Controlled Aqueous Synthesis of 2D Hybrid Perovskites with Bright Room-Temperature Long-Lived Luminescence

Abstract

Recently, some organic–inorganic hybrid perovskites (OIHPs) have been reported to exhibit strong subgap broadband luminescence. While the origin of such luminescence has been proposed by several groups, a strategy to prepare OIHP with the desired subgap emission properties has remained elusive. Here, we report controlled synthesis of a broadband-emitting single-crystal 2D OIHP with an average quantum yield of >80 %. We demonstrate that the intensity of broadband emission can be tuned by controlling the excess iodine ion concentration during the synthesis in hydroiodic acid. We show that the emitters exhibit characteristics of localized defects such as limited mobility and saturation at high excitation power. Using density functional theory calculations, we show that bond-state iodine interstitials are responsible for the observed long-lived luminescence.

Extrinsic nature of the broad photoluminescence in lead iodide-based Ruddlesden–Popper perovskites

“…Cast from solutions with an excess of PEAI, thin films will show the BE band. This observation is also in line with a separate study on PEA 2 PbI 4 , in which crystals were synthesised under varying amounts of iodide precursor that strongly affects the magnitude of the BE 47 . We thus assume that local concentration variations or precursor depletion during the crystal growth is responsible for the differences in our samples.…”

Effect of Structural Defects and Impurities on the Excited State Dynamics of 2D BA2PbI4 Perovskite

“…[2] All depositions were started from fully synthesized BA 2 PbI 4 crystals in order to minimize the effect of the precursor ratios on the thin film preparation. [26][27][28] Subsequently, solutions of BA 2 PbI 4 were prepared by dissolving the synthesized single crystals or powders in dimethylformamide (DMF) at 343 K under magnetic stirring for 2 h. The fresh solutions were spin-coated on hot quartz substrates at 433 K, with a ramp of for 30 s and post-annealed for 15 min. We optimized the spin-coating conditions in order to obtain the best quality thin films.…”

“…These low wavelength emission peaks have a longer lifetime (~3 -5 ns) than the common exciton emission (~490 nm and 516 nm) in 2D perovskites (~1 -2 ns) (see Figure S1 in Supporting Information) and are attributed in the literature to broadband emission from self-trapped excitons due to strong phononcoupling with the distorted soft crystal structure and/ or in extrinsic defect states. [26][27][28][29][30]33] The intensity of the broad-band emission features (and hence the concentration of self-trapped excitons in defects) is higher for the films prepared from BA 2 PbI 4 amorphous powders and non-optimized films than for the ones prepared from BA 2 PbI 4 single crystals (see Figure 3,b, 3,d and 3,f). These defects, and subsequent changes in photoluminescence spectra and dynamics, are associated to slight differences in stoichiometry and dynamic behavior of ions, particularly the diffusion of halides ions due to vacancies or interstitial defects.…”

“…[21,22] Some studies have reported complex absorption and emission spectra (many transitions energies) at low temperatures of which the origin has been related to several effects such as phase transitions, strong many-body interactions between the excitons in the inorganic layer and/ or formation of higher order biexcitons and selftrapped excitons. [12,[23][24][25][26][27][28][29][30][31] A comparison of all these studies reveals that there are large differences in the relative intensities of the different features in the spectra, especially in the broad band emission intensities at~560-800 nm that are associated with selftrapped excitons. [26][27][28][29][30] Studies to design broadly emitting perovskite compounds associate efficient self-trapped exciton emission from lattice distortions of the inorganic cages.…”

“…[12,[23][24][25][26][27][28][29][30][31] A comparison of all these studies reveals that there are large differences in the relative intensities of the different features in the spectra, especially in the broad band emission intensities at~560-800 nm that are associated with selftrapped excitons. [26][27][28][29][30] Studies to design broadly emitting perovskite compounds associate efficient self-trapped exciton emission from lattice distortions of the inorganic cages. [26 -30] However, the large differences in the relative intensities point to self-trapped excitons in defects introduced during the preparation methods.…”