New Study Reveals Ultra-Sensitive Flexible Photodetectors

Abstract

Side-chain engineering, a powerful approach to tune molecular properties and charge transport, has to the best of our knowledge never been applied to n-type semiconductors in perovskite-organic heterojunction photodetectors (POH-PDs). Herein, we report two n-type non-fullerene acceptors (Y1PhO and Y2PhO), featuring 2D-conjugated outer side chains in which a single oxygen atom is incorporated at distinct positions. The oxygen-position-tuned 2D-conjugated chains afford precise control over bulk photophysics and buried-interface energetics in POH-PDs. Relative to the benchmark non-fullerene acceptor Y6, both molecules exhibit larger dipole moments, higher dielectric constants, and up-shifted frontier-orbital energies. The relaxed backbone planarity serves to inhibit over-aggregation, yielding smoother bulk-heterojunction blend films and superior interfacial coupling with CsFA perovskite layer, most notably in PM6:Y2PhO blend. As a consequence, the Y2PhO-based POH-PD delivers a near-infrared external quantum efficiency exceeding 90%−the highest value reported for solution-processable broadband PDs to date− together with a high responsivity of 0.623 A W−1, shot-noise-limited and noise-based detectivities of 7.05 × 1012 and 1.43 × 1011 Jones, respectively, at 830 nm, and a linear dynamic range of 109.1 dB. These performance metrics significantly surpass those of the Y6-based counterpart, establishing oxygen-position engineering as a compelling molecular design strategy for next-generation, ultrahigh-sensitivity broadband photodetectors.

A research team, affiliated with UNIST has unveiled a groundbreaking flexible photodetector, capable of converting light across a broad spectrum-from visible to near-infrared-into electrical signals. This innovation promises significant advancements in technologies that require simultaneous detection of object colors and internal structures or materials.

Led by Professor Changduk Yang from the Department of Energy & Chemical Engineering, the research team announced the successful development of perovskite-organic heterojunction photodetectors (POH-PDs) that combines high sensitivity with exceptional accuracy in the near-infrared (NIR) region.

Photodetectors are essential components in numerous applications, including smartphone displays that automatically adjust brightness and security systems that utilize vein recognition. The new sensor distinguishes itself by its ability to detect a wider range of wavelengths, from visible light to invisible NIR, thanks to its hybrid structure. This design integrates perovskite materials-renowned for their sensitivity in visible wavelengths-with organic semiconductors optimized for NIR detection.

Heterojunction structures often face challenges such as reduced detection efficiency and accuracy in the NIR range. The UNIST team addressed these issues through precise molecular engineering-specifically, by controlling the position of oxygen atoms attached to the organic semiconductor molecules. This subtle adjustment enhances charge separation efficiency, suppresses excessive molecular aggregation, and ensures a seamless interface between the organic and perovskite layers.

By optimizing interfacial contact, the researchers minimized charge loss during transfer, significantly boosting sensor accuracy and sensitivity.

First author Jeewon Park explained, "This simple and effective molecular design-manipulating only the position of oxygen atoms-demonstrates a practical solution to longstanding challenges in extending detection ranges and improving accuracy in perovskite-organic heterojunction sensors."

Experimental results showed that sensors incorporating the organic semiconductor Y2PhO achieved an external quantum efficiency (EQE) exceeding 90% at a wavelength of 830 nm. This means that over 90 out of 100 incident photons are successfully converted into electrical signals, setting a new benchmark among solution-processed broadband photodetectors.

The device also exhibits a significantly reduced dark current, enabling the detection of extremely weak signals. Its linear dynamic range (LDR)-a measure of the sensor's ability to distinguish different light intensities-reached 109.1 dB, allowing precise operation even in environments with a mixture of bright and dim light.

Professor Yang remarked, "Broadband, flexible sensing technology that covers both visible and near-infrared wavelengths has the potential to serve as a foundational platform for advances in optical communication, imaging, and wearable electronics."

The findings of this research have been published in the online version of Advanced Functional Materials on December 22, 2025. The study was supported by the National Research Foundation of Korea (NRF) and the Ministry of Science and ICT (MSIT).

Journal Reference

Jeewon Park, Seoyoung Kim, Hee Jin Kwak, et al., "Oxygen-Positional 2D Side-Chain Engineering of n-Type Acceptors for Record >90% Near-Infrared External Quantum Efficiency in Broadband Perovskite-Organic Photodetectors," Adv. Funct. Mater., (2025).