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Importance of interfacial crystallinity to reduce open-circuit voltage loss in organic solar cells
摘要： Reducing the energy loss in output voltage is critically important for further enhancing the ef?ciency of organic solar cells (OSCs). Here, we report that OSCs with high mobility and highly crystalline donor (D) and acceptor (A) materials were able to reduce an open-circuit voltage (VOC) loss. The crystallinity of the acceptor layer could be altered by appropriate selection of the three molecules with different alkyl side chain lengths. The VOC was found to increase as the crystallinity of the acceptor layer increased. The origin of the high VOC was that the highly crystalline D/A interface reduced the energy loss in the output voltage by realizing ideal band-to-band recombination. Especially, the high crystallinity of the several molecular layers (less than 6 nm) in the vicinity of the D/A interface was important for realizing the high VOC. Our results demonstrate that the careful design of the D/A interface enables high power conversion ef?ciencies to be achieved in OSCs by reducing open-circuit voltage loss.
关键词： power conversion efficiency,interfacial crystallinity,open-circuit voltage loss,organic solar cells,donor/acceptor interface
更新于2025-09-16 10:30:52
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The effect of molecular structure on the properties of quinoxaline-based molecules for OLED applications
摘要： Different donor-acceptor-donor (D-A-D) and donor-π-bridge-acceptor-π-bridge-donor (D-π-A-π-D) systems based on quinoxaline acceptor are compared. A significant difference in electrochemical and photophysical properties was found depending on molecular structure. A luminescence shift from 539 nm up to 671 nm was observed upon extension of conjugation length. The studied compounds were tested in fluorescent organic light emitting diodes (OLEDs) demonstrating an external quantum efficiency up to 4.5 % for the deep red non-doped device and 7% for the doped into the exciplex host device. A quantum-chemical interpretation of the electroluminescence spectra for the fabricated OLEDs was carried out including modelling of excimers and exciplexes.
关键词： OLEDs,conjugation length,Quinoxaline,donor-acceptor,organic emitter,exciplex
更新于2025-09-12 10:27:22
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Charge photogeneration and recombination in single-material organic solar cells and photodetectors based on conjugated star-shaped donor-acceptor oligomers
摘要： Single-material organic solar cells (SMOSC) are attracted by their simple structure and ease of fabrication so that they are virtually free from a number of drawbacks of heterojunction organic solar cells. However, the performance of SMOSC is still low, first of all because of poor understanding of losses on the way of energy conversion from light to electricity. In this work, we present solution-processed SMOSC based on star-shaped π-conjugated donor-acceptor oligomers with triphenylamine donor (N-Ph3) and alkyl- or phenyl dicyanovinyl acceptor (DCV-R) of general formulae N(Ph-nT-DCV-R)3, where nT stands for n-oligothiophene, and study charge photogeneration and recombination in them. SMOSC demonstrate small energy losses resulting in high open-circuit voltage of 1.08 – 1.19 V and the power conversion efficiency up to 1.22% under illumination intensity of 0.45 sun (1.13% under one sun) with the maximum external quantum efficiency up to 24% for N(Ph-2T-DCV-Ethyl)3, which are among the highest for SMOSC based on conjugated donor-acceptor small molecules or oligomers. It was found that monomolecular recombination dominates at the short-circuit condition and the maximum power point, but at the open-circuit condition the photoinduced charges recombine nearly bimolecularly. The bottleneck in the SMOSC performance was shown to be the field-assisted charge generation perfectly described by the Onsager model in the limit of weak electric fields. The results obtained suggest that intermolecular charge delocalization in conjugated donor-acceptor molecules would be beneficial for further progress in SMOSC.
关键词： conjugated molecule,charge recombination,donor-acceptor molecule,Onsager model,organic solar cell,charge generation
更新于2025-09-12 10:27:22
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Origin of the High Donor-Acceptor Composition Tolerance in Device Performance and Mechanical Robustness of All-Polymer Solar Cells
摘要： High tolerance regarding photovoltaic performance in terms of donor:acceptor (D:A) composition ratio is reported for all-polymer solar cells (all-PSCs), which is a crucial advantage in producing large-scale devices with high reproducibility. To understand the origin of high D:A ratio tolerance in all-PSCs, we investigate the molecular weight (MW) effects of the P(NDI2OD-T2) polymer acceptor (PA) on photovoltaic and mechanical robustness of PBDB-T:P(NDI2OD-T2) all-PSCs. Also, we compare the all-PSCs with other types of PSCs consisting of the same polymer donor but using small molecule acceptors (SMAs) including ITIC and PC71BM. It is observed that the D:A ratio tolerances of both the photovoltaic and mechanical properties are highly dependent on the PA MW and the acceptor material types. For example, at a high D:A ratio of 15:1, all-PSCs using high MW PA (number-average molecular weight (Mn)= 97 kg mol-1) exhibit 13 times higher normalized power conversion efficiency (PCE) than all-PSCs using low MW PA (Mn= 11 kg mol-1), and 20 times higher than ITIC-based PSCs. In addition, the electron mobilities in all-PSCs based on high MW PA are well maintained even at very high D:A ratio, whereas the electron mobilities in low MW PA all-PSCs and SMA-based PSCs decrease by 3- and 4-orders of magnitude, respectively, when the D:A ratio increases from 1:1 to 15:1. Thus, we suggest that the formation of tie molecules and chain entanglements by long polymer chains bridging adjacent crystalline domains is the main origin of excellent D:A tolerance in both mechanical robustness and photovoltaic performance. This work provides an important material design guideline for the reproducible production of flexible and stretchable all-PSCs.
关键词： molecular weight effects,mechanical robustness,donor-acceptor composition tolerance,photovoltaic performance,all-polymer solar cells
更新于2025-09-12 10:27:22
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Covalently linked donor–acceptor dyad for efficient single material organic solar cells
摘要： A novel covalently linked donor–acceptor dyad comprising a dithienopyrrol-based oligomeric donor and a fullerene acceptor was synthesized and characterized. The concomitant effect of favorable optoelectronic properties, energy levels of the frontier orbitals, and ambipolar charge transport enabled the application of the dyad in simplified solution-processed single material organic solar cells reaching a power conversion efficiency of 3.4%.
关键词： donor–acceptor dyad,organic solar cells,ambipolar charge transport,solution-processed,power conversion efficiency
更新于2025-09-12 10:27:22
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Structurally simple OLEDs based on a new fluorinated poly(oxindolylidenearylene)
摘要： Organic light emitting diodes (OLEDs) based on a new polymer; are reported. This new polymer; Poly[(Benzo[c][1,2,5]thiadiazole-4,7-diylbis(9,9-dimethyl-9H-fluorene-7,2-diyl))-3,3-diyl(1-(3-(trifluoromethyl)phenyl)-2-oxindole)] (PF-2F), was used as emissive layer (EML), with a relatively simple architecture ITO/PEDOT:PSS/polymer/(LiF or PFN)/A, which is a modified version of our previously reported; PF-1: Poly[(Benzo[c][1,2,5]thiadiazole-4,7-diylbis(9,9-dimethyl-9H-fluorene-7,2-diyl(1-phenyl-2-oxindole)], applied in OLEDs and lasing devices. The main difference between these two polymers, is the trifluoromethyl (CF3) group addition to the PF-2F. CF3 leads to improved OLEDs electroluminescence and better EQEmax; due to enhanced mechanical properties, higher solubility and higher fluorescence quantum yield (FLQY). PF-1 and PF-2F polymers have an excellent FLQY: ~1. Polymer films (by spin coating) show low roughness value (~ 1-2 nm), just like polymers in OLEDs. OLEDs based on the modified polymer (with yellow-green electroluminescence (EL) emission) showed luminances of up to 1937 cd/m2, current efficiencies of up to 35 cd/A and maximum external quantum efficiency (EQEmax) of up to 2.6 %. Additionally, promising preliminary results on flexible OLEDs using PF-2F and PEDOT: PSS conductive (PH1000) (as anode) are reported.
关键词： Donor-Acceptor,Spin coating,Fluorinated polymer PF-2F,simple OLEDs
更新于2025-09-11 14:15:04
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Molecular Engineering of Simple Metal‐Free Organic Dyes Derived from Triphenylamine for Dye‐Sensitized Solar Cell Applications
摘要： Two new metal-free organic sensitizers, L156 and L224, were designed, synthesized, and characterized for application in dye-sensitized solar cells (DSCs). The structures of the dyes contain a triphenylamine (TPA) segment and 4-(benzo[c][1,2,5]thiadiazol-4-yl)benzoic acid as electron-rich and -deficient moieties, respectively. Two different π bridges, thiophene and 4,8-bis(4-hexylphenyl)benzo[1,2-b:4,5-b’]dithiophene, were used for L156 and L224, respectively. The influence of iodide/triiodide, [Co(bpy)3]2+/3+ (bpy = 2,2’-bipyridine), and [Cu(tmby)2]2+/+ (tmby = 4,4’,6,6’-tetramethyl-2,2’-bipyridine) complexes as redox electrolytes and 18 NR-T and 30 NR-D transparent TiO2 films on the DSC device performance was investigated. The L156-based DSC with [Cu(tmby)2]2+/+ complexes as the redox electrolyte resulted in the best performance of 9.26 % and a remarkably high open-circuit voltage value of 1.1 V (1.096 V), with a short-circuit current of 12.2 mA cm?2 and a fill factor of 0.692, by using 30 NR-D TiO2 films. An efficiency of up to 21.9 % was achieved under a 1000 lx indoor light source, which proved that dye L156 was also an excellent candidate for indoor applications. The maximal monochromatic incident-photon-to-current conversion efficiency of L156–30 NR-D reached up to 70 %.
关键词： electrochemistry,donor–acceptor systems,dyes/pigments,sensitizers,solar cells
更新于2025-09-11 14:15:04
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Molecular origin of photostability for fluorene-based donor–acceptor type photovoltaic polymers
摘要： Quantitative analyses of photodegradation for three fluorene-based photovoltaic polymers, poly[2,7-(9,9-dioctyl-fluorene)-alt-5,5-(4’,7’-di-2-thienyl-2’,1’,3’-benzothiadiazole)] (APFO3), polyfluorene (PFO), and poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) were conducted to understand the molecular origin of photostability for polymers. The Fourier transform infrared (FT-IR) spectra of polymer thin-films varied by irradiating white light at 100 mW?cm-2 irrespective of their molecular architectures. The absorption peaks corresponding to alkyl side chains in a fluorene unit decreased, whereas those for polymers that did not comprise carbonyl groups increased. This spectral variation indicates that alkyl side chains in the fluorene unit decompose when the molecular structure of fluorene varies to that of fluorenone. The reaction rate constant of formation of C=O bond for APFO3 was 1.64×10-5 s-1, lower than PFO (7.59×10-5 s-1) and F8BT (2.64×10-5 s-1), under light irradiation at 30 ?C. The photostability of the polymers improves by designing a donor–acceptor type molecular architecture—incorporating photostable electron deficient benzothiadiazole units with photo-unstable fluorene units.
关键词： fluorene-based,photostability,FT-IR,donor–acceptor,UV-vis,photovoltaic polymers
更新于2025-09-11 14:15:04
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Dipolar and Quadrupolar Luminophores Based on 1,8‐Dimethylcarbazole?Triazine Conjugates for High‐Efficiency Blue Thermally Activated Delayed Fluorescence OLEDs
摘要： Highly efficient blue thermally activated delayed fluorescence emitters combining 1,8-dimethylcarbazoles as a donor (D) unit with a triazine acceptor (A) core are designed and synthesized. A D-A-D-type emitter exhibits superior photo- and electroluminescence (EL) properties compared to a D-A-type counterpart and displays a brilliant blue EL emission with a maximum external EL quantum efficiency as high as 21.2 %.
关键词： organic light-emitting diodes,optoelectronics,donor-acceptor systems,electroluminescence,delayed fluorescence
更新于2025-09-11 14:15:04
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UV-Ozone Modified Sol-Gel Processed ZnO for Improved Diketopyrrolopyrrole-Based Hybrid Photodetectors
摘要： Organic-inorganic interfaces in photodiodes have recently gathered significant interest due to the realization of intrinsic p-n junctions and unique physical properties. Nanopatterned sol-gel ZnO films provide an alternate path for fullerene-free organic photodetectors. However, naturally occurring oxygen vacancies in ZnO often act as trap sites and can degrade device performance if left unchecked. Here, we focus on the role of UV-ozone treatment for filling oxygen vacancies in sol-gel processed ZnO for improving the hybrid interface with thienothiophene linked diketopyrrolopyrrole (DPP) films. The ZnO films are characterized by x-ray diffraction, ultraviolet photoelectron spectroscopy (UPS), cross-sectional electron microscope images, and electron energy loss spectroscopy (EELS). UV-ozone treatment shows no change in the crystal structure, but UPS indicates that the treated films are more resistive and have a higher oxygen concentration at the surface. The EELS spectra show gradual passivation of oxygen vacancies within the bulk of the ZnO films. Fullerene-free photodetectors fabricated from ZnO:DPP interfaces show dark currents reduced by half and photoresponsivities nearly doubled, on average, when the ZnO surface is UV-ozone treated compared to non-treated ZnO films, indicating this simple technique to be excellent for improving photodiode performance when ZnO is used as an electron transport layer.
关键词： ZnO,UV-Ozone,Defects,Sol-Gel,Donor-Acceptor Copolymer,Photodiode
更新于2025-09-11 14:15:04