Near-infrared Organic Photodetectors Research Articles

Improving the Active Layer Crystallization Process by Promoting Acceptor Aggregation for High-Performance Near-Infrared Organic Photodetectors

Improving the Active Layer Crystallization Process by Promoting Acceptor Aggregation for High-Performance Near-Infrared Organic Photodetectors

Long-term noninvasive cardiac monitoring via Neutralized interfacial design for noise-suppressed near-infrared organic photodetectors

Organic photodetectors (OPDs) are the prime candidates for realizing commercial photoplethysmography (PPG) sensors in the future, although their performance and stability limitations remain as challenges. This study presents a strategy for fabricating high-precision, long-term, sustainable OPDs for non-invasive cardiac monitoring. In this work, the use of appropriate amounts of heterocyclic 1,3-diazoles (solid surfactants) enhances the morphology of PEDOT:PSS films and optimizes its energy level alignment, thus directly reducing the leakage current noise and improving the stability of the OPD. The OPDs with 0.5 wt% heterocyclic 1,3-diazole demonstrate enhanced dark current suppression and detectivity enhancement in the photoconductive and self-powered modes. Improved charge recombination dynamics and optimal resistance ratios lead to better performance of the champion device under low-intensity illumination. The champion device yields a more precise Photoplethysmography (PPG) signal under normal and exercise conditions when using a near-infrared light source, and it maintains a PPG signal intensity of more than 90 % after 315 days (7560 h) of storage in a nitrogen atmosphere. Optimized PPG sensors based on flexible substrates maintain signal intensity after seven days of air storage. The low hysteresis behavior also verifies that the optimized device has higher driving stability. High-reliability, high-validity accelerated photoplethysmography (APG) demonstrated that the champion PPG sensor would be used for accurate cardiovascular diagnostics, even over an extended period.

Improved Performance of Inverted Near-Infrared Organic Photodetectors Based on ZnO/PFN as Double-Layer Interfacial Materials

Improved Performance of Inverted Near-Infrared Organic Photodetectors Based on ZnO/PFN as Double-Layer Interfacial Materials

A fully-fluorinated all-fused-ring acceptor for highly sensitive near-infrared organic photodetectors

A fully-fluorinated all-fused-ring acceptor for highly sensitive near-infrared organic photodetectors

Ultralow dark current in near-infrared organic photodetector via crosslinked conjugated polyelectrolyte hole-transporting layer

Ultralow dark current in near-infrared organic photodetector via crosslinked conjugated polyelectrolyte hole-transporting layer

Atto-Scale Noise Near-Infrared Organic Photodetectors Enabled by Controlling Interfacial Energetic Offset through Enhanced Anchoring Ability.

The near-infrared (NIR) sensor technology is crucial for various applications such as autonomous driving and biometric tracking. Silicon photodetectors (SiPDs) are widely used in NIR applications; however, their scalability is limited by their crystalline properties. Organic photodetectors (OPDs) have attracted attention for NIR applications owing to their scalability, low-temperature processing, and notably low dark current density (JD), which is similar to that of SiPDs. However, the still high JD (at NIR band) and few measurements of noise equivalent powers (NEPs) pose challenges for accurate performance comparisons. This study addresses these issues by quantitatively characterizing the performance matrix and JD generation mechanism using electron-blocking layers (EBLs) in OPDs. The energy offset at an EBL/photosensitive layer interface determines the thermal activation energy and directly affects JD. A newly synthesized EBL (3PAFBr) substantially enhances the interfacial energy barrier by forming a homogeneous contact owing to the improved anchoring ability of 3PAFBr. As a result, the OPD with 3PAFBr yields a noise current of 852 aA (JD = 12.3 fAcm⁻2 at V → -0.1V) and several femtowatt-scale NEPs. As far as it is known, this is an ultralow ofJD in NIR OPDs. This emphasizes the necessity for quantitative performance characterization.

Advancing Detectivity and Stability of Near-Infrared Organic Photodetectors via a Facile and Efficient Cathode Interlayer.

Near-infrared (NIR) organic photodetectors (OPDs) are pivotal in numerous technological applications due to their excellent responsivity within the NIR region. Polyethylenimine ethoxylated (PEIE) has conventionally been employed as an electron transport layer (hole-blocking layer) to suppress dark current (JD) and enhance charge transport. However, the limitations of PEIE in chemical stability, processing conditions, environmental impact, and absorption range have spurred the development of alternative materials. In this study, we introduced a novel solution: a hybrid of sol-gel zinc oxide (ZnO) and N,N'-bis(N,N-dimethylpropan-1-amine oxide)perylene-3,4,9,10-tetracarboxylic diimide (PDINO) as the electron transport layer for NIR-OPDs. Our fabricated OPD exhibited significantly improved responsivity, reduced internal traps, and enhanced charge transfer efficiency. The detectivity, spanning from 400 to 1100 nm, surpassed ∼5 × 1012 Jones, reaching ∼1.1 × 1012 Jones at 1000 nm, accompanied by an increased responsivity of 0.47 A/W. Also, the unpackaged OPD remarkedly demonstrated stable JD and external quantum efficiency (EQE) over 1000 h under dark storage conditions. This innovative approach not only addresses the drawbacks of conventional PEIE-based OPDs but also offers promising avenues for the development of high-performance OPDs in the future.

Development of Intramolecular Exciton-Coupled Bis-Squaraine Dyes for Application to Near-Infrared Organic Photodetectors

Development of Intramolecular Exciton-Coupled Bis-Squaraine Dyes for Application to Near-Infrared Organic Photodetectors

An A-D-A'-D-A-Type Narrow Bandgap Electron Acceptor Based on Selenophene-Flanked Diketopyrrolopyrrole for Sensitive Near-Infrared Photodetection.

Near-infrared organic photodetectors possess great application potential in night vision, optical communication, and image sensing, but their development is limited by the lack of narrow bandgap organic semiconductors. A-D-A'-D-A-type molecules, featuring multiple intramolecular charge transfer effects, offer a robust framework for achieving near-infrared light absorption. Herein, we report a novel A-D-A'-D-A-type narrow bandgap electron acceptor named DPPSe-4Cl, which incorporates a selenophene-flanked diketopyrrolopyrrole (Se-DPP) unit as its central A' component. This molecule demonstrates exceptional near-infrared absorption properties with an absorption onset reaching 1120 nm and a low optical bandgap of 1.11 eV, owing to the strong electron-withdrawing ability and quinoidal resonance effect induced by the Se-DPP unit. By implementing a doping compensation strategy assisted by Y6 to reduce the trap density in the photoactive layer, the optimized organic photodetector based on DPPSe-4Cl exhibited efficient spectral response and remarkable sensitivity in the range of 300-1100 nm. Particularly, a specific detectivity surpassing 1012 Jones in the wavelength range of 410-1030 nm is achieved. This work offers a promising approach for developing highly sensitive visible to near-infrared broadband photodetection technology using organic semiconductors.

Near-Infrared Organic Photodetectors with Spectral Response over 1200 nm Adopting a Thieno[3,4-c]thiadiazole-Based Acceptor.

The nonclassical ten-pi-electron 5,5-fused thieno[3,4-c]thiadiazole (TTD) unit is an excellent building block for constructing sub-silicon-band gap organic semiconductors. However, no small molecule acceptor (SMA) materials based on TTD have been reported despite the fact that high-sensitivity near-infrared organic photodetectors (OPDs) are generally achieved by using SMAs. In this work, we report a TTD-based narrow band gap (0.95 eV) SMA material TTD(DTC-2FIC)2 with strong near-infrared absorption. Employing PTB7-Th as a donor, OPDs based on TTD(DTC-2FIC)2 exhibit an optimized responsivity of 0.095 (±0.007) A W-1 at 1100 nm and sustain a decent responsivity of 0.074 (±0.008) A W-1 at 1200 nm. Moreover, a good specific detectivity over 1 × 1011 Jones is achieved at a wavelength of 1200 nm. Detailed characterizations imply that the performance of TTD(DTC-2FIC)2-based OPDs may be substantially improved by choosing lower-mixing donors with shallower energy levels. This work demonstrates that SMAs incorporating TTD as the core unit hold promise for constructing high-sensitivity sub-silicon-band gap OPDs.

High-speed and sensitivity near-infrared organic photodetector achieved by halogen substitution strategy for optical wireless communication

High-speed and sensitivity solution-processed organic photodetectors (OPDs) have drawn great attention for their promising applications in next-generation optoelectronics, including optical communication, imaging, autonomous driving, and military security. However, current OPDs commonly suffer from slow response speed due to low charge mobility, significantly hindering their applications in optical wireless communication. Herein, a pair of nonfullerene acceptors (NFAs), featuring a prominent π extension in the central units with respect to Y6, are synthesized with the same backbone but different halogenations in end cap groups, namely, CH-4Cl and CH-4F. The OPD based on CH-4Cl exhibits a remarkably short response time of 270 ns (λ = 850 nm) and detectivity of >1013 Jones in a self-powered mode, improving 34% and 500% compared to the values of OPD with CH-4F NFA, respectively, which ranks the highest speed among self-powered solution-processed binary OPD-based on NFAs. This outstanding performance is attributed to the low trap states and energetic disorders of OPDs with CH-4Cl. Furthermore, the high-speed OPD demonstrates a promising application in high-speed optical wireless communication.

Visible-blind near-infrared organic photodetectors

The presently available commercial photodetectors have a broadband photoresponse and require different external optical filters to block the undesired light outside the detection spectrum window, e.g., near-infrared (NIR) detection. The use of an NIR bandpass has technical limitations in curved or flexible large-area photodetectors, as an NIR bandpass depends critically on the difference in the interference of the optical path in the filter. This work reports the effort to develop a high-performance filter-free organic photodetector (OPD) with a double bulk heterojunction (BHJ) structure. The visible-blind NIR photodetection is realized by eliminating the photocurrent generated in the front visible light-absorbing BHJ optical depletion layer, due to the suppression of electron transport by incorporating a copper thiocyanate-based electron-blocking layer in the OPD. Only excitons generated in the rear NIR-absorbing BHJ contribute to photocurrent in the OPD, thereby achieving visible-blind NIR photodetection. The double BHJ OPD has a high responsivity of 0.38 A/W at 1050 nm and a specific detectivity of >1013 Jones over the wavelength range from 800 to 1050 nm, making it an ideal candidate for applications in optical communication, food quality detection, wellness monitoring, and NIR image sensors.

A novel selenophene based non-fullerene acceptor for near-infrared organic photodetectors with ultra-low dark current

Organic photodetectors have great potential in near-infrared applications. Here we develop new non-fullerene acceptors with detection above 800 nm and demonstrated large area devices with record performances.

Flexible near-infrared organic photodetectors based on a high work function anode

Flexible near-infrared organic photodetectors with an optimized PEDOT:PSS anode present more sensitive detectivity than the control flexible device with the traditional ITO anode and achieve heart rate and blood oxygen saturation monitoring.

Towards cost-effective and lightweight surface plasmon resonance biosensing for H5N1 avian influenza virus detection: Integration of novel near-infrared organic photodetectors

H5N1 avian influenza virus (AIV) persists in causing highly fatal human infections, demanding rapid and accurate diagnostic assessment. In this study, we introduce an intensity-based SPR sensor utilizing NIR wavelength excitation in tandem with a specifically engineered NIR-OPD. The active layer of the OPD consists of a PTB7-Th and COTIC-4 F blend, offering an optimized response for a 980 nm excitation wavelength. Key performance metrics of this OPD include a low Jd of 0.185 nA/cm2, a high responsivity of 0.35 A/W, an EQE of 44.74%, and an exceptional detectivity of 4.59 × 1013 Jones at 980 nm wavelength under zero bias. It also exhibits a wide LDR of 113 dB. The integration of such OPDs into our SPR sensor provides advantages in compactness and cost-effectiveness. Employing this sensor, we detected the H5N1 AIV using a custom high-affinity polyclonal antibody against HA envelope of the H5N1 virus, completing analyses of culture medium samples within 12 min. The detection limit of this biosensor for the H5N1 AIV in PBS-diluted culture medium is approximately 4.3 × 104 copies/mL. When compared to a commercial H5-Ag lateral flow test kit, our biosensor showed a sensitivity 37 times higher. Key attributes of our biosensor include 3D printing technology for easy alignment of optical components and a rapid, simplified detection procedure. Collectively, our findings open up the potential of our SPR biosensor as an efficient tool for detecting H5N1 AIV, promising advancements in on-site detection methodologies.

Reverse-distribution phase featured gradient heterojunction: A universal strategy to realize high-performance near-infrared organic photodetectors for real-time arterial monitoring

Near-infrared (NIR) organic photodetectors (OPDs) play significant roles in night vision, optical communication and bio-imaging for low cost, easy fabrication and flexibility. However, their development is facing a serious challenge that efforts on suppressing typically high dark current density (JD) generally encounter photoresponse loss because of accompanying with less exciton generation or poorer carrier extraction. Here, novel structure and mechanism are pioneered to overcome that challenge: forming a reverse-distribution phase featured gradient heterojunction (RP-GHJ) to build an effective charge transport channel. In such structure, increased barriers are established to prevent unfavorable charge injection for suppressing JD. Additionally, photogenerated carriers are wrapped by anti-recombination region in reverse phase for efficient charge extraction. Therefore, RP-GHJ suppresses JD of NIR-OPDs to 8.48 × 10−9 A cm−2 which is far superior to 1.81 × 10−6 A cm−2 of traditional BHJ one (bias of −1 V) and simultaneously keeps high photoresponse. Consequently, RP-GHJ makes NIR-OPD realize stable-high detectivity over 1013 Jones at bias region from 0 to − 0.5 V and when the bias increases from − 0.5 to − 1 V, decrease of specific detectivity is slight (under 830 nm). And more importantly, a very large linear dynamic range of nearly 160 dB is obtained under 0 V bias. The structure is proven to be universally effective in NIR-OPDs and a highly sensitive arterial pulse monitoring is developed. The novel structure and mechanism provide a universal strategy for realizing high-performance NIR-OPDs and their real applications.

A promising non-fullerene acceptor for near-infrared organic photodetectors operating with low dark current and high response speed

By tuning the band gaps of their active layer materials, organic photodetectors (OPDs) can display good responses in the near-infrared (NIR) region, making them useful for applications in biomedical imaging and optical communication. Nevertheless, NIR OPDs have tended to suffer from low specific detectivity (D*), due to a high dark current. In this study, we employed 3TT-FIC, a non-fullerene acceptor (NFA), to develop OPDs capable of operating with extremely low dark currents and high response speeds. After fine tuning the blend ratio of the donor (PM6) and acceptor (3TT-FIC), we obtained an OPD that operated at a low dark current (7.04 × 10-10 A/cm2) at –1 V with a high value of D* (2.6 × 1013 Jones) at the wavelength of 850 nm. We also describe the wider applicability of 3TT-FIC and its good potential for applications as an NFA in NIR OPDs.

Efficient Near-Infrared Organic Photodetectors with Spectral Response up to 1600 nm for Accurate Alcohol Concentration Detection

The development of near-infrared organic photodetectors (NIR-OPDs) in 1000-1700 nm is essential for medical monitoring, food quality inspection, machine vision, and biomedical imaging. However, when solving the high dark current density (JD) in bulk-heterojunction (BHJ) NIR-OPDs based on narrow-bandgap systems, it is often accompanied by photocurrent loss, which is a great challenge in achieving high-performance NIR-OPDs. Here, an ideal hybrid pseudo-PHJ (planar-heterojunction)/BHJ structure is proposed to overcome this challenge, which is introducing the N2200 layer between the cathode and BHJ. The introduction of the N2200 raises the external charge injection barrier and reduces the trap density, thus achieving significant suppression of JD (6.22 × 10-7 A cm-2 at -0.2 V bias, about 2 orders of magnitude lower compared to the BHJ NIR-OPDs). Meanwhile, the hybrid structure combines the advantages of PHJ and BHJ, thus maintaining a high photocurrent, resulting in responsivity and detectivity of 18.71 mA W-1 and 4.19 × 1010 Jones, respectively, at 1400 nm at -0.2 V bias, which is superior to the performance of BHJ NIR-OPDs. And the hybrid structured NIR-OPDs are proven to rapidly quantify the alcohol content of mixtures to within 2% accuracy, which exhibits great potential for application in the food and pharmaceutical industries.

Effect of Cyano Substitution on Non‐Fullerene Acceptor for Near‐Infrared Organic Photodetectors above 1000 nm (Adv. Funct. Mater. 8/2023)

Non-Fullerene Acceptors In article number 2211486, Seo-Jin Ko, Jong H. Kim, Sung Cheol Yoon, and co-workers present a new CN-substituted non-fullerene acceptor COTCN2, which exhibits a deeper highest occupied molecular orbital energy level and a narrower optical bandgap (< 1.10 eV). As a result, the near-infrared organic photodetector (NIR OPD) based on PTB7-Th:COTCN2 provides high non-detectability beyond 1000 nm with dark hole injection well suppressed due to the larger charge injection barrier. Additionally, as a practical implementation of NIR OPD, photoplethysmography sensors are successfully demonstrated.

Highly Efficient Ternary Near-Infrared Organic Photodetectors for Biometric Monitoring.

Near-infrared (NIR) small-molecule acceptors that absorb at wavelengths of up to 1000 nm are attractive for applications in organic photodetectors (OPDs) and biometrics. In this study, we incorporated IEICO-4F as the third component for PffBT4T-2OD:PC71BM-based OPDs to provide an efficient NIR response while greatly suppressing the leakage current at reverse bias. By varying the blend ratio and thickness (250-600 nm), we obtained an NIR OPD displaying an ultralow dark-current density (JD = 2.62 nA cm-2), ultrahigh detectivity [D* = 7.2 × 1012 Jones (850 nm)], high sensitivity, and photoresponsivity covering the region from the ultraviolet to the NIR. We used tapping-mode atomic force microscopy, optical microscopy, grazing-incidence wide-angle X-ray scattering, and contact angle measurements to investigate the effect of IEICO-4F on the performance of the ternary OPDs. The low compatibility of PffBT4T-2OD and IEICO-4F, originating from weak intermolecular interactions, allowed us to manipulate the degree of phase separation between the donor and acceptor in the ternary blends, leading to an optimized blend morphology featuring efficient charge separation, transport, and collection. To demonstrate its applicability, we integrated our OPD with two light-emitting diodes and used the system for precisely calculated transmissive pulse oximetry.