Structural and photoelectrical properties of an MDMO-PPV/n-Si hybrid heterojunction photodiode for broadband detection

Organic–inorganic hybrid photodiodes are attractive for low-cost, broadband photodetection, yet the role of the polymer/Si interface on power- and wavelength-dependent performance is still not fully clarified. In this study, we fabricate a simple Al/MDMO-PPV/n-Si/Al heterojunction photodiode using a solution-processed MDMO-PPV interlayer and systematically correlate its structural, optical and electrical characteristics. UV–Vis spectroscopy reveals a pronounced absorption band at 478nm, and Tauc analysis yields a direct optical band gap of 2.28eV. XRD and SEM measurements indicate a predominantly amorphous, porous polymer film with short-range order, providing interconnected pathways for charge transport. Current–voltage measurements under light illumination from 20 to 100 mWcm-2 show clear rectification with negligible dark current. Thermionic-emission and Cheung analyses give ideality factors of 3.0–3.5 and zero-bias barrier heights of 0.69–0.74eV, while the photocurrent follows a power law Iph∝P1.42, evidencing trap-assisted photoconduction. The device operates over 300–1050 nm, where the responsivity (R) increases from 0.15 to about 0.42AW-1, the photosensitivity (K) rises to ≈4−13, and the specific detectivity (D) improves from ∼1.1×1010to∼1.8×1010Jones. Time-resolved measurements at 0V bias yield rise and fall times of 0.70 s and 0.94 s, respectively. These results demonstrate that an MDMO-PPV interlayer can efficiently extend n-Si photodiodes into the visible–NIR region and provide bias-free broadband detection, offering a scalable and low-cost platform for next-generation optoelectronic and sensing applications.