Asymmetric Electrode Engineering in p‐Si/n‐SnSSe Heterojunction Photodetectors for Enhanced Broadband Responsivity and Self‐Powered Operation

Abstract Advanced imaging, sensing, andtelecommunications demand high‐performance, low‐power broadband photodetectorswith improved responsivity and spectral range. This work fills a key gap bydemonstrating p‐Si/n‐Sn(S _x Se _1‐x ) ₂ verticalheterojunction (HJ) photodetectors with asymmetric Ag (Φ = 4.28 eV) /graphene(Φ = 4.7 eV) electrodes to optimize carrier dynamics and band alignment. Fourdevice configurations; symmetric (D1: Ag/HJ/Ag, D2: Gr/HJ/Gr) and asymmetric(D3: Gr/HJ/Ag, D4: Ag/HJ/Gr) were systematically investigated to elucidate therole of electrode asymmetry in enhancing photoresponse. D4 achievesstate‐of‐the‐art responsivity of 1.01 A/W, external quantum efficiency (EQE) of 197.29%, and specific detectivity of 3.75 × 10 ¹¹ Jones at 635 nm(130 µW/cm ² , +3 V), driven by efficient hole injection at Ag/p‐Si (Φ _Bp ≈ 0.87 eV) and electron extraction at Gr/n‐SnSSe (Φ _Bn ≈ 0.38 eV), augmented by photoconductive gain from trap‐assisted carrier multiplication.The D3 device operates self‐powered, producing 16.6 nA at 0 V under white lightdue to a strong built‐in field from the Gr/Ag work‐function contrast. Thedevices show broadband response (505–940 nm) with high sensitivity performanceeven at low light intensities (<150 µW/cm ² ). This work presentsa scalable, material‐efficient route to high‐efficiency self‐poweredphotodetectors for energy‐efficient broadband sensing.