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Charge Density Modulation on Asymmetric Fused-Ring Acceptors for High-Efficiency Photovoltaic Solar Cells
摘要： Charge density modulation on thieno[2'',3'':5',6']-s-indaceno[2',1':4,5]dithieno[3,2-b:2’,3’-d]pyrrole (IPT) core has been conducted for a systematic study of its impact on the electronic structure, molecular packing and photovoltaic performance of asymmetric fused-ring acceptors (FRAs). Herein, a series of IPT-based FRAs (ca. IN-4F, INO-4F, IPT-4F and IPCl-4F) are designed by adopting a corresponding side-chain of 2-ethylhexyl, 2-ethylhexyloxy, hydrogen or chloro onto IPT core. Enhanced electron-withdrawing side-chains contract the optical bandgap but lower the lowest unoccupied molecular orbital (LUMO) level, which yields a trade-off between JSC and VOC in organic solar cells (OSCs). Furthermore, the FRAs exhibit tuned miscibility and crystallinity, reflected on the FF and JSC values of the OSCs. By pairing with polymer donor PM6, IPT-4F based devices achieve the highest PCE of 14.62% with balanced VOC of 0.88 V and JSC of 22.15 mA cm-2 and high FF of 75.01%. Our research demonstrates that electronic density modulation on asymmetric FRAs is an effective way to systematically optimize the device parameters in pursuit of high performance OSCs.
关键词： asymmetric fused-ring acceptors,Charge density modulation,electron-withdrawing side-chains,organic solar cells,photovoltaic performance
更新于2025-09-23 15:21:01
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Conjugated side-chains engineering of polymer donor enabling improved efficiency for polymer solar cells
摘要： Generally, molecular optimization is widely used to fine-tune the absorption features and energy levels of photovoltaic materials to improve their photovoltaic performance for polymer solar cells (PSCs). In this work, we demonstrate an example that the morphological properties can be effectively optimized by conjugated side-chains engineering on benzo[1,2-b:4,5-b']dithiophene (BDT) unit. The polymer donors PBNT-S with alkylthio-thienyl substitution and PBNP-S with alkylthio-phenyl substitution have identical absorption spectra and energy levels, while exhibit significantly different morphological properties when blended with nonfullerene acceptor Y6. The PBNT-S:Y6 blend shows obviously over crystallinity with excessive domain sizes, while the PBNP-S:Y6 blend realizes better nanoscale phase separation. As a result, a notable power conversion efficiency (PCE) of 14.31% with a high fill factor (FF) of 0.694 is achieved in the PBNP-S:Y6-based device, while the PBNT-S:Y6-based device yields a moderate PCE of 11.10% and a relatively low FF of 0.605. Additionally, PBNP-S shows great potential in semitransparent PSCs, that the PBNP-S:Y6-based semitransparent PSC achieves an outstanding PCE of 11.86%, with an average visible transmittance of 24.3%. The results demonstrate a feasible strategy to manipulate the morphological properties of blend film via rational molecular optimization to improve the photovoltaic performance.
关键词： polymer solar cells,morphological properties,conjugated side-chains engineering,semitransparent PSCs,power conversion efficiency
更新于2025-09-23 15:21:01
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Alignment of Lyotropic Liquid Crystalline Conjugated Polymers in Floating Films
摘要： Directed alignment of polymer chains plays an indispensable role in charge transport properties. We focus not only on a specific method to induce the alignment but also on the design of a liquid crystalline (LC) conjugated polymer to take advantage of an intrinsic self-assembly characteristic. We synthesized a lyotropic LC conjugated polymer, CP1-P, having o-nitrobenzyl (ONB) esters as photocleavable side chains and adopted a floating film transfer method to induce the polymer chain alignment through a lyotropic LC phase transition. An optimum amount of a high boiling point solvent (1,2-dichlorobenzene) in chloroform turned out to be an important factor to maximize the polymer chain alignment. The hole transport mobility along the polymer chain alignment direction was 13?14 times higher than that in the direction perpendicular to the alignment. In addition, the removal of side chains resulted in the solvent resistivity while maintaining the alignment feature in organic thin-film transistors.
关键词： floating films,liquid crystalline conjugated polymers,photocleavable side chains,polymer chain alignment,charge transport properties
更新于2025-09-23 15:21:01
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Doping of Donor-Acceptor Polymers with Long Side Chains via Solution Mixing for Advancing Thermoelectric Properties
摘要： One-step doping of conjugated polymers by solution mixing is typically performed instead of sequential doping because of its simplicity. However, doped polymer solutions often exhibit poor solubility, and the presence of dopants in the produced films can disturb the molecular ordering of polymer structures. In this work, effective pairs of two donor-acceptor (D-A) type polymers and a molecular dopant characterized by high solution stability and good thermoelectric properties of the prepared thin films have been reported. The presence of long side chains in the polymer structures preserves their original solubilities and crystallinity in the solution and thin-film states, respectively, even at large amounts of added dopant (up to 38 mol%). Furthermore, the relatively shallow levels of the highest occupied molecular orbitals of the selected D-A polymers enable efficient charge transfer from the dopant species. Owing to their good charge transport properties, the doped D-A polymers exhibit outstanding thermoelectric properties with a maximum power factor of 31.5 μW m?1 K?2, which is more than an order of magnitude higher than those of the control samples prepared from donor-only poly(3-hexylthiophene).
关键词： molecular doping,donor-acceptor polymers,power factors,long side chains,solution mixing,organic thermoelectric materials
更新于2025-09-19 17:15:36
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Asymmetric Siloxane-Functional Side Chains Enable High-Performance Donor Copolymers for Photovoltaic Applications
摘要： In this work, three benzodithiophene (BDT)-benzotriazole (BTA) alternated wide bandgap (WBG) copolymers attaching symmetric or asymmetric conjugated side chains, namely PDBTFBTA-2T, PBDTFTBA-TSi and PBDTFBTA-2Si, were developed for efficient nonfullerene polymer solar cells. The symmetry effect of the side chains was investigated in detail on the overall properties of these donor polymers. The results demonstrated that the introduced siloxane functional groups showed less effect on the absorptions and frontier orbital levels of the prepared polymers but had significant effect on the miscibility between these polymer donors and nonfullerene acceptor. If increasing the content of siloxane functional groups, the miscibility of the polymer donors and Y6 would be improved, leading to the decreased domain size and more mixed domains. Interestingly, the active blend based on PBDTFTBA-TSi with asymmetric side chains exhibited more balanced miscibility, carrier mobility and phase separation, benefiting exciton diffusion and dissociation. Therefore, a champion power conversion efficiency (PCE) of 14.18% was achieved finally in PBDTFTBA-TSi devices, which was 20.6% and 19.0% higher than the symmetric counterparts of PBTFBTA-2T devices (PCE = 11.76%) and PBDTFBTA-2Si devices (PCE = 11.92%), respectively. This work highlights that the asymmetric side chain engineering based on siloxane functional groups is a promising design strategy for high-performance polymer donor semiconductors.
关键词： molecular design strategy,nonfullerene polymer solar cells,siloxane functional group,wide bandgap copolymers,asymmetric side chains
更新于2025-09-19 17:13:59
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Asymmetrical side-chain engineering of small-molecule acceptors enable high-performance nonfullerene organic solar cells
摘要： Three new small molecules based on the benzo[1,2-b:4,5-b’]dithiophene (BDT) fused central core with different side-chains, namely DPBDT-4Cl, POBDT-4Cl and COBDT-4Cl, are designed and synthesized to investigate the side-chain effect on the properties of nonfullerene acceptors. DPBDT-4Cl has symmetrical phenylalkyl side-chains on the central BDT unit. In order to narrow the bandgap and reduce the steric hindrance, the phenylalkyl chains are systematically replaced with the flexible electron-donating alkoxy side-chain (POBDT-4Cl) and alkyl side-chain (COBDT-4Cl). As a result, POBDT-4Cl and COBDT-4Cl are characterized with asymmetry-featured side-chains. From DPBDT-4Cl to POBDT-4Cl to COBDT-4Cl, their light absorption abilities, molecular packing behaviors and crystallinity are gradually enhanced. The devices based on these three acceptors all show power conversion efficiencies (PCEs) over 11% with energy loss below 0.55 eV. Compared to DPBDT-4Cl, POBDT-4Cl and COBDT-4Cl obviously exhibit enhanced device performance with improved short-circuit current densities (Jsc) and fill factors (FFs), which mainly ascribe to their reduced charge recombination and enhanced charge transport. In addition, the COBDT-4Cl achieved a high efficiency of 13.5% with a Jsc of 21.8 mA cm-2 and an FF of 0.71. This result is among the best performance obtained from asymmetry-featured small molecules.
关键词： side-chains,benzo[1,2-b:4,5-b’]dithiophene,small-molecule acceptors,asymmetrical
更新于2025-09-19 17:13:59
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Achieving Efficient and Stable Morphology in Organic Solar Cells via Fine-tuning the Side-chains of Small Molecule Acceptors
摘要： Both the efficiency and stability of low cost organic solar cells are central components to meeting the requirements of commercialization for organic photovoltaics (OPV). Furthermore, the relationship between chemical structure of active material and morphology and its effects on efficiency and stability is still largely undetermined. Additionally, both the kinetic and thermodynamic morphology states of active layer can have a large impact on efficiency and stability, even when the chemical structures of materials applied in the active layer are especially same or similar. Here, using two series of acceptor-donor-acceptor (A-D-A) type small molecule acceptors (SMAs) with the similar backbone structure, we demonstrate the relevance of fine-tuned chemical structures with their solution and solid-state properties, further leading to significantly different behavior in terms of both device efficiency and stability. This is also partially due to the different morphology states caused by such fine chemical structure tuning. Our results indicate that a delicate balance of molecular aggregation and ordered stacking morphology is not only required to achieve but also could lead to both high efficiency and stability. Thus, among the two series of molecules, UF-EH-2F with both optimal length and steric hindrance of side-chains achieves the preponderant morphology in its corresponding device, where its morphology “Efficient State” and “Stable State” are almost overlapped and thus lead to both the highest efficiency (PCE = 13.56%) and best stability. Our results indicate that it is highly possible to achieve the morphology state required for both high efficiency and stability simultaneously by fine-tuning the chemical structure of active materials for organic solar cells.
关键词： small molecule acceptors,efficiency,side-chains,morphology,organic solar cells,stability
更新于2025-09-16 10:30:52
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The Crucial Role of Fluorine in Fully Alkylated Ladder Type Carbazole Based Non-fullerene Organic Solar Cells
摘要： Two fused ladder type non‐fullerene acceptors, DTCCIC and DTCCIC‐4F, based on an electron‐donating alkylated dithienocyclopentacarbazole core flanked by electron‐withdrawing non‐fluorinated or fluorinated 1,1‐dicyanomethylene‐3‐indanone (IC or IC‐4F), are prepared and utilized in organic solar cells (OSCs). The two new molecules reveal planar structures and strong aggregation behavior, and fluorination is shown to red shift the optical band gap and down shift energy levels. OSCs based on DTCCIC‐4F exhibit a power conversion efficiency of 12.6 %, much higher than that of DTCCIC based devices (6.2 %). Microstructural studies reveal that while both acceptors are highly crystalline, bulk heterojunction blends based on the non‐fluorinated DTCCIC result in overly coarse domains, while blends based on the fluorinated DTCCIC‐4F exhibit a more optimal nanoscale morphology. These results highlight the importance of end group fluorination in controlling molecular aggregation and miscibility.
关键词： fluorine effect,carbazole,fully alkylated side chains,organic solar cells,non‐fullerene acceptors
更新于2025-09-16 10:30:52
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Difluorobenzoxadiazole-based conjugated polymers for efficient non-fullerene polymer solar cells with low voltage loss
摘要： Two donor-acceptor (D-A) conjugated copolymers based on difluorobenzoxadiazole (ffBX) and oligothiophenes, i.e., PffBX-2T and PffBX-TT, were designed and synthesized for polymer solar cells (PSCs). Compared to the polymers based on difluorobenzothiadiazole (ffBT) units, the two ffBX-based polymers presented identical optical bandgaps (~1.62 eV), but lower highest occupied molecular orbital (HOMO) energy levels. Owing to the down-shifted HOMO levels, the PSCs based on PffBX-2T and PffBX-TT showed lower voltage loss, and the open-circuit voltage (Voc) was ~0.1 V higher than that of the devices with the ffBT-based polymer. As a result, higher photovoltaic performance was achieved for the devices based on the ffBX-based polymers. The power conversion efficiencies (PCEs) of the non-fullerene PSCs with PffBX-2T and PffBX-TT as the donor were 8.72% and 10.12%, respectively. The superior device performance of PffBX-TT resulted from the efficient exciton dissociation and charge transport as well as weak charge recombination, which could be ascribed to the favorable face-on packing of the conjugated backbones and the desired morphology in the blend film. Our study demonstrates that difluorobenzoxadiazole is a promising building block for constructing conjugated polymers for high-performance non-fullerene PSCs.
关键词： voltage loss,difluorobenzoxadiazole,alkylthiophene side chains,non-fullerene polymer solar cells
更新于2025-09-12 10:27:22
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Side chain effect on conjugated polymer/fullerene interfaces in organic solar cells: a DFT study
摘要： Considerable experimental research has been conducted on the influence of polymer alkyl side chains on the performance of bulk heterojunction organic solar cells. However, greater insight into the role of alkyl side chains in the polymer/fullerene interfacial regions is still needed. Using the dispersion-corrected density functional theory, we investigate the effect of alkyl side chains on the binding energies and electronic structures of various molecular pairings of fullerenes and monomers of organic copolymers (e.g. a pair of PC71BM and a monomer of copolymer PTB7 based on the thieno[3,4-b]thiophene/benzodithiophene repeat unit, PCBM and a copolymer PCDTBT based on 2,7-carbazole/dithienyl-2,1,3-benzothiazole and PC71BM and a copolymer PffBT4T-2OD based on difluorobenzothiadiazole/quaterthiophene). We find that the trends of the magnitudes of the binding energies vary with the lengths, types (branched or linear), and branching positions of alkyl side chains. Whenever possible, these results are compared with the efficiency trends of the corresponding organic solar cells. With the help of this comparison optimal side chain arrangements in bulk heterogeneous organic solar cells are identified. It is expected that these insights will aid in the production of more efficient organic photovoltaics.
关键词： binding energies,polymer alkyl side chains,organic solar cells,dispersion-corrected density functional theory,bulk heterojunction,electronic structures
更新于2025-09-12 10:27:22