Abstract
Lead halide perovskites have emerged as promising materials for various optoelectronic applications. For photovoltaics, the reference compound is the 3D perovskite (MA)PbI3 (MA+ = methylammonium). However, this material suffers from instabilities towards humidity or light. This makes the search of new stable 3D lead halide materials very relevant. A strategy is the use of intermediate size cations instead of MA, which are not suitable to form the 3D ABX3 perovskites or 2D perovskites. Here, we report on a novel 3D metal halide hybrid material based on the intermediate size cation hydroxypropylammonium (HPA+), (HPA)6(MA)Pb5I17. We will see that extending the carbon chain length from two CH2 units (in the hydroxylethylammonium cation, HEA+) to three (HPA+) precludes the formation of a perovskite network as found in the lead and iodide deficient perovskite (HEA,MA)1+xPbxI3−x. In (HPA)6(MA)Pb5I17 the 3D lead halide network results from a 2D perovskite subnetworks linked by a PbI6 octahedra sharing its faces. DFT calculations confirm the direct band gap and reveal the peculiar band structure of this 3D network. On one hand the valence band has a 1D nature involving the p orbitals of the halide. On the other, the conduction band possesses a clear 2D character involving hybridization between the p orbitals of the metal and the halide.
Highlights
Halide perovskites became superstar semiconductors in recent years, especially for photovoltaic applications [1,2,3,4]
The reference compound is (MA)PbI3 (MA+ = methylammonium) which adopts an ABX3 perovskite structure. This structure can be described by corner-sharing BX6 octahedra which extend along the three directions of space
The electronic structure has a 3D character, meaning that charge transport can occur effectively in the whole space which is key for an efficient photovoltaic effect [1]
Summary
Halide perovskites became superstar semiconductors in recent years, especially for photovoltaic applications [1,2,3,4]. The general formula of the most familiar family is (RNH3 ) (A)n−1 Pbn X3n+1 , known as Ruddlesden–Popper (RP) phases [12,13] In such structures, long-size organic cations RNH3 + separate layers (n = 1) or multilayers (n > 1) of perovskite type (PbX6 corner-sharing mode). Cation leads to maintain a corner-sharing 3D connectivity in which some (PbI)+ units are replaced by HEA+ in materials called d-HP (lead and iodide deficient-perovskites), (HEA, MA)1+x Pbx I3−x ) which appear more stable than the reference compounds (MA)PbI3 or (Cs,FA)PbI3 [15,16] Dications such as ethylendiammonium or propylenediammonium afford such compounds called hollow perovskites (disordered structures) [17,18]. The properties of the newly synthetized material are further investigated based on DFT electronic structure calculations and optical absorption measurements revealing a direct band gap and reduced electronic dimensionality
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