Ge Octahedral Perovskite Stabilization Beyond Goldschmidt Limits

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Solution Overview

Problem

Non-toxic metal halide perovskites, such as Ge-based perovskites, face challenges in forming stable octahedral structures due to their small ionic radius, leading to structural distortions and unsuitability for optoelectronic applications.

Innovation Solution

Employing strong intermolecular interactions between organic A site cations, specifically halogen and hydrogen bonding, to stabilize the symmetric Ge octahedral perovskite structure beyond Goldschmidt's rules, allowing the formation of octahedral Ge perovskites with direct bandgaps and improved carrier mobility.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If non-Pb metal atoms (Ge, Cu, Ga, Sb) are used to replace Pb in perovskite structures, then toxicity is reduced, but the metal atomic radius is too small to form a stable octahedron

Engineering Contradiction:

ImprovetoxicityVSAvoidoctahedral structure stability

Core Design Contradiction:

Object-affected harmful factorsVSStability of the object's composition

Solution Approach 1:

The patent changes the dimensionality parameter of the perovskite structure from 3D to 2D, which fundamentally alters the structural stability requirements. In 2D perovskites with formula A2BX4, the smaller metal atoms can form stable structures because the reduced dimensionality decreases the coordination number and structural constraints, allowing metals with smaller ionic radii to maintain stable octahedral configurations without requiring the large atomic radius needed for 3D perovskites

Inventive Principle:

Principle #35Parameter changes

2Object-affected harmful factors

If the ionic radius of the metal center is below the Goldschmidt threshold (e.g., 0.85 Å for iodide perovskite), then non-toxic alternatives become available, but X sites start to overlap and destabilize the octahedral coordination

Engineering Contradiction:

ImprovetoxicityVSAvoidoctahedral coordination stability

Core Design Contradiction:

Object-affected harmful factorsVSStability of the object's composition

Solution Approach 1:

The patent transitions from 3D to 2D perovskite structures, which changes the spatial arrangement and coordination geometry. In 2D perovskites, the reduced dimensionality allows for different packing arrangements where the halide ions are positioned differently relative to the metal center, preventing the overlapping issues that occur in 3D structures with small metal ions

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Object-affected harmful factors

If Ge-based perovskites are formed with small ionic radius, then non-toxic alternative is achieved, but structural distortion occurs and pyramid-like structures form instead of symmetric perovskites

Engineering Contradiction:

ImprovetoxicityVSAvoidsymmetric octahedral structure

Core Design Contradiction:

Object-affected harmful factorsVSShape

Solution Approach 1:

The patent changes the dimensionality from 3D to 2D, which fundamentally alters the structural preferences. In 2D perovskites with A2BX4 stoichiometry, the structural constraints are relaxed compared to 3D perovskites, allowing Ge and other small metal atoms to form stable structures while maintaining octahedral coordination geometry without the severe distortions that would occur in 3D structures

Inventive Principle:

Principle #35Parameter changes

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The stabilized octahedral Ge perovskites exhibit enhanced carrier mobility and direct bandgaps, enabling effective applications in optoelectronics like photodetectors and solar cells, competing with Sn- and Pb-based perovskites.

Implementation Method 1

Employing strong intermolecular interactions between organic A site cations, specifically halogen and hydrogen bonding, to stabilize the symmetric Ge octahedral perovskite structure

Methodology Applied

Scientific EffectHalogen bonding:

Implementation Method 2

Employing strong intermolecular interactions between organic A site cations, specifically halogen and hydrogen bonding, to stabilize the symmetric Ge octahedral perovskite structure

Methodology Applied

Scientific EffectHydrogen bonding:

Data Source

PatentUS12538697B2Octahedral perovskite materials with small radius metal center and uses thereof

Publication Date: 2026.01.27 HUAWEI TECH CANADA CO LTD

AI summary

Ge-centered octahedral perovskites have heretofore not been achievable due to collapse of the perovskite structure into non-octahedral units due to a lack of B site support from the small-radius Ge atom, which breaks Goldschmidt's rules for constructing octahedral perovskites. To overcome this shortcoming, a strategy was developed to form a strong cage with the A sites in which the octahedron is forced to remain intact. Strong intermolecular interaction between the organic A site cations were used to stabilize the symmetric Ge octahedral perovskite beyond the Goldschmidt's rules. The molecules used based on Y-PMA (Y: F, Cl, Br, I) that facilitated strong halogen bonding to form the cage around the octahedral. Octahedral Ge perovskites exhibit a direct bandgap in contrast to the indirect bandgap of non-octahedral Ge perovskites are demonstrated. In addition, the octahedral Ge perovskite exhibited a dramatic increase in the carrier mobility. A photodetector made with the stabilized octahedral perovskite material exhibited a vastly better responsivity than non-octahedral Ge perovskites.