Stacking Arrangement and Orientation of Aromatic Cations Tune Bandgap and Charge Transport of 2D Organic-Inorganic Hybrid Perovskites

Variable Mechanical Properties in Layered Copper Bromide Hybrid Solids Based on Configuration of Organic Cations

Organic-inorganic organohalide hybrid solids have garnered significant attention due to their unique structural diversity, desirable electronic structures, and excellent optoelectronic properties. Here, we investigate the mechanical properties of a homologous series of 2D copper bromide hybrids (A2CuBr4, ACuBr4) through nanoindentation to analyze the contribution of organic interlayer interactions to bulk mechanical response. We identify a direct correlation between the identity of the organic spacer and the bulk mechanical response, where stronger bonding interactions in the organic interlayer resulted in increased hardness and elasticity. Additionally, we uncover a unique conformational dependence within the series of arylammonium spacers which was found to periodically modulate pi-pi interactions between neighboring molecules, leading to an alternating even-odd bulk material response.

Orientation of Thiocyanate Ions Tuning the Electron-Phonon Interactions in Pseudohalide Perovskites

Although the importance of electron-phonon interactions on the optoelectronic properties of perovskites has been well documented, the structural origin of electron-phonon interactions remains largely unexplored. In this study, using pseudohalide perovskites Cs2Pb(SCN)2I2(1-x)Br2x as a model, we have revealed how the orientation of SCN- anions tunes the electron-phonon interactions and the effective charge-carrier mobility by utilizing femtosecond sum frequency generation vibrational spectroscopy, supplemented by photoluminescence spectroscopy and femtosecond optical-pump terahertz-probe spectroscopy. The coupling between neighboring SCN- anions decreases as the Br content (x) increases but does not have a significant effect on the electron-phonon interactions. In contrast, the orientation angle of SCN- anions has a strong correlation with the electron-phonon interaction and effective charge-carrier mobility, that is, a more parallel orientation of SCN- anions leads to a higher electron-phonon interaction and lower effective charge-carrier mobility. This finding provides a molecule-level understanding of the inorganic lattice structure in tuning electron-phonon interactions and may offer valuable guidance for optimizing the optoelectronic properties of perovskites.