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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on CsGeI3 by Materials Project

CsGeI3 is (Cubic) Perovskite structured and crystallizes in the trigonal R3m space group. The structure is three-dimensional. Cs1+ is bonded to twelve equivalent I1- atoms to form CsI12 cuboctahedra that share corners with twelve equivalent CsI12 cuboctahedra, faces with six equivalent CsI12 cuboctahedra, and faces with eight equivalent GeI6 octahedra. There are a spread of Cs–I bond distances ranging from 4.26–4.41 Å. Ge2+ is bonded to six equivalent I1- atoms to form GeI6 octahedra that share corners with six equivalent GeI6 octahedra and faces with eight equivalent CsI12 cuboctahedra. The corner-sharing octahedral tilt angles are 12°. There are three shorter (2.80 Å) and three longer (3.34 Å) Ge–I bond lengths. I1- is bonded in a 6-coordinate geometry to four equivalent Cs1+ and two equivalent Ge2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CsGeI3 by Materials Project

CsGeI3 crystallizes in the monoclinic Cm space group. The structure is three-dimensional. Cs1+ is bonded to twelve I1- atoms to form distorted CsI12 cuboctahedra that share corners with twelve equivalent CsI12 cuboctahedra, faces with six equivalent CsI12 cuboctahedra, and faces with eight equivalent GeI6 octahedra. There are a spread of Cs–I bond distances ranging from 4.16–4.61 Å. Ge2+ is bonded to six I1- atoms to form distorted GeI6 octahedra that share corners with six equivalent GeI6 octahedra and faces with eight equivalent CsI12 cuboctahedra. The corner-sharing octahedra tilt angles range from 5–19°. There are a spread of Ge–I bond distances ranging from 2.77–3.49 Å. There are two inequivalent I1- sites. In the first I1- site, I1- is bonded in a 6-coordinate geometry to four equivalent Cs1+ and two equivalent Ge2+ atoms. In the second I1- site, I1- is bonded in a 1-coordinate geometry to four equivalent Cs1+ and two equivalent Ge2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Regulating off-centering distortion maximizes photoluminescence in halide perovskites

Abstract Metal halide perovskites possess unique atomic and electronic configurations that endow them with high defect tolerance and enable high-performance photovoltaics and optoelectronics. Perovskite light-emitting diodes have achieved an external quantum efficiency of over 20%. Despite tremendous progress, fundamental questions remain, such as how structural distortion affects the optical properties. Addressing their relationships is considerably challenging due to the scarcity of effective diagnostic tools during structural and property tuning as well as the limited tunability achievable by conventional methods. Here, using pressure and chemical methods to regulate the metal off-centering distortion, we demonstrate the giant tunability of photoluminescence (PL) in both the intensity (>20 times) and wavelength (>180 nm/GPa) in the highly distorted halide perovskites [CH3NH3GeI3, HC(NH2)2GeI3, and CsGeI3]. Using advanced in situ high-pressure probes and first-principles calculations, we quantitatively reveal a universal relationship whereby regulating the level of off-centering distortion towards 0.2 leads to the best PL performance in the halide perovskites. By applying this principle, intense PL can still be induced by substituting CH3NH3+ with Cs+ to control the distortion in (CH3NH3)1-xCsxGeI3, where the chemical substitution plays a similar role as external pressure. The compression of a fully substituted sample of CsGeI3 further tunes the distortion to the optimal value at 0.7 GPa, which maximizes the emission with a 10-fold enhancement. This work not only demonstrates a quantitative relationship between structural distortion and PL property of the halide perovskites but also illustrates the use of knowledge gained from high-pressure research to achieve the desired properties by ambient methods.

halide perovskites↗