Crystallography, Packing Mode, and Aggregation State of Chlorinated Isomers for Efficient Organic Solar Cells

Abstract

Open AccessCCS ChemistryRESEARCH ARTICLE25 May 2022Crystallography, Packing Mode, and Aggregation State of Chlorinated Isomers for Efficient Organic Solar Cells Hanjian Lai†, Xue Lai†, Zi-Yi Chen†, Yulin Zhu, Hengtao Wang, Hui Chen, Pu Tan, Yiwu Zhu, Yuanzhu Zhang and Feng He Hanjian Lai† Department of Chemistry, Shenzhen Grubbs Institute, Southern University of Science and Technology, Shenzhen 518055 School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin 150001 †H. Lai, X. Lai, and Z.-Y. Chen contributed equally to this work.Google Scholar More articles by this author , Xue Lai† Department of Chemistry, Shenzhen Grubbs Institute, Southern University of Science and Technology, Shenzhen 518055 School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin 150001 †H. Lai, X. Lai, and Z.-Y. Chen contributed equally to this work.Google Scholar More articles by this author , Zi-Yi Chen† Department of Chemistry, Shenzhen Grubbs Institute, Southern University of Science and Technology, Shenzhen 518055 †H. Lai, X. Lai, and Z.-Y. Chen contributed equally to this work.Google Scholar More articles by this author , Yulin Zhu Department of Chemistry, Shenzhen Grubbs Institute, Southern University of Science and Technology, Shenzhen 518055 Google Scholar More articles by this author , Hengtao Wang Department of Chemistry, Shenzhen Grubbs Institute, Southern University of Science and Technology, Shenzhen 518055 Google Scholar More articles by this author , Hui Chen Department of Chemistry, Shenzhen Grubbs Institute, Southern University of Science and Technology, Shenzhen 518055 Google Scholar More articles by this author , Pu Tan Department of Chemistry, Shenzhen Grubbs Institute, Southern University of Science and Technology, Shenzhen 518055 Google Scholar More articles by this author , Yiwu Zhu Department of Chemistry, Shenzhen Grubbs Institute, Southern University of Science and Technology, Shenzhen 518055 Google Scholar More articles by this author , Yuanzhu Zhang Department of Chemistry, Shenzhen Grubbs Institute, Southern University of Science and Technology, Shenzhen 518055 Google Scholar More articles by this author and Feng He * Corresponding author: E-mail Address: [email protected] Department of Chemistry, Shenzhen Grubbs Institute, Southern University of Science and Technology, Shenzhen 518055 Guangdong Provincial Key Laboratory of Catalysis, Southern University of Science and Technology, Shenzhen 518055 Google Scholar More articles by this author https://doi.org/10.31635/ccschem.022.202201875 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Revealing the molecular packing, intermolecular interactions, and aggregation behaviors in the nanocrystalline bulk heterojunction (BHJ) domains undertake the tasks for future materials design for efficient solar cells, especially in understanding the structure–property relationship of isomeric non-fullerene acceptors (NFAs). Theoretical calculations reveal that 2ClIC-βδ, with β- and δ-chlorine-substituted terminal groups, achieves a relatively higher dipole moment for enhanced intermolecular interactions. More importantly, when comparing the single-crystal X-ray diffraction patterns of three isomeric NFAs, BTIC-BO4Cl-βδ, BTIC-BO4Cl-βγ, and BTIC-BO4Cl, the synergistic effect of chlorine atoms at the β- and δ-positions endows BTIC-BO4Cl-βδ better molecular planarity with a dihedral angle of 1.14°. In turn, this creates the shortest π∙∙∙π distance (3.28 Å) and smallest binding energies (−51.66 kcal mol−1) of the three NFAs, resulting in the tightest three-dimensional network packing structure with a framework of Lx =14.0 Å and Ly =13.6 Å. Such a structure has multiple intermolecular interactions for better charge transfer. However, the chlorine atom at the γ-position in the other two isomers contributes to non-intermolecular interactions with subordinate packing arrangements. Subsequently, the red-shifted UV-absorption and higher electron mobility observed in neat films of BTIC-BO4Cl-βδ agree well with its more ordered crystallinity. This leads to a more suitable fiber-like phase separation in the corresponding active blend, ultimately improving the device performance with superior charge transport. As a result, the highest power conversion efficiency of 17.04% with a current density of 26.07 mA cm−2 was obtained with the BTIC-BO4Cl-βδ-based device. The carrier dynamics test and grazing incidence wide-angle X-ray scattering measurement indicate that the packing arrangement of molecules in the nanocrystalline BHJ domains is consistent with their crystallinity. This work investigates the structure–property differences in three acceptors and emphasizes the effect of isomeric chlorine substitution, which suggests that changes in the crystal packing arrangement, especially the size of the framework, have a considerable influence on charge carrier transport and ultimately are reflected on the device efficiency elevation. Download figure Download PowerPoint Introduction With the emergence of non-fullerene acceptors (NFAs), including the acceptor–donor–acceptor (A–D–A) type represented by 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno-[1,2-b:5,6-b′]-dithiophene (ITIC)1 and the acceptor–donor–acceptor–donor–acceptor (A–DAD–A) type represented by Y6,2 the power conversion efficiency (PCE) of single-junction organic solar cells (OSCs) has surpassed 18%,3–8 and the PCE of tandem devices is approaching 20%.9,10 Compared with fullerene acceptors,11 NFAs can be easily chemically modified: modifications can be made in the size of the backbones, the length of the alkyl chains, and the substitution of the terminal groups. In this way, the molecular energy levels have been regulated, providing better exciton separation.12,13 The absorption spectra of NFAs for harvesting sunlight14,15 and molecular planarity for ordered packing arrangement16,17 have been ameliorated, and the morphology of active layers for superior charge transfer has been optimized.18,19 The design of new NFA materials is a very effective method for development of OSCs.20–22 However, it is necessary to understand the internal mechanisms of these materials, especially the influence of their packing models and aggregation behavior on charge transfer, which will benefit further research.23,24 Many groups have gained an understanding of NFAs at the molecular level through single-crystal X-ray diffraction technology.16,25–30 For example, by comparing the different terminal groups of hydrogen, fluorine, and chlorine substitution in the A–D–A system,17 we found that chlorine substitution would lead to more regular J-aggregation. We also demonstrated the three-dimensional (3D) network packing structure in A–D–A-type acceptors for the first time.16 The 3D network structures have more intermolecular junctions for electron hopping and are much closer to the isotropic electron transport of fullerene acceptors. More 3D network single-crystal structures with much higher efficiency23,25,28–30 have been reported, especially in A–DAD–A type acceptors. For example, Sun et al. analyzed the impact of alkyl chain length on molecular packing arrangements,26,31 and Marks et al. and Yip et al. investigated the electronic structure, packing structure, and delocalization of excitons combined with in-depth theoretical calculations.28,30,32–34 However, it was noted that the 3D network packing structure changed from the rectangular framework in the A–D–A system to a more compact oval framework in the A–DAD–A system. This would be an important reason for the improvement of the electron mobility in the A–DAD–A type acceptors with more electron hopping junctions.25 The key question to improving the electron transport of nanocrystalline bulk heterojunction (BHJ) domains concerns controlling the size of the 3D framework in those acceptors, which will decide the overlap ranges and also the amounts of intermolecular junctions for electron hopping. Isomerization is an effective strategy to precisely modify molecular structures, and thus adjust the intermolecular packing in crystalline systems. A minor change can often lead to large differences in the properties of molecules.35–37 In all-polymer solar cells, for example, an isomeric bromine-containing unit can lead to opposite solubility and device efficiency of the final polymers as a result of a small configurational difference.38,39 Using an isomeric system to explore packing modes and aggregation behaviors should be a facile and practical method, and it is also possible to progressively control the framework structure of NFA acceptors to continuously monitor performance revolution. As an effective modification strategy, chlorine substitution plays an important role in the regulation of molecular planarity, crystallinity, and aggregation states.16,40 BTIC-BO4Cl (BO-4Cl, Figure 1b), chlorine-substituted NFA, has been used widely in high-performance OSCs.41–45 There are two chlorine substituents at the δ- and γ-positions on the terminal group of BTIC-BO4Cl. Through single-crystal structure analysis,41 we found that only the chlorine atom at the δ-position contributes to the intermolecular interactions, and it was proved that the δ-position is more important than the γ-position in the A–DAD–A system.46,47 We estimated that the combination of δ- and γ-substituent may not be ideal, and consequently, structures containing βγ- and βδ-substitution were designed to explore the impact of different substitutions on the molecular packing arrangement and to investigate the internal reasons for the differences in the properties of the isomers. Theoretical calculations indicated that the βδ-substitution terminal group 2ClIC-βδ and the small molecular acceptor BTIC-BO4Cl-βδ (Figure 1c) upon which it is based possess the highest dipole moment. This can facilitate intermolecular packing for better electron hopping.48,49 The single-crystal analysis also showed that the βδ-substitution was the best combination with a tighter packing structure, supporting a more efficient electron transfer. It was found first that BTIC-BO4Cl-βδ achieves better molecular planarity than BTIC-BO4Cl-βγ (Figure 1a) or BTIC-BO4Cl. Second, the shortest π•••π distance and smallest binding energies were found in BTIC-BO4Cl-βδ, where they facilitate intermolecular charge transfer. Subsequently, the most compact 3D network packing structure was achieved by the BTIC-BO4Cl-βδ acceptor, with the minimum framework of Lx = 14.0 Å (major axis) and Ly = 13.6 Å (minor axis), because the δ-Cl contributes to the intermolecular interactions. Lacking the intermolecular interactions of δ-Cl, BTIC-BO4Cl-βγ shows a maximum framework (Lx = 14.7 Å and Ly = 13.9 Å), while BTIC-BO4Cl exhibits an intermediate framework with Lx = 14.4 Å and Ly = 13.8 Å. The tighter aggregation state of BTIC-BO4Cl-βδ would provide more possible channels for electron hopping, which is consistent with the results of theoretical calculations. The electron mobilities of neat films of BTIC-BO4Cl-βγ, BTIC-BO4Cl, and BTIC-BO4Cl-βδ are 1.3 × 10−4, 1.5 × 10−4, and 2.0 × 10−4 cm2 V−1 s−1, respectively, which are consistent with the results of the single-crystal analysis. The morphology results indicate that the BTIC-BO4Cl-βγ-blend films have a slightly larger phase separation size and root mean square (RMS) value, resulting in lower mobilities by an inferior charge-transfer channel. A champion PCE of 17.04% was achieved by OSC devices based on BTIC-BO4Cl-βδ as a result of its comprehensive advantages. A relatively low PCE of 14.90% and a subordinate PCE of 16.36% were realized by OSC devices based on BTIC-BO4Cl-βγ and BTIC-BO4Cl, respectively. The different chlorine substitution patterns on terminal groups also have a great impact on the energy loss of the devices, and the non-radiative energy loss can be reduced from 0.326 eV for BTIC-BO4Cl-βγ to 0.235 eV for BTIC-BO4Cl-βδ. This also proves that BTIC-BO4Cl-βδ maintained a more regular packing arrangement in the devices. In summary, this research program has investigated the internal reasons for the differences in the properties of isomers by three chlorine-substituted acceptors. Combinations of β- and δ-substitution were found to provide an efficient strategy to achieve optimized framework size, which means more intermolecular junctions and an enhanced overlap range between different molecules, eventually resulting in higher mobilities and superior morphologies for high-performance OSC devices. Figure 1 | The chemical structures of (a) BTIC-BO4Cl-βγ, (b) BTIC-BO4Cl, and (c) BTIC-BO4Cl-βδ. The single-crystal structures of (d) BTIC-BO4Cl-βγ, (e) BTIC-BO4Cl, and (f) BTIC-BO4Cl-βδ. The UV-absorption of the three isomers (g) in solution, and (h) in films. (i) The energy levels by CV test. Download figure Download PowerPoint Experimental Methods Detailed methods of materials synthesis, characterization, cyclic voltammetry (CV), atomic force microscopy (AFM), transmission electron microscopy (TEM), UV–vis absorption, grazing incidence wide-angle X-ray scattering (GIWAXS), OSCs device fabrication, and electron-only and hole-only device fabrication are included in the Supporting Information. In addition, the single-crystal X-ray data of BTIC-BO4Cl-βγ (2121534) and BTIC-BO4Cl-βδ (2121533) can be found in the Cambridge Crystallographic Data Centre. Results and Discussion Theoretical calculations Before beginning the experimental study, theoretical calculations were used to assess its feasibility. We used density functional theory (DFT) calculations by the B3LYP/6-31G(d,p) method to investigate the differences between three chlorine-substituted terminal groups: 2ClIC-βγ (Figure 2a), 2ClIC (Figure 2e), and 2ClIC-βδ (Figure 2i). Figures 2b, 2f, and 2j show that the dipole moments (μm) of the three terminal groups are 3.17, 3.19, and 3.37 D, respectively. The higher μm of 2ClIC-βδ would facilitate intermolecular packing for better electron hopping.48 However, while the electron cloud distributions of the three terminal groups are all similar, the calculated energy levels values are different: the lowest unoccupied molecular orbital (LUMO) values (Figures 2c, 2g, and 2k) are −3.49 eV for 2ClIC-βγ, −3.50 eV for 2ClIC, and −3.54 eV for 2ClIC-βδ; and the highest occupied molecular orbital (HOMO) values (Figures 2d, 2h, and 2l) are −7.40 eV for 2ClIC-βγ, −7.47 eV for 2ClIC, and −7.64 eV for 2ClIC-βδ. The deeper energy levels of 2ClIC-βδ indicate its stronger electron-withdrawing ability; the weakest electron-withdrawing ability belongs to 2ClIC-βγ as a result of its high energy levels. When combined with the electron-donor core, the molecule based on 2ClIC-βδ would exhibit the red-shifted absorption due to the enhanced intramolecular charge transfer (ICT) by the D–A effect. The final NFAs, with the same electron-donating cores but different electron-withdrawing terminal groups, were also analyzed by DFT calculations. As shown in Supporting Information Figure S1, the μm of BTIC-BO4Cl-βγ, BTIC-BO4Cl, and BTIC-BO4Cl-βδ are 0.55, 0.66, and 0.78, respectively. Evidently, the increasing dipole moment is consistent with the previous calculations concerning the terminal groups and gives rise to stronger intermolecular interactions and benefits for charge separation in D–A blends.22 The calculated LUMO values of BTIC-BO4Cl-βγ, BTIC-BO4Cl, and BTIC-BO4Cl-βδ are −3.59, −3.64, and −3.63 eV, respectively, and their HOMO values are −5.61, −5.65, and −5.62 eV, respectively. In all three molecules, the HOMO energy levels are concentrated on the electron-donating backbone, whereas the LUMO energy levels are delocalized over the whole molecule and focused only slightly on the terminal group. Figure 2 | Theoretical calculations result in three combinations of chlorine-substituted terminal groups. (a–d) 2ClIC-βγ; (e–h) 2ClIC; and (i–l) 2ClIC-βδ. Download figure Download PowerPoint The theoretical calculations show that BTIC-BO4Cl-βδ may have a molecular packing that is better for charge transfer. To verify the experimental design concept, three chlorine-substituted isomers were synthesized by the Knoevenagel reaction between BT-2CHO and 2ClIC-βγ, 2ClIC, and 2ClIC-βδ. 2ClIC was obtained previously,17 while 2ClIC-βγ and 2ClIC-βδ were obtained from 2,3-dichlorobenzoyl chloride and 2,4-dichlorobenzoyl chloride, respectively (for details, see the Supporting Information Scheme S1). BTIC-BO4Cl-βγ, BTIC-BO4Cl, and BTIC-BO4Cl-βδ can be dissolved in chloroform, chlorobenzene, toluene, or tetrahydrofuran, and thus tolerate the conditions of device solution processing. Single-crystal analysis The aggregation behavior of a molecule has a major influence on its solubility, UV absorption, electrochemical energy level, mobility, and domain size in the blend film,50 and to understand the internal reasons for the different properties of molecules by the single-crystal diffraction technique, it is necessary to study its intermolecular interactions and packing modes. Here, the single crystallographic data from BTIC-BO4Cl were obtained from the Cambridge Crystallographic Data Centre (CCDC, #1965956), while the BTIC-BO4Cl-βγ and BTIC-BO4Cl-βδ were slowly crystallized by a process in which a poor solvent (EtOH) was diffused into a good solvent (CH2Br2) over 1–2 weeks at room temperature. The single-crystal structures of BTIC-BO4Cl-βγ, BTIC-BO4Cl, and BTIC-BO4Cl-βδ are shown in Figures 1d, 1e, and 1f, respectively. The three acceptors have an inverted ‘Y’ shape caused by the intramolecular non-covalent bond interactions between electron-donating cores and the electron-withdrawing terminal groups with S•••O interlock distances of 2.67, 2.65, and 2.57 Å, respectively. Significantly, the 2.57 Å S•••O interlock distance of BTIC-BO4Cl-βδ is among the shortest of reported NFA single-crystal structures. The smallest dihedral angle of 1.14° was achieved in BTIC-BO4Cl-βδ, indicating the best molecular planarity when compared with that of BTIC-BO4Cl-βγ and BTIC-BO4Cl. This would benefit molecular packing. The molecular packing modes of BTIC-BO4Cl-βγ (Figure 3a–3c), BTIC-BO4Cl (Figure 3d–3f), and BTIC-BO4Cl-βδ (Figure 3g–3i) are analyzed. There are three packing modes in the single-crystal structure of the three isomers: the TT-1 dimer (intermolecular interaction between terminal groups with the same molecular orientation), the TT-2 dimer (intermolecular interaction between terminal groups with the opposite molecular orientation), and the CT dimer (intermolecular interaction between core and terminal group). For BTIC-BO4Cl-βγ, BTIC-BO4Cl, and BTIC-BO4Cl-βδ, the π•••π distances are 3.33, 3.32, and 3.32 Å, respectively, for the TT-1 dimers; 3.35, 3.39, and 3.28 Å, respectively, for the TT-2 dimers; and 3.38, 3.35, and 3.35 Å, respectively, for the CT dimers. BTIC-BO4Cl-βδ possesses the shortest π•••π distances while BTIC-BO4Cl-βγ and BTIC-BO4Cl are similar to one another. To further illustrate the intermolecular packing strength, the molecular binding energies under different packing states were calculated from the single-crystal data by the B3LYP/6-31G(d,p) method, and the results are shown in Supporting Information Figure S2. BTIC-BO4Cl-βδ achieves the smallest binding energies of −51.66, −23.75, and −50.73 kCal/mol for the TT-1, TT-2, and CT dimer, respectively. Inferior binding energies of −41.05, −43.12, and −51.42 kCal/mol were found in BTIC-BO4Cl, and the largest binding energies of −13.84, −26.98, and −36.20 kCal/mol were observed in BTIC-BO4Cl-βγ. The superior molecular planarity of BTIC-BO4Cl-βδ leads to the shortest π•••π distance and the smallest binding energies. This will facilitate intermolecular charge transfer and is consistent with the results from previous theoretical calculations (Figure 2 and Supporting Information Figure S1). Figure 3 | The different packing modes by single-crystal data analysis and the corresponding binding energies for (a–c) BTIC-BO4Cl-βγ, (d–f) BTIC-BO4Cl, and (g–i) BTIC-BO4Cl-βδ. Download figure Download PowerPoint The aggregation states of BTIC-BO4Cl-βγ, BTIC-BO4Cl, and BTIC-BO4Cl-βδ are analyzed in Figures 4a and 4b and Supporting Information Figures S3–S5; Figures 4c and 4d and Supporting Information Figures S6–S8; and Figures 4e and 4f and Supporting Information Figures S9–S11, respectively. All three acceptors show similar frame structures surrounded by four molecules. The 3D network packing structure is formed by non-covalent bonding between those frameworks, while there are some differences in the intermolecular interactions. There are only intermolecular π•••π and intramolecular Cl•••O interactions in one framework. The chlorine atom at the γ-position does not play a connecting role in BTIC-BO4Cl-βγ, and the connection between frameworks is only from π•••π stack interactions (CT dimer state). Focusing on the BTIC-BO4Cl, the chlorine atom at the δ-position leads to Cl•••S (3.56 Å) and Cl•••N (3.57 Å) intermolecular interactions, and other intermolecular interactions of S•••N (3.67 Å) and N•••O (3.63 Å) were also found in one framework. The connection between frameworks involves Cl•••S, Cl•••N, and π•••π stack interactions (the CT and TT dimer states), which is quite different from BTIC-BO4Cl-βγ. There is also no intermolecular interaction involving the chlorine atom at the γ-position. Finally, there are multiple non-covalent interactions in BTIC-BO4Cl-βδ, such as intramolecular Cl•••O (3.07 Å); intermolecular Cl•••O (3.48 Å), Cl•••N (3.60 and 3.55 Å), Cl•••S (3.57 Å); and two interlocking S•••N (3.70 Å) interactions. The connection between frameworks is due to Cl•••S, Cl•••N, and π•••π stack interactions (the CT dimer state), and is similar to BTIC-BO4Cl. As a result, BTIC-BO4Cl-βγ shows a 3D network packing structure with the maximum framework with Lx = 14.7 Å (major axis) and Ly = 13.9 Å (minor axis) due to its minimal intermolecular interactions, while BTIC-BO4Cl exhibits an intermediate framework in which Lx = 14.4 Å and Ly = 13.8 Å. As a result of the multiple intermolecular interactions, the most compact 3D network packing structure was achieved by BTIC-BO4Cl-βδ with the minimum framework of 14.0 Å (Lx) and 13.6 Å (Ly). The tighter aggregation state of BTIC-BO4Cl-βδ provides more possible channels for electron hopping. Therefore, we found that the position of the chlorine substituents on terminal groups will alter the size of the 3D framework, which determines the overlap ranges and the number of intermolecular junctions for charge transfer. Figure 4 | The intermolecular interactions and aggregation behaviors calculated by single-crystal analysis for (a and b) BTIC-BO4Cl-βγ, (c and d) BTIC-BO4Cl, and (e and f) BTIC-BO4Cl-βδ. Download figure Download PowerPoint Based on the results of this single-crystal data analysis, we conclude that the synergistic effect of a chlorine atom at the δ- and β-positions gives BTIC-BO4Cl-βδ better molecular planarity and leads to the shortest π•••π distance and smallest binding energies. The result is the tightest 3D network packing structure with multiple intermolecular interactions and better charge transfer. No intermolecular interaction was found to be attributable to the chlorine atom at the γ-position. These results indicate that the influence on the molecular planarity, packing, and aggregation states of the different substitution positions of chlorine atoms at terminal group cannot be ignored. Physicochemical properties To confirm the results of the single-crystal analysis, the electron mobilities of neat BTIC-BO4Cl-βγ, BTIC-BO4Cl, and BTIC-BO4Cl-βδ were determined by a space charge limited current method with a device structure of indium tin oxide (ITO)/ZnO/isomeric acceptors/PNDIT-F3N/Ag. The electron mobilities of neat films formed by BTIC-BO4Cl-βγ, BTIC-BO4Cl, and BTIC-BO4Cl-βδ are 1.3 × 10−4, 1.5 × 10−4, and 2.0 × 10−4 cm2 V−1 s−1, respectively ( Supporting Information Figure S12). The higher mobility of BTIC-BO4Cl-βδ neat film stems from its more regular packing arrangement and compact aggregation state. The UV–vis absorption in CHCl3 solution and neat films are shown in Figures 1g and 1h. The maximum absorption peaks of BTIC-BO4Cl-βγ, BTIC-BO4Cl, and BTIC-BO4Cl-βδ in solution are 743, 745, and 751 nm, and that in the film are 827, 834, and 842 nm, respectively. The red-shifted absorption in the solution of BTIC-BO4Cl-βδ corresponds to the enhanced ICT effect by the stronger electron-withdrawing ability of the terminal group, 2ClIC-βδ (discussed above). In addition, there are 84, 89, and 91 nm redshifts in absorption when shifting from solution to films for BTIC-BO4Cl-βγ, BTIC-BO4Cl, and BTIC-BO4Cl-βδ, respectively. This shows that the strongest aggregation is in the βδ-substitution system, which is consistent with the single-crystal data. The red-shifted absorption of BTIC-BO4Cl-βδ would be favorable to light harvest, leading to enhanced currents in final OSC devices. Electrochemical tests indicate that the LUMO/HOMO energy levels of BTIC-BO4Cl-βγ, BTIC-BO4Cl, and BTIC-BO4Cl-βδ are −3.97/−5.51, −3.99/−5.49, and −3.97/−5.46 eV, respectively (Figure 1i); the corresponding curves are shown in Supporting Information Figure S13. The respective electrochemical bandgaps of three acceptors were calculated as 1.54, 1.50, 1.49 eV, in which the narrowest electrochemical bandgap of BTIC-BO4Cl-βδ corresponds to its red-shifted absorption spectrum. Performance of OSC devices The final OSC devices were fabricated according to the aforementioned factors with BTIC-BO4Cl-βγ, BTIC-BO4Cl, and BTIC-BO4Cl-βδ to assess their use. OSC devices based on these three isomeric acceptors were prepared; the was as the ( Supporting Information Figure The test results efficiency and efficiency are shown in Figures respectively, and the corresponding values are in The highest PCE of 17.04% was achieved by BTIC-BO4Cl-βδ based OSC devices, while the lowest PCE and a subordinate PCE were realized in and OSC devices, respectively. All show similar of The of the different is the current which changes from mA cm−2 for BTIC-BO4Cl-βγ to mA cm−2 for BTIC-BO4Cl and 26.07 mA cm−2 for BTIC-BO4Cl-βδ-based The differences in the packing modes and aggregation states are caused by the molecular crystallinity, which the carrier mobilities as shown in Supporting Information Figure These the and electron mobilities of devices based on the three isomers. The electron mobilities of and BTIC-BO4Cl-βδ-based devices are × 10−4, × 10−4, and × 10−4 cm2 V−1 s−1, and their mobilities are × 10−4, × 10−4, and × 10−4 cm2 V−1 s−1, respectively. The highest carrier mobilities of the BTIC-BO4Cl-βδ-based device benefit from its better molecular packing and tighter aggregation as shown by the aforementioned single-crystal resulting in a higher reason stems from the different absorption the absorption of BTIC-BO4Cl-βγ leads to its current from to nm, while BTIC-BO4Cl and BTIC-BO4Cl-βδ based devices the curves from to nm, leading to the higher The between and light of and BTIC-BO4Cl-βδ-based devices were determined to explore the charge mechanisms by the (Figure in which better charge transfer can be realized when (the is to The values are calculated to be and for OSC devices based on BTIC-BO4Cl-βγ, BTIC-BO4Cl, and BTIC-BO4Cl-βδ, respectively. The of of and BTIC-BO4Cl-βδ-based devices were also the results are shown in Supporting Information Figure The values of the three devices are and respectively.

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