A Molecular-Switch-Embedded Organic Photodiode for Capturing Images against Strong Backlight

Area of Science:

• Organic electronics
• Photodetector technology
• Molecular switches

Background:

• Organic photodiodes (OPDs) suffer from early photocurrent saturation under high light intensities.
• This limits their ability to detect objects against strong backlights, such as sunlight.
• A novel approach is needed to extend the linear photoresponse range of OPDs.

Purpose of the Study:

• To develop an organic photodiode (OPD) with an extended linear photoresponse range.
• To overcome the limitation of early photocurrent saturation in OPDs under high light intensity.
• To demonstrate a light-intensity-dependent transition of the operation mode in OPDs.

Main Methods:

• Synthesized and doped the photoactive layer of OPDs with a molecular switch, 1,2-bis-(2-methyl-5-(4-cyanobiphenyl)-3-thienyl)tetrafluorobenzene (DAB).
• Investigated the light-intensity-dependent transition of the OPD operation mode.
• Performed photophysical analyses to understand the mechanism of photocyclization/photocycloreversion.

Main Results:

• The proposed OPD exhibited a transition from typical performance (EQE <100%) to photomultiplication behavior (EQE >100%) with increasing light intensity.
• Achieved an extended photoresponse linearity up to a light intensity of 434 mW cm⁻².
• Demonstrated a prototype image sensor with molecular-switch-embedded OPD pixels showing high sensitivity in strong light.

Conclusions:

• A molecular switch enables a reversible, light-intensity-dependent transition in OPD operation mode, overcoming early saturation.
• This technology significantly enhances the linear dynamic range and sensitivity of organic photodiodes.
• The developed OPDs and prototype image sensor show promise for applications requiring detection in high-light environments.