A high‐performing UV photodetector that uses large energy bandgap materials of p‐type NiO and n‐type ZnO without an opaque metal electrode is reported. A quality heterojunction is formed by large‐area applicable sputtering deposition method that has an extremely low saturation current density of 0.1 μA cm−2. This abrupt p‐NiO/n‐ZnO heterojunction device is visible‐light transparent and shows the fastest photoresponse time of 24 ms among NiO‐based UV photodetectors, along with the highest responsivity (3.85 A W−1) and excellent detectivity (9.6 × 1013 Jones) properties. Structural, physical, optical, and electrical properties of nanocrystalline NiO are systematically investigated. Mott–Schottky analyses are applied to develop the interface of NiO and ZnO by establishing energy diagrams. Defects existing inside the nanocrystalline NiO film enhance the UV detection performance by defect‐assisted carrier transportation. The results provide a solid scheme of manipulation of NiO defects for functional photoelectric device applications.

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A high performing broadband photodetector is designed using a NiO passivated rear contact. This paper demonstrates that the diode properties of an Al/p‐Si/ITO device can be improved by inserting an ultrathin sandwich NiO layer between Al/p‐Si. In addition, current‐voltage‐temperature characteristics reveal a significant enhancement of activation energy from 0.61 to 0.95 eV over the reference device. The effective barrier height is improved from 0.69 to 1.20 eV with the insertion of the NiO layer. Moreover, significant improvements in the responsivity and detectivity over a broadband wavelength from 300 to 1100 nm are verified. Comprehensive photodetection performance studies show a threefold reduction in the dark saturation current by inserting the ultrathin NiO layer, which creates zero bias photodetection with an impressive photoresponse ratio of more than 1500 and a responsivity of 1.52 A/W. The presented devices respond well even at an extremely low intensity 24 nW cm−2 of photodetection, suggesting the potential of the rear passivated contact for advanced photoelectric devices.