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Influence of Polymer Aggregation and Liquid Immiscibility on Morphology Tuning by Varying Composition in PffBT4Ta??2DT/Nonfullerene Organic Solar Cells
摘要： The temperature-dependent aggregation behavior of PffBT4T polymers used in organic solar cells plays a critical role in the formation of a favorable morphology in fullerene-based devices. However, there is little investigation into the impact of donor/acceptor ratio on morphology tuning, especially for nonfullerene acceptors (NFAs). Herein, the influence of composition on morphology is reported for blends of PffBT4T-2DT with two NFAs, O-IDTBR and O-IDFBR. The monotectic phase behavior inferred from differential scanning calorimetry provides qualitative insight into the interplay between solid–liquid and liquid–liquid demixing. Transient absorption spectroscopy suggests that geminate recombination dominates charge decay and that the decay rate is insensitive to composition, corroborated by negligible changes in open-circuit voltage. Exciton lifetimes are also insensitive to composition, which is attributed to the signal being dominated by acceptor excitons which are formed and decay in domains of similar size and purity irrespective of composition. A hierarchical morphology is observed, where the composition dependence of size scales and scattering intensity from resonant soft X-ray scattering (R-SoXS) is dominated by variations in volume fractions of polymer/polymer-rich domains. Results suggest an optimal morphology where polymer crystallite size and connectivity are balanced, ensuring a high probability of hole extraction via such domains.
关键词： PffBT4T-2DT,nonfullerene organic solar cells,liquid immiscibility,O-IDTBR,polymer aggregation,O-IDFBR,morphology tuning
更新于2025-09-16 10:30:52
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Modulation of Building Block Size in Conjugated Polymers with D–A Structure for Polymer Solar Cells
摘要： D?A conjugated polymers have played critical roles in recently reported nonfullerene acceptors-based polymer solar cells (NF-PSCs) with high performance. Although the molecular design of the D?A polymers is getting more mature, there are still some fundamental unknowns to be unveiled. Here, three new D?A polymers with varied conjugated length for the D-units in their backbones, namely, PDB-1, PDB-2, and PDB-3, were designed, synthesized, and characterized. It was demonstrated that a longer D-unit leads to stronger interchain interaction and higher hole mobility for pristine polymer films. While blending with IT-4F to fabricate photoactive layers in PSCs, it was found that the domain purity, aggregation size, and π?π stacking effect of the polymers can be greatly affected by the D-unit size. Compared to polymers with shorter D-units, for the polymer with the largest D-units (PDB-3), hole and electron transport channels can be much more easily formed in the blend films. Interestingly, the highest efficiency was obtained in the PSCs based on a PDB-2:IT-4F blend, in which PDB-2 shows similar D-unit size to the polymers with state-of-the-art high photovoltaic performance. The correlations between the molecular structure and photovoltaic property of PDB-x polymers demonstrate that the modulation of building block size is an important method for designing high-performance D?A conjugated polymers for PSCs.
关键词： polymer solar cells,nonfullerene acceptors,D?A conjugated polymers,building block size,photovoltaic performance
更新于2025-09-16 10:30:52
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A new medium-bandgap fused-[1]benzothieno[3,2-b][1]benzo-thiophene (BTBT) nonfullerene acceptor for organic solar cells with high open-circuit voltage
摘要： A new nonfullerene small molecule acceptor, namely DBTIC, based on a octocyclic thieno[3,2-b]thienodi(indenothiophene) unit using [1]benzothieno[3,2-b][1]-benzothiophene as the core unit, was developed. Despite the medium-bandgap of DBTIC (1.71 eV), a power conversion efficiency of 8.64% can be delivered by the solar cells combining DBTIC and a wide-bandgap polymer donor J52. The high open-circuit voltage (Voc) of 0.94 V is also rare for J52 based devices owing to the high-lying lowest unoccupied molecular orbital level of DBTIC. Moreover, using J71 with lower highest occupied molecular orbital level as polymer donor, a higher Voc up to 1.05 V can be achieved.
关键词： high open-circuit voltage,nonfullerene acceptor,organic solar cells,BTBT,medium-bandgap
更新于2025-09-12 10:27:22
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Subtle Molecular Tailoring Induces Significant Morphology Optimization Enabling over 16% Efficiency Organic Solar Cells with Efficient Charge Generation
摘要： Manipulating charge generation in a broad spectral region has proved to be crucial for nonfullerene-electron-acceptor-based organic solar cells (OSCs). 16.64% high efficiency binary OSCs are achieved through the use of a novel electron acceptor AQx-2 with quinoxaline-containing fused core and PBDB-TF as donor. The significant increase in photovoltaic performance of AQx-2 based devices is obtained merely by a subtle tailoring in molecular structure of its analogue AQx-1. Combining the detailed morphology and transient absorption spectroscopy analyses, a good structure–morphology–property relationship is established. The stronger π–π interaction results in efficient electron hopping and balanced electron and hole mobilities attributed to good charge transport. Moreover, the reduced phase separation morphology of AQx-2-based bulk heterojunction blend boosts hole transfer and suppresses geminate recombination. Such success in molecule design and precise morphology optimization may lead to next-generation high-performance OSCs.
关键词： solar cell morphology,organic solar cells,power conversion efficiency,nonfullerene acceptors,charge generation
更新于2025-09-12 10:27:22
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13.7% Efficiency Small‐Molecule Solar Cells Enabled by a Combination of Material and Morphology Optimization
摘要： Compared with the quick development of polymer solar cells, achieving high-efficiency small-molecule solar cells (SMSCs) remains highly challenging, as they are limited by the lack of matched materials and morphology control to a great extent. Herein, two small molecules, BSFTR and Y6, which possess broad as well as matched absorption and energy levels, are applied in SMSCs. Morphology optimization with sequential solvent vapor and thermal annealing makes their blend films show proper crystallinity, balanced and high mobilities, and favorable phase separation, which is conducive for exciton dissociation, charge transport, and extraction. These contribute to a remarkable power conversion efficiency up to 13.69% with an open-circuit voltage of 0.85 V, a high short-circuit current of 23.16 mA cm?2 and a fill factor of 69.66%, which is the highest value among binary SMSCs ever reported. This result indicates that a combination of materials with matched photoelectric properties and subtle morphology control is the inevitable route to high-performance SMSCs.
关键词： morphology,energy loss,power conversion efficiency,small-molecule solar cells,nonfullerene acceptors
更新于2025-09-12 10:27:22
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Hole Transfer Originating from Weakly Bound Exciton Dissociation in Acceptor–Donor–Acceptor Nonfullerene Organic Solar Cells
摘要： The underlying hole-transfer mechanism in high-efficiency OSC bulk heterojunctions based on acceptor?donor?acceptor (A?D?A) nonfullerene acceptors (NFAs) remains unclear. Herein, we study the hole-transfer process between copolymer donor J91 and five A?D?A NFAs with different highest occupied molecular orbital energy offsets (ΔEH) (0.05?0.42 eV) via ultrafast optical spectroscopies. Transient absorption spectra reveal a rapid hole-transfer rate with small ΔEH, suggesting that a large energy offset is not required to overcome the exciton binding energy. Capacitance?frequency spectra and time-resolved photoluminescence spectra confirm the delocalization of an A?D?A-structured acceptor exciton with weak binding energy. Relative to the hole-transfer rate, hole-transfer efficiency is the key factor affecting device performance. We propose that holes primarily stem from weakly bound acceptor exciton dissociation, revealing a new insight into the hole-transfer process in A?D?A NFA-based OSCs.
关键词： hole-transfer mechanism,organic solar cells,exciton dissociation,ultrafast optical spectroscopies,nonfullerene acceptors
更新于2025-09-12 10:27:22
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Regulation of Molecular Packing and Blend Morphology by Finely Tuning Molecular Conformation for High-Performance Nonfullerene Polymer Solar Cells
摘要： The asymmetric thienobenzodithiophene (TBD) structure is first systematically compared with the benzo[1,2-b:4,5-b′]dithiophene (BDT) and dithieno[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b′]dithiophene (DTBDT) units in donor-acceptor (D-A) copolymers and applied as the central core in small molecule acceptors (SMAs). Specific polymers including PBDT-BZ, PTBD-BZ, and PDTBDT-BZ with different macromolecular conformations are synthesized and then matched with four elaborately designed acceptor-donor-acceptor (A-D-A) SMAs with structures comparable to their donor counterparts. The resulting polymer solar cell (PSC) performance trends are dramatically different from each other and highly material-dependent, and the active layer morphology is largely governed by the polymer conformation. Due to its more linear backbone, the PTBD-BZ film has higher crystallinity and more ordered and denser π–π stacking than those of the PBDT-BZ and PDTBDT-BZ films. Thus, PTBD-BZ shows excellent compatibility with and strong independence on the SMAs with varied structures, and PTBD-BZ-based cells deliver high power conversion efficiency (PCE) of 10~12.5%, whereas low PCE is obtained by cells based on PDTBDT-BZ due to its zigzag conformation. Overall, this study reveals control of molecular conformation as a useful approach to modulate the photovoltaic (PV) properties of conjugated polymers.
关键词： morphology,nonfullerene solar cell,power conversion efficiency,asymmetrical backbone,molecular conformation
更新于2025-09-12 10:27:22
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Design of New n-Type Porphyrin Acceptors with Subtle Side-Chain Engineering for Efficient Nonfullerene Solar Cells with Low Energy Loss and Optoelectronic Response Covering the Near-Infrared Region
摘要： A series of tailor-made highly efficient and near-infrared porphyrin-based acceptors is designed and synthesized for fullerene-free bulk-heterojunction (BHJ) organic solar cells (OSCs). Constructing BHJ active layers using a PTB7-Th donor and porphyrin acceptors (P-x), which have complementary absorption, accomplish panchromatic photon-to-current conversion from 300 to 950 nm. Our study shows that side-chains of the porphyrin acceptors fairly influences the molecular ordering and nanomorphology of the BHJ active layers. Significantly, porphyrin acceptor with four dodecoxyl side-chains (P-2) achieves an open-circuit voltage (VOC) of 0.80 V, a short-circuit current density (JSC) of 13.94 mA cm-2, a fill factor (FF) of 64.8%, and overall power conversion efficiency (PCE) of 7.23%. This great performance is attributable to the ascendant light-harvesting capability in the visible and NIR region, a high-lying LUMO energy level, a relatively high and more balanced carrier mobilities, and more ordered face-on molecular packing, which is beneficial for obtaining high VOC and JSC.
关键词： near-infrared absorption,porphyrins,organic solar cells,nonfullerene acceptors,n-type porphyrins
更新于2025-09-12 10:27:22
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A medium-bandgap small molecule donor compatible with both fullerene and unfused-ring nonfullerene acceptors for efficient organic solar cells
摘要： Here we designed and synthesized a new small molecule donor DRC4TB with an alkylthiothienyl-substituted benzodithiophene as the core and 3-butyl rhodanine as the terminal group, which showed an optical bandgap of 1.87 eV. DRC4TB was compatible with both a fullerene acceptor (PC71BM) and an unfused-ring non-fullerene acceptor (HF-PCIC). The optimized DRC4TB:PC71BM and DRC4TB:HF-PCIC solar cells delivered comparable power conversion efficiencies (PCEs) of 8.53% and 8.68%, respectively.
关键词： small molecule donor,nonfullerene acceptor,organic solar cells,fullerene acceptor,power conversion efficiencies
更新于2025-09-12 10:27:22
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Enhancing phase separation with a conformation-locked nonfullerene acceptor for over 14.4% efficiency solar cells
摘要： To fine-tune the morphology and miscibility of the active layer of organic solar cells (OSCs), the molecular backbone design and sidechain control are necessary but complex and challenging for acceptor–donor–acceptor type nonfullerene acceptors. In this work, both fluorination on accepting ends and sidechain modification on the central donating core were optimized for the design of fused-ring electron acceptors (FREAs). The sidechain-locked conformation finely modulates the molecular energy levels and improves the miscibility with weakened structural order. Fluorination effectively enhances the crystallinity to afford an enlarged phase separation and higher domain purity. Benefiting from their synergistic effects, the as-designed ITC6-4F when blended with the PM7 polymer donor enables an impressive power conversion efficiency of 14.47% with a high VOC of 0.90 V and improved FF of 74.31%, which is much higher than those of the devices based on reference FREAs without fluorination (8.21%) or conformation lock (12.48%). Our results demonstrate that enhancing phase separation with a conformation-locked nonfullerene acceptor could be an effective way for further improving the related performance of OSCs.
关键词： nonfullerene acceptors,organic solar cells,fluorination,power conversion efficiency,phase separation
更新于2025-09-12 10:27:22