Flexible Phototransistor Array Enhanced by Coupling the Piezo‐Phototronic Effect and the Flexoelectric Effect for Strain/Optical Sensing and Imaging

The piezo‐phototronic effect is widely used to regulate the interface of multilayer structures to tune the transportation of carriers by mechanical strain‐induced piezoelectric polarization charges. Besides, such modulation of the interface can also be achieved by the flexoelectric polarization charges induced by the mechanical strain gradients. Therefore, it is expected these two kinds of polarization charges can cooperate. In this work, a flexible phototransistor array based on n‐AZO/p‐Si/n‐ZnO structure is successfully demonstrated. The piezoelectric and flexoelectric polarization charges generated at the interfaces of the collector junction and the emitter junction, combined with the natural hole barrier at the emitter‐based interface, leads to the excellent performance of phototransistor for the ultraviolet (UV) –near infrared (NIR) range. Moreover, strain/optical imaging based on the flexible phototransistor array under different wavelengths of light is systematically investigated. The physical mechanism of the coupling between piezo‐phototronic and flexoelectric effects is further studied by analyzing the energy band and found to be attributed to the improvement of the emission efficiency and base transport efficiency. This work not only proposes a high‐performance flexible phototransistor array but also provides a new methodology to effectively modulate the interface by coupling the piezo‐phototronic effect and the flexoelectric effect.