Data-driven discovery of high performance layered van der Waals piezoelectric NbOI(2)

Using high-throughput first-principles calculations to search for layered van der Waals materials with the largest piezoelectric stress coefficients, we discover NbOI(2) to be the one among 2940 monolayers screened. The piezoelectric performance of NbOI(2) is independent of thickness, and its electromechanical coupling factor of near unity is a hallmark of optimal interconversion between electrical and mechanical energy. Laser scanning vibrometer studies on bulk and few-layer NbOI(2) crystals verify their huge piezoelectric responses, which exceed internal references such as In(2)Se(3) and CuInP(2)S(6). Furthermore, we provide insights into the atomic origins of anti-correlated piezoelectric and ferroelectric responses in NbOX(2) (X = Cl, Br, I), based on bond covalency and structural distortions in these materials. Our discovery that NbOI(2) has the largest piezoelectric stress coefficients among 2D materials calls for the development of NbOI(2)-based flexible nanoscale piezoelectric devices.