Fluorination Effects on Indacenodithienothiophene Acceptor Packing and Electronic Structure, End-Group Redistribution, and Solar Cell Photovoltaic Response

Aldrich, Thomas J.; Matta, Micaela; Zhu, Weigang; Swick, Steven M.; Stern, Charlotte L.; Schatz, George C.; Facchetti, Antonio; Melkonyan, Ferdinand S.; Marks, Tobin J.

doi:10.1021/jacs.8b13653

Cited by 379 publications

(393 citation statements)

References 109 publications

(223 reference statements)

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“…The blend films processed with additives showed the same trend as those of Y6 pure films. The main absorption peak of GCl‐processed blend film showed a redshift from 812 to 819 nm, and became broader compared with those processed with CN, probably arising from the improved stacking of Y6 molecules . The driving force behind this could be ascribed to the heterogeneous nucleation induced by GCl.…”

Section: Detailed Photovoltaic Parameters Of Devices Employing Pm6:y6mentioning

confidence: 95%

Graphdiyne Derivative as Multifunctional Solid Additive in Binary Organic Solar Cells with 17.3% Efficiency and High Reproductivity

et al. 2020

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Morphology tuning of the blend film in organic solar cells (OSCs) is a key approach to improve device efficiencies. Among various strategies, solid additive is proposed as a simple and new way to enable morphology tuning. However, there exist few solid additives reported to meet such expectations. Herein, chlorine‐functionalized graphdiyne (GCl) is successfully applied as a multifunctional solid additive to fine‐tune the morphology and improve device efficiency as well as reproductivity for the first time. Compared with 15.6% efficiency for control devices, a record high efficiency of 17.3% with the certified one of 17.1% is obtained along with the simultaneous increase of short‐circuit current (Jsc) and fill factor (FF), displaying the state‐of‐the‐art binary organic solar cells at present. The redshift of the film absorption, enhanced crystallinity, prominent phase separation, improved mobility, and decreased charge recombination synergistically account for the increase of Jsc and FF after introducing GCl into the blend film. Moreover, the addition of GCl dramatically reduces batch‐to‐batch variations benefiting mass production owing to the nonvolatile property of GCl. All these results confirm the efficacy of GCl to enhance device performance, demonstrating a promising application of GCl as a multifunctional solid additive in the field of OSCs.

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Section: Detailed Photovoltaic Parameters Of Devices Employing Pm6:y6mentioning

confidence: 95%

Graphdiyne Derivative as Multifunctional Solid Additive in Binary Organic Solar Cells with 17.3% Efficiency and High Reproductivity

et al. 2020

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“…Recently, both MD simulations and single‐crystal diffraction analyses have shown that the ITIC and IT‐4F molecules are inclined to interact with each other by end‐group π−π stacking due to the large steric hindrance of the four alkyl phenyl groups pended on the central unit. [ 55 − 57 ] As the TDM directions of ITIC and IT‐4F are along their long molecular axes, the end‐group π−π stacking can form J‐type or V‐type dimers in the films. For the “C‐like” Y6, the TDM direction is perpendicular to its symmetrical axis, and the favorable J‐type and V‐type dimers can also form through such stacking mode in the film.…”

Section: Figurementioning

confidence: 99%

Reducing the Singlet−Triplet Energy Gap by End‐Group π−π Stacking Toward High‐Efficiency Organic Photovoltaics

2020

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S CT) or triplet ( T CT) character in a 1:3 ratio following the spin statistics. [8] These nearly energetically degenerate S CT and T CT excitons will recombine or separate again into FC. The recombination of S CT to the ground state (S0) can be effectively suppressed because of the high enough S CT energy (E CT ), according to the energygap law ( Figure S1a, Supporting Information). [9−12] Although the recombination from T CT to S0 is spin-forbidden, T CT can relax to the lower-lying triplet state (T1) on the material with lower S1 excitation energy (E S1 , which determines optical gap of the device, E g ) via back electron transfer (BET). [13−18] The singlet−triplet energy gap (ΔE ST = E S1 -E T1 , where E T1 is the T1 excitation energy) is usually very large (≈0.7 eV) in the organic π-conjugated molecules and polymers with strong optical absorption and emission. [19−21] If the CT driving force (ΔE CT = E S1 -E CT ) is small (as required to maximize open-circuit voltage, V OC ), the speed of T1 to thermalize back into T CT will be limited due to the large difference between E CT and E T1 (ΔE BET = E CT -E T1 , Figure S1b, Supporting Information); the decay of T1 to S0 via intersystem crossing (ISC) and tripletcharge annihilation can thus constitute a major terminal loss channel of photocurrent. [13−18] Therefore, in order to reduce both voltage loss and NG recombination, the ΔE ST needs to be minimized ( Figure 1b). [22,23] Here, we have investigated the critical role of end-group π−π stacking in reducing ΔE ST in the state-of-the-art narrowbandgap nonfullerene (NF) acceptors (ITIC, IT-4F, and Y6, [24−26] Figure 2a) by means of (time-dependent) density functional theory (TD)DFT calculations in combination with molecular dynamics (MD) simulations (see Supporting Information for details). Owing to a modest degree of intramolecular push−pull effect, these acceptors show moderate ΔE ST while large oscillator strength ( f, ≈3) in the isolated molecules. Importantly, the ΔE ST is further reduced to 0.3−0.4 eV in the end-group π−π stacking dimers that are frequently present in the films. Such small ΔE ST proves to be able to suppress the T1 decay even in the case of very low ΔE CT of 0.1−0.2 eV. Accordingly, high J SC (>20 mA cm −2 ) and fill factor (FF, 75-80%) as well as low ΔV OC (≈ 0.6 V) have been achieved simultaneously, leading to high power conversion efficiencies (PCEs) of 13-18% in the OPVs based on these acceptors. [25−40] In principle, the ΔE ST value is determined by the electron exchange energy. Normally, the S1 and T1 states are both To improve the power conversion efficiencies for organic solar cells, it is necessary to enhance light absorption and reduce energy loss simultaneously. Both the lowest singlet (S1) and triplet (T1) excited states need to energertically approach the charge-transfer state to reduce the energy loss in exciton dissociation and by triplet recombination. Meanwhile, the S1 energy needs to be decreased to broaden light absorption. Therefore, it is imperative to reduce the...

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“…Despite the success of superior photovoltaic performance in nonfullerene OSCs, it is highly desired that the continued progress and improvement will be acquired in the organic photovoltaic (OPV) field, thereby accelerating the process of commercialization. In a standpoint of molecular design, halogenation is currently the extremely promising new strategy to further enhance device efficiency, which mainly concentrates on the modulation of π electron properties deriving from the strong electronegativity of halogen elements . Among all halogen group elements, fluorination and chlorination are the most extensive and effective material modification approaches and present their respective unique superiorities, including lowering the energy levels, regulating molecular packing, improving the intramolecular charge transfer (ICT) effects, and so forth.…”

Section: Introductionmentioning

confidence: 99%

Multiple Temporal‐Scale Photocarrier Dynamics Induced by Synergistic Effects of Fluorination and Chlorination in Highly Efficient Nonfullerene Organic Solar Cells

et al. 2020

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Fluorination and chlorination have yielded a novel class of materials and achieved tremendous progress in enhancing photovoltaic efficiency in organic solar cells (OSCs). However, their effects on photocarrier dynamics remain elusive in these organic photovoltaic systems. Herein, a comprehensive study on the underlying mechanisms is conducted based on a 2 × 2 photovoltaic matrix, consisting of PBDB‐T, PBDB‐T‐2Cl, ITIC, and IT4F. Chlorination of donors enhances exciton migration and relaxation rates and promotes the extraction of polarons. The more efficient charge transfer and a larger proportion of long‐lived polarons are observed in fluorine‐containing acceptor‐based systems, which are in favor of charge generation in the actual devices. According to the enlarged dielectric constant in the PBDB‐T‐2Cl:IT4F blend, the improved exciton delocalization, the decreased exciton binding energy, and Coulomb capture radius are obtained relative to other three binary systems, which can increase charge separation efficiency and reduce the probability of bimolecular recombination. The simultaneous fluorination and chlorination can optimize molecular packing and nanoscale phase separation, facilitating effective exciton diffusion, exciton dissociation, and charge transport. These results highlight the important role of fluorination and chlorination on these fundamental mechanisms, possibly resulting in some new molecular design principles toward high‐performance OSCs.

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Fluorination Effects on Indacenodithienothiophene Acceptor Packing and Electronic Structure, End-Group Redistribution, and Solar Cell Photovoltaic Response

Cited by 379 publications

References 109 publications

Graphdiyne Derivative as Multifunctional Solid Additive in Binary Organic Solar Cells with 17.3% Efficiency and High Reproductivity

Graphdiyne Derivative as Multifunctional Solid Additive in Binary Organic Solar Cells with 17.3% Efficiency and High Reproductivity

Reducing the Singlet−Triplet Energy Gap by End‐Group π−π Stacking Toward High‐Efficiency Organic Photovoltaics

Multiple Temporal‐Scale Photocarrier Dynamics Induced by Synergistic Effects of Fluorination and Chlorination in Highly Efficient Nonfullerene Organic Solar Cells

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