Bulk Heterojunction Organic Photovoltaics Research Articles

Cover Picture: Novel low‐band gap non‐fullerene acceptors based on IDIC core as potential photovoltaic materials (BKCS 9/2024) Radhiha Ravindran, Inchan Kim, Yun‐Hi Kim, Soon‐Ki Kwon

Organic photovoltaics (OPVs) attracted a lot of research attention owing to its advantages such as convenient processing technique, unsubstantial weight, low cost, flexibility and use of environmentally benign materials. In general, these are bulk heterojunction (BHJ) OPVs obtained through a solution process and the large‐area OPV production is achieved via roll‐to‐roll process. In OPVs, the BHJ active layer consists of electron donor (D) and electron acceptor (A) materials blended together by dissolving them in a common organic solvent. The new low band gap non‐fullerene based acceptors could be used as potential candidates for the fabrication of OPVs in combination with suitable donor polymers. More details are available in the article by Radhiha Ravindran, Inchan Kim, Yun‐Hi Kim, Soon‐Ki Kwon image

Novel low‐band gap non‐fullerene acceptors based on IDIC core as potential photovoltaic materials

AbstractThree novel non‐fullerene acceptors (NFAs) (PhBu‐IDT‐BT‐IC, PhBu‐IDT‐BT‐IC4F and PhBu‐IDT‐BT‐IC4Cl) based on 3,8‐dioctyl‐indaceno[1,2‐b:5,6‐b’]dithiophene (IDT) core have been designed and synthesized with and without halogen (F and Cl) substitution. The NFAs showed high thermal stability. The ultraviolet–visible absorption studies in solution and thin film for the three acceptors revealed maximum absorption from 687 to 732 nm and 731 to 847 nm, respectively. The onset of absorption in the thin film was found to be extending up to around 960 nm for PhBu‐IDT‐BT‐IC4Cl. The optical band gap ranged from 1.30 to 1.41 eV, which are very low and useful for photovoltaic application. The introduction of halogen appreciably altered the LUMO energy levels, whereas the HOMO energy levels were nearly intact. These small molecule non‐fullerene acceptors could be used as potential acceptors in bulk heterojunction organic photovoltaic (BHJ‐OPV) applications.

Spray-Coated MoO3 Hole Transport Layer for Inverted Organic Photovoltaics.

This study focuses on the hole transport layer of molybdenum trioxide (MoO3) for inverted bulk heterojunction (BHJ) organic photovoltaics (OPVs), which were fabricated using a combination of a spray coating and low-temperature annealing process as an alternative to the thermal evaporation process. To achieve a good coating quality of the sprayed film, the solvent used for solution-processed MoO3 (S-MoO3) should be well prepared. Isopropanol (IPA) is added to the as-prepared S-MoO3 solution to control its concentration. MoO3 solutions at concentrations of 5 mg/mL and 1 mg/mL were used for the spray coating process. The power conversion efficiency (PCE) depends on the concentration of the MoO3 solution and the spray coating process parameters of the MoO3 film, such as flow flux, spray cycles, and film thickness. The results of devices fabricated from solution-processed MoO3 with various spray fluxes show a lower PCE than that based on thermally evaporated MoO3 (T-MoO3) due to a limiting FF, which gradually increases with decreasing spray cycles. The highest PCE of 2.8% can be achieved with a 1 mg/mL concentration of MoO3 solution at the sprayed flux of 0.2 mL/min sprayed for one cycle. Additionally, S-MoO3 demonstrates excellent stability. Even without any encapsulation, OPVs can retain 90% of their initial PCE after 1300 h in a nitrogen-filled glove box and under ambient air conditions. The stability of OPVs without any encapsulation still has 90% of its initial PCE after 1300 h in a nitrogen-filled glove box and under air conditions. The results represent an evaluation of the feasibility of solution-processed HTL, which could be employed for a large-area mass production method.

Deuteration-enhanced neutron contrasts to probe amorphous domain sizes in organic photovoltaic bulk heterojunction films

An organic photovoltaic bulk heterojunction comprises of a mixture of donor and acceptor materials, forming a semi-crystalline thin film with both crystalline and amorphous domains. Domain sizes critically impact the device performance; however, conventional X-ray scattering techniques cannot detect the contrast between donor and acceptor materials within the amorphous intermixing regions. In this study, we employ neutron scattering and targeted deuteration of acceptor materials to enhance the scattering contrast by nearly one order of magnitude. Remarkably, the PM6:deuterated Y6 system reveals a new length scale, indicating short-range aggregation of Y6 molecules in the amorphous intermixing regions. All-atom molecular dynamics simulations confirm that this short-range aggregation is an inherent morphological advantage of Y6 which effectively assists charge extraction and suppresses charge recombination as shown by capacitance spectroscopy. Our findings uncover the amorphous nanomorphology of organic photovoltaic thin films, providing crucial insights into the morphology-driven device performance.

Understanding the correlation between energy‐state mismatching and open‐circuit voltage loss in bulk heterojunction solar cells

AbstractPhotoinduced intermolecular charge transfer (PICT) determines the voltage loss in bulk heterojunction (BHJ) organic photovoltaics (OPVs), and this voltage loss can be minimized by inducing efficient PICT, which requires energy‐state matching between the donor and acceptor at the BHJ interfaces. Thus, both geometrically and energetically accessible delocalized state matching at the hot energy level is crucial for achieving efficient PICT. In this study, an effective method for quantifying the hot state matching of OPVs was developed. The degree of energy‐state matching between the electron donor and acceptor at BHJ interfaces was quantified using a mismatching factor (MF) calculated from the modified optical density of the BHJ. Furthermore, the correlation between the open‐circuit voltage (Voc) of the OPV device and energy‐state matching at the BHJ interface was investigated using the calculated MF. The OPVs with small absolute MF values exhibited high Voc values. This result clearly indicates that the energy‐state matching between the donor and acceptor is crucial for achieving a high Voc in OPVs. Because the MF indicates the degree of energy‐state matching, which is a critical factor for suppressing energy loss, it can be used to estimate the Voc loss in OPVs.

High‐Performance Organic Photovoltaics Incorporating Bulk Heterojunction and p–i–n Active Layer Structures

In the past five years, significant advancements in the development of novel conjugated polymer donors (D) and non‐fullerene acceptors (A), such as small molecules, have substantially boosted the power conversion efficiency of bulk heterojunction (BHJ) organic photovoltaics (OPVs) devices to over 19%. Recently, in the pursuit of broader impact and heightened efficiency for OPVs, an alternative processing approach has emerged; this approach involves a sequential deposition (SD) technique or a layer‐by‐layer method, creating active layers with p–i–n structures (p and n stand for D and A region, respectively; i stands for BHJ region). Notably, this SD method is particularly effective in semitransparent organic photovoltaics (ST‐OPVs), despite the material requirements it entails. SD‐processing methods enable the creation of vertical multiple junctions and controllable D/A interfaces, facilitating exciton dissociation and charge transport through a well‐designed pseudo p–i–n structure. Furthermore, ST‐OPVs can be integrated into building‐incorporated photovoltaic modules, offering potential applications in greenhouses and agricultural modernization. This integration allows for the comprehensive utilization of solar spectrum energy. In this review, current literature is consolidated on new materials, such as conjugated polymers and non‐fullerene small molecules as electron‐donating and electron‐withdrawing materials, aimed at high‐efficiency OPVs and ST‐OPVs with BHJ‐ and p–i–n structured active layers, and perspectives are offered for future developments.

Decoration of transition metal carbide nanoparticles on reduced graphene oxide for the efficient bulk heterojunction organic photovoltaics

Herein, we fabricated the bulk heterojunction organic photovoltaics (OPV) using the different hybrid composites doped novel combination of PBDB-T:PCBM/hybrid-nanostructures with the architecture of ITO/HTL/active-layer/LiF/Al. Structural and morphological characteristics were evidently established the formation of W2C@rGO and Mo2C@rGO composites by the simple chemical reduction process. The different concentrations of prepared nanocomposites were doped with polymer PBDB-T:PCBM matrix to modify the active layer properties in the OPV devices. The Mo2C@rGO and W2C@rGO (10 vol%) composites using tuned active realized the improved power conversion efficiency (PCE) of 6.98 and 6.84%, respectively which is quite high compared to the pure PBDB-T: PCBM active layer (PCE = 5.61%) and bare rGO (6.66%), Mo2C (6.43%) and W2C (6.20%) outcomes. The procured results explored that the W2C@rGO and Mo2C@rGO hybrid incorporated active layers facilitate the swift charge transport and extraction possibility to achieve the high efficiency photovoltaic devices.

Optimization of Bulk Heterojunction Organic Photovoltaics

The performance of poly(3-hexylthiophene) (P3HT): phenyl-C61-butyric acid methyl ester (PCBM) organic photovoltaic (OPV) devices was found to be strongly influenced by environmental during preparation, thermal annealing conditions, and the material blend composition. We optimized laboratory fabricated devices for these variables. Humidity during the fabrication process can cause electrode oxidation and photo-oxidation in the active layer of the OPV. Thermal annealing of the device structure modifies the morphology of the active layer, resulting in changes in material domain sizes and percolation pathways which can enhance the performance of devices. Thermal annealing of the blended organic materials in the active layer also leads to the growth of crystalline for P3HT domains due to a more arrangement packing of chains in the polymer. Poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) acts as a hole transport layer in these P3HT:PCBM devices. Two commercially materials of PEDOT:PSS were utilizing in the optimization of the OPV in this research; high conductivity PEDOT:PSS-PH1000 and PEDOT:PSS-Al4083, which is specifically designed for OPV interfaces. It was demonstrated that OPVs were prepared with PEDOT:PSS-PH1000 have a less than the average performance of PEDOT:PSS-Al4083. The power conversion efficiency (PCE) decreased clearly with a reducing in masking area devices from 5 mm2 to 3.8 mm2 for OPVs based on PH1000 almost absolutely due to the reduced short circuit current (Jsc). This work provides a roadmap to understanding P3HT:PCBM OPV performance and outlines the preparation issues which need to be resolved for efficient device fabrication

Additive-free molecular acceptor organic solar cells processed from a biorenewable solvent approaching 15% efficiency.

We report on the use of molecular acceptors (MAs) and donor polymers processed with a biomass-derived solvent (2-methyltetrahydrofuran, 2-MeTHF) to facilitate bulk heterojunction (BHJ) organic photovoltaics (OPVs) with power conversion efficiency (PCE) approaching 15%. Our approach makes use of two newly designed donor polymers with an opened ring unit in their structures along with three molecular acceptors (MAs) where the backbone and sidechain were engineered to enhance the processability of BHJ OPVs using 2-MeTHF, as evaluated by an analysis of donor-acceptor (D-A) miscibility and interaction parameters. To understand the differences in the PCE values that ranged from 9-15% as a function of composition, the surface, bulk, and interfacial BHJ morphologies were characterized at different length scales using atomic force microscopy, grazing-incidence wide-angle X-ray scattering, resonant soft X-ray scattering, X-ray photoelectron spectroscopy, and 2D solid-state nuclear magnetic resonance spectroscopy. Our results indicate that the favorable D-A intermixing that occurs in the best performing BHJ film with an average domain size of ∼25 nm, high domain purity, uniform distribution and enhanced local packing interactions - facilitates charge generation and extraction while limiting the trap-assisted recombination process in the device, leading to high effective mobility and good performance.

Recent Advances of Solid Additives Used in Organic Solar Cells: Toward Efficient and Stable Solar Cells

Bulk heterojunction (BHJ) organic photovoltaics (OPVs) are considered to be the most promising generation of green energy technology due to their outstanding device performance and simple processing technology. The morphology of the active layer of OPVs is the key to its device performance and stability. So for, various strategies have been proposed to optimize the morphology, such as thermal annealing, solvent annealing, adding solvent additives and so on. However, the posting annealing is not compatible with large-area printing. In addition, solvent additives are easy to remain in active layer, which continuously deteriorate the morphology and performance of OPVs. Recently, the addition of solid additives has drawn significant attentions due to its unique characteristics, including improved device stability, precise morphology control as well as easy accessibility. Hence, it gradually becomes a universal and popular strategy for optimizing the morphology of OPVs with high power conversion efficiency (PCE). However, the relationship between properties of solid additives and morphologies of active layers is still ambiguous, which inhibit the further development of solid additive and its application in new emerging OPVs systems. To this end, we summarized the recently reported solid additives according to their volatility, i.e., whether solid additives remain in final active layer or not. Furthermore, the different mechanisms that solid additives optimize the morphology of active layer are intensively discussed, including the free volume and diffusivity, intermolecular adsorption energy, interaction among donor and acceptor, and crystal nucleation and growth, which may give predictions for selecting proper solid additives in new emerging blends. Finally, the challenges and future development of solid additives in OPVs are briefly prospected.

Revealing conflicting effects of solvent additives on morphology and performance of non-fullerene organic photovoltaics under different illuminance conditions

The use of solvent additives is effective for controlling the morphology and efficiency of non-fullerene bulk-heterojunction (BHJ) organic photovoltaics (OPVs) under both indoor and outdoor conditions. In this study, we examined the effects of solvent additives on the morphology and photovoltaic operation of non-fullerene OPVs under different illuminance conditions. Solvent additives (e.g., 1,8-diiodooctane) improved molecular packing and charge transport in non-fullerene BHJ layers, increasing the power conversion efficiency (PCE) under 1-sun illumination. However, incorporating the solvent additives promoted the formation of a crystallization-induced roughened surface and an isolated-non-fullerene domain in the intermixing region. These unexpected morphological features increased the degree of trap-assisted charge recombination and leakage current, significantly reducing the PCE of non-fullerene OPVs at low light levels corresponding to indoor lighting. Understanding the effect of solvent additives inspires us to further control the morphological features of the non-fullerene OPVs by fine-tuning the solvent-additive concentration beyond the globally accepted level. This was effective for optimizing the indoor PCE of non-fullerene OPVs (21.71%), which exceeded that of the conventionally accepted reference (18.02%). This study provides guidelines for understanding the critical roles of solvent additives and optimizing the morphology of non-fullerene BHJs for high-performance indoor OPV applications.

Microscopic Structures, Dynamics, and Spin Configuration of the Charge Carriers in Organic Photovoltaic Solar Cells Studied by Advanced Time-Resolved Spectroscopic Methods.

Organic photovoltaics (OPVs) are promising solutions for renewable energy and sustainable technologies and have attracted much attention in recent years. Two types of organic semiconductors are used as donor materials to fabricate OPV cells. One type is a photoconductive polymer, and the other type is a small-molecule-based compound. The discovery of a bulk-heterojunction (BHJ) structure using a mixture of p- and n-type organic semiconductors has dramatically increased the power conversion efficiency (PCE) of OPV cells. In this feature article, we review our recent studies on organic BHJ thin films and OPVs by using advanced time-resolved spectroscopic techniques. Two topics regarding the microscopic behaviors of the charge carriers are discussed. The first topic is focused on how to quantify the local mobility of the charge carriers. Here, we discuss charge carrier dynamics in diketopyrrolopyrrole-linked tetrabenzoporphyrin (DPP-BP) BHJ thin films studied by time-resolved terahertz spectroscopy on a subpicosecond to several tens of picoseconds time scale and by transient photocurrent measurements on a microsecond time scale. The second topic concerns the spin configuration and interaction of the electron and hole of the polaron pairs in polymer-based BHJ thin films and OPV cells studied by the time-resolved electron paramagnetic resonance method, time-resolved simultaneous optical and electrical detection, and measurement of the magnetoconductance effect.

Metal-Organic Framework Nanosheets as Templates to Enhance Performance in Semi-Crystalline Organic Photovoltaic Cells.

Optimizing the orientation, crystallinity, and domain size of components within organic photovoltaic (OPV) devices is key to maximizing their performance. Here a broadly applicable approach for enhancing the morphology of bulk heterojunction OPV devices using metal–organic nanosheets (MONs) as additives is demonstrated. It is shown that addition of porphyrin‐based MONs to devices with fully amorphous donor polymers lead to small improvements in performance attributed to increased light absorption due to nanosheets. However, devices based on semi‐crystalline polymers show remarkable improvements in power conversion efficiency (PCE), more than doubling in some cases compared to reference devices without nanosheets. In particular, this approach led to the development of PffBT4T2OD‐MON‐PCBM device with a PCE of 12.3%, which to the authors’ knowledge is the highest performing fullerene based OPV device reported in literature to date. Detailed analysis of these devices shows that the presence of the nanosheets results in a higher fraction of face‐on oriented polymer crystals in the films. These results therefore demonstrate the potential of this highly tunable class of two‐dimensional nanomaterials as additives for enhancing the morphology, and therefore performance, of semi‐crystalline organic electronic devices.

Improving Thermal and Photostability of Polymer Solar Cells by Robust Interface Engineering.

As the power conversion efficiency (PCE) of organic photovoltaics (OPVs) approaches 19%, increasing research attention is being paid to enhancing the device's long-term stability. In this study, a robust interface engineering of graphene oxide nanosheets (GNS) is expounded on improving the thermal and photostability of non-fullerene bulk-heterojunction (NFA BHJ) OPVs to a practical level. Three distinct GNSs (GNS, N-doped GNS (N-GNS), and N,S-doped GNS (NS-GNS)) synthesized through a pyrolysis method are applied as the ZnO modifier in inverted OPVs. The results reveal that the GNS modification introduces passivation and dipole effects to enable better energy-level alignment and to facilitate charge transfer across the ZnO/BHJ interface. Besides, it optimizes the BHJ morphology of the photoactive layer, and the N,S doping of GNS further enhances the interaction with the photoactive components to enable a more idea BHJ morphology. Consequently, the NS-GNS device delivers enhanced performance from 14.5% (control device) to 16.5%. Moreover, the thermally/chemically stable GNS is shown to stabilize the morphology of the ZnO electron transport layer (ETL) and to endow the BHJ morphology of the photoactive layer grown atop with a more stable thermodynamic property. This largely reduces the microstructure changes and the associated charge recombination in the BHJ layer under constant thermal/light stresses. Finally, the NS-GNS device is demonstrated to exhibit an impressive T80 lifetime (time at which PCE of the device decays to 80% of the initial PCE) of 2712 h under a constant thermal condition at 65°Cin a glovebox and an outstanding photostability with a T80 lifetime of 2000 h under constant AM1.5G 1-sun illumination in an N2 -controlled environment.

Significant Stability Improvement of Fullerene Organic Photovoltaics via ZnO Film Modification through the Intermittent Spray Pyrolysis Technique.

Morphological control of the layers within the bulk heterojunction organic photovoltaics (BHJ-OPVs) is a key feature that governs their performance. In the present work, we demonstrate that zinc oxide—ZnO—interlayers sprayed via the intermittent spray pyrolysis technique, employing a low-concentration precursor solution, can yield inverted BHJ-OPVs as efficient as the standard reported ones using the conventional laboratory-scale spin-coating technique. However, we record a pioneer stability behavior of the fabricated inverted fullerene organic photovoltaics (iF-OPVs) with various sprayed ZnO conditions. Thus, after optimizing the sprayed ZnO interfacial layer morphology for the inverted PTB7-Th:PC70BM devices, by carefully inspecting the interdependence between the sprayed ZnO thin film morphology and the figures of merit of the optimized iF-OPVs, we conducted a distinct analysis on the optical and electronic properties of the fresh and degraded devices using external quantum efficiency measurements and impedance spectroscopy. Hence, we showed that the most proper ZnO microstructural morphology was obtained by spraying 25 running cycles (25R). Remarkably, we observed that 25R-ZnO-based iF-OPV devices showed a stunning stability behavior and maintained 85% of their initial power conversion efficiency even after 16.7 months without encapsulation in a dry nitrogen glovebox, demonstrating an excellent shelf stability. Accordingly, this approach might facilitate the scalability of inverted OPVs for industrial production visibility.

Theoretical Study of Charge-Transfer Exciplexes in Organic Photovoltaics.

The photogeneration of charges in bulk heterojunction organic photovoltaics is of crucial importance in the mechanism of charge separation. This results in the formation of both locally excited and charge-transfer exciplex states. While the former states are prone to radiative or nonradiative recombination, the latter ones can have a sufficiently long lifetime. In this work, the formation of charge-transfer exciplex states in pairs of PC61BM (acceptor) with different oligothiophenes (donors) is studied theoretically using density functional theory. The ground and excited states of three oligothiophene-PC61BM complexes are studied. It is found that the intensively absorbing state is localized on the oligothiophene. Another excited state is localized on PC61BM, being characterized by only slight absorption. The charge-transfer (CT) excited state of the complex lies either below or slightly higher than the locally excited (LE) states. The latter case is unfavorable for charge separation. Criteria for the efficient formation of charge-transfer exciplexes are found, and the possibility of oligothiophene modification to facilitate the formation of such exciplexes is explored. Shifting the donor absorption to the near IR, which is important for organic solar cells, is another goal of oligothiophene modification. A modified oligothiophene satisfying these two criteria is proposed. The structure and radiative lifetimes of the LE and CT states and also the binding energy of the CT states with respect to their dissociation into a radical cation and a radical anion are calculated. It is demonstrated that the lifetime of the CT exciplexes is sufficiently long to accomplish charge separation.

Meso-π-Extended/Deficient BODIPYs and Low-Band-Gap Donor–Acceptor Copolymers for Organic Optoelectronics

The realization of π-deficient acceptors and their donor–acceptor copolymers has become a key research focus for the realization of versatile organic optoelectronic materials and devices. Herein, we demonstrate the theoretical design, synthesis, and physicochemical/optoelectronic characterization of two meso-π-extended/deficient BODIPY building blocks (2OD–T2BDY and 2OD–TTzBDY) and a library of donor–acceptor copolymers with low band gap (Eg = 1.30–1.35 eV) based on these building blocks. These building blocks, to the best of our knowledge, are the first examples of BODIPYs with meso-π-extension. A library of BODIPY building blocks with varied meso units/substituents is studied to reveal the meso effects on the semiconducting BODIPY’s optoelectronic properties. The building blocks showed favorable π-acceptor electronic/structural properties with meso-π-delocalized and stabilized LUMOs (ca. −3.6 eV) and large ground-state dipole moments of 4.9–5.5 D. Consistent with the theoretical/experimental π-electronic structures, all copolymers functioned as p-type semiconductors in field-effect transistors and as donor materials in the bulk heterojunction organic photovoltaics. Power conversion efficiencies of up to 4.4% with a short-circuit current of 12.07 mA cm–2 were achieved. This study demonstrates a unique meso-π-extension strategy to realize BODIPYs with favorable π-acceptor properties, and our findings could open up future materials design avenues in various organic optoelectronic applications.

Reduction of Electric Current Loss by Aggregation-Induced Molecular Alignment of a Non-Fullerene Acceptor in Organic Photovoltaics.

Y6 is a recently developed non-fullerene electron acceptor (NFA) with dithienothiophen[3.2-b]-pyrrolobenzothiadiazole as the central unit and improves the performance of organic photovoltaics (OPVs) in combination with many electron-donor polymers. Although Y6 has desirable electronic properties for OPVs, the origin of its superiority as an acceptor is unclear. This study empirically investigates why Y6 is an excellent acceptor by comparing Y6 with F8IC, an analogue with a similar electronic structure, in bulk heterojunction (BHJ) OPVs with various electron-acceptor concentrations. The difference in the performance between Y6 and F8IC appears only at high concentrations, suggesting that it originates from the aggregation structures of the NFAs in the BHJs. Electric current loss analysis reveals that the exciton loss and non-geminate recombination are suppressed more strongly in Y6 OPVs than in F8IC OPVs. Variable angle spectroscopic ellipsometry shows that Y6 molecules align in the in-plane direction at high concentrations, contributing to the high charge generation rate via efficient exciton collection.

Uncovering the out-of-plane nanomorphology of organic photovoltaic bulk heterojunction by GTSAXS

The bulk morphology of the active layer of organic solar cells (OSCs) is known to be crucial to the device performance. The thin film device structure breaks the symmetry into the in-plane direction and out-of-plane direction with respect to the substrate, leading to an intrinsic anisotropy in the bulk morphology. However, the characterization of out-of-plane nanomorphology within the active layer remains a grand challenge. Here, we utilized an X-ray scattering technique, Grazing-incident Transmission Small-angle X-ray Scattering (GTSAXS), to uncover this new morphology dimension. This technique was implemented on the model systems based on fullerene derivative (P3HT:PC71BM) and non-fullerene systems (PBDBT:ITIC, PM6:Y6), which demonstrated the successful extraction of the quantitative out-of-plane acceptor domain size of OSC systems. The detected in-plane and out-of-plane domain sizes show strong correlations with the device performance, particularly in terms of exciton dissociation and charge transfer. With the help of GTSAXS, one could obtain a more fundamental perception about the three-dimensional nanomorphology and new angles for morphology control strategies towards highly efficient photovoltaic devices.

Enhanced Efficiency and Excellent Thermostability in Organic Photovoltaics via Ternary Strategy with Twisted Conjugated Compound.

The thermal stability of high-efficiency organic photovoltaics (OPVs) is critical to the manufacturing of this technology. Therefore, targeted strategies and approaches shall be developed to improve efficiency and stability, simultaneously. Herein, a seleno twisted benzodiperylenediimides (TBD-PDI-Se) acceptor-doping strategy is taken advantage of to demonstrate the ternary bulk heterojunction OPVs with excellent stability, achieving outstanding power conversion efficiency of 14.43% and 17.25% based on PM6:IT-4F and PM6:Y6 ternary blend devices, respectively, which are superior to the corresponding binary devices. As evidenced by the active layer morphology, exciton dynamic study and the characterizations of the enabled device, the ternary blend device keeps nearly 90% original efficiency (t= 1000 h) under continuous constant heating at 140°C. Furthermore, the application of acceptor as the third component in PBDB-T:ITIC, J71:ITIC, and PBDB-T:PC71 BM systems is also verified, proving the good universality of acceptor-doping ternary strategy.