Self-Powered BroadbandTa2NiSe5/PdSe2 Heterojunction Photodetectorwith Mid-InfraredResponse

Abstract Broadband photodetectors capable of extending into the mid-infrared region are of great interest for applications requiring access to molecular vibrational and thermal radiation information, yet their realization under low-power or self-powered conditions remains challenging. Here, we report a self-powered van der Waals heterojunction photodetector composed of narrow-band gap Ta2NiSe5 and semimetal PdSe2. First-principles calculations reveal band alignment giving rise to a strong built-in electric field that enables efficient carrier separation under zero bias. Benefiting from this interfacial band engineering, the device delivers a responsivity of 212 mA/W and a detectivity of 9 × 109 Jones at 638 nm, while maintaining a measurable of 0.05 mA/W at 4000 nm. At a low modulation frequency of 7 Hz, a noise-equivalent power as low as 1.06 × 10–10 W Hz–1/2 is obtained, allowing sensitive low-frequency weak-light detection. Stable and relatively fast photoresponse is achieved, with rise and decay times of 407 and 457 μs, respectively. Moreover, the heterojunction exhibits a broadband spectral response into the mid-infrared regime around 4 μm. These results highlight Ta2NiSe5/PdSe2 heterojunctions as a promising platform for low-power, broadband optoelectronic applications.