Direct Growth of Black Phosphorus (p-Type) on a Flexible Substrate with Dual Role of Two-Dimensional ZnO (n-Type) as Effective Passivation and Enabling Highly Stable Broadband Photodetection

The key issue with fabricating black phosphorus (BP) based devices, despite its excellent electronic properties, is its instability in air. Thus, most reports on BP focus on passivating it with polymers or a dielectric which, however, degrade its properties. Further, the lack of chemical methods for the direct growth of BP on flexible substrates restricts its use in flexible electronics. Addressing all these issues, this work demonstrates the direct growth of BP on flexible indium tin oxide (ITO) coated polyethylene terephthalate (PET) substrate and its encapsulation by 2D ZnO as a broadband photodetector. 2D ZnO, which was hydrothermally grown on BP, acts as an ideal passivation material that serves the dual purpose of ensuring long-term stability of up to 68 days by preventing the degradation of BP and also enhancing the functionality of the device by increasing the spectral absorbance of the device from Near Infrared (NIR) toward visible and ultraviolet (UV). The responsivity values calculated were 104.3 μA/W, 50 μA/W, and 192.7 μAW for UV, visible, and NIR illumination, respectively. The method provides a novel strategy for the growth and passivation of BP on different substrates and opens up new avenues of research which find applications in the fields of sensors, electronic devices, etc.