Tunable photoluminescence and enhanced stability in two-dimensional (C3H7NH3)2(MA)n-1PbnBr3n+1 perovskite colloidal nanocrystals

Abstract

In contrast with three-dimensional perovskites, their two-dimensional (2D) analogues have been demonstrated to effectively improve the moisture tolerance due to the hydrophobicity of the long-chain organic layers. However, the insulating property of the long-chain organic layers will deteriorate the charge transport properties of the materials, limiting their applications in photovoltaics and optoelectronics. Short-chain organic cation with less carbon atoms may be a good substitution for the preparation of 2D perovskites with superior environmental stability and optoelectronic properties. In this research, quasi-2D (C3H7NH3)2(MA)n-1PbnBr3n+1 perovskite nanocrystals with an average size smaller than 10 nm were synthesized by a one-pot method, showing tunable emissions in the range of 406–524 nm for n = 1∼∞, with corresponding band-gaps of 3.63–2.30 eV. Time-resolved photoluminescence (PL) decays show that (C3H7NH3)2PbBr4 has the shortest average PL lifetime of 4.4 ns with the fast decay process occupying weighting proportion of 87.3%. When the nominal perovskite layers increases up to 2–4, the average PL lifetime raises up to 10.1–41.7 ns, with the slow decay process taking up most weighting percentage of >70%. MAPbBr3 possesses the longest PL lifetime of 151.2 ns. The perovskite nanocrystals were then attempted to modify with oleic acid or to embed in PMMA matrix in order to improve their environmental stability. Results show that the stability of oleic acid and PMMA encapsulated nanocrystals improves greatly in comparison with bare nanocrystals.