,51–54] . Here, reliable models for the halide perovskite material are obtained by cutting out a finite cluster [55] .…”

Electrochemical Oxidative Fluorination of an Oxide Perovskite

“…To clarify the ambiguity of the PDF data, solid-state 19 (Table T3, Supporting Information), which is consistent with fluoride in a diamagnetic perovskite environment. 40,41 Interestingly, all of the other signals correspond to much shorter 19 F T 1 values of 0.3-0.4 s (Table T3), consistent with fluoride environments that are influenced by conducting or donor electrons. [40][41][42] DFT calculations of several structural models selected from the phase diagram for fluoride intercalation into ReO 3 predict an isotropic 19 F chemical shift of -141 ppm for mono-ReO 3 F, close to the values of several of the measured signals.…”

“…40,41 Interestingly, all of the other signals correspond to much shorter 19 F T 1 values of 0.3-0.4 s (Table T3), consistent with fluoride environments that are influenced by conducting or donor electrons. [40][41][42] DFT calculations of several structural models selected from the phase diagram for fluoride intercalation into ReO 3 predict an isotropic 19 F chemical shift of -141 ppm for mono-ReO 3 F, close to the values of several of the measured signals. By comparison, the DFT calculations predict the isotropic chemical shift of a model structure with 7-coordinate distorted-octahedra to be near -73 ppm and of tet-FReO 3 to be near -11 ppm, neither of which are experimentally observed ( Figure S10).…”