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Molecular Packing: Another Key Point for the Performance of Organic and Polymeric Optoelectronic Materials
摘要： Optoelectronic material properties are governed by the whole collective of organic moieties, and these aggregate states present the characteristic performance of extended assemblies with different molecular packing, not only of single molecules themselves. Thus, controlling molecular packing is an essential issue for obtaining the optimized optical and electronic properties. It is also a great challenge because of the unclear structures and complicated intermolecular interactions, including dispersion forces, electrostatic interactions and hydrogen bonding. Moreover, upon the introduction of some external force as the stimulus source, dynamic optical properties can be achieved with the transformation of the photoinduced room temperature molecular packing in some cases, phosphorescence (RTP) effect, mechanochromic luminescence, treatment-dependent mechanoluminescence effect, and the optimized nonlinear optical (NLO) property achieved after electric poling. Therefore, it is essential to understand the relation between characteristics of molecular packing and the resultant optoelectronic performance at the molecular level, which becomes increasingly demanding for the further development of functional materials for their applications in organic light-emitting diodes (OLEDs), chemo- and biosensors, organic solar cells, data storage, and anticounterfeiting devices.
关键词： aggregate states,dynamic optical properties,optoelectronic materials,molecular packing,intermolecular interactions
更新于2025-09-23 15:21:01
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Ideal alloys of two donor isomers with non-covalently conformational locking for ternary organic solar cells
摘要： Ternary organic solar cells (OSCs) based on the alloy model have great potential in maximizing the improvement of device performance due to the probability of simultaneously enhancing the photocurrent through morphology optimization and improving open circuit voltage (Voc) by energy level adjustment. However, rationally designing compatible materials and constructing an effective alloy remain difficult. In this manuscript, two donor isomers, BT-TO-ID and BT-OT-ID with non-covalently conformational locking of alkoxy groups at different position, were designed and synthesized to obtain an ‘‘ideal alloy’’. A linearly tunable Voc was observed between the Voc limitation of binary blends with the changes of the composition across the full range, indicating the behavior of an ideal alloy in the ternary blends. A face-on molecular packing and an appropriate phase separation was observed in the ternary blends due to the strong interactions between the two isomers, which facilitated charge transport and charge recombination suppression. Notable improvements of 76% and 29% in device performance were obtained for the ternary blends compared with BT-OT-ID based and BT-OT-ID based binary devices, respectively. Therefore, this work provided a probable molecular design strategy to guide the construction of an effective alloy in ternary OSCs.
关键词： Open circuit voltage,Non-covalently conformational locking,Alloy model,Device performance,Molecular packing,Phase separation,Ternary organic solar cells,Donor isomers
更新于2025-09-23 15:21:01
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Improving the Electron Mobility of ITIC by End-Group Modulation: The Role of Fluorination and π-Extension
摘要： Nonfullerene organic solar cells (OSCs) using ITIC derivatives as electron acceptors have achieved power conversion efficiencies up to 14%, yet optimal active-layer thicknesses are still limited to (cid:1)100 nm, ascribed mainly to the (cid:3)4 cm2/Vs) of these acceptors. Because of the large steric hindrance of the bulky side chains on the fused-ring core, ITIC favors a local π–π stacking between the electron-withdrawing end groups (IC), which provides the main electron transport channel across the bulk volume. Here, the influence of different fluoro-substituted and π-extended (i.e., benzene-fused) positions in the phenyl moiety of IC on the electron transport properties is systematically investigated by multiscale theoretical simulations. It is found that the electron mobility can be remarkablely improved by proper fluorination and π-extension, especially by π-extension, due to the lower reorganization energy and stronger end-group π-π interaction. Moreover, a judicious combination of π-extension and fluorination can lead to a nearly six-fold increase of the electron mobility with respect to ITIC. This work shows that the electron mobility of A-D-A nonfullerene acceptors can be effectively improved by end-group engineering, paving the way toward higher-performance organic solar cells.
关键词： electron mobility,molecular packing,nonfullerene acceptor,end-group engineering
更新于2025-09-23 15:21:01
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Over 14% Efficiency Nonfullerene All-Small-Molecule Organic Solar Cells Enabled by Improving the Ordering of Molecular Donor via Side-Chains Engineering
摘要： Improving the short current density (Jsc) is a big challenge for gaining highly efficient nonfullerene all-small-molecule organic solar cells (NFASM-OSCs). Herein, a novel small molecular donor, BT-2F which is derived from previously reported BTEC-2F, was designed and synthesized. The shortened alkyl-chains with higher regularity endow BT-2F with more ordered packing arrangement and more compact lamellar stacking as evidenced by the characterization of differential scanning calorimetry and grazing incidence X-ray diffraction. By blending BT-2F with Y6 or N3, BT-2F based devices showed impressive power conversion efficiencies (PCEs) of 13.80% and 14.09% respectively, much higher than the reported PCE of 13.34% for BTEC-2F:Y6. Besides, the efficiency of 14.09% is also among the highest PCE value reported so far for NFASM-OSCs. The distinctly improved Jsc devoted major efforts to enhancing the PCE values, meanwhile both BT-2F:Y6 and BT-2F:N3 still keep the high fill factors over 70%, which are ascribed to the good balance between high crystallinity and proper phase separation.
关键词： Morphology control,Crystallinity,Highly efficient nonfullerene organic solar cells,Molecular packing arrangement,Molecule design
更新于2025-09-23 15:19:57
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Reducing the Singleta??Triplet Energy Gap by Enda??Group ??a???? Stacking Toward Higha??Efficiency Organic Photovoltaics
摘要： To improve the power conversion efficiencies for organic solar cells, it is necessary to enhance light absorption and reduce energy loss simultaneously. Both the lowest singlet (S1) and triplet (T1) excited states need to energetically approach the charge-transfer state to reduce the energy loss in exciton dissociation and by triplet recombination. Meanwhile, the S1 energy needs to be decreased to broaden light absorption. Therefore, it is imperative to reduce the singlet?triplet energy gap (ΔEST), particularly for the narrow-bandgap materials that determine the device T1 energy. Although maximizing intramolecular push?pull effect can drastically decrease ΔEST, it inevitably results in weak oscillator strength and light absorption. Herein, large oscillator strength (≈3) and a moderate ΔEST (0.4?0.5 eV) are found for state-of-the-art A?D?A small-molecule acceptors (ITIC, IT-4F, and Y6) owing to modest push?pull effect. Importantly, end-group π?π stacking commonly in the films can substantially decrease the S1 energy by nearly 0.1 eV, but the T1 energy is hardly changed. The obtained reduction of ΔEST is crucial to effectively suppress triplet recombination and acquire small exciton dissociation driving force. Thus, end-group π?π stacking is an effective way to achieve both small energy loss and efficient light absorption for high-efficiency organic photovoltaics.
关键词： energy loss,triplet recombination,molecular packing,nonfullerene acceptors
更新于2025-09-23 15:19:57
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Mechanochromism induced through the interplay between excimer reaction and excited state intramolecular proton transfer
摘要： Excited-state intramolecular proton transfer (ESIPT) and excimer formation are unimolecular and bimolecular reactions, respectively. The coupling between these two reactions has been rarely observed. Here we show the interplay between ESIPT and excimer formation in CF3-HTTH (2,2′-(thiazolo[5,4-d]thiazole-2,5-diyl)bis(4-(trifluoromethyl)phenol) solid crystal, resulting in the extensively broad multiple emissions spanning from 420 to 750 nm. Comprehensive structural, time-resolved spectroscopic, and two-photon microscopic studies of CF3-HTTH in crystal lattice unveil the pre-equilibrium ESIPT between the normal (N*) and tautomer (T*) form, for which the slow population decay and well-ordered lattice packing facilitate excimeric (E*) formation, rendering N* (460 nm), T* (520 nm) and E* (600 nm) triple emissions. In contrast, the lower degree of packing on the solid surface prohibits excimer formation, showing only the ESIPT process. The correlation between luminescence properties and packing structure sheds light on the corresponding mechanochromic effect based on molecular solid architecture and provide new insight into the aggregation-induced properties.
关键词： Solid-state emission,Excimer formation,Excited-state intramolecular proton transfer,Molecular packing,Mechanochromism
更新于2025-09-19 17:15:36
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π–π Stacking Distance and Phase Separation Controlled Efficiency in Stable All-Polymer Solar Cells
摘要： The morphology of the active layer plays a crucial role in determining device performance and stability for organic solar cells. All-polymer solar cells (All-PSCs), showing robust and stable morphologies, have been proven to give better thermal stability than their fullerene counterparts. However, outstanding thermal stability is not always the case for polymer blends, and the limiting factors responsible for the poor thermal stability in some All-PSCs, and how to obtain higher efficiency without losing stability, still remain unclear. By studying the morphology of poly [2,3-bis (3-octyloxyphenyl) quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl](TQ1)/poly[4,8-bis[5-(2-ethylhexyl)-2-thienyl]benzo[1,2-b:4,5-b′]dithiophene-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl]] (PCE10)/PNDI-T10 blend systems, we found that the rearranged molecular packing structure and phase separation were mainly responsible for the poor thermal stability in devices containing PCE10. The TQ1/PNDI-T10 devices exhibited an improved PCE with a decreased π–π stacking distance after thermal annealing; PCE10/PNDI-T10 devices showed a better pristine PCE, however, thermal annealing induced the increased π–π stacking distance and thus inferior hole conductivity, leading to a decreased PCE. Thus, a maximum PCE could be achieved in a TQ1/PCE10/PNDI-T10 (1/1/1) ternary system after thermal annealing resulting from their favorable molecular interaction and the trade-off of molecular packing structure variations between TQ1 and PCE10. This indicates that a route to efficient and thermal stable All-PSCs can be achieved in a ternary blend by using material with excellent pristine efficiency, combined with another material showing improved efficiency under thermal annealing.
关键词： morphology,device stability,crystallinity,all-polymer solar cells,thermal annealing,molecular packing structure
更新于2025-09-19 17:13:59
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Molecular and Energetic Order Dominate the Photocurrent Generation Process in Organic Solar Cells with Small Energetic Offsets
摘要： Minimizing the energetic offset between donor (D) and acceptor (A) in organic solar cells (OSCs) is pivotal to reduce the charge-transfer (CT) loss and improve the open-circuit voltage (Voc). This nevertheless intrigues a disputable topic on the driving force for the charge separation in OSCs with small energetic offsets. The molecular packing geometries in the active layer determine the energetic levels and trap density, while their relationship with driving force is yet seldom considered. Limited by the complicated demixing morphology and inaccurate measurements of energy levels in the prototypical bulk-heterojunction (BHJ) devices, we thereby demonstrate a concise and robust planar-heterojunction model of PM7/N2200 to investigate the origin of driving force for charge generation. It is surprising to note that the device with smaller energy offset shows higher efficiency. Further analysis reveals that bilayer device with short-range packing PM7 exhibits smaller energetic offsets along with less morphological defects and traps compared to its long-range packing counterparts. This molecular packing characteristic diminishes the energetic disorder at the D/A interfaces and inhibits the trap-assisted charge recombination, contributing to the increased short-circuit current (Jsc) and Voc. Our results suggest that the energetic offset actually has limited influence on charge separation, while the synergetic control of molecular and energetic order is vital to the photocurrent generation and energy loss reduction in OSCs.
关键词： energetic offset,organic solar cells,molecular packing,photocurrent generation,charge separation
更新于2025-09-16 10:30:52
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Markedly different molecular formation in DPP-based small-molecule solar cells probed by grazing-incidence wide-angle X-ray scattering
摘要： This study comprehensively explores the nanostructural properties of two diketopyrrolo[3,4-c]pyrrole-1,4-dione (DPP)-based small molecules with different alkyl side groups and their blends with the fullerene derivative PC71BM, using grazing-incidence wide-angle X-ray scattering synchrotron techniques. Preferentially relative face-on orientation within the larger and more ordered stacking phase of SM1 with its shorter side group (ethylhexyl) was observed in the majority of both pristine and blend thin films, whereas SM2 crystals showed strictly perpendicular orientation. These contrasting crystalline characteristics led to significant differences in the results, from which crystalline structure–performance property correlations are proposed. Thus, the results not only demonstrate important scientific insights into the relationship between molecular structure and crystalline formation but also provide molecular design directions that will facilitate further improvement to the morphology and performance of DPP-based small-molecule solar cells.
关键词： small-molecule donors,diketopyrrolopyrrole,grazing-incidence wide-angle X-ray scattering,molecular packing structure,small-molecule solar cells
更新于2025-09-11 14:15:04
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Tuning the molecular packing and energy level of fullerene acceptors for polymer solar cells
摘要： Fullerenes are considered to be promising acceptor materials for fabrication of bulk-heterojunction polymer solar cells (PSCs) due to their excellent physical and chemical properties. Herein, two novel fullerene derivatives with different specific functional groups, 2-benzylthiophene-C60 bis-adduct (BTCBA) and 2-(4-methoxybenzyl)thiophene-C60 bis-adduct (MBTCBA), were synthesized and utilized as the acceptors for PSCs with the purpose of investigating the influence of the fullerene derivative substituents on the device performance. Compared with BTCBA, MBTCBA exhibits a higher lowest unoccupied molecular orbital (LUMO) energy level due to the electron donating properties of the 2-(4-methoxybenzyl)thiophene functional group. Meanwhile, the appropriate intermolecular interaction of MBTCBA molecules promotes favorable nanophase separation of the P3HT/MBTCBA based blending film, resulting in higher electron mobility. Therefore, the PSCs incorporating P3HT as donor and MBTCBA as acceptor yield a power conversion efficiency (PCE) of 5.29% with an open-circuit voltage (VOC) of 0.81 V, which is obviously higher than that of BTCBA (3.54%) and PCBM (3.76%) based devices. Our work proves that the PSCs performance can be readily improved by modification of fullerene acceptors using electron donating group, tuning the LUMO energy level and the molecular packing behavior.
关键词： Bis-adduct fullerene derivatives,Fullerenes,LUMO energy level,Molecular packing,Polymer solar cells
更新于2025-09-11 14:15:04