In 1999, D. B. Mitzi has proposed a very convenient description of 2D hybrid perovskites (HP) from the 3D ABX3 mother structure by using cross sections of the latter in specific planes and addition of extra halides (dimensionnal reduction concept), leading to the well known &lt;100&gt;, &lt;110&gt; and &lt;111&gt; series. Such a process, however, cannot define all perovskite networks. Here, a new way to describe any perovskite network from the 3D mother structure through an elimination or a substitution process is proposed. As examples, 2D perovskites (B and X vacancies in planes) and B and X deficient 3D perovskites such as the d-HP family (A’)3.48x(A)1-2.48x[Pb1-xI3-x] (A= MA+, FA+, and A’= hydroxyethylammonium or thioethylammonium) that we discovered recently, will be described. In a second part, we will present the remarkable mechanochromic luminescence (MCL) properties of composites consisting of 2D and 3D hybrid perovskites, as crystallized powders. 2D HP are known to give rise to RT narrow or broad band emission due to high exciton binding energies or strong exciton–phonon interactions, while in contrast 3D HP have low exciton binding energies, resulting in low radiative recombination rates. A strategy to have high EQE PeLEDs consists of preparing thin films based on layered perovskites (A’)2(A)PbnX3n+1 together with the 3D material which result in fast energy funnelling from high band gap domains (small n) into low band gap domains (large n = 3D component). In our work, composites consisting of a 2D component such as (GABA)PbBr4 (GABA+= 4-ammoniumbutyric acid) and the 3D component (CH3NH3)PbBr3 are prepared as crystallzed powders. We will first show that the whitish emission of (GABA)PbBr4 turns into orange in the composite due to an energy transfer process at the interface, and that a bright green emission is observed as soon as the composite is slightly crushed, originating from the 3D HP after efficient energy funnelling from the multi-layered 2D HP (n=2, 3) produced at the 2D/3D interface by the mechanical treatment (reversible process by fuming). Some recent results obtained starting from other types of 2D components (narrow emission, 2D HP belonging to the m series,..) will be also discussed. Not only these results highlight the key role of the interfaces in light emission of HP, but aslo pave the way of using hybrid perovskites as highly sensitive MCL smart materials for various applications such as mechanosensors, security papers,…

Key role of the interface in the mechanochromic luminescence properties of hybrid perovskites

ACS Spring Meeting 2021

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