Spin-Coated Integration of a Visible-Transparent Organic Photodiode on Si-CMOS for Dual VIS–NIR Imaging

Vertically stacked image sensors that can detect both visible (VIS) and near-infrared (NIR) light are important for multispectral imaging applications, including mobile electronics and biomedical diagnostics. However, conventional strategies often compromise pixel resolution or suffer from limited NIR sensitivity because of the inherent spectral response of silicon.

Here, we demonstrate a visibly transparent NIR-sensitive organic photodiode (OPD) that is monolithically integrated on top of a silicon photodiode, enabling pixel-aligned dual-mode VIS–NIR imaging. The OPD employs a newly synthesized donor polymer, P(BDT-TQ), which exhibits strong NIR absorption and a deep HOMO energy level. Its photoactive layer is further optimized using a ternary blend with poly(methyl methacrylate), improving visible-light transparency while reducing trap density.

The optimized device achieves high visible transmittance above 67%, high detectivity exceeding 10¹² Jones in the 800–1100 nm range, and low dark current. Because the OPD is fabricated entirely through low-temperature spin-coating, it is compatible with CMOS processing. When integrated with a 120 × 64 silicon pixel array and dual-tap readout architecture, the stacked sensor enables low spectral crosstalk and offers a compact platform for high-resolution multispectral VIS–NIR imaging.