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(a) Chemical structures of CTIC-4F, CO1-4F, and COTIC-4F. Absorption spectra (b) in chloroform solution and (c) thin film. (d) Energy level diagram of active layer components estimated from thin film CV measurements.
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Narrow bandgap n-type molecular semiconductors are relevant as key materials components for the fabrication near-infrared organic solar cells (OSCs) and organic photodetectors (OPDs). We thus designed nearly isostructural non-fullerene electron acceptors, except for the choice of solubilizing units, which absorb from 600 nm to 1100 nm. Specific mol...
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... We recently reported what we termed an ultra-NBG NFA, namely COTIC-4F, which is characterized by an optical bandgap (E g ) of ~1.10 eV. 22 As shown in Figure 1a, the general design of COTIC-4F can be summarized by an A−D'−D−D'−A molecular configuration that is based on an electron rich internal core comprised of cyclopentadithiophene (CPDT) as the central donor (D) unit flanked with alkoxythienyl units (D'). The structure is completed with molecular termini containing 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (IC-2F) acceptor (A) units. ...
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... this contribution, we examine the impact of side chain modifications on the optoelectronic properties of NFAs built on the COTIC-4F conjugated framework ( Figure 1a). ...
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... of OSC devices show that CTIC-4F and CO1-4F blended with the donor conjugated polymer PTB7-Th are able to display power conversion efficiency (PCEs) of over A comparison of the optical absorption spectra of the key compounds in chloroform solution is provided in Figure 1b. One observes that the D" (alkyl side group) replacement by D' (alkoxy side group), i.e. ...
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... processed with only CB, one observes that CTIC-4F and CO1-4F crystallites orient face-on relative to the substrate (Figure 4a and 4b), while crystallites of COTIC-4F adopt an edge-on orientation (Figure 4c). In contrast to the CTIC-4F film processed with only CB, processing with CN (Figure 4d) leads to a film with a sharp and intense (100) Figure S11). However, the organization of NFA crystallites in the blend is perturbed by the presence of PTB7-Th, when compared to the observations for the neat films. ...
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... features of the blend films were also studied by using transmission electron microscopy (TEM). Films processed without CN show a well-mixed morphology of PTB7-Th and NFA components ( Figure S12). Such an intimate mixing may be beneficial for exciton splitting, but would tend to favor charge recombination, which reduces the photocurrent. ...
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... Based on electron energy loss spectroscopy (EELS), it is possible to distinguish between the PTB7-Thand NFA-rich phases, since only the NFA components contain nitrogen. As shown in the EELS images shown in Figure S13, the dark regions observed in the TEM images in Figure 5 correspond to NFA-rich phases. Thus, the processing additive CN leads to unusually organized NFA phases in the blends, especially for CTIC-4F and CO1-4F. ...
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Citations
... [120,121,122] Initially, some of the first investigated NFAs were PDI derivatives, [123,124] although since several years now, state-of-the-art NFAs are based on other building blocks. [125,126,127,128] Since PDIs tend to form excimers, especially in solid films, the role of excimers or excimer-like states in OPVs has been investigated by several research groups. In general, a cofacial orientation of PDIs favors the formation of H-aggregates and excimers; steric groups may inhibit the formation. ...
... 6,7 One of these aforementioned thresholds has recently been exceeded in laboratory scale devices (PCE 4 19%), [8][9][10][11][12][13] which can mostly be attributed to the successful use of non-fullerene acceptors (NFA) that were developed through continuous efforts to replace the hitherto ubiquitous fullerene-based acceptors, such as PC 60 BM. [14][15][16][17][18][19][20][21][22][23][24] In particular, solar cells based on the polymer donor PM6 and the NFA Y6 are representative of this recent performance increase. [25][26][27] Furthermore, numerous different synthetic strategies have been employed and investigated in search for viable NFAs in the past. ...
The efficiency of organic solar cells has increased significantly in the recent years due to the continued improvement in material properties, including the charge carrier mobilities within the bulk heterojunction. However, common strategies to measure the mobility of electrons and holes, such as the space-charge-limited-current approach, rely on purpose-made single carrier diodes, which are operated in the injection regime. Alternatively, impedance spectroscopy measurements can yield an effective mobility as well as a photoconductance mobility for solar cells under realistic operating conditions. There exist various theoretical interpretations that relate the experimentally determined values of the effective mobility with the mobility of the individual charge carriers (i.e. electrons and holes). Furthermore, the relationship between the effective and photoconductance mobility has not been clarified yet. This study shows how the effective and photoconductance mobilities can be combined in a system of equations to calculate the individual mobilities of the faster and slower carriers. Finally, these considerations are applied to determine individual carrier mobilities in several blend systems, including fullerene-based P3HT:PC60BM solar cells, as well as non-fullerene devices based on PM6:Y11-N4, PM6:Y5, PPDT2FBT:Y6, PM6:Y11, PM6:N4, and PM6:Y6. These results were validated with mobility values obtained via the space-charge-limited-current approach.
... In order to overcome this deficiency, it is important to develop a narrow band gap n-type semiconductors and use them in OSCs. Recently, nearly isostructural non-fullerene electron acceptors have been designed by Lee et al., apart from using solubilizer units with absorbance between 600 and 1100 nm 30 . They designed CTIC-4F, CO1-4F and COTIC-4F molecules with band gaps of 1.3, 1.2 and 1.1 eV, respectively, and obtained strong absorption in NIR 30 . ...
... Recently, nearly isostructural non-fullerene electron acceptors have been designed by Lee et al., apart from using solubilizer units with absorbance between 600 and 1100 nm 30 . They designed CTIC-4F, CO1-4F and COTIC-4F molecules with band gaps of 1.3, 1.2 and 1.1 eV, respectively, and obtained strong absorption in NIR 30 . They also designed and synthesized a series of A-π-D-π-A-type NFAs by side-chain engineering to increase NIR absorption in PTB7-based OSCs 31 . ...
Novel semi-transparent organic solar cells (ST-OSC) can be designed with high average visible transmittance (AVT) while at the same time exhibiting superior photovoltaic performance. This reach requires their design to be based not only on conventional window applications but also on functional industrial applications that require exceptional optical performance. In ST-OSC, high AVT can be achieved by photonic-based dielectric/metal/dielectric (DMD) transparent contact engineering. Functional optical modification can also be made with a fine-tuned design of DMD that includes a light management engineering-based approach. Thus, ST-OSCs can be suitable for aesthetic, colourful and decorative industrial windows that provide natural lighting. In this study, we determined optimal ST-OSCs based on a novel PTB7:PC71BM polymer blend with MoO3/Ag/WO3 asymmetric DMD top contact by examining extraordinary optical properties such as AVT, colour rendering index, correlated colour temperature and colour perception over 10 thousand designs. In addition to determining the optimality and extraordinary optical limits for PTB7, we also evaluated the photon-harvesting and photovoltaic performance of ST-OSCs from external quantum efficiency and quantum utilization efficiency. In optimal situations, ST-OSCs offering 48.75% AVT, 99.08 CRI, and sky-blue colours were designed and determined to generate short-circuit current densities of 9.88 mA·cm⁻², 13.64 mA·cm⁻², and 13.06 mA·cm⁻², respectively.
... Infrared-to-visible upconversion devices [the compact stacking of infrared sensing photodetector in conjunction with visible light-emitting diode (LED)] offer an attractive prospect of reifying infrared images into vision at a relatively low cost, i.e., a high-quality pixel-free infrared image can be realized without high-density readout integrated circuits. In the past decade, the photon-tophoton upconversion efficiency (η p-p ), a leading figure of merit assessing the infrared photon utilization rate on quantum efficiency, has witnessed remarkable growth from 0.2% addressing the lattice mismatch issue with the hybrid heterogeneous interface (7) to 25.52% based on an all-organic structure with single photoactive component ( fig. S1) (8). ...
... To tackle these issues, we proposed a semitransparent, large-area, all-organic infrared upconversion device, selectively resolving infrared light density down to submicrowatt per square centimeter (Fig. 1B). A narrow-bandgap NFA of COTIC-4F (E g of 1.10 eV) with an acceptor-donor-acceptor (A-D′-D-D′-A) chemical configuration was used (24,25), developing BHJ blend (3:2 in weight) with a typical low-bandgap conjugated copolymer (PTB7-Th) as the CGL, expanding the absorption spectrum comparable to that of a standard silicon photodiode (Fig. 1C). Note that the BHJ thin film with a thickness of 70 nm followed a minimum absorption at the wavelength of 520 nm, which could alleviate the efficiency loss of upconversion luminance peaked at 523 nm in principle (12). ...
... A broadband response stretching cut-off wavelength beyond 1000 nm provides an appealing potential for biomedical applications. A decent value of 37.84% at the wavelength of 1050 nm was achieved without external bias despite a relatively small highest occupied molecular orbital offset between PTB7-Th and COTIC-4F (25). The low field-dependent responsivity suggests minor geminate recombination loss under bias in the BHJ blend. ...
Crystalline photodiodes remain the most viable infrared sensing technology of choice, yet the opacity and the limitation in pixel size reduction per se restrict their development for supporting high-resolution in situ infrared images. In this work, we propose an all-organic non-fullerene–based upconversion device that brings invisible infrared signal into human vision via exciplex cohost light-emissive system. The device reaches an infrared-to-visible upconversion efficiency of 12.56% by resolving the 940-nm infrared signal (power density of 103.8 μW cm ⁻² ). We tailor a semitransparent (AVT, ~60%), large-area (10.35 cm ² ), lightweight (22.91 g), single-pixel upconversion panel to visualize the infrared power density down to 0.75 μW cm ² , inferring a bias-switching linear dynamic range approaching 80 dB. We also demonstrate the possibility of visualizing low-intensity infrared signals from the Face ID and LiDAR, which should fill the gap in the existing technology based on pixelated complementary metal-oxide semiconductors with optical lenses.
... In addition, OPDs and PPDs exhibit tunable bandgaps, which can be controlled from the ultraviolet (UV) to the NIR via material composition and leveraged to vary the type (broad-and narrowband) of spectral sensitivity. For instance, NIR-sensitive PDs have been demonstrated by blending narrow-bandgap polymers in bulk heterojunctions (BHJs) (21)(22)(23) or by introducing tin (Sn) in lead halide perovskites (24)(25)(26)(27). PDs with narrow or multiwavelength responsivity have been achieved without the use of optical filters, by using narrowband organic (28)(29)(30)(31) and perovskite absorbers (32), by using the antibatic responsivity of thick active layers (33)(34)(35)(36), or by constructing hybrid perovskite/organic hierarchical structures that self-filter parts of the visible spectrum (37)(38)(39)(40). ...
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... 25) Recent state-of-the-art photodetectors based on polymers such as poly(3-hexylthiophene) (P3HT), PTB7-Th:CTIC-4F and PTB7-Th:CO1-4Cl were reported to have reached R levels of 0.42 A W −1 , 0.51 A W −1 and 0.53 A W −1 , respectively, in the NIR spectral region. 7,26,27) However, due to the unreliability of the polymerization reaction, synthesis and exact reproduction of polymers are inherently difficult. Organic small molecule semiconductors can circumvent this issue as they can be synthesized and reproduced with precision. ...
In this study, near-infrared (NIR) organic photodetectors (OPDs) based on a liquid crystalline phthalocyanine derivative, octaoctyl-phthalocyanine (8H2Pc), and phenyl-C61-butyric-acid-methyl-ester (PC61BM) were realized. The champion device was found at the blend ratio of 1:1 by weight and exhibited responsivity of 0.2 A/W, external quantum efficiency of 29%, and shot-noise-limited specific detectivity of 1.3 × 1012 Jones at 740 nm with -1 V reverse bias. This notable performance was attributed to the uniformity and smooth surface morphology of the spin-coated active layer and the intermixed condition of the liquid crystalline 8H2Pc and PC61BM, resulting in smaller domain sizes and better separation of photo generated exciton pairs. Finally, the future prospect of the realized NIR OPD in practical applications was demonstrated by monitoring the vital signals of a human subject with a very simple experimental setup.
... 18%), [11][12][13] which can mostly be attributed to the successful use of non-fullerene acceptors (NFAs) that were developed through continuous efforts to replace the hitherto ubiquitous fullerene-based acceptors, such as PCBM. [14][15][16][17][18][19][20][21][22][23][24] In particular, solar cells based on the polymer donor PM6 and the NFA Y6 are representative for this recent performance increase. [25][26][27] Yet, a detailed, in-depth understanding of the relevant loss-processes and the extraction dynamics is necessary for further improvements. ...
... Such corrections are not necessary, if the TPV/TPC approach was used to determine the chemical capacitance C μ since the series resistance R s does not have any influence on the value of the open-circuit voltage V OC . This fact can be easily understood, if one considers Eq.(20) under opencircuit conditions, where the current-density should approach J ¼ 0. ...
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conditions and illumination intensities is a prerequisite to quantify the recombination and extraction dynamics. Differential charging
techniques are a promising approach to experimentally obtain the charge carrier density under the aforementioned conditions. In particular,
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past studies to determine the charge carrier density of organic solar cells. In this Tutorial, these experimental techniques will be discussed in
detail, highlighting fundamental principles, practical considerations, necessary corrections, advantages, drawbacks, and ultimately their limitations.
Relevant references introducing more advanced concepts will be provided as well. Therefore, the present Tutorial might act as an
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... In a more recent study from Lee et al., a blend of a polymer and a non-fullerene SM acceptor showed a very similar trend in which, depending on the active layer deposition conditions, the CITIQ-4F nonfullerene acceptor (NFA) can form crystallites with an extremely well-arranged pattern. Figure 2b shows the GIWAXS image of films composed of pristine CITIQ-4F, indicative of single-crystal-like packing patterns of a pure or polymorphic form, as suggested by the authors [36]. corresponding to a very limited number of diffraction planes, the case of small molecules can be significantly more complex depending on their crystallisation habits. ...
... In a more recent study from Lee et al., a blend of a polymer and a non-fullerene SM acceptor showed a very similar trend in which, depending on the active layer deposition conditions, the CITIQ-4F non-fullerene acceptor (NFA) can form crystallites with an extremely well-arranged pattern. Figure 2b shows the GIWAXS image of films composed of pristine CITIQ-4F, indicative of single-crystal-like packing patterns of a pure or polymorphic form, as suggested by the authors [36]. This crystallisation habit is maintained when CITIQ-4F is blended with the polymer (PTB7-th), however the texture (crystal orientation) decreases, as seen by the appearance of Debye rings instead of well-defined diffraction spots. ...
... Likewise, a slight modification of CITIQ-4F chemical structure, namely adding an ether group on one of the alkyl chains, shows again a liquid-crystalline-like behaviour. In this case, the extremely ordered single crystal-like packing is not observed even using additives [36]. These experiments are capital in demonstrating that subtle changes in either processing conditions or molecular structure This crystallisation habit is maintained when CITIQ-4F is blended with the polymer (PTB7-th), however the texture (crystal orientation) decreases, as seen by the appearance of Debye rings instead of well-defined diffraction spots. ...
Crystallinity has played a major role in organic solar cells (OSCs). In small molecule (SM) bulk-heterojunction (BHJ) OSCs, the crystallinity and crystalline packing of SM donors have been shown to have a dramatic impact on the formation of an optimum microstructure leading to high-power conversion efficiency (PCE). Herein we describe how crystallinity differs from polymers to SMs, and how the packing habits of SMs (particularly donors) in active layers of BHJ devices can be described as following two different main modes: a single crystal-like and a liquid crystal-like packing type. This notion is reviewed from a chronological perspective, emphasising milestone donor structures and studies focusing on the crystallinity in SM-BHJ OSCs. This review intends to demonstrate that a shift towards a liquid crystalline-like packing can be identified throughout the history of SM-BHJ, and that this shift can be associated with an increase in overall PCE.
... where D* is the detectivity (Jones), q is the basic charge (1.6 × 10 -19 C), and J dark is the dark current density, which is dominated by shot noise when ignoring the Johnson noise and Flicker noise (1 f −1 ). We recorded the plots of D* under 0 and −1. Figure 5c reveals the best device that the value of D* was greater than 2 × 10 12 Jones (at −1.5 V), with a maximum value of 1.1 × 10 13 Jones at 830 nm. Figure S6 compares our values of D* with those described previously in the literature; our reported values represent the best performance among the broadband OPDs [2,10,[18][19][20]22,29,31,32,[54][55][56][57][58][59][60]. Thus, appropriate blending of PC 71 BM can improve the dark current performance and detectivity of OPD devices. ...
With the advancement of portable optoelectronics, organic semiconductors have been attracting attention for their use in the sensing of white and near-infrared light. Ideally, an organic photodiode (OPD) should simultaneously display high responsivity and a high response frequency. In this study we used a ternary blend strategy to prepare PM6: BTP-eC9: PCBM–based OPDs with a broad bandwidth (350–950 nm), ultrahigh responsivity, and a high response frequency. We monitored the dark currents of the OPDs prepared at various PC71BM blend ratios and evaluated their blend film morphologies using optical microscopy, atomic force microscopy, and grazing-incidence wide-angle X-ray scattering. Optimization of the morphology and energy level alignment of the blend films resulted in the OPD prepared with a PM6:BTP-eC9:PC71BM ternary blend weight ratio of 1:1.2:0.5 displaying an extremely low dark current (3.27 × 10−9 A cm−2) under reverse bias at −1 V, with an ultrahigh cut-off frequency (610 kHz, at 530 nm), high responsivity (0.59 A W–1, at −1.5 V), and high detectivity (1.10 × 1013 Jones, under a reverse bias of −1 V at 860 nm). Furthermore, the rise and fall times of this OPD were rapid (114 and 110 ns), respectively.
... , with the narrowest band gap (E g = 1.10 eV) NFA, COTIC-4F (2,2′-((2Z,2′Z)-(((4,4-bis(2-ethylhexyl)-4Hcyclopenta[2,1-b:3,4-b′]dithiophene-2,6-diyl)bis(4-(heptan-3yloxy)thiophene-5,2-diyl))bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile), which serves as a model system for future narrow-band-gap semitransparent OPVs and near-infrared (NIR) sensing organic photodetectors (OPDs). 10,30,31 We investigate the effect of the electrode interface for this blend system by comparing four devices, two in an inverted and two in a conventional architecture, that have the same active layer thickness (105 nm) but four different front electrodes: namely, ZnO, ZnO functionalized with PFN-Br, PEDOT:PSS, and CPE-K. ZnO is commonly used for inverted devices, thanks to its low work function, high stability, transparency, and charge mobility as well as its simplicity of fabrication. ...
