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A Nonfullerene Acceptor with Alkylthio‐ and Dimethoxy‐Thiophene‐Groups Yielding High‐Performance Ternary Organic Solar Cells
摘要： Herein, an A–D–A-type nonfullerene acceptor (named IDTS-4F) with an alkyl thiophenyl side chain and dimethoxy thiophene bridging unit is reported. The use of an alkyl thiophenyl group is important, as the insertion of sulfur atoms can slightly downshift the highest occupied molecular orbital (HOMO) level of the molecule and allows IDTS-4F to match with state-of-the-art donor polymer PM6 (or PM7). Compared with conventional nonfullerene acceptors, IT-4F, the IDTS-4F molecule, has a smaller optical bandgap and higher lowest unoccupied molecular orbital (LUMO) level, which are beneficial to increase the Voc and Jsc of the devices. Nonfullerene organic solar cell devices are fabricated using IDTS-4F. Although the binary device based on IDTS-4F exhibits a lower fill factor (FF, 70%), the ternary device by incorporating 0.2 of IDTS-4F and 0.8 of IT-4F (with PM6 as the donor polymer) can simultaneously achieve a higher Voc and Jsc, while maintaining the high FF (77%) of IT-4F based system. Morphology characterizations indicate the formation of homogeneous film morphology, the large increase in phase purity and crystallinity, and the reduction in domain size upon addition of crystalline IDTS-4F, while the electron/hole mobilities and recombination losses of the IT-4F system are both maintained.
关键词： polymer solar cells,nonfullerene acceptors,fullerene-free,organic solar cells,ternary solar cells
更新于2025-09-19 17:13:59
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17.1% Efficient Singlea??Junction Organic Solar Cells Enabled by na??Type Doping of the Bulka??Heterojunction
摘要： Molecular doping is often used in organic semiconductors to tune their (opto)electronic properties. Despite its versatility, however, its application in organic photovoltaics (OPVs) remains limited and restricted to p-type dopants. In an effort to control the charge transport within the bulk-heterojunction (BHJ) of OPVs, the n-type dopant benzyl viologen (BV) is incorporated in a BHJ composed of the donor polymer PM6 and the small-molecule acceptor IT-4F. The power conversion efficiency (PCE) of the cells is found to increase from 13.2% to 14.4% upon addition of 0.004 wt% BV. Analysis of the photoactive materials and devices reveals that BV acts simultaneously as n-type dopant and microstructure modifier for the BHJ. Under optimal BV concentrations, these synergistic effects result in balanced hole and electron mobilities, higher absorption coefficients and increased charge-carrier density within the BHJ, while significantly extending the cells’ shelf-lifetime. The n-type doping strategy is applied to five additional BHJ systems, for which similarly remarkable performance improvements are obtained. OPVs of particular interest are based on the ternary PM6:Y6:PC71BM:BV(0.004 wt%) blend for which a maximum PCE of 17.1%, is obtained. The effectiveness of the n-doping strategy highlights electron transport in NFA-based OPVs as being a key issue.
关键词： nonfullerene acceptors,molecular doping,additives,organic photovoltaics
更新于2025-09-19 17:13:59
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Critical Role of Polymer Aggregation and Miscibility in Nonfullerenea??Based Organic Photovoltaics
摘要： Understanding the correlation between polymer aggregation, miscibility, and device performance is important to establish a set of chemistry design rules for donor polymers with nonfullerene acceptors (NFAs). Employing a donor polymer with strong temperature-dependent aggregation, namely PffBT4T-2OD [poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3″′-di(2-octyldodecyl)-2,2′;5′,2″;5″,2″′-quaterthiophen-5,5-diyl)], also known as PCE-11 as a base polymer, five copolymer derivatives having a different thiophene linker composition are blended with the common NFA O-IDTBR to investigate their photovoltaic performance. While the donor polymers have similar optoelectronic properties, it is found that the device power conversion efficiency changes drastically from 1.8% to 8.7% as a function of thiophene content in the donor polymer. Results of structural characterization show that polymer aggregation and miscibility with O-IDTBR are a strong function of the chemical composition, leading to different donor–acceptor blend morphology. Polymers having a strong tendency to aggregate are found to undergo fast aggregation prior to liquid–liquid phase separation and have a higher miscibility with NFA. These properties result in smaller mixed donor–acceptor domains, stronger PL quenching, and more efficient exciton dissociation in the resulting cells. This work indicates the importance of both polymer aggregation and donor–acceptor interaction on the formation of bulk heterojunctions in polymer:NFA blends.
关键词： nonfullerene acceptors,charge transport,morphology,charge generation,polymer aggregation
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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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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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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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
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Nonfullerene acceptors comprising a naphthalene core for high efficiency organic solar cells
摘要： A fused-ring electron acceptor (FREA) NDIC is designed and synthesized. Inspired by IDIC, NDIC was constructed by replacing the benzene with a naphthalene ring in its core unit. IDIC exhibits an optical bandgap of 1.60 eV and a lower lowest unoccupied molecular orbital (LUMO) energy level of ?3.92 eV. In comparison, NDIC displays an optical band gap of 1.72 eV and a higher lying LUMO energy level of ?3.88 eV. Due to the higher energy level, inverted devices based on NDIC exhibit a higher open circuit voltage (Voc) of 0.90 V, which is much higher than that of IDIC (0.77 V). After a series of optimizations, a power conversion efficiency (PCE) of 9.43% was obtained with a PBDB-T:NDIC blend active layer, in comparison, a PCE of 9.19% was achieved based on IDIC. Our results demonstrate that a tiny variation in the molecular structure could dramatically affect the optical and electrochemical properties, and thus the photovoltaic performance.
关键词： Nonfullerene acceptors,organic solar cells,fused-ring electron acceptor,photovoltaic performance,naphthalene core
更新于2025-09-12 10:27:22