Abstract
Cation engineering provides a route to control the structure and properties of hybrid halide perovskites, which has resulted in the highest performance solar cells based on mixtures of Cs, methylammonium, and formamidinium. Here, we present a multi-technique experimental and theoretical study of structural phase transitions, structural phases and dipolar dynamics in the mixed methylammonium/dimethylammonium MA1-xDMAxPbBr3 hybrid perovskites (0 ≤ x ≤ 1). Our results demonstrate a significant suppression of the structural phase transitions, enhanced disorder and stabilization of the cubic phase even for a small amount of dimethylammonium cations. As the dimethylammonium concentration approaches the solubility limit in MAPbBr3, we observe the disappearance of the structural phase transitions and indications of a glassy dipolar phase. We also reveal a significant tunability of the dielectric permittivity upon mixing of the molecular cations that arises from frustrated electric dipoles.
Highlights
Cation engineering provides a route to control the structure and properties of hybrid halide perovskites, which has resulted in the highest performance solar cells based on mixtures of Cs, methylammonium, and formamidinium
The initial powder X-ray diffraction (XRD), Raman spectroscopy, and light absorption characterization of the samples proved the successful incorporation of the DMA cations into the crystal lattice
The obtained increase of the activation energies with the DMA concentration indicates a gradual rise of the rotational barrier for the MA cation motion (Fig. 7b)
Summary
Cation engineering provides a route to control the structure and properties of hybrid halide perovskites, which has resulted in the highest performance solar cells based on mixtures of Cs, methylammonium, and formamidinium. We present a multi-technique experimental and theoretical study of structural phase transitions, structural phases and dipolar dynamics in the mixed methylammonium/dimethylammonium MA1-xDMAxPbBr3 hybrid perovskites (0 ≤ x ≤ 1). Our results demonstrate a significant suppression of the structural phase transitions, enhanced disorder and stabilization of the cubic phase even for a small amount of dimethylammonium cations. The methylammonium (MA, CH3NH3+) lead halides MAPbX3 (X = I, Br, Cl) are extensively investigated perovskite-structured materials for effective and affordable solar cells[1,2,3]. The FAPbI3 and CsPbI3 compounds crystallize to the photoinactive yellow phases at room temperature, but the desirable photoactive black phases can be stabilized by the mixing of the A-site cations[25,26,27]
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