Realizing an Unprecedented Fill Factor of 82.2% in Ternary Organic Solar Cells via Co-Crystallization of Non-Fullerene Acceptors

Ternary strategy is demonstrated as an efficient approach to achieve high short-circuit current and open-circuit voltage to boost the performance of organic solar cells (OSCs), however, the realization of high fill-factor (FF) in ternary OSCs has been rare. In this study, three thiophene terminated non-fullerene acceptors (NFAs) with methyl or chlorine substitutions on their end-groups are designed and synthesized, and further incorporated into the state-of-the-art PM6:L8-BO system to construct ternary OSCs. Subtle changes in their chemical structures significantly modify the molecular packings of these thiophene terminated NFAs. While BTP-ThMe and BTP-ThCl have limited forms of dimer, versatile molecular dimers, including “Z” shaped D-D, “S” shaped A-A, and “F” shaped A-D packings exist in BTP-ThMeCl, which lead to the formation of compact 3D honey-comb network and this is analogous to the host acceptor L8-BO. This synergetic molecular packing between BTP-ThMeCl and L8-BO contributes to maintain the 3D charge transport network in the ternary system via the formation of NFA co-crystals at the molecular level, and consequently realizing a maximum power conversion efficiency of 19.1% with a superior FF of 82.2%, which is the highest FF reported so far for OSCs.     

Smartly Optimizing Crystallinity,Compatibility, and Morphology for Polymer Solar Cells by Small Molecule Acceptor with Unique 2D-EDOT Side Chain

A desired morphology is essential for achieving efficient polymer solar cells. Donors and acceptors with appropriate crystallization can lead to a suitable phase-separated morphology for effective photocurrent generation process. Inspired by the success of Y6 acceptors and the 2D side chain engineering on popular polymer donors and small molecule acceptors, the usage of unique 2D 3,4-ethylene dioxythiophene (EDOT) side chains on Y6 to regulate its crystallinity, compatibility, and thus the related blend morphology is explored. In this study, two molecules of BTP-EDOT-4F and BTP-EDOT-4Cl with such unique 2D EDOT side chains are designed and synthesized. Due to the advantage of EDOT side chain, when these molecules are blended with PM6, the decent power conversion efficiencies (PCEs) of 16.78% and 15.87% are obtained. Furthermore, BTP-EDOT-4F is selected as the third component and added into PM6:L8-BO binary system to form ternary blends. The optimized crystallinity, compatibility, and morphology of such ternary blend are discovered in the presence of BTP-EDOT-4F, which enables efficient exciton dissociation and charge transport as well as decreased recombination, resulting in higher short circuit current density (J_sc) and fill factor. Finally, the outstanding PCE of 18.56% is achieved in ternary blends containing PM6, L8-BO, and BTP-EDOT-4F.     

Rational Mutual Interactions in Ternary Systems Enable High-Performance Organic Solar Cells

Ternary organic solar cells (TOSCs) offer a facile and efficient approach to increase the power conversion efficiencies (PCEs). However, the critical roles that guest components play in complicated ternary systems remain poorly understood. Herein, two acceptors named LA1 and LA9 with differing crystallinity are investigated. The overly crystalline LA9 induces large self-aggregates in PM6:LA9 binary system, resulting in a lower PCE (13.12%) compared to PM6:LA1 device (13.89%). Encouragingly, both acceptors are verified as efficient guest candidates into the host binary PM6:NCBDT-4Cl (PCE = 13.48%) and afford markedly improved PCEs up to 15.39% and 15.75% in LA1 and LA9 ternary devices, respectively. Interestingly, the higher crystallinity LA9 reveals smaller interaction energies with both the host acceptor and donor PM6. Compared to LA1, the appropriate mutual interactions in the LA9 ternary system not only induces the orderly crystallinity of PM6 but also better compatibility with the host acceptor, generating further optimized molecular orientations and ternary morphology. Therefore, enhanced charge transport and minimized recombination loss are detected in LA9 ternary devices, affording the most competitive performance among Y6-sbsent TOSCs. This work suggests that complicated intermolecular interactions should be seriously considered when fabricating state-of-the-art multiple components OSCs.     

Naphthodithiophene Diimide (NDTI)-Based Cathode Interlayer Material Enables 19% Efficiency Binary Organic Solar Cells

A fused naphthodithiophene diimide (NDTI) derivative is first used as cathode interlayer materials (CIMs) in organic solar cells, by introducing two dimethylamine-functionalized fluorenes on both sides, namely NDTI1 . Meanwhile, two non-fused naphthalene diimide (NDI) derivatives are synthesized as the control CIMs to validate the design strategy of fused NDI. All three CIMs show high thermal stability, robust adhesion, and strong electrode modification capability. Compared with two NDI-based materials, NDTI1 possesses excellent film-forming capacity and strong crystallinity, simultaneously. Besides, NDTI1 presents a strong self-doping effect and distinct intermolecular interaction with non-fullerene acceptors. As expected, the NDTI1 -based OSCs achieve a power conversion efficiency (PCE) of 18.02% using the PM6:Y6 active layer and a champion PCE of 19.01% employing the active layer PM6:L8-BO, which is attributed to improve charge transport and extraction, and suppressive charge recombination. More importantly, NDTI1 retains 91% of the optimal PCE when the film thickness increases from 7 to 20 nm. Furthermore, NDTI1 also exhibits satisfactory universality for different active layer materials and excellent device stability.     

Ternary organic solar cells with improved efficiency and stability enabled by compatible dual-acceptor strategy

To further elevate the power conversion efficiency (PCE) of organic solar cells (OSCs), ternary strategy is one of the most efficient methods via simply incorporating a suitable third component. Here, a nonfullerene small molecule acceptor MOITIC was incorporated into the state-of-art PM6:Y6 binary system to further enhance the photovoltaic performance. Detailed investigation revealed that MOITIC exhibited a good miscibility and compatibility with Y6, forming alloy-like acceptors in the ternary blends. The alloy-like phase promoted the phase separation and optimized the morphology of ternary blend, which afforded higher and more balanced carrier mobility and reduced charge recombination in devices. Moreover, the larger energy offset between PM6 and MOITIC:Y6 acceptor alloy is beneficial to enhance open-circuit voltage (V_oc) of corresponding devices. As a consequence, the optimized ternary OSC (PM6:Y6:MOITIC = 1:1:0.1) showed a significantly increased PCE of 17.1% with simultaneously enhanced V_oc of 0.882 V, short-circuit current density (J_sc) of 25.6 mA cm⁻², and fill factor (FF) of 75.7%, which has about 9% enhancement compared to the control binary PM6:Y6 (15.7%). In addition, the optimized ternary device exhibited better stability. This work indicates that ternary strategy via combining two compatible small molecule acceptors is effective to simultaneously improve the efficiency and stability of OSCs.     

18.9% Efficiency Ternary Organic Solar Cells Enabled by Isomerization Engineering of Chlorine-Substitution on Small Molecule Donors

Ternary organic solar cells (OSCs) represent an efficient and facile strategy to further boost the device performance. However, the selection criteria and rational design of the third guest small molecule (SM) material still remain less understood. In this study, two new SM donor isomers, with α-chlorinated thiophene (αBTCl) and β-chlorinated thiophene (βBTCl) as side chains, are systematically designed, synthesized and incorporated as a third component in PM6:L8-BO binary blends. It is noticed that introducing the SM donors guest has extended the absorption of photo-active layer, induced desired component distribution vertically with enhanced crystallinity and reduced recombination process, leading to increased short-circuit current (J_SC) and improved fill factor. Moreover, due to the synergetic suppressed nonradiative loss and preferable morphology, the ternary OSCs feature improves open-circuit voltage (V_OC). Consequently, an impressive champion power conversion efficiency of 18.96% and 18.55% is achieved by αBTCl-based and βBTCl-based ternary OSCs, respectively. Furthermore, a record efficiency of 17.46% is obtained with a 330 nm thickness of αBTCl-based ternary OSCs. This study demonstrates that molecular isomerization can be a promising design approach for SM donors to construct high-performance ternary OSCs with simultaneous enhancement of all photovoltaic parameters.     

Anthracene-Assisted Morphology Optimization in Photoactive Layer for High-Efficiency Polymer Solar Cells

Currently, morphology optimization methods for the fused-ring nonfullerene acceptor-based polymer solar cells (PSCs) empirically follow the treatments originally developed in fullerene-based systems, being unable to meet the diverse molecular structures and strong crystallinity of the nonfullerene acceptors. Herein, a new and universal morphology controlling method is developed by applying volatilizable anthracene as solid additive. The strong crystallinity of anthracene offers the possibility to restrict the over aggregation of fused-ring nonfullerene acceptor in the process of film formation. During the kinetic process of anthracene removal in the blend under thermal annealing, donor can imbed into the remaining space of anthracene in the acceptor matrix to form well-developed nanoscale phase separation with bi-continuous interpenetrating networks. Consequently, the treatment of anthracene additive enables the power conversion efficiency (PCE) of PM6:Y6-based devices to 17.02%, which is a significant improvement with regard to the PCE of 15.60% for the reference device using conventional treatments. Moreover, this morphology controlling method exhibits general application in various active layer systems to achieve better photovoltaic performance. Particularly, a remarkable PCE of 17.51% is achieved in the ternary PTQ10:Y6:PC₇₁BM-based PSCs processed by anthracene additive. The morphology optimization strategy established in this work can offer unprecedented opportunities to build state-of-the-art PSCs.     

Balancing Intermolecular Interactions between Acceptors and Donor/Acceptor for Efficient Organic Photovoltaics

Promoted by uninterrupted materials and device innovation, organic solar cells have achieved impressive development. However, the complicated intermolecular interactions inside active layers are less understood. Herein, the intermolecular interactions are studied from the dual perspectives of acceptor/acceptor (A/A) and donor/acceptor (D/A), and how these interactions synergistically control the final efficiencies. Three small molecular acceptors (SMAs) are designed with different end-caps, which manipulate the crystallinity and electrostatic potential (ESP) distributions of acceptors, and accordingly, the A/A and D/A intermolecular interactions. The results show that SMA LA17 with low A/A interactions exhibits inferior performance around 12%, owing to its strong D/A interaction with donor PM6, which shapes too miscible morphology and increases charge recombination. Instead, LA16 with strong A/A interactions and moderate D/A interactions delivers improved bulk-heterojunction (BHJ) networks, and therefore, enhances charge transport and diminishes geminate or trap-assisted charge recombination. Consequently, PM6:LA16 records the competitive efficiency of up to 13.74% among the three systems. Therefore, this study deepens the synergistic or balancing effect of the D/A and A/A interactions on BHJ blends for efficient organic solar cells.     

Regulating crystallization to maintain balanced carrier mobility via ternary strategy in blade-coated flexible organic solar cells

Regulating the crystallization of donor and acceptor to maintain balanced carrier mobility is of great importance to fabricate efficient organic solar cells (OSCs). Herein, the balanced crystallinity between donor and acceptor was finely controlled in blade-coated OSCs. By adding high crystalline FOIC into PBDB-T:ITIC system, a balanced carrier mobility was achieved, resulting in the much improved fill factor. The optimized ternary device exhibits an increased current density, due to the enhanced light-harvesting efficiency with complementary absorption and the morphology change. Morphology characterization demonstrated that the ternary film exhibits a highly balanced crystallinity between the donor and acceptor on account of the formation of acceptor alloy. Moreover, the ternary film not only possesses a small domain size, but also exhibits a high domain purity as compared to both binary films. Encouragingly, a highest power conversion efficiency (PCE) of 10.68% was obtained for the blade-coated ternary OSCs. In addition, the blade-coated flexible large-area (105 mm²) OSC based on PBDB-T:ITIC:FOIC ternary system also exhibits a high PCE of 9.81%, showing great potential in the high-throughput fabrication of OSCs.     

High-Performance Ternary Organic Solar Cells Enabled by Integrating a 3D-Shaped Guest Acceptor Derived from Perylene Diimide

Integrating a third component into the binary system is considered to be one of the most effective strategies to further enhance the power conversion efficiency (PCE) in organic solar cells (OSCs). Here, a novel perylene diimide (PDI) derivative featuring 3D structure, TPA-4PDI, with tetraphenyladamantane central core is developed as a guest electron acceptor to be incorporated into the PM6:Y6 binary system. The champion PCE of ternary OSC is recorded to be 18.29% by adding 7.5 wt.% of TPA-4PDI in the ternary blend, which photovoltaic performance is enhanced with synergistically increased open-circuit voltage (V_oc) of 0.849 V, short-circuit current density (J_sc) of 27.55 mA cm⁻², and fill factor (FF) of 78.21%. TPA-4PDI exhibits a complementary absorption band with PM6 and Y6 while its lowest unoccupied molecular orbital (LUMO) energy level falls between the two host materials. The addition of TPA-4PDI can effectively suppress the recombination behavior, inhibit the excessive aggregation of Y6 and improve the morphology of PM6:Y6 blend. All these effects function synergistically and then lead to the enhancement of V_oc, J_sc, and FF in ternary OSCs. This study suggests that developing PDI derivatives as the third component is an effective method to further improve the performance of ternary OSCs.     

Efficient ternary blend polymer solar cells with a bipolar diketopyrrolopyrrole small molecule as cascade material

We present a ternary strategy to enhance the power conversion efficiency (PCE) of bulk heterojunction polymer solar cells (PSCs) with a bipolar small molecule as cascade material. A bipolar diketopyrrolopyrrole small molecule (F(DPP)₂B₂), as the second electron acceptor, was incorporated into poly(3-hexylthiophene) (P3HT): [6,6]-phenyl-C₆₁-butyric-acidmethyl-ester (PC₆₁BM) blend to fabricate ternary blend PSCs. The introduction of the bipolar compound F(DPP)₂B₂ can not only broaden the light absorption of the active layer because of its absorption in near infrared region but also play a bridging role between P3HT and PC₆₁BM due to the cascaded energy level structure, thus improving the charge separation and transportation. The optimized ternary PSC with 5 wt% F(DPP)₂B₂ content delivered a high PCE of 3.92% with a short-circuit current density (J_sc) of 9.63 mA cm⁻², an open-circuit voltage (V_oc) of 0.62 V and a fill factor (FF) of 64.90%, showing an 23% improvement of PCE as compared to the binary systems based on P3HT:PC₆₁BM (3.18%) or P3HT:F(DPP)₂B₂ (3.17%). The results indicate that the ternary PSCs with a bipolar compound have the potential to surpass high-performance binary PSCs after carefully device optimization.     

High-Efficiency All-Small-Molecule Organic Solar Cells Based on New Molecule Donors with Conjugated Symmetric/Asymmetric Hybrid Cyclopentyl-Hexyl Side Chains

All small molecule organic solar cells (ASM-OSCs) have numerous advantages but lower power conversion efficiencies (PCEs) than their polymer equivalents, which is largely due to the suboptimal nanoscale network structure in a bulk heterojunction (BHJ). Herein, new small molecule donors with symmetric/asymmetric hybrid cyclopentyl-hexyl side chains are designed, accounting for manipulated intermolecular interactions and BHJ morphology. Theoretical and experimental results reveal that the asymmetric cyclopentyl-hexyl side chains modification has a significant influence on potential energy surface and intermolecular interaction that can ensure preferable molecular assembly and regulate the D/A interfacial energetics, thus boosting the exciton dissociation and charge transport when pairing with a wide-used acceptor L8-BO. Concurrently, a nanoscale bicontinuous interpenetrating network with optimal domain size can be fully evolved in the BHJ layer. As a consequence, the As-TCp-based binary device achieves a superior PCE of 16.46% in comparison to that of the controlled symmetric counterparts S-BF (14.92%) and A-TCp (15.77%), and ranks one of best performance among ASM-OSCs. This study demonstrates that precise manipulation of the cyclo-alkyl chain in combination with the asymmetric 2D side chain strategy is an effective synergistic approach to control intermolecular interaction and nanoscale bicontinuous phase separation for achieving high-performance ASM-OSCs.     

A Novel Wide‐Bandgap Polymer with Deep Ionization Potential Enables Exceeding 16% Efficiency in Ternary Nonfullerene Polymer Solar Cells

Ternary strategies have attracted extensive attention due to their potential in improving power conversion efficiencies (PCEs) of single‐junction polymer solar cells (PSCs). In this work, a novel wide bandgap polymer donor (E_g^opt ≈ 2.0 eV) named PBT(E)BTz with a deep highest occupied molecular orbital (HOMO) level (≈?5.73 eV) is designed and synthesized. PBT(E)BTz is first incorporated as the third component into the classic PBDB‐T‐SF:IT‐4F binary PSC system to fabricate efficient ternary PSCs. A higher PCE of 13.19% is achieved in the ternary PSCs with a 5% addition of PBT(E)BTz over binary PSCs (12.14%). Similarly, addition of PBT(E)BTz improves the PCE for PBDB‐T:IT‐M binary PSCs from 10.50% to 11.06%. The study shows that the improved PCE in ternary PSCs is mainly attributed to the suppressed charge carrier recombination and more balanced charge transport. The generality of PBT(E)BTz as a third component is further evidenced in another efficient binary PSC system—PBDB‐TF:BTP‐4Cl: an optimized PCE of 16.26% is realized in the ternary devices. This work shows that PBT(E)BTz possessing a deep HOMO level as an additional component is an effective ternary PSC construction strategy toward enhancing device performance. Furthermore, the ternary device with 5% PBT(E)BTz displays better thermal and light stability over binary devices.     

Enhancing the photovoltaic performance with two similar structure polymers as donors by broadening the absorption spectrum and optimizing the molecular arrangement

Ternary organic photovoltaics (OPVs) were fabricated with two polymers (PM6 and D18) as the donor and the fullerene-free small molecule Y6 as the acceptor in an inverted structure. The blueshifted absorption spectrum of neat D18 relative to neat PM6 can enable harvesting of more short and medium wavelength photons in the ternary photoactive layer, which is beneficial to increasing the short-circuit current density (J_SC). The enhancement of the open-circuit voltage (V_OC) of the ternary OPVs can be explained by the deeper HOMO level of D18 than that of PM6, which is beneficial to broadening the energy bandgap. In addition, the combination of the cascade LUMO levels among D18, PM6 and Y6 and the enhanced crystallinity can lead to more efficient exciton dissociation and charge transport within the ternary films. As a result, the power conversion efficiency of the optimize ternary OPV is 15.85%, which is higher than those of the PM6:Y6- and D18:Y6-base binary OPVs (PCEs of 14.70% and 14.95%, respectively). The results indicate that ternary OPVs with a blend of two similar chemical structure polymers as the donor could achieve high performance by broadening the light spectrum and optimizing the phase separation and crystallinity.     

Alkoxy- and Alkyl-Side-Chain-Functionalized Terpolymer Acceptors for All-Polymer Photovoltaics Delivering High Open-Circuit Voltages and Efficiencies

A new terpolymer acceptor is presented, comprising various ratios of the same dithienothienopyrrolobenzothiadiazole (BTP) core with different side chains—alkoxy side chains (BTPO-IC) and alkyl side chains (BTP-IC)—and thiophene units, for use in all-polymer organic photovoltaics. Devices incorporating binary blends of this terpolymer and the polymer PM6 as the active layer displayed open-circuit voltages (V_OC) that increase linearly upon increasing the molar ratio of BTPO-IC. For example, the optimized device incorporating PM6:PY-0.2OBO (i.e., with 20 mol% of BTPO-IC) (1:1.2 wt.%) blend, with the smallest domain sizes but largest coherence length and combined face-on and edge-on orientation fractions among all blends, have a champion power conversion efficiency (PCE) of 16.7% (V_OC = 0.97 V; J_SC = 25.2 mA cm⁻²; FF = 0.68), whereas the device containing a similar blend ratio of the PM6:PY-OD:PY-OBO ternary blend (1:0.96:0.24 wt.%) displayed a PCE of 8.6% (V_OC = 0.969 V; J_SC = 18.7 mA cm⁻²; FF = 0.48). The device with PM6:PY-0.2OBO displays better thermal stability than the devices with PM6: PY-OD or PY-OBO. Thus, employing terpolymer acceptors with differently functionalized side-chain units can be an effective approach for simultaneously optimizing the aggregation domain and enhancing the PCEs and thermal stabilities of all-polymer devices.     

High-Performance Green Thick-Film Ternary Organic Solar Cells Enabled by Crystallinity Regulation

The power conversion efficiency (PCE) of organic solar cells (OSCs) has reached high values of over 19%. However, most of the high-efficiency OSCs are fabricated by spin-coating with toxic solvents and the optimal photoactive layer thickness is limited to 100 nm, limiting practical development of OSCs. It is a great challenge to obtain ideal morphology for high-efficiency thick-film OSCs when using non-halogenated solvents due to the unfavorable film formation kinetics. Herein, high-efficiency ternary thick-film (300 nm) OSCs with PCE of 15.4% based on PM6:BTR-Cl:CH1007 are fabricated by hot slot-die coating using non-halogenated solvent (o-xylene) in the air. Compared to PM6:BTR-Cl:Y6 blends, the stronger pre-aggregation of CH1007 in solution induces the earlier aggregation of CH1007 molecules and longer aggregation time, and thus results in high and balanced crystallinity of donors and acceptor in CH1007-based ternary film, which led to high-carrier mobility and suppressed charge recombination. The ternary strategy is further used to fabricate high-efficiency, thick-film, large-area, and flexible devices processed from non-halogenated solvents, paving the way for industrial development of OSCs.     

Ternary Polymer Solar Cells with High Efficiency of 14.24% by Integrating Two Well‐Complementary Nonfullerene Acceptors

Ternary polymer solar cells (PSCs) are one of the most promising device architectures that maintains the simplicity of single‐junction devices and provides an important platform to better tailor the multiple performance parameters of PSCs. Herein, a ternary PSC system is reported employing a wide bandgap polymeric donor (PBTA‐PS) and two small molecular nonfullerene acceptors (labeled as LA1 and 6TIC). LA1 and 6TIC keep not only well‐matched absorption profiles but also the rational crystallization properties. As a result, the optimal ternary PSC delivers a state of the art power conversion efficiency (PCE) of 14.24%, over 40% higher than the two binary devices, resulting from the prominently increased short‐circuit current density (J_sc) of 22.33 mA cm^?2, moderate open‐circuit voltage (V_oc) of 0.84 V, and a superior fill factor approaching 76%. Notably, the outstanding PCE of the ternary PSC ranks one of the best among the reported ternary solar cells. The greatly improved performance of ternary PSCs mainly derives from combining the complementary properties such as absorption and crystallinity. This work highlights the great importance of the rational design of matched acceptors toward highly efficient ternary PSCs.     

Efficient ternary polymer solar cells by optimizing photogenerated exciton dissociation and photon harvesting with a short wavelength absorption polymer acceptor as the third component

Ternary blend films, obtained by introducing a third component (a second acceptor as the third component) to a binary polymer solar cell (PSC), are a promising ternary strategy because the light absorption range, surface morphology, and charge carrier transport of the photoactive layer may be optimized, as can the energy level alignment between the donor and the acceptor. In this work, acceptors such as the short-wavelength-absorption polymer N2200 and the long-wavelength-absorption small molecule FOIC were combined with the donor PBDB-T-2F to construct ternary blends. The optimized ternary PSC could achieve a power conversion efficiency (PCE) of 13.98%, which is higher than the efficiencies of binary PSCs based on PBDB-T-2F:FOIC (12.65%) and PBDB-T-2F:N2200 (9.36%). The enhanced PCE of the ternary PSC is based on the high electron mobility, balanced charge transport, optimized surface morphology and charge carrier kinetics and the extended light absorption of the ternary photoactive layer, realized by adjusting the ratio of FOIC:N2200. Our results indicate that mixing a polymer acceptor into a binary photoactive layer to form a ternary blend photoactive layer is a valuable strategy for improving photovoltaic performance.     

As‐Cast Ternary Organic Solar Cells Based on an Asymmetric Side‐Chains Featured Acceptor with Reduced Voltage Loss and 14.0% Efficiency

A new small‐molecule nonfullerene acceptor based on the benzo[1,2‐b:4,5‐b′]dithiophene (BDT) fused central core with asymmetrical alkoxy and thienyl side chains, namely TOBDT , is designed and synthesized. The alkoxy unit helps narrow the bandgap, and thienyl side chain helps enhance the intermolecular interaction. As a result, TOBDT is suitable to match the deep‐lying highest occupied molecular orbital (HOMO) of polymer donor PM6 . Then, a strong crystalline acceptor IDIC is introduced as the third component to fabricate as‐cast nonfullerene ternary devices to achieve absorption and morphology control. Addition of IDIC not only mixes well with TOBDT but modulates the morphology of the blend film, which helps to balance the charge transport properties and reduce the photovoltage loss of ternary devices. All these contribute to synergetic improvement of J_sc, V_oc, and fill factor parameters, leading to a power conversion efficiency of 14.0% for the as‐cast fullerene‐free ternary device.     

Highly Efficient Ternary All-Polymer Solar Cells with Enhanced Stability

Developing organic solar cells (OSCs) based on a ternary active layer is one of the most effective approaches to maximize light harvesting and improve their photovoltaic performance. However, this strategy meets very limited success in all-polymer solar cells (all-PSCs) due to the scarcity of narrow bandgap polymer acceptors and the challenge of morphology optimization. In fact, the power conversion efficiencies (PCEs) of ternary all-PSCs even lag behind binary all-PSCs. Herein, highly efficient ternary all-PSCs are realized based on an ultranarrow bandgap (ultra-NBG) polymer acceptor DCNBT-TPC, a medium bandgap polymer donor PTB7-Th, and a wide bandgap polymer donor PBDB-T. The optimized ternary all-PSCs yield an excellent PCE of 12.1% with a remarkable short-circuit current density of 21.9 mA cm⁻². In fact, this PCE is the highest value reported for ternary all-PSCs and is much higher than those of the corresponding binary all-PSCs. Moreover, the optimized ternary all-PSCs show a photostability with ≈ 68% of the initial PCE retained after 400 h illumination, which is more stable than the binary all-PSCs. This work demonstrates that the utilization of a ternary all-polymer system based on ultra-NBG polymer acceptor blended with compatible polymer donors is an effective strategy to advance the field of all-PSCs.