Near-infrared (NIR) spectral detector have emerged as key components of next-generation wearable healthcare systems, enabling continuous, non-invasive monitoring of vital physiological signals.[1] Cd- and Pb-based chalcogenide quantum dots (QDs) exhibit excellent tunable optical properties in this spectral region, but their commercialisation is restricted by toxicity and environmental regulations. Among RoHS (Restriction of Hazardous Substances) certified safer alternatives, especially InP, a III-V QD system stands tall in this spectral region.[2] Conventional hot-injection synthesis typically produces zinc-blende InP QDs, which often suffer from poor size control and result in a broader spectrum in the NIR region.[3] In contrast, wurtzite InP (w-InP) QDs prepared by cationic exchange of Cu_3-xP QDs, followed by extraction of copper impurities, show much better control over particle size and enable a tunable optical response upto NIR spectral region (~810 nm) by changing the size of the QDs.[4] Moreover, due to spin-orbit and crystal-field splitting, w-InP QDs show multiple absorption peaks, which can be utilised for multi-purpose bioelectronic applications.[5] Conventional photodetectors require an external energy source for better sensitivity but are less portable and suffer from power dissipation. Therefore, in this work, we introduced large-sized w-InP QDs (average diameter ~12 nm) for the first time in a self-powered photodetector, enabling multispectral detection around the NIR spectral region. This designed self-powered detector can be portable and well compatible with cutting-edge optoelectronic devices, and it can also address the energy crisis with the highest priority by operating without any external bias.[6] The electron transporting layer (ETL, ZnO) and w-InP QDs were spin-coated subsequently on a conductive indium tin oxide (ITO)-coated glass substrate, followed by evaporation of the hole transporting layer (HTL, MoO₃) and metal electrode (Au) to form a layer-by-layer structured self-powered detector. The fabricated devices exhibited multispectral photodetection with spectral detectivity peaks around the NIR spectral region, at ~820 nm, ~790 nm and ~725 nm, measured at zero external bias. Then we systematically investigated the influence of different ultrathin (a few nm) metal interlayers evaporated between QDs and the HTL layer on the overall optoelectronic characteristics of the self-powered device. Systematic comparison of different metal interlayers reveals that the interfacial electronic structure can be effectively tailored to enhance the charge transfer process. Among the investigated metals, Ti demonstrated the most significant improvement in device performance by promoting efficient carrier extraction without compromising the self-powered characteristics. Notably, after introducing Ti-metal as an interlayer (w-InP/Ti), nearly a threefold (~3-fold) increase in external quantum efficiency (EQE) was observed under NIR light, whereas specific detectivity lies in the range of ~3–8 × 10¹¹ Jones in NIR to visible-red light region. Furthermore, the w-InP/Ti device detected very weak 800 nm NIR light (~4.16 μW cm^-2) while operating at 0 V bias, highlighting its capability for highly sensitive light detection, which can be suitable for sophisticated health monitoring devices. In addition, the Ti interface passivated the surface defects, which enabled faster charge extraction and sped up the detector response by nearly two (~2) times. Therefore, it can be concluded that by combining interface engineering with metals and w-InP QDs, we demonstrated a high-performance, self powered photodetector capable of sensitive multispectral detection around NIR region. This approach offers a scalable pathway for III-V QDs utilisation towards next-generation, energy efficient and environmentally friendly optoelectronic devices.