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Photodetectors made from low‐toxicity organic materials are considered a promising alternative to conventional inorganic photodetectors. However, the performance of current organic photodetectors (OPD) needs to be further enhanced. This study aims to introduce acid‐free poly(3,4‐ethylenedioxythiophene)‐(polystyrene sulfonate) (PEDOT‐(PSS)) films in order to improve the performance of OPDs in practical applications. Utilization of heterocyclic 1,3‐diazole (HDZ) in PEDOT‐(PSS) improves the polymerization degree, carrier mobility, and other physicochemical properties. These enhanced properties also improve the comprehensive performance of OPD. In this flow, the enhanced noise suppression is also confirmed by elucidating the device's performance limitations. Consequently, the presented OPD‐based photoplethysmography sensor has the ability to diagnose blood circulation status and cardiovascular diseases. This accomplishment marks the first in single pixel‐based organic photodiode research. [ABSTRACT FROM AUTHOR]

Organic photodetectors (OPDs) with high photodetection abilities are essential requirements for ubiquitous light‐sensing devices. This work presents a simple nonfused ring electron acceptor (NFREA) named "TPDC‐4F" having optical bandgap of 1.42 eV, being designed as an efficient OPD via thickness control and additive engineering of the photosensitive layer. The optimized photosensitive layer composed of poly[(2,6‐(4,8‐bis(5‐(2‐ethylhexyl‐3‐fluoro)thiophen‐2‐yl)‐benzo[1,2‐b:4,5‐b′]dithiophene))‐alt‐(5,5‐(1′,3′‐di‐2‐thienyl‐5′,7′‐bis(2‐ethylhexyl)benzo[1′,2′‐c:4′,5′‐c′]dithiophene‐4,8‐dione))] (PM6) donors and TPDC‐4F acceptors shows a dramatically suppressed dark current of 3.55 × 10−9 A cm−2. Moreover, it shows improved photoelectric properties and fast charge transfer even though the photosensitive layer thickness is as large as 330 nm. OPDs based on the 330‐nm‐thick PM6:TPDC‐4F with 1‐chloronaphthalene additive exhibit a high specific detectivity (D*) of 1.27 × 1013 cm Hz1/2 W−1 at 800 nm and a linear dynamic range of 122 dB under a bias of −0.1 V. The device also exhibits fast rise and fall times of 6.81 and 5.41 µs, respectively. This work demonstrates that the NFREA‐based OPDs offer competitive device performance compared to those based on fused‐ring electron acceptors. [ABSTRACT FROM AUTHOR]

Charge injection is known as the major source of dark current under an applied reverse bias, which directly influences the performance of organic photodetectors with diode architecture. However, it is unclear which of various contributions, such as electron flow through the junction, shunt leakage, thermionic emission, and tunnelling, are dominant. This study investigates the thermionic emission and tunneling models to describe the origin of experimentally measured dark current generated in an organic photodetector. To elucidate the dominant mechanism, the barrier energies at anodic contacts are set from 0.6 to 1.0 eV using photosensitive layers composed of different acceptors. A linear relation is found between the natural logarithm of the dark current density under reverse bias and the square root of the barrier height, which strongly suggests direct tunneling as dominant mechanism for dark current injection. This conclusion is strengthened by temperature dependent dark current analysis. Further knowledge of the dominant mechanism by charge injection can help devise an effective strategy to suppress dark current for effective organic photodetector device implementation. [ABSTRACT FROM AUTHOR]

In this study, a promising film formation technique is highlighted, named mold‐assisted decal‐coating, as a thin film transfer printing process using the polyurethane acrylate‐based stamping mold. By optimizing the surface energy of the mold with wetting coefficient theory, the mold‐assisted decal‐coating process is successfully demonstrated by transferring the photoactive layer composed of the polymer donor, poly[4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b;4,5‐b′]dithiophene‐2,6‐diyl‐alt‐(4‐(2‐ethylhexyl)‐3‐fluorothieno[3,4‐b]thiophene‐)‐2‐carboxylate‐2‐6‐diyl)] and a narrow bandgap non‐fullerene acceptor (NFA), 2,2′‐[[4,4,9,9‐tetrakis(4‐hexylphenyl)‐4,9‐dihydro‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene‐2,7‐diyl]bis[[4‐[(2‐ethylhexyl)oxy]‐5,2‐thiophenediyl]methylidyne(5,6‐difluoro‐3‐oxo‐1H‐indene‐2,1(3H)‐diylidene)]]bis[propanedinitrile]. This process induces a well‐ordered morphology of photoactive material, prevents damage to the underlying layer by suppressing the solvent penetration. Both photovoltaic cells and photodetectors prepared by the decal‐coated photoactive layers containing fluorinated NFAs showed higher performance (power conversion efficiency = 10.69% and specific detectivity = 1.27 × 1012 A cm Hz1/2 W−1, respectively) than those of cells prepared by the spin‐coating method owing to morphology inversion and smoother interface that led to suppressed internal resistance and enhanced charge flow in normal structure. Thus, the reproducible decal‐coating process using a customized elastomeric mediator is an important thin film coating technique for efficient next‐generation organic optoelectronic materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • Carbazole-based thiophen and pyrene, Cb-Th-Py is newly designed for solid additive. • Cb-Th-Py improves the crystallinity of the donor and the π-π stacking of the acceptor. • Optoelectronics with Cb-Th-Py establish enhanced charge transport pathway. • Modulation of the LUMO of the Cb-Th-Py BHJ forms an enhanced injection barrier. • Photodetectors with Cb-Th-Py exhibit dark current suppression and high detectivity. Modulating the nanostructures of the active layers of optoelectronic devices via various techniques is crucial for enhancing the performances of these devices. However, commonly used liquid additives pose challenges in ensuring device-to-device reproducibility due to their effects on polymer solubility and the restriction of kinetic dynamics during film formation. To address these challenges, designing and incorporating solid additives that are independent of dynamics yet possess properties conducive to efficient charge transport into morphology modulation are important. Herein, a novel small molecule (9-(heptadecan-9-yl)-3,6-bis(5-(pyren-1-yl) thiophen-2-yl)-9H-carbazole (Cb-Th-Py)) is synthesized by combining a carbazole derivative with pyrene in an A-D-A structure. The bulk-heterojunction (BHJ) PM6:Y6 comprising Cb-Th-Py exhibits a smooth morphology. Additionally, via energy-level regulation, a higher electron injection barrier at reverse bias is induced, contributing to effective reduction of dark current. Particularly, Cb-Th-Py demonstrates high miscibility with Y6, ensuring an efficient charge transport pathway via strengthened π–π stacking, leading to a dense BHJ surface. This improves the charge mobility, decreases the trap density, and enhances the photocurrent of BHJ in addition to considerably suppressing noise. These Cb-Th-Py BHJ-based devices offer a more reproducible and effective avenue for performance enhancement of optoelectronics. [ABSTRACT FROM AUTHOR]