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Donor-acceptor based bulk-heterojunctions (BHJ) are commonly used as the photoactive layer in organic photodetectors (OPDs) to utilize the energetic offset formed at the donor and acceptor interface for exciton dissociation. However, this strategy often complicates optimization procedures and raises the concerns over device reproducibility and stability. Herein, we demonstrate that solution-processed single-component organic semiconductors can operate as efficient OPDs. We use non-fullerene acceptors (NFAs) as the single-component photoactive layer, where the intermolecular charge transfer excitonic (CTE) states are formed within -9 A cm-2), high responsivity (≥ 0.15 A W-1), high specific detectivity (> 1012 Jones) and fast photo-response time (< 10 μs), comparable to the state-of-the-art BHJ OPDs. We find these excellent single-component NFA OPD performances are strongly correlated with the high quadrupole moments of NFA molecules, which generate the energetic offset required for CTE state separation. Our work opens a new way to realize efficient OPD devices using single-component organic semiconductors via solution processing and provides the important molecular design rules required for single-component photoactive materials.

The accelerated photoresponse of OPD devices for axial fluorinated SubPc was confirmed by photovoltaic analysis and theoretical simulations.

A novel series of donor (D)-π-acceptor (A) merocyanine molecules harnessed with intramolecular chalcogen bonding (ChaB) is designed, synthesized, and characterized. ChaB comprises periodic chalcogen atoms, S, Se, and Te, and a neighboring oxygen atom of a carbonyl moiety. Compared to the D-π-A merocyanine dye with nontraditional intramolecular hydrogen bonding, the novel molecules with an intramolecular ChaB exhibit remarkably smaller absorption spectral widths and higher absorption coefficients attributed to their cyanine-like characteristics approaching the resonance parameter (

[60]Fullerene derivatives with high thermal stability can be used for vacuum deposition under heating to fabricate thin films for organic electronic devices. Here, we investigated the thermal stability of [60]fullerene derivatives with various bulky substituents for thermal evaporation under vacuum by means of thermogravimetric analysis under reduced and normal pressure. We found sterically bulky groups such as tert-butyl groups of [60]fullerene derivatives lowered the vacuum deposition temperature. Also, we performed isothermal thermogravimetric analysis to examine the long-term thermal stability of the designed compounds under heating conditions. Furthermore, we investigated the UV-Vis absorption patterns of the deposited films. Absorption in the blue wavelength range, which was attributed to intermolecular HOMO-LUMO transitions among the molecular orbitals of adjacent [60]fullerenes, was dramatically modified. These results were associated with the prevention of aggregation among neighboring [60]fullerene by the sterically bulky groups. This concept could contribute to expanding the use of evaporable [60]fullerene derivatives in organic thin-film electronics research fields.

Stacked structures employing wavelength-selective organic photodiodes (OPDs) have been studied as promising alternatives to the conventional Si-based image sensors because of their color constancy. Herein, novel donor (D)-π-acceptor (A) molecules are designed, synthesized, and characterized as green-light-selective absorbers for application in organic-on-Si hybrid complementary metal-oxide-semiconductor (CMOS) color image sensors. The p-type molecules, combined with two fused-type heterocyclic donors and an electron-accepting unit, exhibit cyanine-like properties that are characterized by intense and sharp absorption. This molecular design leads to improved absorption properties, thermal stability, and higher photoelectric conversion compared to those of a molecular design based on a nonfused ring. A maximum external quantum efficiency of 66% (λ

The present work describes the development of an organic photodiode (OPD) receiver for high-speed optical wireless communication. To determine the optimal communication design, two different types of photoelectric conversion layers, bulk heterojunction (BHJ) and planar heterojunction (PHJ), are compared. The BHJ-OPD device has a -3 dB bandwidth of 0.65 MHz (at zero bias) and a maximum of 1.4 MHz (at -4 V bias). A 150 Mbps single-channel visible light communication (VLC) data rate using this device by combining preequalization and machine learning (ML)-based digital signal processing (DSP) is demonstrated. To the best of the authors' knowledge, this is the highest data rate ever achieved on an OPD-based VLC system by a factor of 40 over the previous fastest reported. Additionally, the proposed OPD receiver achieves orders of magnitude higher spectral efficiency than the previously reported organic photovoltaic (OPV)-based receivers.

The demand for high-definition complementary metal-oxide–semiconductor (CMOS) image sensors has increased considerably over the past few years in industry as well as in academia. Here we propose transparent green-sensitive organic photodetectors (TG-OPDs) with both dark-current-based high detectivity (over 10 14 c m H z 1 / 2 W − 1 at a wavelength of 550 nm under 3 V) and high responsivity ( 0.34 A W − 1 under 3 V) for organic–silicon hybrid CMOS image sensors. A b a t h o c u p r o i n e : C 60 electron-transporting layer provided the fabricated TG-OPDs with a minimal junction resistivity, smooth morphology, and desirable energy level modulation, resulting in exceptional light sensitivity, a low dark current (below 10 − 11 A c m − 2 ), and a high rectification ratio spanning 10 orders of magnitude. The TG-OPDs had high-temperature endurance (up to 150°C for 2 h) and operational stability under intense heat (above 85°C) for 50 d. We expect this performance to enable the industrialization of these TG-OPDs for optoelectronic sensor applications, such as photoplethysmography, fingerprint recognition, proximity sensing, and imaging.

A bulk-heterojunction (BHJ) structure of organic semiconductor blend is widely used in photon-to-electron converting devices such as organic photodetectors (OPD) and photovoltaics (OPV). However, the impact of the molecular structure on the interfacial electronic states and optoelectronic properties of the constituent organic semiconductors is still unclear, limiting further development of these devices for commercialization. Herein, the critical role of donor molecular structure on OPD performance is identified in highly intermixed BHJ blends containing a small-molecule donor and C60 acceptor. Blending introduces a twisted structure in the donor molecule and a strong coupling between donor and acceptor molecules. This results in ultrafast exciton separation (

Utilizing organic electronics compatible with conventional semiconductor fabrication processes is extremely difficult because of their low chemical resistivity and poor environmental durability. To preserve the intrinsic functionality of organic materials, only a few fabrication processes can be used. Moreover, it is essential to achieve process expandability and silicon-process compatibility to develop high-resolution electronics suitable for mass production. Therefore, we developed wet-process-compatible organic photodetectors by replacing the conventional shadow-mask process with photolithography. This suppresses particle deposition during the serial fabrication processes, providing high operational stability. The fabricated green organic photodiodes exhibit a low dark current (1.0 × 10−11 A/cm2) with high photon–electron conversion efficiency (EQE = 65%). The charge collection and charge separation efficiencies are stable (ηcc = 84.6% and ηcs = 97.7%, respectively). Moreover, the organic semiconductors are compatible with conventional wet- and dry-etching processes owing to thin-film encapsulation layers. Finally, the novel organic image sensor can withstand 500 h under 85 °C/85% relative humidity and 1000 thermal cycles (−55–125 °C). Because of its robustness and strong barrier properties, the novel process architecture reported herein can be extended to any organic electronic devices, including widely commercialized organic light-emitting diodes and organic photovoltaic devices.

In this work, organic photodiodes (OPDs) based on two newly synthesized p-type dipolar small molecules are reported for application to green-light-selective OPDs. In order to reduce the blue-color absorption induced by the use of C60 as the n-type material in a bulk heterojunction (BHJ), the electron donor:electron acceptor composition ratio is tuned in the BHJ. With this light manipulation approach, the blue-wavelength external quantum efficiency (EQE) is minimized to 18% after reducing the C60 concentration in the center part of the BHJ. The two p-type molecules get a cyanine-like character with intense and sharp absorption in the green color by adjusting the strength of their donating and accepting parts and by choosing a selenophene unit as a π-linker. When combined to C60, the green-wavelength EQE reaches 70% in a complete device composed of two transparent electrodes. Finally, the optical simulation shows the good color-balance performance of hybrid full-color image sensor without an additional filter by using the developed green OPD as the top-layer in stacked device architecture.

Charge transfer (CT) states at the donor–acceptor interfaces play an important role in organic optoelectronic devices, yielding photocarrier generation or recombination losses. In this study, we fabricate and characterize vacuum-deposited organic photodiodes (OPDs) composed of SubPc:C60 with various active-layer thicknesses and mixing ratios in terms of the charge separation efficiency (CSE) and charge collection efficiency (CCE). We demonstrate that the combined field-assisted quenching study using both photoluminescence (PL) and electroluminescence (EL) reveals detailed information on the device physics of bulk heterojunction photodiodes as related to the CT state. Our modified PL quenching efficiency approach allows us to reasonably evaluate the CSE. In addition, we find that the EL energy is closely related to the recombination loss factor, and the energy gap between PL and EL exhibits a strong linear relationship with the CCE. As a result, the energy gap is proved to be a meaningful indicator of the ...

Although the morphology of the active layer in bulk heterojunction organic photovoltaic (BHJ-OPV) cells is critical for determining the quantum efficiency (QE), predicting the real QE for a 3-dimensional (3D) morphology has long been difficult because structural information on the composition complexity of donor (D): acceptor (A) blends with small domain size is limited to 2D observations via various image-processing techniques. To overcome this, we reconstruct the 3D morphology by using an isotropic statistical approach based on 2D energy-filtered transmission electron microscopy (EF-TEM) images. This new reconstruction method is validated to obtain the internal QE by using a dynamic Monte Carlo simulation in the BHJ-OPV system with different additives such as 4 vol% 1-chloronaphthalene (CN) and 4 vol% 1,8-diiodooctane (DIO) (compared to the case of no additive); the resulting trend is compared with the experimental QE. Therefore, our developed method can be used to predict the real charge transport performance in the OPV system accurately.

We report on two novel p-type small molecules with a donor–acceptor molecular structure for application to green-light-selective organic photodiodes (OPDs). To achieve the requirement of high light selectivity and sensitivity, an electron-donating aryl amino moiety is combined with two respective electron-accepting heterocycles so that the molecules approach cyanine-like character, characterized by intense and sharp absorption. Molecular stacking is controlled by the addition of bulky aryl functional groups to the main backbone to further control the electrical charge transport properties. With this molecular design, a maximum external quantum efficiency close to 61% (λmax = 550 nm) and a dark-current density below 1.6 nA cm−2 (or specific detectivity D* = 1.19 × 1013 cm Hz1/2 W−1) at an applied reverse bias of 3 V are obtained when mixed with fullerene (C60) in an inverted-structure bulk heterojunction OPD composed of two transparent electrodes. The potential construction of a full-color photodetector or an image sensor is demonstrated by combining the green-light-selective OPD with a silicon photodiode containing solely blue and red color filters in a stacked architecture.

The characterization of the vertical molecular distribution of organic bulk heterojunction (BHJ) structures is crucial to the development of high-performance organic photovoltaic (OPV) devices. Herein, we report a novel and direct method for the characterization of the vertical composition gradient of a BHJ structure. Ar gas cluster ion beam (GCIB) sputtering provided a uniform sputtering yield that preserved the chemical structure of the organic semiconducting materials. The combination of X-ray photoelectron spectroscopy (XPS) and Ar GCIB sputtering facilitated the accurate analysis of the vertical molecular distribution of a regioregular poly(3-​hexylthiophene) (P3HT) and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) BHJ structure. The J-V characteristics and depth profiles of the as-deposited, ethanol-annealed, and chloroform-annealed devices were examined to demonstrate the usefulness of Ar GCIB sputtering in optimizing the BHJ morphology. Chloroform-annealed device exhibited both the best performance and the most homogeneous morphology among the three prepared samples, and the thickness of the P3HT-rich region was substantially reduced from 20 to 10 nm. Consequently, these results provide important information about the correlation between the vertical molecular distribution of a BHJ blend structure and power conversion efficiency of an OPV device.

Work-function-adjustable TimSinOx provides an opportunity to optimize the energy-level alignment at the photoactive/cathode interface in the polymer bulk heterojunction solar cell. The work function of TimSinOx is engineered by adjusting the Si mol% during the sol–gel reaction. The controlled work function provides an energetically downhill cascade pathway for electrons from the electron acceptor to the cathode, which contributes to improvement in electron collection at the cathode. The valence band maxima of TimSinOx also become deeper as the Si mol% increases and the hole-blocking ability of TimSinOx is enhanced as a result. Accordingly, polymer solar cells fitted with the optimized TimSinOx exhibit enhanced performance.

Typical CMOS colour image sensors consist of Si-based photodetectors (PDs) attached with colour filter arrays (i.e., the Bayer pattern). Recent trends on the development of high resolution image sensors, however, require downsizing the pixel dimension, which inevitably results in the loss of sensitivity due to the reduction in the photon acquisition. Very recently, hybrid stacks of organic photodetectors (OPDs) on conventional CMOS technologies have been proposed as one of the promising approaches to realise highly sensitive image sensors by doubling the light detecting area in the limited pixel size. Specifically, OPDs with orthogonal photosensitivity to green light and Si-based PDs with red and blue colour filters serve as the top and bottom photo-conversion layers, respectively. In this presentation, we will introduce the recent development of high performance green light sensitive OPDs and the demonstration of colour images from hybrid CMOS image sensors proposed. OPDs consisting of small molecule organic bulk heterto-junction structures, hole/electron buffer layers, and transparent top/bottom ITO electrodes exhibited peak external quantum efficiencies of 60-65% at 550-560 nm wavelengths and full width at half maximum of ~120 nm at reverse bias of 3 V. Extremely low dark current densities in the range of 0.2-0.5 nA/cm2 at reverse bias of 3V and consequently high specific detectivities over 2×10^13 Jones were obtained from the developed OPD system. Further investigations in terms of the molecular structures of organic light absorbing materials, buffer materials, layer sequences, and even integration issues of the OPD on the CMOS will be described in detail.

We investigated the formation of mixed self-assembled monolayers (SAMs), comprising two silanes terminated with an amine and a non-reactive functional group, to demonstrate the autocatalysis of the mixed SAMs by the amine-terminated precursors. Measurements of surface energy and angle-resolved X-ray photoelectron spectroscopy on the mixed SAMs revealed that the final composition and the surface coverage of the mixed SAMs after deposition strongly depended on the presence and the concentration of the aminesilane precursor in solution. To explain the observed dependence, we further suggested a mechanism based on the autocatalytic effect of the aminesilane precursor on the mixed SAM. These results highlight the complex role of the aminesilane, which behaves simultaneously as a component of the mixed SAM and a catalyst. An important implication of this is that the compositions of mixed SAMs can be significantly influenced by the autocatalytic effect of the component carrying a reactive functional group such as amine.

There are growing opportunities and demands for image sensors that produce higher-resolution images, even in low-light conditions. Increasing the light input areas through 3D architecture within the same pixel size can be an effective solution to address this issue. Organic photodiodes (OPDs) that possess wavelength selectivity can allow for advancements in this regard. Here, we report on novel push–pull D−π–A dyes specially designed for Gaussian-shaped, narrow-band absorption and the high photoelectric conversion. These p-type organic dyes work both as a color filter and as a source of photocurrents with linear and fast light responses, high sensitivity, and excellent stability, when combined with C60 to form bulk heterojunctions (BHJs). The effectiveness of the OPD composed of the active color filter was demonstrated by obtaining a full-color image using a camera that contained an organic/Si hybrid complementary metal-oxide-semiconductor (CMOS) color image sensor.

Energy level, band gap, and hole mobility of photovoltaic donor polymers are crucial factors in achieving high power conversion efficiency. Controlling these characteristics, however, requires complicated synthesis routes. This work reports an effective way to control these properties simultaneously by introducing a simple terpolymer system. Simulation of energy level (band gap), synthesis of donor polymers, and calculation of solubility were systematically coordinated to explain the advantages of the terpolymer system. Anthradithiophene was introduced to elucidate the effect of the extended conjugation length on band gap and hole mobility of donor polymers. Benzodithiophene and thienothiophene which have shown good properties in bulk heterojunction organic solar cells were used as comonomers. Based on the result of the energy level calculation, terpolymers with various mole ratios of the monomers were synthesized; as the ratio of anthradithiophene to benzodithiophene increased, band gap of the terpolymers decreased while hole mobility increased. In addition, we explained the morphology of the terpolymer:fullerene bulk heterojunction films using solubility parameters of materials. With this method, we investigated the relationship between the properties of donor polymers and device performances systematically. The terpolymer system can be widely utilized for tuning the material properties in a systematic way which is quite similar to the band gap engineering in the inorganic semiconductors.

A gallium-doped ZnO (GZO) layer was investigated and compared with a conventional indium-tinoxide (ITO) layer for use as a cathode in an inverted polymer solar cell based on poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C61 butyric acid methyl ester (PCBM) bulk heterojunctions (BHJ). By modifying the GZO cathode with a ZnO thin layer, a high power conversion efficiency (3.4%) comparable to that of an inverted solar cell employing the same P3HT:PCBM BHJ photoactive layer with a conventional ITO/ZnO cathode was achieved. This result indicates that GZO is a transparent electrode material that can potentially be used to replace high-cost ITO.

Enhanced performance of an inverted-type polymer solar cell is reported by controlling the surface energy of a zinc oxide (ZnO) buffer layer, on which a photoactive layer composed of a polymer:fullerene-derivative bulk heterojunction is formed. With the approach based on a mixed self-assembled monolayer, the surface energy of the ZnO buffer layer can be controlled between 40 mN m − 1 and 70 mN m − 1 with negligible changes in its work function. For the given range of surface energy the power conversion effi ciency increases from 3.27% to 3.70% through enhanced photocurrents. The optimized morphology obtained by surface energy control results in the enhanced photocurrent and transmission electron microscopy analysis verifi es the correlation between the surface energy and the phase morphology of the bulk heterojunction. These results demonstrate that surface energy control is an effective method for further improving the performance of polymer solar cells, with potentially important implications for other organic devices containing an interface between a blended organic active layer and a buffer or an electrode layer.

We demonstrate the feasibility of controlling the density of ZnO nanorod arrays by using mixed self-assembled monolayers (SAMs) composed of molecules with hydrophobic methyl end groups and hydrophi...

Coupling of flexible (PAAS: polyacrylic acid sodium salt) and semiflexible (λ DNA) polyelectrolytes onto an oppositely charged lipid monolayer (DOTAP: dioleoyl trimethylammonium propane chloride) at the air-liquid interface leads distinctive collapse behavior with lateral compression. In both cases, trilayer domains form by nucleation growth mechanism followed by multilayer formation with further compression. The flexible chain induces circular, fluid domains while the semiflexible chain induces elongated, solid-like domains. These morphological differences show that the flexibility of adsorbed polymers strongly affects the rigidity of the lipid membrane.

The lateral and vertical distributions of organic p/n bulk heterojunctions for an organic solar cell device are, respectively, investigated using nanometer-scale Auger electron mapping and using X-ray photoelectron spectroscopy (XPS) with Ar gas cluster ion beam (GCIB) sputtering. The concentration of sulfur, present only in the p-type material, is traced to verify the distribution of p-type (donor) and n-type (acceptor) materials in the blended structure. In the vertical direction, a considerable change in atomic sulfur concentration is observed using XPS depth profiling with Ar GCIB sputtering. In addition, Auger electron mapping of sulfur reveals the lateral 2-dimensional distribution of p- and n-type materials. The combination of Auger electron mapping with Ar GCIB sputtering should thereby allow the construction of 3-dimensional distributions of p- and n-type materials in organic photovoltaic cells.

In this paper, we present a simple, low-cost and flexible hybrid cell that converts individually or simultaneously low-frequency mechanical energy and photon energy into electricity using piezoelectric zinc oxide (ZnO) in conjunction with organic solar cell design. Since the hybrid cell is designed by coupled piezoelectric and photoconductive properties of ZnO, this is a naturally hybrid architecture without crosstalk and an additional assembling process to create multi-type energy scavengers, thus differing from a simple integration of two different energy generators. It is demonstrated that the behavior of a piezoelectric output is controlled from alternating current (AC) type to direct current (DC)-like type by tailoring mechanical straining processes both in the dark and under light illumination. Based on such controllability of output modes, it is shown that the performance of the hybrid cell is synergistically enhanced by integrating the contribution made by a piezoelectric generator with a solar cell under a normal indoor level of illumination. Our approach clearly demonstrates the potential of the hybrid approach for scavenging multi-type energies whenever and wherever they are available. Furthermore, this work establishes the methodology to harvest solar energy and low-frequency mechanical energies such as body movements, making it possible to produce a promising multi-functional power generator that could be embedded in flexible architectures.