Studying Hydrogen–Halide Interactions in Lead Halide Perovskite with Isoelectronic Cations

• Published in: Chemistry of materials Vol. 35; no. 20; pp. 8417 - 8425
• Main Authors: Huang, Yunping, Shi, Yangwei, Cohen, Theodore A., Ho, Kevin, Luscombe, Christine K.
• Format: Journal Article
• Language: English
• Published: American Chemical Society 24.10.2023
• ISSN: 0897-4756; 1520-5002
• DOI: 10.1021/acs.chemmater.3c01149

A-site cations in lead halide perovskite (LHP) can significantly impact the optoelectronic device efficiency and stability. These efficiency impacts have not been correlated to cation structural features because it is difficult to isolate the independent contributions from the sizes of these A-site cations and hydrogen–halide interaction between the A-site cations and PbX6 octahedra. To address this, we designed two isoelectronic cationic ligands (guanidinium and uronium) that are nearly identical in size but have different numbers of N–H moieties that can interact with PbX6 octahedra and studied their differences in passivating LHP solar cell interfaces. While the solar cells showed little improvement after being treated by the alkylated uronium ligand, the alkylated guanidinium ligand increased both the fill factor (from 72.4% to ∼80%) and power conversion efficiency (from 15.4% to 17.7%) compared to the untreated device, along with an increased hysteresis index (from 0.02 to 0.12). While the guanidinium-based ligand or uronium-based ligand does not have significant impacts on the morphology of the LHP, the guanidinium-based ligand demonstrated a much more pronounced effect on surface passivation of the (Cs0.17FA0.83)­Pb­(I0.75Br0.25)3 films (FA = formamidinium). NMR and XRD data together suggested the guanidinium-based ligand interacts with the (Cs0.17FA0.83)­Pb­(I0.75Br0.25)3 and the CsPbI3 lattice with 5 H–X interactions, while the uronium-based ligand interacts with 4 due to the different lattice sizes. Raman spectra indicate that the H–X interaction between the cations and the PbX6 octahedra alters the electron distribution of the resulting materials. By using a pair of isoelectronic organic cations, we excluded other variables and demonstrated the importance of the hydrogen–halide interactions between cations and PbX6 octahedra on the surface passivation and optoelectronic properties of the LHP materials.