Dynamic Nuclear Polarization Enables NMR of Surface Passivating Agents on Hybrid Perovskite Thin Films

• DOI: 10.1021/jacs.2c05316
• Publication Date: 2022-08-12T12:11:40Z
• Authors: Aditya Mishra; Michael A. Hope; Masaud Almalki; Lukas Pfeifer; Shaik Mohammed Za...; Michael Grätzel; Lyndon Emsley
• Keywords: Thin-film; spectroscopy; cation dynamics; 02 engineering and technology; 01 natural sciences; 7. Clean energy; efficient; 0104 chemical sciences; methylammonium; lead halide perovskites; solar-cells; enhanced nmr; solid-state nmr; Surface Passivation; Perovskites; iodide; MAS DNP NMR; 0210 nano-technology; phase segregation

Surface and bulk molecular modulators are the key to improving efficiency stability of hybrid perovskite solar cells. However, due their low concentration, heterogeneous environments, sample mass, it remains challenging characterize structure dynamics at atomic level, as required establish structure–activity relationships. Nuclear magnetic resonance (NMR) spectroscopy has revealed a wealth information on atomic-level perovskites, but inherent insensitivity NMR severely limits its utility thin-film samples. Dynamic nuclear polarization (DNP) can enhance sensitivity by orders magnitude, DNP methods for materials have so far been limited. Here, we determined factors that limit samples systematically studying layered analogues. We find fast-relaxing dynamic cation is major impediment higher efficiency, while microwave absorption particle morphology play secondary role. then show former be mitigated deuteration, enabling 1H enhancement up 100, which harnessed signals from dopants or additives present in very concentrations. Specifically, using this new methodology high field with small volumes, recorded spectrum 20 nm (6 μg) passivating layer single thin film, revealing two-dimensional (2D) surface resembles n = 1 homologue greater disorder than perovskites.