A Pyrene-Fused Dimerized Acceptor for Ternary Organic Solar Cells with 19% Efficiency and High Thermal Stability

A pyrene-fused dimerized electron acceptor has been successfully synthesized and subsequently incorporated as the third component in ternary organic solar cells (OSCs). Diverging from the traditional dimerized acceptors with a linear configuration, this novel electron acceptor displays a distinctive “butterfly-like” structure, comprising two Y-acceptors as wings fused with a pyrene-based backbone. The extended π-conjugated backbone and the electron-donating nature of pyrene enable the new acceptor to show low solubility, elevated glass transition temperature (T_g), and low-lying frontier energy levels. Consequently, the new dimerized acceptor seamlessly integrates as the third component into ternary OSCs, enhancing electron transporting properties, reducing non-radiative voltage loss, and elevating open-circuit voltage. These merits have enabled the ternary OSCs to show an exceptional efficiency of 19.07%, a marked improvement compared to the 17.6% attained in binary OSCs. More importantly, the high T_g exhibited by the pyrene-fused electron acceptor helps to stabilize the morphology of the photoactive layer thermal-treated at 70 °C, retaining 88.7% efficiency over 600 hours. For comparison, binary OSCs experience a decline to 73.7% efficiency after the same duration. These results indicate that the “butterfly-like” design and the incorporation of a pyrene unit is a promising strategy in the development of dimerized electron acceptors for OSCs.     

Dimer Acceptor Adopting a Flexible Linker for Efficient and Durable Organic Solar Cells

Organic solar cells (OSCs) have advanced rapidly due to the development of new photovoltaic materials. However, the long-term stability of OSCs still poses a severe challenge for their commercial deployment. To address this issue, a dimer acceptor (dT9TBO) with flexible linker is developed for incorporation into small-molecule acceptors to form molecular alloy with enhanced intermolecular packing and suppressed molecular diffusion to stabilize active layer morphology. Consequently, the PM6 : Y6 : dT9TBO-based device displays an improved power conversion efficiency (PCE) of 18.41 % with excellent thermal stability and negligible decay after being aged at 65 °C for 1800 h. Moreover, the PM6 : Y6 : dT9TBO-based flexible OSC also exhibits excellent mechanical durability, maintaining 95 % of its initial PCE after being bended repetitively for 1500 cycles. This work provides a simple and effective way to fine-tune the molecular packing with stabilized morphology to overcome the trade-off between OSC efficiency and stability.     

Giant Molecule Acceptor Enables Highly Efficient Organic Solar Cells Processed Using Non-halogenated Solvent

High efficiency organic solar cells (OSCs) based on A-DA′D-A type small molecule acceptors (SMAs) were mostly fabricated by toxic halogenated solvent processing, and power conversion efficiency (PCE) of the non-halogenated solvent processed OSCs is mainly restricted by the excessive aggregation of the SMAs. To address this issue, we developed two vinyl π-spacer linking-site isomerized giant molecule acceptors (GMAs) with the π-spacer linking on the inner carbon (EV-i) or out carbon (EV-o) of benzene end group of the SMA with longer alkyl side chains (ECOD) for the capability of non-halogenated solvent-processing. Interestingly, EV-i possesses a twisted molecular structure but enhanced conjugation, while EV-o shows a better planar molecular structure but weakened conjugation. The OSC with EV-i as acceptor processed by the non-halogenated solvent o-xylene (o-XY) demonstrated a higher PCE of 18.27 % than that of the devices based on the acceptor of ECOD (16.40 %) or EV-o (2.50 %). 18.27 % is one of the highest PCEs among the OSCs fabricated from non-halogenated solvents so far, benefitted from the suitable twisted structure, stronger absorbance and high charge carrier mobility of EV-i. The results indicate that the GMAs with suitable linking site would be the excellent candidates for fabricating high performance OSCs processed by non-halogenated solvents.     

Unsymmetrically Chlorinated Non-Fused Electron Acceptor Leads to High-Efficiency and Stable Organic Solar Cells

Searching the cost-effective organic semiconductors is strongly needed in order to facilitate the practice of organic solar cells (OSCs), yet to be fulfilled. Herein, we have succeeded in developing two non-fused ring electron acceptors (NFREAs), leading to the highest efficiency of 16.2 % for the NFREA derived OSCs. These OSCs exhibit the superior operational stabilities under one sun equivalent illumination without ultraviolet (UV) filtration. It is revealed that the modulation of halogen substituents on aromatic side chains, as the new structural tool to tune the intermolecular interaction and optoelectronic properties of acceptors, not only promotes the interlocked tic-tac-toe frame of three-dimensional stacks in solid, but also improves charge dynamics of acceptors to enable high-performance and stable OSCs.     

Development of Organic Dye‐Based Molecular Materials for Use in Fullerene‐Free Organic Solar Cells

This personal account describes the pursuit of non‐fullerene acceptors designed from simple and accessible organic pi‐conjugated building blocks and assembled through efficient direct (hetero)arylation cross‐coupling protocols. Initial materials development focused on isoindigo and diketopyrrolopyrrole organic dyes flanked by imide‐based terminal acceptors. Efficiencies in solution‐processed organic solar cells were modest but highlighted the potential of the material design. Materials performance was improved through structural engineering to pair perylene diimide with these organic dyes. Optimization of active layer processing and solar cell device fabrication identified the perylene diimide flanked diketopyrrolopyrrole structure as the best framework, with fullerene‐free organic solar cells achieving power conversion efficiencies above 6 %. This material has met our criteria for a simple wide band gap fullerene alternative for pairing with a range of donor polymers.     

Biselenophene Imide: Enabling Polymer Acceptor with High Electron Mobility for High-Performance All-Polymer Solar Cells

The shortage of narrow band gap polymer acceptors with high electron mobility is the major bottleneck for developing efficient all-polymer solar cells (all-PSCs). Herein, we synthesize a distannylated electron-deficient biselenophene imide monomer (BSeI-Tin) with high purity/reactivity, affording an excellent chance to access acceptor–acceptor (A–A) type polymer acceptors. Copolymerizing BSeI-Tin with dibrominated monomer Y5-Br, the resulting A–A polymer PY5-BSeI shows a higher molecular weight, narrower band gap, deeper-lying frontier molecular orbital levels and larger electron mobility than the donor–acceptor type counterpart PY5-BSe. Consequently, the PY5-BSeI-based all-PSCs deliver a remarkable efficiency of 17.77 % with a high short-circuit current of 24.93 mA cm⁻² and fill factor of 75.83 %. This efficiency is much higher than that (10.70 %) of the PY5-BSe-based devices. Our study demonstrates that BSeI is a promising building block for constructing high-performance polymer acceptors and stannylation of electron-deficient building blocks offers an excellent approach to developing A–A type polymers for all-PSCs and even beyond.     

Facile,Versatile and Stepwise Synthesis of High-Performance Oligomer Acceptors for Stable Organic Solar Cells

Oligomer acceptors have recently emerged as promising photovoltaic materials for achieving high power conversion efficiency (PCE) and long-term stability in organic solar cells (OSCs). However, the limited availability of diverse acceptors, resulting from the sole synthetic approach, has hindered their potential for future industrialization. In this study, we present a facile and effective stepwise approach that utilizes two consecutive Stille coupling reactions for the synthesis of oligomer acceptors. To demonstrate the feasibility of the novel approach, we successfully synthesize a trimer acceptor, Tri-Y6-OD, and further systematically investigate the impact of oligomerization on device performance and stability. The results reveal that this approach has significant advantages compared to the conventional method, including reduced formation of unwanted by-products and lower difficulties in purification. Remarkably, the OSC based on PM6 : Tri-Y6-OD achieves an impressive PCE of 18.03 % and maintains 80 % of the initial PCE (T₈₀) for 1523 h under illumination, surpassing the performance of the corresponding small molecule acceptor Y6-OD-based device. Furthermore, the versatility of the synthetic strategy in obtaining diverse acceptors is further demonstrated. Overall, our findings provide a facile, versatile and stepwise way for synthesizing oligomer acceptors, thereby facilitating the development of stable and efficient OSCs.     

Low-Cost Fully Non-fused Ring Acceptor Enables Efficient Organic Photovoltaic Modules for Multi-Scene Applications

Organic photovoltaic (OPV) cells, with highly tunable light-response ranges, offer significant potential for use in driving low-power consumption off-grid electronics in multi-scenarios. However, development of photoactive layer materials that can meet simultaneously the requirements of diverse irradiation conditions is a still challenging task. Herein, a low-cost fully non-fused acceptor (denoted as GS60) featuring well-matched absorption spectra with solar, scattered light and artificial light radiation was designed and synthesized. Systematic characterizations revealed that GS60 possessed outstanding photoelectron properties and ideal morphology, which resulted in reduced voltage loss and suppressed charge recombination. By blending with a non-fused ring polymer PTVT−T, the as-obtained GS60 based OPV cells achieved a good power conversion efficiency (PCE) of 14.1 %, a high value for the cells based on non-fused ring bulk heterojunction. Besides, manufactured large-area OPV modules based on PTVT−T:GS60 yielded PCEs of 11.2 %, 11.8 %, 12.1 %, 23.1 %, and 20.3 % under irradiation of AM 1.5G, natural light of cloudy weather, natural light in shadow, laser and indoor, respectively. The PTVT−T:GS60 devices exhibited considerable potential in terms of improving photostability and reducing material cost. Overall, this work provides novel insight into the molecular design of low-cost non-fused ring acceptors, and extended potential of medium band gap acceptors based OPV cells used in various application scenarios.     

Optimized Crystal Framework by Asymmetric Core Isomerization in Selenium-Substituted Acceptor for Efficient Binary Organic Solar Cells

Both the regional isomerization and selenium-substitution of the small molecular acceptors (SMAs) play significant roles in developing efficient organic solar cells (OSCs), while their synergistic effects remain elusive. Herein, we developed three isomeric SMAs (S-CSeF, A-ISeF, and A-OSeF) via subtly manipulating the mono-selenium substituted position (central, inner, or outer) and type of heteroaromatic ring on the central core by synergistic strategies for efficient OSCs, respectively. Crystallography of asymmetric A-OSeF presents a closer intermolecular π–π stacking and more ordered 3-dimensional network packing and efficient charge-hopping pathways. With the successive out-shift of the mono-selenium substituted position, the neat films give a slightly wider band gap and gradually higher crystallinity and electron mobility. The PM1 : A-OSeF afford favourable fibrous phase separation morphology with more ordered molecular packing and efficient charge transportation compared to the other two counterparts. Consequently, the A-OSeF-based devices achieve a champion efficiency of 18.5 %, which represents the record value for the reported selenium-containing SMAs in binary OSCs. Our developed precise molecular engineering of the position and type of selenium-based heteroaromatic ring of SMAs provides a promising synergistic approach to optimizing crystal stacking and boosting top-ranked selenium-containing SMAs-based OSCs.     

Self-Driven Prenucleation-Induced Perovskite Crystallization Enables Efficient Perovskite Solar Cells

Perovskite film with high crystal quality is fundamental to achieving high-performance solar cells. A fast nucleation process is crucial to improving the crystallization quality. Here, we propose a self-driven prenucleation strategy to achieve fast nucleation. This is realized through rational solvent design. The key characteristics of different solvents are systematically evaluated. Among them, formamide, with ultra-high dielectric constant, low Gutman donor number, and a high boiling point, is selected as the co-solvent. These unique characteristics render formamide a double-face solvent that is a good solvent for formamidinium iodide (FAI) and CsI while a poor solvent for PbI₂. As a result, formamide induces the self-driven prenucleation of PbI₂-DMSO seeding crystals and accelerates the nucleation, improving the crystalline quality of perovskite film. The efficiency of the hole transport layer-free carbon-based perovskite solar cells is boosted beyond 19 % for the first time.     

Macrocyclic Encapsulation in a Non-fused Tetrathiophene Acceptor for Efficient Organic Solar Cells with High Short-Circuit Current Density

Non-fullerene acceptors have shown great promise for organic solar cells (OSCs). However, challenges in achieving high efficiency molecular system with conformational unicity and effective molecular stacking remain. In this study, we present a new design of non-fused tetrathiophene acceptor R4T-1 via employing the encapsulation of tetrathiophene with macrocyclic ring. The single crystal structure analysis reveals that cyclic alkyl side chains can perfectly encapsulate the central part of molecule and generate a conformational stable and planar molecular backbone. Whereas, the control 4T-5 without the encapsulation restriction displays cis- and twisted conformation. As a result, R4T-1 based OSCs achieved an outstanding power conversion efficiency (PCE) exceeding 15.10 % with a high short-circuit current density (J_sc) of 25.48 mA/cm², which is significantly improved by ≈30 % in relative to that of the control. Our findings demonstrate that the macrocyclic encapsulation strategy could assist fully non-fused electron acceptors (FNEAs) to achieve a high photovoltaic performance and pave a new way for FNEAs design.     

Molecular Stacking and Aggregation Optimization of Photoactive Layer through Solid Additive Enables High-Performance Organic Solar Cells

Regulating molecular packing and aggregation of photoactive layer is a critical but challenging issue in developing high-performance organic solar cells. Herein, two structurally similar analogues of anthra[2,3-b : 6,7-b′]dithiophene (ADT) and naphtho[1,2-b : 5,6-b′]dithiophene (NDT) are developed as solid additive to exploit their effect in regulating the molecular aggregation and π-stacking of photoactive layer. We clarify that the perpendicular arrangements of NDT can enlarge the molecular packing space and improve the face-on stacking of Y6 during the film formation, favoring a more compact and ordered long-range π-π stacking in the out-of-plane direction after the removal of NDT under thermal annealing. The edge-to-face stacked herringbone-arrangement of ADT along with its non-volatilization under thermal annealing can induce the coexistence of face-on and edge-on stacking of blend film. As a result, the NDT treatment shows encouraging effect in improving the photovoltaic performance of devices based on various systems. Particularly, a remarkable PCE of 18.85 % is achieved in the PM6 : L8-BO-based device treated by NDT additive, which is a significant improvement with regard to the PCE of 16.41 % for the control device. This work offers a promising strategy to regulate the molecular packing and aggregation of photoactive layer towards significantly improved performance and stability of organic solar cells.     

Thermodynamic Phase Transition of Three-Dimensional Solid Additives Guiding Molecular Assembly for Efficient Organic Solar Cells

Fine-tuning the thermodynamic self-assembly of molecules via volatile solid additives has emerged to be an effective way to construct high-performance organic solar cells. Here, three-dimensional structured solid molecules have been designed and applied to facilitate the formation of organized molecular assembly in the active layer. By means of systematic theory analyses and film-morphology characterizations based on four solid candidates, we preselected the optimal one, 4-fluoro-N,N-diphenylaniline (FPA), which possesses good volatility and strong charge polarization. The three-dimensional solids can induce molecular packing in active layers via strong intermolecular interactions and subsequently provide sufficient space for the self-reassembly of active layers during the thermodynamic transition process. Benefitting from the optimized morphology with improved charge transport and reduced energy disorder in the FPA-processed devices, high efficiencies of over 19 % were achieved. The strategy of three-dimensional additives inducing ordered self-assembly structure represents a practical approach for rational morphology control in highly efficient devices, contributing to deeper insights into the structural design of efficient volatile solid additives.     

Structural Fusion Yields Guest Acceptors that Enable Ternary Organic Solar Cells with 18.77 % Efficiency

The design and selection of a suitable guest acceptor are particularly important for improving the photovoltaic performance of ternary organic solar cells (OSCs). Herein, we designed and successfully synthesized two asymmetric silicon–oxygen bridged guest acceptors, which featured distinct blue-shifted absorption, upshifted lowest unoccupied molecular orbital energy levels, and larger dipole moments than symmetric silicon–oxygen-bridged acceptor. Ternary devices with the incorporation of 14.2 wt % these two asymmetric guest acceptors exhibited excellent performance with power conversion efficiencies (PCEs) of 18.22 % and 18.77 %, respectively. Our success in precise control of material properties via structural fusion of five-membered carbon linkages and six-membered silicon–oxygen connection at the central electron-donating core unit of fused-ring electron acceptors can attract considerable attention and bring new vigor and vitality for developing new materials toward more efficient OSCs.     

Regulating the Sequence Structure of Conjugated Block Copolymers Enables Large-Area Single-Component Organic Solar Cells with High Efficiency and Stability

Single-component organic solar cells (SCOSCs) based on conjugated block copolymers (CBCs) by covalently bonding a polymer donor and polymer acceptor become more and more appealing due to the formation of a favorable and stable morphology. Unfortunately, a deep understanding of the effect of the assembly behavior caused by the sequence structure of CBCs on the device performance is still missing. Herein, from the aspect of manipulating the sequence length and distribution regularity of CBCs, we synthesized a series of new CBCs, namely D18(20)-b-PYIT, D18(40)-b-PYIT and D18(60)-b-PYIT by two-pot polymerization, and D18(40)-b-PYIT(r) by traditional one-pot method. It is observed that precise manipulation of sequence length and distribution regularity of the polymer blocks fine-tunes the self-assembly of the CBCs, optimizes film morphology, improves optoelectronic properties, and reduces energy loss, leading to simultaneously improved efficiency and stability. Among these CBCs, the D18(40)-b-PYIT-based device achieves a high efficiency of 13.4 % with enhanced stability, which is an outstanding performance among SCOSCs. Importantly, the regular sequence distribution and suitable sequence length of the CBCs enable a facile film-forming process of the printed device. For the first time, the blade-coated large-area rigid/flexible SCOSCs are fabricated, delivering an impressive efficiency of 11.62 %/10.73 %, much higher than their corresponding binary devices.     

Design of Furan-Based Acceptors for Organic Photovoltaics

We explore a series of furan-based non-fullerene acceptors and report their optoelectronic properties, solid-state packing, photodegradation mechanism and application in photovoltaic devices. Incorporating furan building blocks leads to the expected enhanced backbone planarity, reduced band gap and red-shifted absorption of these acceptors. Still, their position in the molecule is critical for stability and device performance. We found that the photodegradation of these acceptors originates from two distinct pathways: electrocyclic photoisomerization and Diels–Alder cycloaddition of singlet oxygen. These mechanisms are of general significance to most non-fullerene acceptors, and the photostability depends strongly on the molecular structure. Placement of furans next to the acceptor termini leads to better photostability, well-balanced hole/electron transport, and significantly improved device performance. Methylfuran as the linker offers the best photostability and power conversion efficiency (>14 %), outperforming all furan-based acceptors reported to date and all indacenodithiophene-based acceptors. Our findings show the possibility of photostable furan-based alternatives to the currently omnipresent thiophene-based photovoltaic materials.     

High-Performance Organic Solar Cells Containing Pyrido[2,3-b]quinoxaline-Core-Based Small-Molecule Acceptors with Optimized Orbit Overlap Lengths and Molecular Packing

The central core in A-DA₁D-A-type small-molecule acceptor (SMAs) plays an important role in determining the efficiency of organic solar cells (OSCs), while the principles governing the efficient design of SMAs remain elusive. Herein, we developed a series of SMAs with pyrido[2,3-b]quinoxaline (PyQx) as new electron-deficient unit by combining with the cascade-chlorination strategy, namely Py1, Py2, Py3, Py4 and Py5. The introduction of chlorine atoms reduces the intramolecular charge transfer effects but elevates the LUMO values. Density functional theory (DFT) reveals that Py2 with ortho chlorine substituted PyQx and Py5 with two chlorine atoms yield larger dipole moments and smaller π⋅⋅⋅π stacking distances, as compared with the other three acceptors. Moreover, Py2 shows the strongest light absorption capability induced by extended orbit overlap lengths and more efficient packing structures in the dimers. These features endow the best device performance of Py2 due to the better molecular packing and aggregation behaviors, more suitable domain sizes with better exciton dissociation and charge recombination. This study highlights the significance of incorporating large dipole moments, small π⋅⋅⋅π stacking distances and extended orbit overlap lengths in dimers into the development of high-performance SMAs, providing insight into the design of efficient A-DA₁D-A-type SMAs for OSCs.     

Crystallization Regulation by Self-Assembling Liquid Crystal Template Enables Efficient and Stable Perovskite Solar Cells

It is found that the disordered growth of bottom perovskite film deteriorates the buried interface of perovskite solar cells (PSCs), so developing a new material to modify the buried interface for regulating the crystal growth and defect passivation is an effective approach for improving the photovoltaic performance of PSCs. Here, we developed a new ionic liquid crystal (ILC, 1-Dodecyl-3-methylimidazolium tetrafluoroborate) as both crystal regulator and defect passivator to modify the buried interface of PSCs. The high lattice matching between this ILC and perovskite promotes preferential growth of perovskite film along [001] direction, while the oriented ILC with mesomorphic phase has a strong chemical interaction with perovskite to passivate the interface defect, as a result, the modified buried interface exhibits suppressed defects, improved band alignment, reduced nonradiative recombination losses, and enhanced charge extraction. The ILC-modified PSC delivers a power conversion efficiency of 24.92 % and maintains 94 % of the original value after storage in ambient for 3000 h.     

Diazabicyclic Electroactive Ionenes for Efficient and Stable Organic Solar Cells

Electroactive ionenes combining caged-shaped diazabicyclic cations and aromatic diimides were developed as interlayers in organic solar cells (OSCs). These ionenes reduce the work-function of air-stable metal electrodes (e.g., Ag, Cu and Au) by generating strong interfacial dipoles, and their optoelectronic and morphological characters can be modulated by aromatic diimides, leading to high conductivity and good compatibility with active layers. The optimal ionene exhibits superior charge-transport, desirable crystallinity, and weak visible-absorption, boosting the efficiency of benchmark PM6 : Y6-based OSCs up to 17.44 %. The corresponding normal devices show excellent stability at maximum power point test under one sun illumination for 1000 h. Replacing Y6 with L8-BO promotes the efficiency to 18.43 %, one of the highest in binary OSCs. Notably, high efficiencies >16 % are maintained as the interlayer thickness increasing to 105 nm, the best result with interlayer-thickness over 100 nm.     

Volatile Perovskite Precursor Ink Enables Window Printing of Phase-Pure FAPbI3 Perovskite Solar Cells and Modules in Ambient Atmosphere

Despite the great success of perovskite photovoltaics in terms of device efficiency and stability using laboratory-scale spin-coating methods, the demand for high-throughput and cost-effective solutions remains unresolved and rarely reported because of the complicated nature of perovskite crystallization. In this work, we propose a stable precursor ink design strategy to control the solvent volatilization and perovskite crystallization to enable the wide speed window printing (0.3 to 18.0 m/min) of phase-pure FAPbI₃ perovskite solar cells (pero-SCs) in ambient atmosphere. The FAPbI₃ perovskite precursor ink uses volatile acetonitrile (ACN) as the main solvent with DMF and DMSO as coordination additives is beneficial to improve the ink stability, inhibit the coffee rings, and the complicated intermediate FAPbI₃ phases, delivering high-quality pin-hole free and phase-pure FAPbI₃ perovskite films with large-scale uniformity. Ultimately, small-area FAPbI₃ pero-SCs (0.062 cm²) and large-area modules (15.64 cm²) achieved remarkable efficiencies of 24.32 % and 21.90 %, respectively, whereas the PCE of the devices can be maintained at 23.76 % when the printing speed increases to 18.0 m/min. Specifically, the unencapsulated device exhibits superior operational stability with T₉₀>1350 h. This work represents a step towards the scalable, cost-effective manufacturing of perovskite photovoltaics with both high performance and high throughput.