Green-Solvent Processed Blade-Coating Organic Solar Cells with an Efficiency Approaching 19% Enabled by Alkyl-Tailored Acceptors

A Janus Smart Window for Temperature-Adaptive Radiative Cooling and Adjustable Solar Transmittance

The advancement of sophisticated smart windows exhibiting superior thermoregulation capabilities in both solar spectrum and long-wave infrared range maintains a prominent objective for researchers in this field. In this study, a Janus window is proposed and prepared based on polymer-stabilized liquid-crystal films/thermochromic materials. It can achieve switchable front long-wave infrared emissivity (εFront) and solar modulation ability (ΔTsol) through dynamic flipping, making it suitable for different seasonal energy-saving requirements. Outdoor experiments show that under daytime illumination, the indoor temperature decreases by 8 °C, and the nighttime temperature drops by 5 °C. MATLAB simulation calculations indicate that the daytime cooling power is 93 W m-2, while the nighttime cooling power reaches 142 W m-2. Interestingly, by modifying the conductive layer, it can effectively shield electromagnetic radiation (within the X-band frequency range (8.2-12.4) GHz). Energy simulation reveals the substantial superiority of this device in energy savings compared with single-layer polymer-stabilized liquid crystal, poly(N-isopropyl acrylamide), and normal glass when applied in different climate zones. This research presents a compelling opportunity for the development of sophisticated smart windows characterized by exceptional thermoregulation capabilities.

Evolving Role of Conjugated Polymers in Nanoelectronics and Photonics

Conjugated polymers (CPs) have emerged as an interesting class of materials in modern electronics and photonics, characterized by their unique delocalized π-electron systems that confer high flexibility, tunable electronic properties, and solution processability. These organic polymers present a compelling alternative to traditional inorganic semiconductors, offering the potential for a new generation of optoelectronic devices. This review explores the evolving role of CPs, exploring the molecular design strategies and innovative approaches that enhance their optoelectronic properties. We highlight notable progress toward developing faster, more efficient, and environmentally friendly devices by analyzing recent advancements in CP-based devices, including organic photovoltaics, field-effect transistors, and nonvolatile memories. The integration of CPs in flexible sustainable technologies underscores their potential to revolutionize future electronic and photonic systems. As ongoing research pushes the frontiers of molecular engineering and device architecture, CPs are poised to play an essential role in shaping next-generation technologies that prioritize performance, sustainability, and adaptability.

Lowering Toxicity of Solvent in Organic Solar Cells Manufacturing for 20% Efficiency

Thin film organic photovoltaics (OPVs) aim to harness solar energy environmentally friendly, highly efficient, and cost-effective means, thereby offering a sustainable solution for energy production and ecological preservation. Efforts are undertook to optimize engineering preparation technology for OPV devices and mini-modules, through the development of low-ecological-impact solvent processing method. A newly developed solvent engineering strategy employing environmentally benign o-xylene (OXY) with synergistic dual additives (DIM and DIB) achieved an optimal power conversion efficiency (PCE) of 20.0% (JSC of 26.6 mA cm-2, VOC of 0.935 V, FF of 80.3%) alongside exceptional stability metrics (82%-1500h). The mini-module processed with optimized TCE:OXY (1:3 v/v) solvent demonstrated scalable performance reaching 17.6% (18.4 cm2), representing the highest performance achieved in the development safe solvent based OPVs. Suitable microscale patterns contributed to a broader range of receiving angles, enabling more flexible installation geometries for building-integrated applications.

Constructing Controlled Vertical Gradient Morphology in Pseudo-Planar Heterojunction Organic Photovoltaics via Self-Assembled Interface Orthogonal Strategy

Precisely regulating vertically distributed morphology by blade-coating process is crucial to realize high-performance large-scale pseudo-planar heterojunction organic photovoltaics (OPVs). However, the thermodynamic motion and random diffusion of donor/acceptor (D/A) generated from the differences in surface energy and concentration during sequentially blade-coating process will cause great challenges for obtaining ideal active layer morphology. Herein, this study have proposed a self-assembled interface orthogonal strategy by introducing low surface energy guest (N2200) to form protective layer on PM6 surface, which counteracts erosion from orthogonal solution of acceptor to enhance continuity of D/A phases, thus promoting directional carrier migration and effectively suppressing energetic disorder. Finally, N2200-modified device achieves the highest power conversion efficiency (PCE) of 19.86%, and large-area module (16.94 cm2) exhibits exceptional PCE (16.43%). This investigation presents innovative insights into morphology issue triggered by molecular motion and provides an effective method for air-printing large-scale OPVs with precisely controlled morphology based on non-halogenated solvent.

Triplet State Suppression for Energy Loss Reduction in 20% Nonhalogenated Solvent Processed Binary Organic Solar Cells

Boosting power conversion efficiency (PCE) of organic solar cells (OSCs) has been restricted by its undesirably high energy loss, especially for those nonhalogenated solvent-processed ones. Here,a dichloro-methoxylated terminal group in an asymmetric small molecular acceptor design, which realizes a significantly reduced non-radiative energy loss (0.179 eV) compared to its symmetric counterpart (0.202 eV), is reported. Consequently, the device efficiency is improved by up to 20% for PM6:BTP-eC9-4ClO, without sacrificing the photon harvest or charge transport ability of the control system PM6:BTP-eC9. Further characterizations reveal the asymmetric acceptor BTP-eC9-4ClO's blend film demonstrates a suppressed triplet state formation, enabled by an enhanced electron delocalization. In addition, the asymmetric BTP-eC9-4ClO is found to be thermally stabler than BTP-eC9, and thus providing an improved device stability, whose T80 value reaches > 7800 h under 80 °C anneal in N2 via linear extrapolation. This work represents state-of-the-art device performance for nonhalogenated solvent-processed binary OSCs with certified results (19.45%).

Kinetics Manipulation Enabled by Solubility Control Toward 19% Organic Solar Cells via Compatible Air Coating

Blade coating is a promising tool for upscaling organic solar cells (OSCs). However, the performances of blade-coated OSCs still lag behind their spin-coated counterparts, limiting their competitive edge towards commercialization. One of the main reasons is that controlling the film aggregation kinetics and morphology becomes challenging during the transition from spin coating to blade coating, especially when using high boiling point solvents, which can result in excessive aggregation. Therefore, a deeper understanding and appraisal of film formation kinetics influenced by coating methods is crucial. In this work, it is demonstrated that ink solubility tuning by incorporating a twisted third component (BTP-4Cl) can induce rapid crystallization behavior and promote fine phase separation between the donor polymer (PM6) and the acceptor (BTP-eC9) in blade coating. As a result, a high power conversion efficiency (PCE) of 19.67% is obtained in OSCs (0.04 cm2), one of the state-of-the-art efficiencies among the reported blade-coated OSCs (19.76% for the spin-coated devices). In addition, it is found that the inhibited phase aggregation contributes to enhancing the light stability of the device. This strategy offered novel insights into the effectiveness of solubility-tuning approaches for achieving highly efficient and stable OSCs under open-air coating conditions.

Dimeric Small Molecule Acceptors via Terminal-End Connections: Effect of Flexible Linker Length on Photovoltaic Performance

The dimerization of small molecule acceptors (SMAs) holds significant potential by combining the advantages of both SMAs and polymer acceptors in realizing high power conversion efficiency (PCE) and operational stability in organic solar cells (OSCs). However, advancements in the selection and innovation of dimeric linkers are still challenging in enhancing their performance. In this study, three new dimeric acceptors, namely DY-Ar-4, DY-Ar-5, and DY-Ar-6 are synthesized, by linking two Y-series SMA subunits via an "end-to-end" strategy using flexible spacers (octyl, decyl, and dodecyl, respectively). The influence of spacer lengths on device performance is systematically investigated. The results indicate that DY-Ar-5 exhibits more compact and ordered packing, leading to an optimal morphology. OSCs based on PM6: DY-Ar-5 achieves a maximum PCE of 15.76%, attributes to enhance and balance carrier mobility, and reduce carrier recombination. This dimerization strategy using suitable non-conjugated linking units provides a rational principle for designing high-performance non-fullerene acceptors.

17.68% Efficiency Nonhalogenated Solvent-Processed Organic Solar Cell Modules Driven by Seed Crystal Strategy

Organic solar cells now surpass 20% efficiency in small-area devices, but the use of chloroform as a solvent poses industrial scalability challenges because of its limited ability of uniform film formation and toxicity. High-boiling, non-halogenated solvents are being studied as alternatives, but their low solubility and slow evaporation complicate crystallization process. Here, the study introduces a seed crystal strategy by incorporating oligo (ethylene glycol)-modified small-molecule donors to optimize the nucleation and crystallization. The asymmetric BDTF-CA2O molecule, which combines the strong crystallinity of rodanine group and the low nucleation barrier of oligo (ethylene glycol) chain, significantly promotes the crystallization of the polymer donor PM6. Moreover, BDTF-CA2O effectively suppresses excessive phase separation, and optimizes vertical distribution, resulting in enhanced exciton extraction, balanced carrier transport, and reduced recombination losses. Small-area toluene-processed devices achieve a power conversion efficiency of 19.67%. In the realm of large-area organic solar cell modules, this strategy leads to a record active area efficiency of 17.68% and aperture area efficiency of 16.80% (certified at 16.26%), which is the highest reported for organic solar cell modules >10 cm2 to date. These achievements highlight the potential of the seed crystal strategy for large-scale production of efficient, large-area organic solar cell modules.

Isomerism Effect of 3D Dimeric Acceptors for Non-Halogenated Solvent-Processed Organic Solar Cells with 20 % Efficiency

Organic photovoltaic materials that can be processed via non-halogenated solvents are crucial for the large-area manufacturing of organic solar cells (OSCs). However, the limited available of electron acceptors with adequate solubility and favorable molecular packing presents a challenge in achieving efficient non-halogenated solvent-processed OSCs. Herein, inspired by the three-dimensional dimeric acceptor CH8-4, we employed a molecular isomerization strategy to synthesize its isomers, CH8-4A and CH8-4B, by tuning the position of fluorine (F) atom in the central unit. The differing intramolecular fluorine-sulfur non-covalent interactions among these isomers led to differences in molecular pre-aggregation abilities (CH8-4B Collapse

Key Words

• Dimeric acceptor
• isomerism effect
• non-halogenated solvent
• organic solar cells

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Grants

• 52303237 National Natural Science Foundation of China
• 21935007 National Natural Science Foundation of China
• 52025033 National Natural Science Foundation of China
• 22361132530 National Natural Science Foundation of China
• 2022YFB4200400 Ministry of Science and Technology of the People's Republic of China
• 2019YFA070590 Ministry of Science and Technology of the People's Republic of China
• 2023YFE0210400 Ministry of Science and Technology of the People's Republic of China
• 023- 632343116 the Fundamental Research Funds for the Central Universities, Nankai University

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Affiliation(s)

Jia Wang School of Materials Science and Engineering, National Institute for Advanced Materials, Nankai University, Tianjin, 300350, China
Peiran Wang School of Materials Science and Engineering, National Institute for Advanced Materials, Nankai University, Tianjin, 300350, China
Tianqi Chen School of Materials Science and Engineering, National Institute for Advanced Materials, Nankai University, Tianjin, 300350, China
Wenkai Zhao School of Materials Science and Engineering, National Institute for Advanced Materials, Nankai University, Tianjin, 300350, China
Jiaying Wang School of Materials Science and Engineering, National Institute for Advanced Materials, Nankai University, Tianjin, 300350, China
Baofa Lan School of Materials Science and Engineering, National Institute for Advanced Materials, Nankai University, Tianjin, 300350, China
Wanying Feng State Key Laboratory and Institute of Elemento-Organic Chemistry, Frontiers Science Center for New Organic Matter, The Centre of Nanoscale Science and Technology and Key Laboratory of Functional Polymer Materials, Renewable Energy Conversion and Storage Center (RECAST), College of Chemistry, Nankai University, Tianjin, 300071, China
Hang Liu State Key Laboratory and Institute of Elemento-Organic Chemistry, Frontiers Science Center for New Organic Matter, The Centre of Nanoscale Science and Technology and Key Laboratory of Functional Polymer Materials, Renewable Energy Conversion and Storage Center (RECAST), College of Chemistry, Nankai University, Tianjin, 300071, China
Yongsheng Liu State Key Laboratory and Institute of Elemento-Organic Chemistry, Frontiers Science Center for New Organic Matter, The Centre of Nanoscale Science and Technology and Key Laboratory of Functional Polymer Materials, Renewable Energy Conversion and Storage Center (RECAST), College of Chemistry, Nankai University, Tianjin, 300071, China
Xiangjian Wan State Key Laboratory and Institute of Elemento-Organic Chemistry, Frontiers Science Center for New Organic Matter, The Centre of Nanoscale Science and Technology and Key Laboratory of Functional Polymer Materials, Renewable Energy Conversion and Storage Center (RECAST), College of Chemistry, Nankai University, Tianjin, 300071, China
Guankui Long School of Materials Science and Engineering, National Institute for Advanced Materials, Nankai University, Tianjin, 300350, China
Bin Kan School of Materials Science and Engineering, National Institute for Advanced Materials, Nankai University, Tianjin, 300350, China
Yongsheng Chen State Key Laboratory and Institute of Elemento-Organic Chemistry, Frontiers Science Center for New Organic Matter, The Centre of Nanoscale Science and Technology and Key Laboratory of Functional Polymer Materials, Renewable Energy Conversion and Storage Center (RECAST), College of Chemistry, Nankai University, Tianjin, 300071, China

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Collaborators Collapse

Manipulating Aggregation Kinetics toward Efficient All-Printed Organic Solar Cells

The power conversion efficiencies (PCEs) of all-printed organic solar cells (OSCs) remain inferior to those of spin-coated devices, primarily due to morphological variations within the bulk heterojunction processed via diverse coating/printing techniques. Herein, cyclohexyl is introduced as outer side chains to formulate a non-fullerene acceptor, BTP-Cy, aimed at modulating the molecular aggregation in solution and subsequent film formation kinetics during printing. Investigations demonstrate that BTP-Cy molecule with cyclohexyl side chains exhibits enhanced intermolecular π-π stacking, optimal solution aggregation size, and favorable phase separation. Consequently, PB3:FTCC-Br:BTP-Cy-based OSCs achieve remarkable PCEs of 20.2% and 19.5% via spin-coating and blade-coating, respectively. Furthermore, a 23.6 cm2 module exhibits a remarkable efficiency of 16.7%. This study offers a fresh perspective on tailoring the film formation kinetics of photoactive materials during printing through molecular design, paving a novel path to enhance the efficiency of all-printed OSCs.

Suppressed Degradation Process of PBDB-TF-T1:BTP-4F-12-Based Organic Solar Cells with Solid Additive Atums Green

Solid additives have garnered significant attention due to their numerous advantages over liquid additives. This study explores the potential of the green-fluorescent conjugated polymer denoted Atums Green as a solid additive in green-solvent-based PBDB-TF-T1:BTP-4F-12 solar cells. Even tiny amounts of Atums Green doping significantly improve the device performance. For the reference solar cell without any additive, we find that device degradation is not caused by chemical redox reactions but by changes in crystallinity and microstructure evolution during aging in air under illumination. Operando GIWAXS and GISAXS are used to investigate the structure evolution. We discover a four-stage degradation process for the reference cell. In general, the lattice spacing and crystallite coherence length decrease, while the domain sizes increase, which causes the loss of shirt-circuit current JSC and fill factor FF. Furthermore, a decomposition component is detected in GIWAXS and GISAXS, corresponding to the loss of the open-circuit voltage VOC. Atums Green doping effectively suppresses the evolution of crystallinity and domain sizes as well as the continuous decomposition, thereby enhancing the device stability under illumination in air. This finding reveals the kinetic degradation process of organic solar cells, establishes a correlation between the morphological properties and device performance, and further demonstrates the promising potential of Atums Green doping in organic solar cells.

New Polymeric Acceptors Based on Benzo[1,2-b:4,5-b'] Difuran Moiety for Efficient All-Polymer Solar Cells

In order to realize high-performance bulk-heterojunction (BHJ) all-polymer solar cells, achieving appropriate aggregation and moderate miscibility of the polymer blends is one critical factor. Herein, this study designs and synthesizes two new polymer acceptors (PAs), namely PYF and PYF-Cl, containing benzo[1,2-b:4,5-b'] difuran (BDF) moiety with/without chlorine atoms on the thiophene side groups. Thanks to the preferred planar structure and high electronegativity of the BDF units, the resultant PAs generate strong intermolecular interactions and π-π stacking in both the neat and blend films. At the same time, the BDF moieties flanked with bulky 2D side groups increase intermolecular space and restrain the excessive entanglement of polymer chains for developed heterojunction miscibility attributes. Consequently, appropriate polymer crystallinity and moderate miscibility between PAs and polymer donor (PD) contribute to harmonious blending morphologies. Eventually, the PM6:PYF-based solar cells achieve an optimal efficiency of 11.82%. More encouragingly, the PYF serves as an efficient guest acceptor and realizes an improved efficiency of 17.05% in the PM6:PYIT:PYF ternary systems, which is much higher than that of the host system (15.87%). This study highlights the importance of BDF moiety in designing new PAs for high-performance all-polymer solar cells.

A Mixed-Pure Planar Heterojunction Structure of Active Layers for Efficient Sequential Blade-Coating Organic Solar Cells

Precise modulating the vertical structure of active layers to boost charge transfer is an effective way to achieve high power conversion efficiencies (PCEs) in organic solar cells (OSCs). Herein, efficient OSCs with a well-controlled vertical structure are realized by a rapid film-forming method combining low boiling point solvent and the sequential blade-coating (SBC) technology. The results of grazing incident wide-angle X-ray scattering measurement show that the vertical component distribution is varied by changing the processing solvent. Novel characterization technique such as tilt resonant soft X-ray scattering is used to test the vertical structure of the films, demonstrating the dichloromethane (DCM)-processed film is truly planar heterojunction. The devices with chloroform (CF) processed upper layer show an increased mixed phase region compared to these devices with toluene (TL) or -DCM-, which is beneficial for improving charge generation and achieving a superior PCE of 17.36%. Despite significant morphological varies, the DCM-processed devices perform slightly lower PCE of 16.66%, which is the highest value in truly planar heterojunction devices, demonstrating higher morphological tolerance. This work proposes a solvent-regulating method to optimize the vertical structure of active layers through SBC technology, and provides a practical guidance for the optimization of the active-layer microstructure.

Enhanced Fill Factor and Efficiency of Ternary Organic Solar Cells by a New Asymmetric Non-Fullerene Small Molecule Acceptor

Asymmetric non-fullerene small molecules acceptor (as-NF-SMAs) exhibit greater vitality in photovoltaic materials compared to their symmetric counterparts due to their larger dipole moments and stronger intermolecular interactions, which facilitate exciton dissociation and charge transmission in organic solar cells (OSCs). Here, we introduced a new as-NF-SMAs, named IDT-TNIC, as the third component in ternary organic solar cells (TOSCs). The asymmetric IDT-TNIC used indacenodithiophene (IDT) as the central core, alkylthio-thiophene as a unilateral π-bridge and extended end groups as electron-withdrawing. Due to the non-covalent conformational lock (NCL) established between O⋅⋅⋅S and S⋅⋅⋅S, the IDT-TNIC molecule preserves its coplanar structure effectively. Furthermore, IDT-TNIC exhibits complementary absorption and excellent compatibility with donor and acceptor materials, as well as optimized ladder energy level arrangement, resulting in a higher and more balanced μh/μe value, more homogeneous and suitable phase separation morphology in TOSCs. Thus, the PCE of the TOSCs reached 17 % when the weight ratio of PM6 : Y6 : IDT-TNIC was 1 : 1.1 : 0.1, and it is noteworthy that when the device area was increased to 1 cm2, the PCE could still be maintained at over 14 %. Detailed studies and analysis indicate that IDT-TNIC has great potential as a third component in OSCs and for large-scale printing in the future.

Tetrahydrofuran Processable Organic Solar Cells with 19.45% Efficiency Realized by Introducing High Molecular Dipole Unit Into the Terpolymer

Developing organic solar cells (OSCs) processable with halogen-free, non-aromatic solvents is crucial for practical applications, yet challenging due to the limited solubility of most photoactive materials. This study introduces high-performance terpolymers processable in tetrahydrofuran (THF) by incorporating dithienophthalimide (DPI) into the PM6 backbone. DPI extends the absorption band, lowers HOMO levels, and improves THF solubility and film crystallinity through its large dipole moment effect. Optimal PBD-10:L8-BO devices processed with THF achieved a competitive power conversion efficiency (PCE) of 18.79%, approaching chloroform-processed devices (19.04%). By introducing PBTz-F as a second donor, ternary OSCs reached an impressive 19.45% PCE when processed with THF. This improvement stems from enhanced photon generation, improved morphology, better charge transport, longer exciton lifetimes, efficient charge dissociation and collection, and suppressed recombination. These PCEs of 18.79% and 19.45% for binary and ternary blend OSCs, respectively, represent the highest reported efficiencies for OSCs processed with halogen-free, non-aromatic solvents. This work demonstrates significant progress in eco-friendly OSC fabrication, paving the way for more sustainable and commercially viable organic photovoltaic technologies.

Frenkel and Charge-Transfer Excitonic Couplings Strengthened by Thiophene-Type Solvent Enables Binary Organic Solar Cells with 19.8 % Efficiency

Overcoming the trade-off between short-circuited current (Jsc) and open-circuited voltage (Voc) is important to achieving high-efficiency organic solar cells (OSCs). Previous works modulated the energy gap between Frenkel local exciton (LE) and charge-transfer (CT) exciton, which served as the driving force of exciton splitting. Differently, our current work focuses on the modulation of LE-CT excitonic coupling (tLE-CT) via a simple but effective strategy that the 2-chlorothiophene (2Cl-Th) solvent utilizes in the treatment of OSC active-layer films. The results of our experimental measurements and theoretical simulations demonstrated that 2Cl-Th solvent initiates tighter intermolecular interactions with non-fullerene acceptor in comparison with that of traditional chlorobenzene solvent, thus suppressing the acceptor's over-aggregation and retarding the acceptor crystallization with reduced trap. Critically, the resulting shorter distances between donor and acceptor molecules in the 2Cl-Th treated blend efficiently strengthen tLE-CT, which not only promotes exciton splitting but also reduces non-radiative recombination. The champion efficiencies of 19.8 % (small-area) with superior operational reliability (T80: 586 hours) and 17.0 % (large-area) were yielded in 2Cl-Th treated cells. This work provided a new insight into modulating the exciton dynamics to overcome the trade-off between Jsc and Voc, which can productively promote the development of the OSC field.

A Difluoro-Methoxylated Ending-Group Asymmetric Small Molecule Acceptor Lead Efficient Binary Organic Photovoltaic Blend

Developing a new end group for synthesizing asymmetric small molecule acceptors (SMAs) is crucial for achieving high-performance organic photovoltaics (OPVs). Herein, an asymmetric small molecule acceptor, BTP-BO-4FO, featuring a new difluoro-methoxylated end-group is reported. Compared to its symmetric counterpart L8-BO, BTP-BO-4FO exhibits an upshifted energy level, larger dipole moment, and more sequential crystallinity. By adopting two representative and widely available solvent additives (1-chloronaphthalene (CN) and 1,8-diiodooctane (DIO)), the device based on PM6:BTP-BO-4FO (CN) photovoltaic blend demonstrates a power conversion efficiency (PCE) of 18.62% with an excellent open-circuit voltage (VOC) of 0.933 V, which surpasses the optimal result of L8-BO. The PCE of 18.62% realizes the best efficiencies for binary OPVs based on SMAs with asymmetric end groups. A series of investigations reveal that optimized PM6:BTP-BO-4FO film demonstrates similar molecular packing motif and fibrillar phase distribution as PM6:L8-BO (DIO) does, resulting in comparable recombination dynamics, thus, similar fill factor. Besides, it is found PM6:BTP-BO-4FO possesses more efficient charge generation, which yields better VOC-JSC balance. This study provides a new ending group that enables a cutting-edge efficiency in asymmetric SMA-based OPVs, enriching the material library and shed light on further design ideas.

Efficient Ternary Organic Solar Cells with Suppressed Nonradiative Recombination and Fine-Tuned Morphology via IT-4F as Guest Acceptor

The large open circuit voltage (VOC) loss is currently one of the main obstacles to achieving efficient organic solar cells (OSCs). In this study, the ternary OSCs comprising PM6:BTP-eC9:IT-4F demonstrate a superior efficiency of 18.2 %. Notably, the utilization of the medium bandgap acceptor IT-4F as the third component results in an exceptionally low nonradiative recombination energy loss of 0.28 V. The desirable energy level cascade is formed among PM6, BTP-eC9, and IT-4F due to the low-lying HOMO and LUMO energy levels of IT-4F. More importantly, the VOC of PM6:BTP-eC9:IT-4F OSCs can reach as high as 0.86 V, which is higher than both binary OSCs without sacrificing JSC and FF. Besides, this strategy proved that IT-4F can not only broaden the absorption range but also work as a morphology modifier in PM6:BTP-eC9:IT-4F OSCs, and there also exists efficient energy transfer between BTP-eC9 and IT-4F. This result provides a promising way to suppress the nonradiative recombination energy loss and realize higher VOC than the two binary OSCs in ternary OSCs to obtain high power conversion efficiencies.

Electron Transporting Polymeric Materials with Partial Quaternization for High-Performance Organic Solar Cells

Efficient cathode interfacial layers (CILs) have become a crucial component of organic solar cells (OSCs). Charge extraction barriers, interfacial trap states, and significant transport resistance may be induced due to the unfavorable cathode interlayer, limiting the device performance. In this study, poly(4-vinylpyridine) is used as the CIL for OSCs, and a new type of CIL named P4VP-I is synthesized through the quaternization strategy. Compared to P4VP, P4VP-I CIL exhibits enhanced conductivity and optimized work function. OSCs employing the P4VP-I ETL demonstrate prolonged carrier lifetime, suppressed charge recombination, and achieve higher power conversion efficiencies (PCE) than the commonly used ETLs such as PFN-Br and Phen-NaDPO.

A High-Performance Organic Photovoltaic System with Versatile Solution Processability

Recently developed organic photovoltaic (OPV) materials have simultaneously closed the gaps in efficiency, stability, and cost for single-junction devices. Nonetheless, the developed OPV materials still pose big challenges in meeting the requirements for practical applications, especially regarding the prevalent issues of solution processability. Herein, a highly efficient polymer donor, named DP3, incorporating an electron-rich benzo[1,2-b:4,5-b']dithiophene unit as well as two similar and simple acceptor units is presented. Its primary objective is to enhance the interchain and/or intrachain interactions and ultimately fine-tune bulk-heterojunction microstructure. The DP3:L8-BO system demonstrates the highest power conversion efficiency (PCE) of 19.12%. This system also exhibits high-performance devices with over 18% efficiencies for five batches with various molecular weights (23.6-80.8 KDa), six different blend thicknesses (95-308 nm), differenced coating speeds (3.0-29.1 m min-1), with promising PCEs of 18.65% and 15.53% for toluene-processed small-area (0.029 cm2) cells and large-area (15.40 cm2) modules, thereby demonstrating versatile solution processability of the designed DP3:L8-BO system that is a strong candidate for commercial applications.

An Indacenodithienothiophene-Based Wide Bandgap Small Molecule Guest for Efficient and Stable Ternary Organic Solar Cells

The strategic and logical development of the third component (guest materials) plays a pivotal and intricate role in improving the efficiency and stability of ternary organic solar cells (OSCs). In this study, a novel guest material with a wide bandgap, named IDTR, is designed, synthesized, and incorporated as the third component. IDTR exhibits complementary absorption characteristics and cascade band alignment with the PM6:Y6 binary system. Morphological analysis reveals that the introduction of IDTR results in strong crystallinity, good miscibility, and proper vertical phase distribution, thereby realizing heightened and balanced charge transport behavior. Remarkably, the novel ternary OSCs have exhibited a significant enhancement in photovoltaic performance. Consequently, open-circuit voltage (VOC), short-circuit current (JSC), and fill factor (FF) have all witnessed substantial improvements with a remarkable power conversion efficiency (PCE) of 18.94% when L8-BO replaced Y6. Beyond the pronounced improvement in photovoltaic performance, superior device stability with a T80 approaching 400 h is successfully achieved. This achievement is attributed to the synergistic interplay of IDTR, providing robust support for the overall enhancement of performance. These findings offer crucial guidance and reference for the design and development of efficient and stable OSCs.

Halogenated Dibenzo[f,h]quinoxaline Units Constructed 2D-Conjugated Guest Acceptors for 19% Efficiency Organic Solar Cells

Halogenation of Y-series small-molecule acceptors (Y-SMAs) is identified as an effective strategy to optimize photoelectric properties for achieving improved power-conversion-efficiencies (PCEs) in binary organic solar cells (OSCs). However, the effect of different halogenation in the 2D-structured large π-fused core of guest Y-SMAs on ternary OSCs has not yet been systematically studied. Herein, four 2D-conjugated Y-SMAs (X-QTP-4F, including halogen-free H-QTP-4F, chlorinated Cl-QTP-4F, brominated Br-QTP-4F, and iodinated I-QTP-4F) by attaching different halogens into 2D-conjugation extended dibenzo[f,h]quinoxaline core are developed. Among these X-QTP-4F, Cl-QTP-4F has a higher absorption coefficient, optimized molecular crystallinity and packing, suitable cascade energy levels, and complementary absorption with PM6:L8-BO host. Moreover, among ternary PM6:L8-BO:X-QTP-4F blends, PM6:L8-BO:Cl-QTP-4F obtains a more uniform and size-suitable fibrillary network morphology, improved molecular crystallinity and packing, as well as optimized vertical phase distribution, thus boosting charge generation, transport, extraction, and suppressing energy loss of OSCs. Consequently, the PM6:L8-BO:Cl-QTP-4F-based OSCs achieve a 19.0% efficiency, which is among the state-of-the-art OSCs based on 2D-conjugated Y-SMAs and superior to these devices based on PM6:L8-BO host (17.70%) and with guests of H-QTP-4F (18.23%), Br-QTP-4F (18.39%), and I-QTP-4F (17.62%). The work indicates that halogenation in 2D-structured dibenzo[f,h]quinoxaline core of Y-SMAs guests is a promising strategy to gain efficient ternary OSCs.

Polymer Fiber Rigid Network with High Glass Transition Temperature Reinforces Stability of Organic Photovoltaics

Organic photovoltaics (OPVs) need to overcome limitations such as insufficient thermal stability to be commercialized. The reported approaches to improve stability either rely on the development of new materials or on tailoring the donor/acceptor morphology, however, exhibiting limited applicability. Therefore, it is timely to develop an easy method to enhance thermal stability without having to develop new donor/acceptor materials or donor-acceptor compatibilizers, or by introducing another third component. Herein, a unique approach is presented, based on constructing a polymer fiber rigid network with a high glass transition temperature (Tg) to impede the movement of acceptor and donor molecules, to immobilize the active layer morphology, and thereby to improve thermal stability. A high-Tg one-dimensional aramid nanofiber (ANF) is utilized for network construction. Inverted OPVs with ANF network yield superior thermal stability compared to the ANF-free counterpart. The ANF network-incorporated active layer demonstrates significantly more stable morphology than the ANF-free counterpart, thereby leaving fundamental processes such as charge separation, transport, and collection, determining the device efficiency, largely unaltered. This strategy is also successfully applied to other photovoltaic systems. The strategy of incorporating a polymer fiber rigid network with high Tg offers a distinct perspective addressing the challenge of thermal instability with simplicity and universality.

Brominated Quaternary Ammonium Salt-Assisted Hybrid Electron Transport Layer for High-Performance Conventional Organic Solar Cells

Interlayer engineering is crucial for achieving efficient and stable organic solar cells (OSCs). Herein, by introducing a commercialized brominated quaternary ammonium salt, hexamethonium bromide (HB), into a perylene diimide (PDI)-structured electron transport layer (ETL), a PDINN:HB hybrid ETL with enhanced charge collection ability and environmental/operational stability is realized. Molecular dynamics simulations and Kelvin probe force microscopy indicate that strong polar bromine and amine groups can form extra interfacial dipoles in the hybrid interlayer, while X-ray photoelectron spectroscopy and electron paramagnetic resonance suggest the hybrid ETL can interact with the Ag cathode, thereby regulating the energy level arrangement at the interface. As for the results, the PDINN:HB hybrid ETL enables improved power conversion efficiency (PCE) from 17.8 to 18.4% and 18.8 to 19.4% in PM6:C5-16 bulk heterojunction- and PM6/L8-BO pseudobulk heterojunction-based OSCs, respectively. The versatility of this method is further verified by introducing a range of brominated quaternary ammonium salts into PDINN, in which a superior PCE and stability are all obtained compared to the reference device.

Non-Fully Conjugated Dimerized Giant Acceptors with Different Alkyl-Linked Sites for Stable and 19.13 % Efficiency Organic Solar Cells

Achieving both high power conversion efficiency (PCE) and device stability is a major challenge for the practical development of organic solar cells (OSCs). Herein, three non-fully conjugated dimerized giant acceptors (named 2Y-sites, including wing-site-linked 2Y-wing, core-site-linked 2Y-core, and end-site-linked 2Y-end) are developed. They share the similar monomer precursors but have different alkyl-linked sites, offering the fine-tuned molecular absorption, packing, glass transition temperature, and carrier mobility. Among their binary active layers, D18/2Y-wing has better miscibility, leading to optimized morphology and more efficient charge transfer compared to D18/2Y-core and D18/2Y-end. Therefore, the D18/2Y-wing-based OSCs achieve a superior PCE of 17.73 %, attributed to enhanced photocurrent and fill factor. Furthermore, the D18/2Y-wing-based OSCs exhibit a balance of high PCE and improved stability, distinguishing them within the 2Y-sites. Building on the success of 2Y-wing in binary systems, we extend its application to ternary OSCs by pairing it with the near-infrared absorbing D18/BS3TSe-4F host. Thanks to the complementary absorption within 300-970 nm and further optimized morphology, ternary OSCs obtain a higher PCE of 19.13 %, setting a new efficiency benchmark for the dimer-derived OSCs. This approach of alkyl-linked site engineering for constructing dimerized giant acceptors presents a promising pathway to improve both PCE and stability of OSCs.

Step-by-Step Modulation of Crystalline Features and Exciton Kinetics for 19.2% Efficiency Ortho-Xylene Processed Organic Solar Cells

With plenty of popular and effective ternary organic solar cells (OSCs) construction strategies proposed and applied, its power conversion efficiencies (PCEs) have come to a new level of over 19% in single-junction devices. However, previous studies are heavily based in chloroform (CF) leaving behind substantial knowledge deficiencies in understanding the influence of solvent choice when introducing a third component. Herein, we present a case where a newly designed asymmetric small molecular acceptor using fluoro-methoxylated end-group modification strategy, named BTP-BO-3FO with enlarged bandgap, brings different morphological evolution and performance improvement effect on host system PM6:BTP-eC9, processed by CF and ortho-xylene (o-XY). With detailed analyses supported by a series of experiments, the best PCE of 19.24% for green solvent-processed OSCs is found to be a fruit of finely tuned crystalline ordering and general aggregation motif, which furthermore nourishes a favorable charge generation and recombination behavior. Likewise, over 19% PCE can be achieved by replacing spin-coating with blade coating for active layer deposition. This work focuses on understanding the commonly met yet frequently ignored issues when building ternary blends to demonstrate cutting-edge device performance, hence, will be instructive to other ternary OSC works in the future.