Bidirectional In-Cell Photodetectors for Adaptive Luminance Control in Stretchable Displays

Stretchable displays are attracting attention as next-generation platforms for wearable and IoT applications owing to their form factor. However, their visibility under external light is often degraded due to light transmission through mechanically stretched regions. To address this issue, we propose an in-cell bidirectional photodetector (B-PD) that can be integrated into subpixels of a stretchable backplane. The B-PD detects front and rear light through intentionally misaligned gate electrodes in a dual-gate indium-gallium-zinc oxide (IGZO) transistor structure. The fabricated stretchable display B-PD shows a distinct photocurrent variation exceeding 1 × 10⁻⁴ A at the detecting voltage under externally simulated solar UV-A illumination (0-20 W/m²), and the persistent photoconductivity (PPC) is effectively reduced by approximately 60% through electrical initialization. This stable and intensity-dependent photoresponse is directly utilized to control the node voltage and luminance of stretchable subpixels in response to external light. The device is implemented within the rigid region of the backplane, where the alignment deviation remains within ±0.5 μm─limited only by photolithographic overlay accuracy, ensuring high reproducibility and structural stability. These results demonstrate the feasibility of integrating reliable light-sensing elements into stretchable backplanes for adaptive luminance control.