Low-dimensional emissive states in non-stoichiometric methylammonium lead halide perovskitesElectronic supplementary information (ESI) available. See DOI: 10.1039/c8ta12184b

• Main Authors: Freestone, Benjamin G, Smith, Joel A, Piana, Giacomo, Kilbride, Rachel C, Parnell, Andrew J, Sortino, Luca, Coles, David M, Ball, Orianna B, Martsinovich, Natalia, Thompson, Courtney J, Alanazi, Tarek I, Game, Onkar S, Tartakovskii, Alexander I, Lagoudakis, Pavlos, Lidzey, David G
• Format: Article
• Language: English
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/c8ta12184b

Mixed-halide perovskites prepared from methylammonium iodide and lead chloride (MAPbI 3− x Cl x ) precursors are becoming increasingly well understood, however the effect of non-stoichiometry in this system is still not clear. Here, we create MAPbI 3− x Cl x perovskites from starting mixtures containing an excess of MAI, and study them using a variety of structural and optical probes. Using grazing incidence X-ray scattering (GIWAXS) we demonstrate the existence of non-perovskite structures, and show that addition of hydroiodic acid (HI) also leads to similar low-dimensional phase formation. Photoluminescence spectroscopy performed at cryogenic temperatures indicates the existence of multiple emissive states between 510 nm and 605 nm resulting from a low dimensional phase (LDP) or multiple phases. By mapping the distribution of luminescence across the surface with submicron resolution, we found strong co-localisation of LDP emissive states. At certain blend ratios, emission is seen from both LDP states and methylammonium lead iodide perovskite (around 770 nm). Photoluminescence excitation spectroscopy of mixed-phase films reveals energy transfer, or a cascade, between different LDP states, but this process only occurs inefficiently to the surrounding perovskite. Time-resolved photoluminescence measurements demonstrate that LDP excited-state lifetimes decrease as a function of increasing temperature; a process consistent with a thermally-activated charge transfer process. Our work suggests that non-stoichiometric materials prepared via this processing route can lead to the formation of metastable LDPs with unique material properties that merit further investigation. Self-assembly of excitonic nanostructures from excess cationic MAI:PbCl 2 perovskite solutions.