- Development of a light sensor over 100 times more economical than existing materials

- Selected as the front cover article of the world-renowned journal Advanced Energy Materials

A research team led by Professor Hyeok Kim of the School of Electrical and Computer Engineering at the University of Seoul has successfully developed a self-powered light sensor with exceptional electrical performance and long-term stability in the near-infrared (NIR) range, based on a newly synthesized hole transport layer.

This research is notable for achieving both practicality and economic feasibility, reducing manufacturing costs by more than a hundredfold compared to existing materials.

▶ Journal cover photo

The results were published on April 22, 2025, in Advanced Energy Materials (Impact Factor: 27.8), a leading journal published by Wiley, under the title “Functionalized Interlayers in Self-Powered Organic Photodiodes for Enhanced Near-Infrared Sensing.” The paper was also selected as the journal’s front cover article.

Near-infrared light sensors can effectively detect internal physiological information such as body temperature, blood flow, and muscle contraction, making them a key technology in diverse fields including healthcare, biosensing, environmental monitoring, and wearable electronics. They also have significant potential as object recognition and LiDAR auxiliary sensors in low-light or night-time environments for autonomous driving systems, and their applications are rapidly expanding across multiple industries.

The core of this research is the development of a new conductive polymer, PPY:PSS, synthesized from polypyrrole (PPY) and polystyrene sulfonic acid (PSS). Conventional hole transport layers, such as PEDOT:PSS conductive polymers, have faced limitations in device lifetime and long-term reliability due to their strong acidity and high hygroscopicity. In addition, their commercialization has been hindered by the high cost of precursors and complex manufacturing processes.

▶ Comparison of properties of conventional PEDOT:PSS and newly synthesized PPY:PSS

: (left) optical transmittance, (middle) acidity (pH) and resistivity, (right) electrical output characteristics

By optimizing the synthesis process and composition ratio, Professor Kim’s team developed PPY:PSS with reduced acidity (pH 1.6 → pH 2.1), enhanced optical transmittance (90.29% → 93.06%), and significantly lower hygroscopicity, thus achieving physical properties well-suited for photosensor devices.

A PTB7-Th:PCBM-based self-powered NIR light sensor fabricated with this material demonstrated an approximately 30% improvement in electrical performance and a 104% increase in long-term stability compared to conventional devices. Incorporating a newly designed NIR filter enabled detection across multiple wavelength ranges (≥650 nm, ≥700 nm, ≥750 nm), and experimental results confirmed excellent sensitivity, detection accuracy, and durability even under actual NIR operating conditions.

▶ Comparison of sensitivity characteristics of photosensors according to hole transport layer type in the NIR wavelength range

This technology also represents a major leap forward in terms of cost effectiveness. Whereas conventional PEDOT:PSS costs approximately $288 per 100 mL, the newly synthesized PPY:PSS can be manufactured for $3 per 100 mL, achieving a more than hundredfold reduction in material cost.

* Final Price Comparison Table

* Synthesis Costing Table

[Comparison of manufacturing costs for conventional PEDOT:PSS and newly synthesized PPY:PSS]

Professor Kim commented: “The near-infrared light sensor developed in this study, based on our newly engineered hole transport layer, operates stably without an external power supply and has demonstrated excellent durability even under high-temperature and high-humidity conditions. By securing both manufacturing process compatibility and material cost efficiency for commercialization, we expect this technology to make a substantial contribution to the wearable healthcare and autonomous driving sensor markets.”

The study’s first author is Yongju Lee, a PhD candidate at the University of Seoul. This research was supported by the Korea Institute of Industrial Technology (KEIT) Advanced Strategic Industry Gap Technology Development (Semiconductor) Project, the National Research Foundation of Korea (NRF) Mid-Career Researcher Program, and the Creative and Challenging Research Foundation Program, all funded by the Ministry of Trade, Industry and Energy and the Ministry of Science and ICT. The work was carried out using advanced research infrastructure from the University of Seoul’s Semiconductor Research Center, Seoul Smart Sensor Research Center (CS4), and Semiconductor Advanced Packaging Center.

▶ Professor Hyeok Kim, first author Yongju Lee