Role of spacer cations and structural distortion in two-dimensional germanium halide perovskites

Abstract

The elucidation of the structure-property correlation in 2D metal halide perovskite is a key issue to understand the dependence of optical properties on structural distortions and to design novel tailored...

Pressure response of decylammonium-containing 2D iodide perovskites

“…A detailed discussion about the relaxation mechanisms in 2D perovskites can be found in Smith and Karunadasa (2018) ( Smith and Karunadasa, 2018 ). The different behavior in the two perovskites investigated here, namely DA 2 PbI 4 (narrow emission) and DA 2 GeI 4 (broad emission) having a different central atom, but showing similar structural features at ambient and under applied pressure, is most likely correlated to the more significant distortion induced by germanium on octahedral bond elongation and bond angle variance, and less on the Ge–Br–Ge bond angle, with respect to Pb-containing perovskite ( Malavasi et al., 2021a ). This also couples to the dependence of the broadband emission with the increase of out-of-plane distortion in similar lead-based 2D perovskites ( Malavasi et al., 2021a ).…”

“…The different behavior in the two perovskites investigated here, namely DA 2 PbI 4 (narrow emission) and DA 2 GeI 4 (broad emission) having a different central atom, but showing similar structural features at ambient and under applied pressure, is most likely correlated to the more significant distortion induced by germanium on octahedral bond elongation and bond angle variance, and less on the Ge–Br–Ge bond angle, with respect to Pb-containing perovskite ( Malavasi et al., 2021a ). This also couples to the dependence of the broadband emission with the increase of out-of-plane distortion in similar lead-based 2D perovskites ( Malavasi et al., 2021a ). It is also known that native (or structural related) defects may contribute to self-trapping phenomena related to broad PL, and it is possible that this phenomenon may contribute to the observed high-pressure optical properties evolution of DA 2 GeI 4 because, in general, lead-free materials are less defect tolerant ( Cortecchia et al., 2017 ).…”

“…It is known that broadband emission in 2D perovskites is closely related to structural distortion induced by the organic spacers and by a wise chemical selection it is possible to modulate such an effect ( Cortecchia et al., 2017 ; Smith et al., 2017 ). In addition, we recently demonstrated that Ge-based 2D perovskite have an intrinsic higher degree of octahedra distortion in the bond-length distribution affecting the optical properties ( Malavasi et al., 2021a ). The emergence of broadband distortion around 2.1 GPa may be also correlated to the emergence of the novel monoclinic phase with reduced c -axes (majority phase) which nicely couples to the trend of the band gap shown in Figure 7 B.…”

“…Moreover, because the metal central atom plays a crucial role on the electronic structure of MHPs, we were interested in comparing the HP effects for a similar system but containing a different metal, namely germanium. We recently started to investigate the structure-property correlation in Ge-based 2D perovskites with the aim of understanding how the replacement of this ion for lead affects the structural, electronic, and optical properties, also considering the significant environmental problem raised by lead use and the necessity of finding possible lead-free alternatives ( Malavasi et al., 2021a , 2021b ). To the best of our knowledge, the present paper not only provides the first high-pressure experimental work on DA 2 PbI 4 and DA 2 GeI 4 , the latter being a novel perovskite, but also represents the only available work of the pressure response of a Ge-based 2D MHPs.…”

Low‐Dimensional Metal‐Halide Perovskites as High‐Performance Materials for Memory Applications

“…As a potential solution, 0D Cs 3 Cu 2 I 5 QDs own both the molecular and structural level low dimensionalities, [233][234][235][236] endowing them with low trap density, small intrinsic carrier mobility, and remarkable operating stability, making them the perfect candidates with a low OFF current for memory applications. Similarly, recently discovered low-dimensional compositions, such as 0D [N(C 2 H 5 ) 4 ] 2 Cu 2 Br 4 , [237] 1D Rb 2 CuX 3 (X = Cl, Br) [238] and (IFA) 3 PbI 5 , [182] 2D (PEA) 2 GeX 4 (X = I, Br), [239] Cs 2 [C(NH 2 ) 3 ] Pb 2 Br 7 , [240] and (CyBMA)PbBr 4 , [241] can be potential candidates to overcome the intrinsic stability issues and realize reliable and high-performance memories in the future. [242] In addition, it is critical to solve the long-term stability issues of low-dimensional perovskite memories for future commercial applications.…”