Unveiling the Fatigue Behavior of 2D Hybrid Organic-Inorganic Perovskites: Insights for Long-Term Durability

Abstract

2D hybrid organic-inorganic perovskites (HOIPs) are commonly found under subcritical cyclic stresses and suffer from fatigue issues during device operation. However, their fatigue properties remain unknown. Here, the fatigue behavior of (C₄ H₉ -NH₃ )₂ (CH₃ NH₃ )₂ Pb₃ I₁₀ , the archetype 2D HOIP, is systematically investigated by atomic force microscopy (AFM). It is found that 2D HOIPs are much more fatigue resilient than polymers and can survive over 1 billion cycles. 2D HOIPs tend to exhibit brittle failure at high mean stress levels, but behave as ductile materials at low mean stress levels. These results suggest the presence of a plastic deformation mechanism in these ionic 2D HOIPs at low mean stress levels, which may contribute to the long fatigue lifetime, but is inhibited at higher mean stresses. The stiffness and strength of 2D HOIPs are gradually weakened under subcritical loading, potentially as a result of stress-induced defect nucleation and accumulation. The cyclic loading component can further accelerate this process. The fatigue lifetime of 2D HOIPs can be extended by reducing the mean stress, stress amplitude, or increasing the thickness. These results can provide indispensable insights into designing and engineering 2D HOIPs and other hybrid organic-inorganic materials for long-term mechanical durability.

Keywords: 2D hybrid organic-inorganic perovskites; failure behaviors; fatigue; in-plane; static dwelling.

Figure 1

AFM‐based fatigue test of 2D HOIPs: a) schematic of AFM‐based fatigue method used in this study. b) Four‐layer thin C4n3 membrane deposited on hole‐patterned silicon oxide substrate. Inset: the measured height profile along the yellow dashed line showing the thickness of the flake. Scale bar: 4 µm. c) Representative fatigue data showing static deflection and displacement change as a function of cycles, where the fatigue failure of the membrane is indicated by the sharp changes in recorded cantilever deflection and z‐piezo displacement. Inset: AFM topographic images of the C4n3 membrane showing before (left) and after (right) fatigue failure. Scale bar: 400 nm.

Figure 2

Fatigue and static‐dwelling of 4‐layer C4n3 2D HOIP membranes: a) number of fatigue cycles survived under various $F_{\mathrm{dc}}/{\overline{F}}_{\mathrm{fracture}}$ (≈ 1 µm diameter, 0.75 nm tip amplitude) showing increasing lifetime at lower average force. Sample sizes are 23, 2, 6, 6, 7, and 5 for F _dc = 100%, 80%, 70%, 60%, 50%, and 40% of ${\overline{F}}_{\mathrm{fracture}}$, respectively. b,c) Are the fracture force and elastic modulus, respectively, of the membranes after 3 million cycles cyclic loaded at $F_{\mathrm{dc}}=60\%{\overline{F}}_{\mathrm{fracture}}$ compared to those from the pristine membranes. Sample sizes are 6 and 5 for (b) and (c), respectively. “*” and “***” indicate P ≤ 0.05 and < 0.001, respectively. d) Lifetime of the membranes under static (red) and cyclic (black) loading under various $F_{\mathrm{dc}}/{\overline{F}}_{\mathrm{fracture}}$. Inset: Fatigue and static dwelling data of $70\%{\overline{F}}_{\mathrm{fracture}}$ showing longer lifetime under static dwell.

Figure 3

Morphology of the C4n3 membranes after fatigue failure at various F _dc: a) 80%, b) 70%, c) 60%, d) 50%, and e) 40% of ${\overline{F}}_{\mathrm{fracture}}$. In (e), the membrane did not fail. Top and bottom rows are tapping mode AFM topographic and amplitude images, respectively. Scale bar: 300 nm.

Figure 4

Morphology of the C4n3 membranes after static dwelling at various F _dc: a) 70%, b) 60%, c) 50%, and d) 40% of ${\overline{F}}_{\mathrm{fracture}}$. In (d), the membrane maintains structural integrity and the red dashed circle marks the sign of damage at the center. Left and right columns are tapping mode AFM topographic and amplitude images, respectively. Scale bar: 300 nm.

Figure 5

Fatigue lifetime of C4n3 2D HOIP membranes under a) different cyclic amplitude and b) at different thicknesses. In both cases, $F_{\mathrm{dc}}=60\%{\overline{F}}_{\mathrm{fracture}}$. Thickness in (a) is 4‐layer and the tip oscillation amplitude in (b) is 0.75 nm. The sample sizes for each thickness in (a) are 6. “ns” and “*” indicate not significant (P > 0.05) and P ≤ 0.05, respectively.