Green‐Synthesized Bi‐Doped PEI N‐GQDs Enabling Long‐Term Stable Silicon Heterojunction Photodetectors

In this study, BiNPs&PEI N-GQDs nanocomposites were synthesized via a green approach by incorporating bismuth nanoparticles (BiNPs) into polyethyleneimine-functionalized nitrogen-doped graphene quantum dots (PEI N-GQDs). The nanocomposites were characterized using Transmission Electron Microscopy, Ultraviolet–Visible Spectroscopy, Fourier-Transform Infrared Spectroscopy, x-ray Photoelectron Spectroscopy, Ultraviolet Photoelectron Spectroscopy, and Photoluminescence Spectroscopy. The photoluminescence spectra exhibited dual emission bands at ∼ 2.95 eV (420 nm) and ∼ 2.42 eV (512 nm). When deposited onto a p-type silicon substrate, the nanocomposites formed a heterojunction with rectifying behavior and pronounced photoresponse under illumination. Current–voltage measurements revealed an illumination-induced shift of the photocurrent onset toward negative bias, suggesting photovoltaic activity. The photocurrent increased significantly with increasing illumination intensity, confirming the photoactive nature of the device. At a bias of 5 V and an illumination intensity of 240 mW cm− 2 , the photodetector exhibited a responsivity of 0.16 A W− 1 and a specific detectivity of ∼ 7.84 ×1010 Jones. A comparative analysis with an undoped PEI N-GQDs/p-Si device fabricated under identical conditions was conducted to assess the effect of Bi incorporation. Furthermore, measurements conducted after 24 months showed that the heterojunction retained its electrical and photodetection characteristics, confirming its long-term stability, highlighting its potential for sustainable and low-complexity optoelectronic applications.