a Schematic diagram of the ultraflexible, self-powered photoplethysmograpm (PPG) sensor on human hands. Ultraflexible organic photovoltaic (OPV) module generates electrical power from sunlight and drives polymer light-emitting diode (PLED) and organic photodiode (OPD). b Schematic diagram of the self-powered PPG sensor with PLED, OPD, and OPV module. c A photograph of the ultraflexible OPV module under one-sun illumination. Scale bar indicates 1 cm. d A top-view photograph of the ultraflexible, self-powered PPG sensor. Scale bar indicates 1 cm. e An electrical circuit of self-powered PPG sensor.