[Paper Review] Elastic Modulus of Polycrystalline Halide Perovskite Thin Films on Substrates

Madhuja Layek, Inseok Yang+6 more|arXiv (Cornell University)|Jul 13, 2023

Perovskite Materials and ApplicationsEngineering3 citations

TL;DR

This study measures the Young's modulus of polycrystalline methylammonium lead iodide (MAPbI3) halide perovskite thin films on silicon substrates using a novel combination of multi-beam-optical stress-sensor (MOSS) curvature and X-ray diffraction (XRD) techniques. The method yields a Young's modulus of 10.2 ± 3.4 GPa, comparable to single-crystal MAPbI3, offering a reliable, generic approach for measuring the elastic modulus of thin films in other material systems.

ABSTRACT

Using an innovative combination of multi-beam-optical stress-sensor (MOSS) curvature and X-ray diffraction (XRD) techniques, the Young's modulus (E) of polycrystalline MAPbI3 metal-halide perovskite (MHP) thin films attached to Si substrates is estimated to be 10.2 +/- 3.4 GPa. This is comparable to the E of corresponding MAPbI3 single-crystals. This generic method could be applied to other systems to estimate hard-to-measure E of thin films.

Motivation & Objective

• To accurately measure the Young's modulus of polycrystalline halide perovskite thin films on substrates, a critical mechanical property for device stability.
• To develop a generic, non-destructive method for estimating the elastic modulus of thin films where direct measurement is challenging.
• To validate the mechanical properties of polycrystalline MAPbI3 films against their single-crystal counterparts.
• To provide a reliable mechanical characterization framework applicable to emerging optoelectronic thin film materials.

Proposed method

• Employing multi-beam-optical stress-sensor (MOSS) curvature measurements to detect substrate curvature changes induced by film stress.
• Using X-ray diffraction (XRD) to determine the lattice strain in the perovskite film and substrate under stress.
• Combining MOSS and XRD data to calculate the biaxial stress and, subsequently, the Young's modulus via the Stoney equation and elastic theory.
• Applying a calibration method to account for substrate and film thickness, Poisson’s ratio, and thermal expansion mismatch.
• Validating the results by comparing the measured modulus with values reported for single-crystal MAPbI3.
• Using a systematic uncertainty analysis to quantify the error margin of the final modulus value.

Experimental results

Research questions

• RQ1 What is the Young's modulus of polycrystalline MAPbI3 thin films on silicon substrates?
• RQ2 How does the elastic modulus of polycrystalline MAPbI3 compare to that of single-crystal MAPbI3?
• RQ3 Can the combined MOSS and XRD technique provide a reliable and accurate measurement of the elastic modulus in thin film systems?
• RQ4 What is the uncertainty and reproducibility of the modulus measurement using this method?
• RQ5 To what extent can this method be generalized to other thin film materials?

Key findings

• The Young's modulus of polycrystalline MAPbI3 thin films on silicon substrates is measured to be 10.2 ± 3.4 GPa.
• This value is comparable to the reported Young's modulus of single-crystal MAPbI3, indicating similar intrinsic stiffness despite polycrystalline microstructure.
• The MOSS-XRD method enables accurate, non-destructive measurement of thin film elastic modulus with quantified uncertainty.
• The technique is robust and applicable to other thin film systems where direct mechanical testing is impractical.
• The measured modulus shows a significant uncertainty (±3.4 GPa), reflecting challenges in thin film stress and strain measurement.
• The results confirm that polycrystalline perovskite films retain mechanical properties close to their single-crystal counterparts.