Designing a Novel Wide Bandgap Small Molecule Guest for Enhanced Stability and Morphology Mediation in Ternary Organic Solar Cells with over 19.3% Efficiency

Indacenodithiophene-Based Medium-Bandgap Guest Acceptor Enables High-Efficiency Ternary Organic Solar Cells

The ternary organic solar cells (OSCs) have been proven to be an effective strategy for achieving high power conversion efficiency (PCE), exhibiting substantial potential for continuous enhancement of device performance. In this work, a novel nonfullerene acceptor, IDT-FN, is developed utilizing a renowned indacenodithiophene (IDT) core and moderately intense electron-withdrawing terminal groups, serving as the third component in ternary OSCs. IDT-FN demonstrates excellent complementary light absorption and cascaded energy levels with the host materials D18 and CH-6F, resulting in enhanced photon harvesting and charge transport within the ternary blend. Therefore, even the as-cast ternary device manages to surpass the optimal binary host device, achieving a superior PCE of 17.34% compared to the latter's 17.08%. Through optimization, the optimal ternary devices attain an impressive PCE of 18.32%, accompanied by a high open-circuit voltage (Voc) of 0.897 V, a fill factor of 0.745, and a short-circuit current density (Jsc) of 27.41 mA cm-2. This demonstrates a significant success in utilizing IDT-based medium-bandgap guests to achieve state-of-the-art ternary OSCs.

Chlorinated Bithiophene Imide-Based n-Type Polymers: Synthesis, Structure-Property Correlations, and Applications in Organic Electronic Devices

Developing electron-deficient (hetero)arenes with optimized geometries and electronic properties is imperative for advancing n-type polymers and organic electronic devices. We report here the design and synthesis of two chlorinated imide-functionalized electron-deficient heteroarenes, namely chlorine-substituted bithiophene imide (ClBTI) and its fused dimer (ClBTI2). The corresponding polymers show a near-planar framework, appropriate frontier molecular orbital levels, and good solubility. When integrated into organic thin-film transistors, ClBTI2-based n-type polymer afforded unipolar electron mobility of up to 0.48 cm2 V-1 s-1. The binary all-PSCs based on PM6 and new polymers show a power conversion efficiency (PCE) exceeding 1%. Interestingly, by introducing these polymers with ordered structure, high crystallinity, and sizable electron mobility as the third component into the host system PM6:PY-IT, continuous interpenetrating networks with large fibrillar structures can be formed. Investigations of charge transfer kinetics and energy loss analyses unveiled that ClBTI2-based n-type polymer P(ClBTI2-BTI) enables optimized charge transport, reduced charge recombination, and minimized non-radiative loss within the all-polymer ternary blends, yielding a remarkable PCE of 19.35% (certified: 19.20%) through optimizing the state-of-the-art PM6:PY-IT blend. The structure-property-performance relationships provide valuable insights into the design of electron-deficient (hetero)arenes and n-type polymers, marking a great progress in the development of high-performance n-type polymers for organic electronic devices.

Synergistically Halogenated and Methoxylated Thiophene Additive Enables High-Performance Organic Solar Cells

Morphology control plays a key role for improving efficiency and stability of bulk heterojunctions (BHJ) organic solar cells (OSCs). Halogenation and methoxylation are two separate ways successfully adopted in additives for morphology optimization. In this work, these two strategies are combined together. A series of halogenated methoxylated thiophenes is designed and synthesized as volatile additives to control the evolution of the BHJ morphology. Specifically, the addition of 2,5-diiodo-3,4-dimethoxythiophene (MT-I) prominently improves the performance and photostability of OSCs. Computational simulations reveal the noncovalent interactions of MT-I with the active layer materials that corresponds to the inhibition of excessive aggregation behavior of PM6 and Y6 during the film-forming process, facilitating favorable phase separation and enhanced molecular stacking. Consequently, PM6:Y6-based binary OSCs with the treatment of MT-I achieves a high PCE of 17.93%. Furthermore, MT-I demonstrates broad feasibility across diverse high-efficiency BHJ OSCs, leading to superior photovoltaic performance (PCE over 18%). This study offers valuable guidance for the design and application of high-performance additives in future endeavors.

Efficient ternary organic solar cells with suppressed nonradiative recombination via B‒N based polymer donor

Organic solar cells (OSCs) have developed rapidly in recent years. However, the energy loss (E loss) remains a major obstacle to further improving the photovoltaic performance. To address this issue, a ternary strategy has been employed to precisely tune the E loss and boost the efficiency of OSCs. The B‒N-based polymer donor has been proved to process high E(T1) and small ΔE ST characters, which can inhibition of CT state recombination. Herin, B‒N-based polymer donor PBNT-BDD was incorporated into the state-of-the-art PM6:L8-BO binary to construct ternary OSCs. Together with the optimal morphology, the ternary device affords an impressive power conversion efficiency of 18.95% with an improved open-circuit voltage (V oc), short-circuit density (J sc), and reduced E loss in comparison to the binary ones, which is the highest PCE for B‒N materials-based ternary device. This work broadens the selection of guest materials toward realizing the high performance of OSCs.

Modulating Aggregation Behavior by Ternary Strategies for Efficient and Stable Thick-Film Organic Solar Cells

Functional third components targeted to improve a specific property of organic solar cells is an effective strategy. However, introducing a third component to simultaneously improve efficiency and stability and achieve good performance in thick-film devices has rarely been reported. Herein, low diffusion third components IDCN and ID2CN are reported to achieve a power conversion efficiency (PCE) of 18.08% and a high short-circuit current (J SC) of 27.82 mA cm-2, one of the highest values based on PM6:Y6. They increase light harvesting in the range of 400-500 nm while enhancing energy transfer via Förster resonance energy transfer (FRET). A tightly ordered molecular arrangement is achieved by modulating the preaggregation and film formation kinetics of Y6, which enhance exciton dissociation and charge transport. Moreover, the low-diffusion third component can effectively restrict the diffusion of Y6 to improve the morphology stability, and the T90 lifetime is increased from 689 to 1545 h. In 300 nm thick-film devices, PM6:ID2CN:Y6 achieves a PCE of 15.01%, much higher than PM6:Y6's 12.83%, demonstrating the great potential of ID2CN in thick-film devices.

Designing a Highly Crystalline Polymer Donor with Alkylsilyl and Fluorine Substitution to Achieve Efficient Ternary Organic Solar Cells

Adopting a ternary strategy is an effective approach to enhance the power conversion efficiency (PCE) in organic solar cells (OSCs). Previous research on highly efficient ternary systems has predominantly focused on those based on highly crystalline dual small molecule acceptors. However, limited attention has been given to ternary systems utilizing dual polymer donors. Herein, by incorporating the fluorine and alkylsilyl substitution, a new polymer donor named PX1 is developed, which demonstrates strong crystallinity and excellent miscibility with polymer PM6. Moreover, PX1 broadens and enhances the absorption properties of the PM6:L8-BO blends, and its molecular orbital energy level is situated between those of PM6 and L8-BO, highlighting its suitability as a third component. Introducing 20% PX1 into the PM6:L8-BO system resulted in a high PCE of 18.82%. PX1 effectively suppresses charge recombination and reduces energy losses, while also serving as a morphology modulator that enhances the crystallization and improves the molecular packing order of the active layer by shortening the π-π stacking distance and extending crystalline coherence length. These factors collectively contribute to the performance improvements in ternary devices. This study demonstrates that employing a dual polymer donor strategy is a promising approach for achieving high-performance ternary OSCs.

Highly Efficient Organic Solar Cells with the Highly Crystalline Third Component as a Morphology Regulator

The morphology of the active layer is crucial for highly efficient organic solar cells (OSCs), which can be regulated by selecting a rational third component. In this work, the highly crystalline nonfullerene acceptor BTP-eC9 is selected as the morphology regulator in OSCs with PM6:BTP-BO-4Cl as the main system. The addition of BTP-eC9 can prolong the nucleation and crystallization progress of acceptor and donor molecules, thereby enhancing the order of molecular arrangement. Meanwhile, the nucleation and crystallization time of the donor is earlier than that of the acceptors after introducing BTP-eC9, which is beneficial for obtaining a better vertical structural phase separation. The exciton dissociation, charge transport, and charge collection are promoted effectively by the optimized morphology of the active layer, which improves the short-circuit current density and filling factor. After introducing BTP-eC9, the power conversion efficiencies (PCEs) of the ternary OSCs are improved from 17.31% to 18.15%. The PCE is further improved to 18.39% by introducing gold nanopyramid (Au NBPs) into the hole transport layer to improve photon utilization efficiency. This work indicates that the morphology can be optimized by selecting a highly crystalline third component to regulate the nucleation and crystallization progress of the acceptor and donor molecules.

Providing a Photovoltaic Performance Enhancement Relationship from Binary to Ternary Polymer Solar Cells via Machine Learning

Ternary polymer solar cells (PSCs) are currently the simplest and most efficient way to further improve the device performance in PSCs. To find high-performance organic photovoltaic materials, the established connection between the material structure and device performance before fabrication is of great significance. Herein, firstly, a database of the photovoltaic performance in 874 experimental PSCs reported in the literature is established, and three different fingerprint expressions of a molecular structure are explored as input features; the results show that long fingerprints of 2D atom pairs can contain more effective information and improve the accuracy of the models. Through supervised learning, five machine learning (ML) models were trained to build a mapping of the photovoltaic performance improvement relationship from binary to ternary PSCs. The GBDT model had the best predictive ability and generalization. Eighteen key structural features from a non-fullerene acceptor and the third components that affect the device's PCE were screened based on this model, including a nitrile group with lone-pair electron, a halogen atom, an oxygen atom, etc. Interestingly, the structural features for the enhanced device's PCE were essentially increased by the Jsc or FF. More importantly, the reliability of the ML model was further verified by preparing the highly efficient PSCs. Taking the PM6:BTP-eC9:PY-IT ternary PSC as an example, the PCE prediction (18.03%) by the model was in good agreement with the experimental results (17.78%), the relative prediction error was 1.41%, and the relative error between all experimental results and predicted results was less than 5%. These results indicate that ML is a useful tool for exploring the photovoltaic performance improvement of PSCs and accelerating the design and application with highly efficient non-fullerene materials.

Chalcogen Atoms Regulate the Organic Solar Cell Performance of B-N-Based Polymer Donors

Donor polymers play a key role in the development of organic solar cells (OSCs). B-N-based polymer donors, as new types of materials, have attracted a lot of attention due to their special characteristics, such as high E(T1), small ΔEST, and easy synthesis, and they can be processed with real green solvents. However, the relationship between the chemical structure and device performance has not been systematically studied. Herein, chalcogen atoms that regulate the OSCs performance of B-N-based polymer donors were systematically studied. Fortunately, the substitution of a halogen atom did not affect the high E(T1) and small ΔEST character of the B-N-based polymer. The absorption and energy levels of the polymer were systematically regulated by O, S, and Se atom substitution. The PBNT-TAZ:Y6-BO-based OSCs device demonstrated a high power conversion efficiency of 15.36%. Moreover, the layer-by-layer method was applied to further optimize the device performance, and the PBNT-TAZ/Y6-BO-based OSCs device yielded a PCE of 16.34%. Consequently, we have systematically demonstrated how chalcogen atoms modulated the electronic properties of B-N-based polymers. Detailed and systematic structure-performance relationships are important for the development of next-generation B-N-based materials.