Chemical Behavior and Local Structure of the Ruddlesden-Popper and Dion-Jacobson Alloyed Pb/Sn Bromide 2D Perovskites

Thealloyed lead/tin (Pb/Sn) halide perovskites have gained significantattention in the development of tandem solar cells and other optoelectronicdevices due to their widely tunable absorption edge. To gain a betterunderstanding of the intriguing properties of Pb/Sn perovskites, suchas their anomalous bandgap's dependence on stoichiometry, itis important to deepen the understanding of their chemical behaviorand local structure. Herein, we investigate a series of two-dimensionalRuddlesden-Popper (RP) and Dion-Jacobson (DJ) phasealloyed Pb/Sn bromide perovskites using butylammonium (BA) and 3-(aminomethyl)pyridinium(3AMPY) as the spacer cations: (BA)(2)(MA)( n-1)Pb x Sn n-x Br3n+1 (n = 1-3) and (3AMPY)(MA)( n-1)Pb x Sn n-x Br3n+1 (n = 1-3) through a solution-based approach.Our results show that the ratio and site preference of Pb/Sn atomsare influenced by the layer thickness (n) and spacercations (A & PRIME;), as determined by single-crystal X-ray diffraction.Solid-state H-1, Sn-119, and (PbNMR)-Pb-207 spectroscopy analysis shows that the Pb atoms prefer the outerlayers in n = 3 members: (BA)(2)(MA)Pb x Sn n-x Br10 and (3AMPY)(MA)Pb x Sn n-x Br10. Layered 2D DJ alloyed Pb/Sn bromide perovskites (3AMPY)(MA)( n-1)Pb x Sn n-x Br3n+1 (n = 1-3) demonstratemuch narrower optical band gaps, lower energy PL emission peaks, andlonger carrier lifetimes compared to those of RP analogs. Densityfunctional theory calculations suggest that Pb-rich alloys (Pb:Sn & SIM;4:1) for n = 1 compounds are thermodynamicallyfavored over 50:50 (Pb:Sn & SIM;1:1) compositions. From grazing-incidencewide-angle X-ray scattering (GIWAXS), we see that films in the RPphase orient parallel to the substrate, whereas for DJ cases, randomorientations are observed relative to the substrate.

Automated summary

This study investigates two-dimensional alloyed Pb/Sn bromide perovskites in the Ruddlesden-Popper (RP) and Dion-Jacobson (DJ) phases using butylammonium and 3-(aminomethyl)pyridinium as spacer cations. The results show that the ratio and site preference of Pb/Sn atoms are influenced by layer thickness and spacer cations. Pb-rich alloys are thermodynamically favored in n = 1 compounds. Films in the RP phase exhibit parallel orientation to the substrate, while random orientations are observed for DJ cases.