Layered polymer-perovskite composite membranes for ultraflexible fatigue-tolerant optoelectronics

Introduction

Soft, lightweight, and electrically robust semiconductors are cornerstones for next-generation flexible electronic devices that function as a nontrivial platform for wearable sensors, soft robotics, and implanted devices^1,2. Organic materials with inherent flexibility have been recognized to be particularly suitable for flexible devices, but they often suffer from unsatisfactory electronic performance caused by the hopping transport behavior³. On the contrary, inorganic semiconductors, like GaAs and silicon, can achieve long carrier diffusion lengths, yet the ionic or covalent nature renders them inherently brittle and susceptible to fracture upon structural deformation⁴. Therefore, a fundamental trade-off occurs between mechanical flexibility and electronic property in most existing materials.

Lead halide perovskites are emerging semiconductors with high absorption coefficients, long carrier diffusion lengths, tunable bandgaps, and defect tolerance, which revolutionized the research field of optoelectronics, including solar cells, light-emitting diodes, and radiation detectors in the past decade^{5, 6, 7, 8–9}. Unlike conventional semiconductors that necessitate vapor or vacuum processing, the solution fabrication of perovskite offers a technical route to integrate these brittle materials with soft organic matters to gain moderate flexibility. For instance, perovskite thin films can be deposited on bendable substrates, e.g., polyethylene terephthalate (PET) and parylene, which serve as the mainstream building blocks for pliable devices¹⁰. However, these devices still suffer from poor bending tolerance and delamination problems^11,12. In recent years, chemical and physical approaches, including molecular cross-linking^13,14, interface strengthening^15,16, perovskite composition engineering^17,18, polymer blending¹⁹, and nanostructure patterning^20,21, have been proposed to minimize the mechanical fatigue of perovskite films. Nevertheless, few of these progresses achieved both super-flexibility and good electronic properties that can deliver a stable output signal under mechanical deformation and angular change. According to Hooke’s law and the series and parallel spring model, the strain distribution of a deformed substrate is correlated with the stiffness of certain localized regions, and that is, the incorporation of soft matrix into perovskite films should be useful to receive the strain experienced by the bulk perovskites^{22, 23–24}. However, both the capacities to transport charges and dissipate mechanical stress, as a prerequisite for the flexible electronic application, cannot be readily realized in typical composite architectures²⁵.