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From rational structural design to enhanced efficiency and stability of light-emitting diodes: 2D and quasi 2D hybrid perovskites

A class of the 3D hybrid perovskites does not stop impressing optoelectronic and photovoltaic community with their rapid improvements in performance since the first demonstration in 2009.[1] Perovskite-based solar cells (SCs) have demonstrated unprecedented progress on efficiency in the history of photovoltaics ; power conversion efficiencies have steeply grown from 3% to 23%.[1] The structure of 3D hybrid perovskite, typically (MA)PbX3 (MA=methyammonium) is a 3D network of corner- shared BX6 octahedrons with an organic cation A located within the octahedral layers. One of the major concerns regarding 3D hybrid perovskite SCs is an insufficient long-lasting stability. [2] To address this issues, a mixing of 3D perovskite with its 2D derivatives (obtained by “slicing” the 3D frameworks into a well-defined 2D slabs) have been recently proposed.[3] The 2D perovskites are described by the formula: A2A’n- 1BnX3n+1 where: A is a large organic cation (typically buthylammonium, BA or phenylethylammonium, PEA) A’ is a smaller organic cation (commonly MA), B is a divalent metal cation (Pb or Sn), X is halide and n is number of [BX6]-4 octahedral layers. Those lower perovskites have higher bandgaps compared to 3D materials, thus they are of significant interest for the light emitting applications. They also represent an excellent working platform, extremely versatile and highly tailorable, because properties can be tuned not only by the choice of organic cations and halide anions, but also by changing n value that defines the thickness of the perovskite layer. This talk will address the correlation between specific structural and compositional features, tailored by the choice of perovskite building blocks (thickness of perovskite slab n, choice of halide anion but particularly the choice of A cation) on improved ambient stability and enhanced efficiency of 2D and quasi-2D halide perovskite materials.[4] In particular, the possibility of utilization of mixed cations in spacer layer will be discussed ; (BA0.5PEA0.5)2MAPb2Br7 do not exhibit the downfalls typical for each endmember, while the advantages of both endmembers are successfully retained. High phase purity of n=2, similar to BA2MAPb2Br7, is retained as well as improved ambient and thermal stability, similar to PEA2MAPb2Br7.

LED ; perovskite

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