Recent development of perylene diimide-based small molecular non-fullerene acceptors in organic solar cells

Triplet Excitation-Energy Transfer Couplings from Subsystem Time-Dependent Density-Functional Theory

We present an implementation of triplet excitation-energy transfer (TEET) couplings based on subsystem-based time-dependent density-functional theory (sTDDFT). TEET couplings are systematically investigated by comparing "exact" and approximate variants of sTDDFT. We demonstrate that, while sTDDFT utilizing explicit approximate non-additive kinetic energy (NAKE) density functionals is well-suited for describing singlet EET processes, it is inadequate for characterizing TEET. However, we show that projection-based embedding (PbE)-based sTDDFT addresses the challenges faced by NAKE-sTDDFT and emerges as a promising method for accurately describing electronic couplings in TEET processes. We also introduce the mixed PbE-/NAKE-embedding procedure to investigate the TEET effects in solvated pairs of chromophores. This approach offers a good balance between accuracy and efficiency, enabling comprehensive studies of TEET processes in complex environments.

Tailoring the Molecular Planarity of Perylene Diimide-Based Third Component toward Efficient Ternary Organic Solar Cells

Incorporating a third component into binary organic solar cells (b-OSCs) has provided a potential platform to boost power conversion efficiency (PCEs). However, gaining control over the non-equilibrium blend morphology via the molecular design of the perylene diimide (PDI)-based third component toward efficient ternary organic solar cells (t-OSCs) still remains challenging. Herein, two novel PDI derivatives are developed with tailored molecular planarity, namely ufBTz-2PDI and fBTz-2PDI, as the third component for t-OSCs. Notably, after performing a cyclization reaction, the twisted ufBTz-2PDI with an amorphous character transferred to the highly planar fBTz-2PDI followed by a semi-crystalline character. When incorporating the semi-crystalline fBTz-2PDI into the D18:L8-BO system, the resultant t-OSC achieved an impressive PCE of 18.56%, surpassing the 17.88% attained in b-OSCs. In comparison, the addition of amorphous ufBTz-2PDI into the binary system facilitates additional charge trap sites and results in a deteriorative PCE of 14.37%. Additionally, The third component fBTz-2PDI possesses a good generality in optimizing the PCEs of several b-OSCs systems are demonstrated. The results not only provided a novel A-DA'D-A motif for further designing efficient third component but also demonstrated the crucial role of modulated crystallinity of the PDI-based third component in optimizing PCEs of t-OSCs.

Full solar spectrum-driven Cu2O/PDINH heterostructure with enhanced photocatalytic antibacterial activity and mechanism insight

Marine biofouling hazards the sustainable development of the environment and has become a potential threat to environmental and ecological security. Photocatalytic antibacterial agents driven by the full solar spectrum are promising antifouling agents for environmental protection. The cuprous oxide/perylene-3,4,9,10-tetracarboximide (Cu₂O/PDINH) heterostructure was successfully constructed by integrating p-type Cu₂O and n-type PDINH to improve photocatalytic antibacterial efficiency. PDINH extended the absorption spectrum from ultraviolet to near-infrared, improving light utilization by 75 %. The Cu₂O/PDINH heterostructure reduced the toxicity risk of Cu₂O for environmental pollution, achieved full solar spectrum drive and overcame the inherent defect that Cu₂O cannot produce singlet oxygen. The Cu₂O/PDINH heterostructure exhibited excellent long-term and photocatalytic antibacterial activity with an antibacterial rate of > 90 % due to the sterilization of copper ions and the continuous generation of ROS driven by the full solar spectrum. This inorganic-organic Cu₂O/PDINH heterostructure shows great application prospects in energy and the environment. The Cu₂O/PDINH heterostructure with effective ROS increase and superior photocatalytic sterilization efficiency has great potential for environmentally friendly marine antifouling agents.

Regiochemically Pure 1,6-Ditriflato-Perylene Diimide: Preparation and Transformation

Preparation of regioisomerically pure 1,6-disubstituted perylene diimide (PDI) is not a trivial task owing to the lack of facile synthetic and separation methodologies for the precursors. Herein, we present a simple synthesis for 1,6-ditriflato-PDI (1,6-diOTf-PDI) using 1,6,9,10-tetrabromo-perylene monoimide 1 as the starting material. The selective methoxylation of 1 at the 1,6-position is the key step. Based on a four-step sequence of selective methoxylation, domino carbonylative amidation, demethylation, and triflation, 1,6-diOTf-PDI can be obtained in a satisfactory yield. Moreover, as a building block, 1,6-diOTf-PDIa can readily undergo Suzuki and Sonogashira cross-coupling reactions.

Structural symmetry-breaking of perylene diimide acceptor at N-position for enhanced photovoltaic performance

The vinylene-bridged helical perylene diimide dimer (PDI2) and derivatives have received considerable attention for application in nonfullerene organic solar cells (OSCs). Benefit from the large natural dipole moment and the...

Layer-by-Layer Solution-Processed Organic Solar Cells with Perylene Diimides as Acceptors

Layer-by-layer (LBL) sequential solution processing of the active layer has been proven as an effective strategy to improve the performance of organic solar cells (OSCs), which could adjust vertical phase separation and improve device performance. Although perylene diimide (PDI) derivatives are typical acceptors with excellent photoelectric properties, there are few studies on PDI-based LBL OSCs. Herein, three PDI acceptors (TBDPDI-C₅, TBDPDI-C₁₁, and SdiPDI) were used to fabricate LBL and bulk heterojunction (BHJ) OSCs, respectively. A series of studies including device optimization, photoluminescence (PL) quenching, dependence of light intensity, carrier mobility, atomic force microscopy (AFM), transmission electron microscopy (TEM), grazing-incidence wide-angle X-ray scattering (GIWAXS), and depth analysis X-ray photoelectron spectroscopy (DXPS) were carried out to make clear the difference of the PDI-based LBL and BHJ OSCs. The results show that LBL OSCs possess better charge transport, higher and more balanced carrier mobility, less exciton recombination loss, more favorable film morphology, and proper vertical component distribution. Therefore, all the three PDI acceptor-based LBL OSCs exhibit higher performance than their BHJ counterparts. Among them, TBDPDI-C₅ performs best with a power conversion efficiency of 6.11% for LBL OSCs, higher than its BHJ OSC (5.14%). It is the first time for PDI small molecular acceptors to fabricate high-efficiency OSCs by using an LBL solution-processed method.

Tackling Solubility Issues in Organic Synthesis: Solid-State Cross-Coupling of Insoluble Aryl Halides

Conventional organic synthesis generally relies on the use of liquid organic solvents to dissolve the reactants. Therefore, reactions of sparingly soluble or insoluble substrates are challenging and often ineffective. The development of a solvent-independent solid-state approach that overcomes this longstanding solubility issue would provide innovative synthetic solutions and access to new areas of chemical space. Here, we report extremely fast and highly efficient solid-state palladium-catalyzed Suzuki-Miyaura cross-coupling reactions via a high-temperature ball-milling technique. This solid-state protocol enables the highly efficient cross-couplings of insoluble aryl halides with large polyaromatic structures that are barely reactive under conventional solution-based conditions. Notably, we discovered a new luminescent organic material with a strong red emission. This material was prepared via the solid-state coupling of Pigment violet 23, a compound that has so far not been involved in molecular transformations due to its extremely low solubility. This study thus provides a practical method for accessing unexplored areas of chemical space through molecular transformations of insoluble organic compounds that cannot be carried out by any other approach.

Propeller-Like All-Fused Perylene Diimide Based Electron Acceptors With Chalcogen Linkage for Efficient Polymer Solar Cells

Perylene diimide (PDI) is a widely explored chromophore for constructing non-fullerene acceptors (NFAs) for polymer solar cells (PSCs). The advantage of using PDI derivatives lies in the readily availability of PDI unit which largely reduces the synthesis cost and improves material stability. Indeed, the recent development of high performance NFAs shed light on the feasibility of the commercialization, but the complex synthesis and poor stability of the top performing NFAs cast a shadow on this bright future. Our previous work has demonstrated a propeller-like structure with three PDIs lined to a benzene center core with a C-C bond which prevented the PDIs to aggregate into undesired large crystals. In this work, we designed and synthesized three new propeller-like PDI derivatives with extra chalcogen linkages between the PDIs and the center core to form all-fused rigid structures. These molecules showed more suitable absorption range than that of their unfused counterparts when blend with donor polymer PTB7-Th. Comparing between the molecules with extra oxygen, sulfur or selenium linkages, the sulfur-based BTT-PDI outperformed the others due to its higher photon absorption and charge transport abilities. This work demonstrated the great potential of PDI derivatives for PSC applications and explored the influences of linkage type on the fused PDI derivatives, which provided a useful tuning knob for molecular design of PDI-based NFAs in the future.

End Group Engineering on the Side Chains of Conjugated Polymers toward Efficient Non-Fullerene Organic Solar Cells

Side chains properties of conjugated polymers, such as the length, branching point, and heteroatom, have been widely studied for application in organic solar cells (OSCs), but the end groups of side chains have been rarely reported. In this work, we systematically explored a series of new conjugated polymers with distinct side-chain end groups for high performance non-fullerene OSCs. The key components for the polymers contained functionalized units as the end groups of side chains, such as Br, alkyloxy (OMe), and alkylthienyl (T) groups. We found that the new conjugated polymers have similar absorption spectra and crystallinity with the polymer without substitution, but they showed distinct photovoltaic performance in solar cells. When the polymer without functionalized units had a power conversion efficiency (PCE) of 9.94%, the modified conjugated polymers provided high PCEs of over 13% with significantly enhanced photocurrent and fill factors. In addition, they also show additive-free and highly stable characteristics. These results demonstrate that end group engineering on side chains is a promising strategy to design new conjugated polymers toward efficient OSCs.

Perylene Diimide Based Organic Photovoltaics with Slot-Die Coated Active Layers from Halogen-Free Solvents in Air at Room Temperature

Herein, we investigate the role of processing solvent additives on the formation of polymer-perylene diimide bulk-heterojunction active layers for organic photovoltaics using both spin-coating and slot-die coating methods. We compare the effect of 1,8-diiodooctane (DIO) and diphenyl ether (DPE) as solvent additives on the aggregation behavior of the non-fullerene acceptor, N-annulated perylene diimide dimer (tPDI₂N-EH), in neat films and blended films with the benzodithiophene-quinoxaline (BDT-QX, QX-3) donor polymer, processed from toluene in air. DIO processing crystallizes the tPDI₂N-EH acceptor and leads to the decreased solar cell performance. DPE processing has a more subtle effect on the bulk-heterojunction morphology and leads to an improved solar cell performance. A comparison of the spin-coating vs slot-die coating methods shows that the effect of DPE is prominent for the slot-die coated active layers. While similar device power conversion efficiencies are achieved with active layers coated with both methods (ca. 7.3% vs 6.5%), the use of DPE improves the film quality when the slot-die coating method is employed.

Benzodithiophene-Fused Perylene Bisimides as Electron Acceptors for Non-Fullerene Organic Solar Cells with High Open-Circuit Voltage

Tandem-junction organic solar cells require solar cells with visible light photo-response as front cells, in which an open-circuit voltage (V_oc ) above 1.0 V is highly demanded. In this work, we are able to develop electron acceptors to fabricate non-fullerene organic solar cells (NFOSCs) with a very high V_oc of 1.14 V. This was realized by designing perylene bisimide (PBI)-based conjugated materials fused with benzodithiophene, in which Cl and S atom were introduced into the molecules in order to lower the frontier energy levels. The fused structures can reduce the aggregation of PBI unit and meanwhile maintain a good charge transport property. The new electron acceptors were applied into NFOSCs by using Cl and S substituted conjugated polymers as electron donor, in which an initial power conversion efficiency of 6.63 % and a high V_oc of 1.14 V could be obtained. The results demonstrate that the molecular design by incorporating Cl and S atom into electron acceptors has great potential to realize high performance NFOSCs.

Additive induced crystallization of a twisted perylene diimide dimer within a polymer matrix

The controlled aggregation of organic π-conjugated molecular semiconductors within a host material (often a polymer) is important for obtaining appropriate organic film morphologies and mechanical properties for optoelectronic applications. In this study, we demonstrate how we have challenged the twisting effect in perylene diimide dimers, which is known to hinder their aggregation. Indeed, a twisted N-annulated perylene diimide dimer (tPDI2N-EH) can be induced to form crystalline aggregates within a host poly-3-hexylthiophene (P3HT) polymer matrix using solution processing. The size of the aggregates can be controlled using varying amounts of the common processing solvent additive 1,8-diiodooctane (DIO) during film formation, by changing the concentration of the molecule within the polymer film, and by adjusting the film drying time. A combination of UV-visible spectroscopy, fluorescence microscopy, cross-polarized light microscopy, and atomic force microscopy were used to characterize the organic films.

A direct comparison of monomeric vs. dimeric and non-annulated vs. N-annulated perylene diimide electron acceptors for organic photovoltaics

A systematic structure–property-function evaluation of four structurally related organic photoactive materials based on the perylene diimide chromophore.