Self-powered transparent photodetectors for broadband applications

Broadband transparent photodetectors are achieved through the formation of a metal oxide heterojunction. A high transmittance of 66.63% for visible light (400–800 nm) results from the wide energy bandgaps of TiO2 (3 eV) and NiO (3.86 eV). The metal-oxide heterojunction generates a photovoltaic effect due to the high open-circuit voltage (0.4 V), which spontaneously drives the NiO/TiO2 photodetector for self-powered operations. Therefore, the transparent NiO/TiO2 photodetector exhibits a self-operation mode with a fast response time (0.1 ms) while providing a high responsivity (0.43 A W−1) and detectivity (8.6 × 109 Jones) without any external bias. Extreme cycle testing (over 20,000 times) was performed to confirm the high stability of the transparent NiO/TiO2 photodetector. The proposed photovoltaic device can be an invisible power generator itself and be adopted for transparent optoelectronics, such as sensors, imaging, and memory applications with its self-operation mode.