High-Performance Organic Photodiodes via Dark- Current Suppression and Their Ultraflexible Device Applications
암전류 제어를 통한 고성능 유기포토다이오드 개발 및 초유연 포토다이오드 응용연구
- 주제(키워드) Near-infrared , Organic semiconductor , Photodiode , Photodetector , Dark current , Non-fullerene acceptor , Cyano substitution , Resonant cavity effect , Ultra-flexible device , Pulse oximetry
- 주제(DDC) 547
- 발행기관 아주대학교 일반대학원
- 지도교수 김종현
- 발행년도 2026
- 학위수여년월 2026. 2
- 학위명 박사
- 학과 및 전공 일반대학원 분자과학기술학과
- 실제URI http://www.dcollection.net/handler/ajou/000000035909
- 본문언어 한국어
- 저작권 아주대학교 논문은 저작권에 의해 보호받습니다.
초록/요약
Near-infrared organic photodetectors (NIR-OPDs) are utilized in various applications, such as night vision cameras, near-infrared optical communication, and biomedical sensing, leveraging their long wavelength and invisible properties. Currently commercialized inorganic NIR-PDs face difficulties in device miniaturization at the nanoscale due to the formation of thick films (3μm~) caused by the low absorption coefficient of inorganic semiconductor materials. In contrast, organic NIR-PDs, based on the high absorption coefficient of organic semiconductor materials, can absorb light even at wavelengths below 200 nm. However, despite these advantages, near-infrared organic photodetectors face challenges such as low dielectric constants, high exciton binding energies, and the formation of trap state in the bandgap due to low crystallinity of organic semiconductors is due to their amorphous crystal structure based on secondary bonding. Furthermore, if the bandgap of the organic semiconductor, which is essential for absorbing near-infrared light, is designed to be narrow, below 1.6 eV (~780 nm), the narrow bandgap leads to problems such as easier exciton recombination and increased dark current generated by thermal excitation. Therefore, improving the high dark current and low photocurrent of near-infrared organic photodetectors is currently an important challenge. In this thesis, research was conducted to overcome the problems of near-infrared organic photodetectors and implement high-performance near-infrared photodetectors that can detect biological signals on ultra-flexible substrates. This was achieved by suppressing dark current through non-fullerene and introducing a resonant structure to increase photocurrent in the near-infrared region. Chapter 1 provides a detailed explanation of the definition, operating principles, and performance metrics of near-infrared organic photodetectors. Specifically, this paper summarizes previously reported literature on the formation mechanism of dark current and strategies for suppressing it and discusses the direction for suppressing dark current in near- infrared organic photodetectors. Chapter 2 introduces a strategy to suppress dark current by replacing fullerene derivative acceptors in the active layer of near-infrared organic photodetectors with non-fullerene acceptors. By suppressing the energy disorder and trap levels of fullerene derivative acceptors, the suppression of crystallinity and trap-mediated recombination has been achieved, thereby reducing dark current. Chapter 3 introduces research on suppressing the dark current of near-infrared organic photodetectors by substituting cyano groups into non-fullerene acceptors. The deep HOMO level of the non-fullerene acceptor formed when the cyano group is substituted creates an increased barrier energy between the electrode and the non-fullerene acceptor, effectively suppressing the dark current injected from the electrode. Chapter 4 reports on the fabrication of a near-infrared organic photodetector with a resonant structure on a flexible parylene substrate, employing a strategy to reduce dark current and increase photocurrent in the near-infrared region. The thick film thickness (220– 300 nm) of the active layer, which forms a resonant structure in the near-infrared region, effectively suppresses dark current while significantly increasing photocurrent in the near- infrared region. This device performance enhancement due to the resonant effect was also confirmed to be possible even on flexible substrates. This paper effectively suppresses the dark current of organic photodetectors with near- infrared absorption, enhances the photocurrent in the near-infrared region while achieving dark current suppression, thereby increasing the specific detectivity. Furthermore, the implemented device, which successfully operates on an ultra-flexible substrate, demonstrates that biological signals can be successfully measured even at low near-infrared intensities. This presents performance enhancement strategies for the commercialization of near-infrared organic photodetectors and their potential for flexible applications.
more목차
Chapter 1. Introduction 1
1.1. Research motivation 1
1.2. Near-infrared organic photodetectors 2
1.3. Figure of merits 6
1.3.1. Photo-response 6
1.3.2. Dark current and noise spectral density 6
1.3.3. Light intensity dependence of photo-response 8
1.3.4. Specific detectivity and noise equivalent power 8
1.3.5. Photo-response speed 10
1.4. Mechanism in near-infrared organic photodetectors 10
1.5. Research problems of near-infrared organic photodetectors 12
1.6. Strategies of suppressed dark current 14
1.7. Strategies for enhanced photo current 16
Chapter 2. Dark Current Suppression using Non-Fullerene Acceptors for Near-Infrared Organic Photodiodes 18
2.1. Introduction 18
2.2. Experimental section 20
2.2.1. Materials 20
2.2.2. Fabrication of near-infrared organic photodetectors 20
2.2.3. Measurements and characterization 20
2.3. Results and discussion 21
2.4. Conclusions 30
Chapter 3. Enhanced Energetic Barrier Using Cyano Substitution on Non-Fullerene Acceptors for High-Performance Near-Infrared Organic Photodiodes 31
3.1. Introduction 31
3.2. Experimental section 34
3.2.1. Materials 34
3.2.2. Device fabrication 34
3.2.3. Measurements and characterization 34
3.3. Results and discussion 35
3.4. Conclusions 51
Chapter 4. Enhanced Signal-to-Noise Ratio Using Resonant Cavity Effect on Ultraflexible Near-Infrared Organic Photodiode 52
4.1. Introduction 52
4.2. Experimental section 54
4.2.1. Materials and device fabrication on rigid substrates 54
4.2.2. Materials and device fabrication on ultraflexible substrates 55
4.2.3. Measurement and characterization 56
4.3. Results and discussion 58
4.4. Conclusions 75
Chapter 5. Conclusion 76
Reference 78
Chapter 1. References 78
Chapter 2. References 81
Chapter 3. References 83
Chapter 4. References 87
List of Publications 91
List of Presentations 95
List of Patents 97
Korean Abstract (국문 초록) 98
