Strong piezoelectric response in layered CuInP₂S₆ nanosheets for piezoelectric nanogenerators

Piezoelectricity in two-dimensional (2D) materials have received particular attention because of their great potential in realizing nanoscale piezotronic devices. However, most 2D layered piezoelectric materials found so far possess only in-plane piezoelectricity and require the induction of stress by bending flexible substrate, which limits their integration with conventional rigid substrates such as silicon wafer. CuInP₂S₆ is a promising 2D layered material that has attracted widespread devotion due to its diverse excellent properties including out-of-plane ferroelectricity and high stability at room-temperature. However, comprehensive investigation of piezoelectric effect in 2D CuInP₂S₆ and its relevant piezoelectric device application is still at an initial stage compared to the extensive investigation of its ferroelectricity. Herein, we perform a quantitative analysis of the large out-of-plane piezoelectricity in multilayer CuInP₂S₆ and therefore demonstrate the device application for 2D piezoelectric nanogenerator (PENG). Few-layer CuInP₂S₆ nanosheet shows a high d₃₃ piezoelectric coefficient of 17.4 pm/V, outperforming other 2D layered piezoelectrics currently reported. Moreover, the PENG based on a single CuInP₂S₆ nanoflake illustrates a maximum piezoelectric current and voltage responses of 1.7 nA and 12 mV, respectively. The experimental results are discussed based on the piezotronic effect. The strong piezoelectric response achieved in 2D CuInP₂S₆ nanosheets warrants their potential to be adopted for future strain-modulable nanoelectronic and piezotronic devices integrated with silicon-based chips.