Near-Infrared All-Fused-Ring Nonfullerene Acceptors Achieving an Optimal Efficiency-Cost-Stability Balance in Organic Solar Cells
Wenrui Liu, Shengjie Xu, Hanjian Lai, Wuyue Liu, Feng He, Xiaozhang Zhu
Abstract
Open AccessCCS ChemistryRESEARCH ARTICLE28 Apr 2022Near-Infrared All-Fused-Ring Nonfullerene Acceptors Achieving an Optimal Efficiency-Cost-Stability Balance in Organic Solar Cells Wenrui Liu†, Shengjie Xu†, Hanjian Lai†, Wuyue Liu, Feng He and Xiaozhang Zhu Wenrui Liu† Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 School of Chemical Sciences, University of Chinese Academy of Sciences, Beijing 100049 , Shengjie Xu† Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 , Hanjian Lai† Department of Chemistry, Shenzhen Grubbs Institute, Southern University of Science and Technology, Shenzhen 518055 , Wuyue Liu Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 School of Chemical Sciences, University of Chinese Academy of Sciences, Beijing 100049 , Feng He Department of Chemistry, Shenzhen Grubbs Institute, Southern University of Science and Technology, Shenzhen 518055 and Xiaozhang Zhu *Corresponding author: E-mail Address: [email protected] Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 School of Chemical Sciences, University of Chinese Academy of Sciences, Beijing 100049 https://doi.org/10.31635/ccschem.022.202201963 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Synergistically achieving stability, cost, and efficiency is crucial for the commercialization of organic solar cells (OSCs). Despite the rapid development of 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile-type nonfullerene acceptors (NFAs), they are inherently unstable due to the vulnerable exocyclic double bond and possess high synthesis complexity (SC). Based on the "all-fused-ring electron acceptor (AFAR)" concept, we report two new near-infrared NFAs, F11 and F13, featuring all fused dodecacyclic rings. By developing a whole set of synthetic procedures, F11 and F13 can be conveniently prepared at a 10 g scale within a notably short period, displaying both the low SC and the lowest costs among reported NFAs, even comparable to the classical photovoltaic material, P3HT. In comparison with the one-dimensional stacking of ITYM (ITYM = 2,2′-(7,7,15,15-tetrahexyl-7,15-dihydro-s-indaceno[1,2-b:5,6-b′]diindeno[1,2-d]thiophene-2,10(2H)-diylidene)dimalononitrile), the first AFRA, and mixed J- and H-aggregations in Y6, F-acceptors show a compact honeycomb-type three-dimensional stacking with exclusive J-aggregations, favoring multichannel charge transport. By matching a medium-bandgap polymer donor, F13 delivers greater than 13% power conversion efficiencies, which is the highest performance among non-INCN acceptors, and shows device stability superior to the typical ITIC- and Y6-based OSCs as evidenced by the negligible burn-in losses. This work presents a first and successful example of NFAs achieving an optimal efficiency-cost-stability balance in OSCs. Download figure Download PowerPoint Introduction Organic solar cells (OSCs) are considered a promising device for sustainable energy because of their great potential for low cost, light weight, and large-area processability.1–5 The last few years have witnessed a great breakthrough in the power conversion efficiency (PCE) of OSCs benefiting from the innovation of materials, especially the development of nonfullerene acceptors (NFAs).6–21 Stability and cost, which are another two key issues for the commercialization of OSCs, are being paid increasing attention.14,22–25 In comparison with a fullerene-based counterpart, the NFA-based device exhibiting the optimal efficiency-cost-stability balance is a competitive choice for practical applications,14 which is critical but challenging and yet to be achieved. Acceptor–donor–acceptor (A–D–A)-type NFAs consisting of multiple conjugated heteroaromatic rings as donors (Ds) and 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile (INCN) as the acceptor (A) are inherently unstable because of the vulnerable exocyclic double bond, which is the main factor limiting the device lifetime of high-performance nonfullerene OSCs,26 as proved by less degradation within polymer donors.27,28 Jiang et al.27 reported the photodegradation of the high-performance NFAs (IT-4F, ITIC, and IEICO-4F) assisted by the photocatalytic properties of ZnO, leading to disruption of the C=C linkage between the D and A. Park and Son29 confirmed that ITIC reacted with hydroxyl radicals, while the ITIC radical product acted as an electrophile and thus attacked the enone group of another ITIC molecule, resulting in the cleavage of the double bond. In addition to extrinsic influence, NFAs can react with an amine-containing interfacial layer.30,31 Quite recently, it has been reported that INCN-type NFAs produced fused-ring isomers involving intramolecular six-electron electrocyclizations in the photodegradation.32 To address the stability issue, molecular engineering, considered the essential solution, was presented. Liu et al.33 identified that structural confinement by installing an outward-chain in the A–D–A NFAs suppressed the photoisomerization of vinyl groups; however, the vulnerable exocyclic double bond still exists. Moreover, replacing INCN with rhodanine can boost stability to a great extent; for example,34,35 Gasparini et al.34 presented that OSCs based on rhodanine-benzothiadiazole-coupled indacenodithiophene are free of burn-in, the commonly observed rapid performance loss. Later, Liu et al.36 presented a molecular design strategy by introducing ring-locked carbon–carbon double bonds into acceptors to enhance chemical and photochemical stability. However, these OSCs sacrificed efficiency for stability. Materials suitable for OSC commercialization must be inexpensive and available in large volumes, such as classic donor poly(3-hexylthiophene) (P3HT),14 the only organic photovoltaic material that is commercially available at a 10 kg scale. Most innovations to achieve high efficiency of NFAs also increase the synthesis complexity (SC) and cost, resulting in the preparation of NFAs only at the milligram scale and typically taking more than a week. Designing new NFAs with low cost or low SC has drawn great attention. Li et al.37 reported two low-cost acceptors MO-IDIC and MO-IDIC-2F that were synthesized by simplifying the synthetic route towards the central core. NFAs with partially or fully unfused backbones have recently been explored due to their simple molecular structures.38–41 For example, Lu et al.39 developed a few non-fused-ring electron acceptors synthesized from single aromatic units. However, large-scale preparation of NFAs that meets both low cost and low SC has not been realized. Recently, our group proposed the "all-fused-ring electron acceptor (AFAR)" concept and reported an AFRA (ITYM) (ITYM = 2,2′-(7,7,15,15-tetrahexyl-7,15-dihydro-s-indaceno[1,2-b:5,6-b′]diindeno[1,2-d]thiophene-2,10(2H)-diylidene)dimalononitrile)42–44 displaying intrinsically better chemical, photochemical, and thermal stability than those based on INCN-type terminals, and a promising PCE close to 10%. Here, we report the design of two new AFRAs named F11 and F13 by introducing a benzothiadiazole-based core (Figure 1)45 to achieve near-infrared responsiveness for promoting PCE. To tackle the issue of the large-scale preparation for NFAs, we developed an entire preparation route that enables the scalable preparation of F11 and F13 at a 10 g scale in the lab within a notably short period, demonstrating the lowest cost among reported NFAs (even comparable to that of P3HT) as well as smaller SC values than those of other low-cost NFAs.37,38 The higher highest occupied molecular orbital (HOMO), the lower optical gap with the main absorption located in the near-infrared region, and compact 3D honeycomb-type stacking with exclusively favorable J-aggregation allowed the PCEs of F13 to exceed 13%. Inspiringly, this is the efficiency record among non-INCN acceptors including fullerene-,46–48 perylene diimide (PDI)-,49–51 and rhodanine-type52–55 acceptors that also play a critical role in the development of OSCs. Compared with ITYM, F11 and F13 exhibit compact stacking and excellent photochemical stability in thin films, which contributes to the superior device stability as evidenced by miniscule burn-in losses. Figure 1 | Design of dodecacyclic AFRAs, F11 and F13. Download figure Download PowerPoint Experimental Methods 4,7-Dibromo-5,6-dinitrobenzo[c][1,2,5]thiadiazole (yield: 74%) and tributyl(thieno[3,2-b]thiophen-2-yl)stannane were synthesized by reported methods.41 Unless stated otherwise, starting materials were obtained from Anhui Zesheng Technology Co., Ltd., Shanghai Sinopharm Chemical Reagent Co., Ltd., Beijing J&K Scientific Ltd., and so on and were used without further purification. Anhydrous tetrahydrofuran (THF) and toluene were distilled over Na/benzophenone prior to use. Anhydrous dimethylformamide (DMF) was purchased from Energy Chemical. Synthesis of compound 1 4,7-Dibromo-5,6-dinitrobenzo[c][1,2,5]thiadiazole (10.2 g, 26.6 mmol) and tributyl(thieno[3,2-b]thiophen-2-yl)stannane (56.5 mmol) were dissolved in toluene (60 mL) in nitrogen atmosphere. Then tris(dibenzylideneacetone)dipalladium (469 mg, 0.5 mmol) and tris(2-methylphenyl)phosphine (622 mg, 2.0 mmol) were added to the above mixture. The reaction solution was heated at 90 °C for 15 min, and then toluene was removed under reduced pressure. The residue was filtered by methane and washed with dichloromethane to obtain 10.7 g black crude product. Synthesis of compound 2 Compound 1 (10.7 g, 21.3 mmol) and triphenylphosphine (44.5 g, 170 mmol) were dissolved in 1,2-dichlorobenzene (70 mL). The reaction mixture was purged with nitrogen for 2 min and then was heated at 180 °C for 2 h. Then reddish-brown powder (6.7 g) was obtained by immediate thermal filtration and washing with dichloromethane. Synthesis of compound 3 The crude product 2 (6.7 g, 15.3 mmol), potassium carbonate (31.2 g, 226.1 mmol), potassium iodide (125 mg, 0.75 mmol) and 1-bromo-2-hexyldecane (14 g, 45.9 mmol) in DMF (50 mL) solvent was heated to 140 °C for 2 h. The reaction solution was extracted with ethyl acetate. The organic layer was washed with water and brine and was dried over MgSO4. The solvent and excess 1-bromo-2-hexyldecane was removed by distillation under reduced pressure. The resulting mixture in dichloromethane was filtered through a diatomite layer to provide almost pure orange liquid (12.4 g). 1H NMR (400 MHz, CDCl3): δ 7.42 (m, 4H), 4.63 (d, 3J = 7.6 Hz, 4H), 2.06 (m, 2H), 1.18–0.68 (m, 60H); 13C NMR (100 MHz, CDCl3): δ 147.7, 141.7, 136.7, 131.9, 124.7, 124.3, 123.7, 121.4, 111.6, 54.9, 38.7, 31.8, 31.6, 30.4, 29.7, 29.4, 29.1, 25.5, 25.5, 22.6, 22.5, 14.1, 14.0. Synthesis of compound 4a 2-Bromobenzoyl chloride (7.74 g, 35.2 mmol) and aluminum chloride (9.3 g, 70.5 mmol) were dissolved in dichloromethane (70 mL). Then compound 3 (12.4 g, 14.0 mmol) in dichloromethane was added dropwise to the above solution over 10 min. Immediately, the solution was quenched with ice water. The organic layer was washed with water and brine, and was dried over MgSO4. The organic layer was filtered through a diatomite layer and then the product was solidified by filtration with methanol (16.6 g, 50% over four steps). 1H NMR (400 MHz, CDCl3): δ 7.72 (d, 3J = 8.0 Hz, 2H), 7.68 (s, 2H), 7.53 (dd, 3J = 7.2 Hz, 4J = 2.0 Hz, 2H), 7.48 (t, 3J = 7.2 Hz, 2H), 7.41 (t, 3J = 7.6 Hz, 2H), 4.67 (d, 3J = 8.0 Hz, 4H), 2.07 (m, 2H), 1.18–0.68 (m, 60H); 13C NMR (100 MHz, CDCl3): δ 187.8, 147.5, 142.6, 141.6, 140.2, 136.8, 133.6, 133.1, 131.5, 131.5, 130.5, 128.9, 128.4, 127.3, 119.7, 112.6, 55.3, 38.9, 31.7, 31.5, 30.4, 29.7, 29.3, 29.3, 29.12, 25.5, 25.4, 22.6, 22.5, 14.1, 13.9. Synthesis of compound 4b The synthetic route of 4b was similar to that of compound 4a (51% for four steps). 1H NMR (400 MHz, CDCl3): δ 7.69 (s, 2H), 7.55 (dd, 3J = 8.4 Hz, 4J = 5.6 Hz, 2H), 7.48 (dd, 3J = 8.4 Hz, 4J = 2.4 Hz, 2H), 7.20 (td, 3J = 8.0 Hz, 4J = 2.4 Hz, 2H), 4.67 (d, 3J = 8.0 Hz, 4H), 2.06 (m, 2H), 1.18–0.68 (m, 60H); 13C NMR (100 MHz, CDCl3): δ 186.8, 164.5, 161.9, 147.5, 142.4, 141.7, 136.7, 136.4, 136.4, 133.1, 131.6, 130.5, 130.5, 130.4, 128.6, 121.2, 121.0, 120.8, 120.7, 114.8, 114.6, 112.6, 55.3, 39.0, 31.7, 31.5, 30.4, 29.7, 29.3, 29.3, 29.1, 25.5, 25.4, 22.6, 22.5, 14.1, 14.0. Synthesis of compound F11 To a solution of compound 4a (16.6 g, 13.2 mmol) in N,N-dimethylacetamide (50 mL) was added palladium(II) acetate (286 mg, 1.3 mmol), tricyclohexylphosphonium tetrafluoroborate (938 mg, 2.5 mmol), and potassium carbonate (5 g, 36.2 mmol) in nitrogen atmosphere and then was heated at 180 °C for 15 min. Then the mixture was poured into water and filtered, and the solid was washed with water and methanol and was directly used for the next step. Pyridine (4 mL) and titanium tetrachloride (6 mL) were added to a mixture of crude product and malononitrile (3.9 g, 59.4 mmol) in chlorobenzene (50 mL). Within 5 min, the solution was extracted with dichloromethane (80 mL) and water. The solvent was removed under reduced pressure. The residue in dichloromethane solvent went through a fast filtration with diatomite and then was purified with recrystallization (petroleum ether/dichloromethane, 4:1 v/v) to give the target molecule (10.4 g, 66%). 1H NMR (400 MHz, CDCl3): δ 8.19 (d, 3J = 7.6 Hz,, 2H), 7.46 (t, 3J = 7.6 Hz, 2H), 7.38 (d, 3J = 7.2 Hz, 2H), 7.31 (t, 3J = 7.6 Hz, 2H), 4.65 (d, 3J = 7.6 Hz, 4H), 2.09 (m, 2H), 1.18–0.68 (m, 60H); 13C NMR (100 MHz, CDCl3): δ 157.1, 147.3, 147.2, 138.3, 137.3, 136.5, 136.4, 134.6, 134.2, 133.6, 133.2, 129.6, 128.9, 126.3, 121.2, 114.2, 113.4, 113.3, 70.9, 55.7, 39.1, 31.8, 31.5, 30.6, 30.5, 30.4, 29.7, 29.4, 29.2, 25.7, 25.6, 25.5, 25.5, 22.6, 22.5, 14.0, 13.9; high-resolution mass spectrometry (HRMS) [matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF)] (m/z): [M]+ calcd for C70H74N8S5, 1186.4634; found, 1186.4627. Anal. Calcd for C70H74N8S5 (%): C, 70.79; H, 6.28; N, 9.43. Found: C,70.48; H, 6.24; N, 9.19. Synthesis of compound F13 The synthetic processes was similar to that of F11 (61%). 1H NMR (400 MHz, CDCl3): δ 8.19 (dd, 3J = 8.4 Hz, 4J = 4.4 Hz, 2H), 7.13 (dd, 3J = 7.6 Hz, 4J = 2.4 Hz, 2H), 6.97 (td, 3J = 8.4 Hz, 4J = 2.4 Hz, 2H), 4.66 (d, 3J = 8.0 Hz, 4H), 2.07 (m, 2H), 1.18–0.68 (m, 60H); 13C NMR (100 MHz, CDCl3): δ 167.2, 164.6, 156.0, 147.3, 145.1, 139.2, 139.1, 137.2, 136.4, 135.7, 134.2, 133.9, 133.8, 133.6, 129.5, 128.0, 127.9, 114.5, 114.3, 114.0, 113.4, 113.1, 110.3, 110.1, 71.3, 55.8, 39.2, 31.8, 31.5, 30.6, 30.6, 30.5, 30.4, 29.7, 29.3, 29.3, 29.2, 25.7, 25.6, 25.5, 25.5, 22.6, 22.5, 14.0, 13.9; HRMS (MALDI-TOF) (m/z): [M]+ calcd for C70H72F2N8S5, 1222.4446; found, 1222.4445. Anal. Calcd for C70H72F2N8S5 (%): C, 68.71; H, 5.93; N, 9.16. Found: C, 68.70; H, 5.91; N, 8.86. F13 shows a good solubility in various commonly used solvents such as chloroform (38 mg/mL), THF (25 mg/mL), toluene (20 mg/mL), chlorobenzene (20 mg/mL), and dichlorobenzene (30 mg/mL). Results and Discussion Large-scale preparation and single-crystal X-ray analysis of AFARs F11 and F13 Because large-scale preparation requires optimization of each synthetic procedure, not just a certain step, we optimized the synthetic route for F11/F13 and the detailed processes are shown in Figure 2. In the first step, we selected an efficient catalytic system of tris(benzylideneacetone)dipalladium and tris(2-methylphenyl)phosphine for the Stille-type cross-coupling reaction, in which the starting materials of 4,7-dibromo-5,6-dinitrobenzo[c][1,2,5]thiadiazole and tributyl(thieno[3,2-b]thiophen-2-yl)stannane are accessible commercially or can be prepared in the lab on a large scale. We took advantage of the solubility difference between the reactants and the product to obtain compound 1 by direct filtration. In comparison with the corresponding synthesis of Y6, the reaction time was drastically reduced from 12 h to 15 min. In the second step of nitrocyclization, we optimized the reaction by replacing triethyl phosphate with the readily available triphenylphosphine. The o-dichlorobenzene solution of compound 1 and triphenylphosphine was heated at 180 °C for 2 h. High temperature affects the product purification equivalent to recrystallization, and the reddish-brown powder of 2 was directly obtained by immediate filtration. In the third step of alkylation, the extracted organic layer was passed through thin-layer diatomite to remove a small amount of excess potassium carbonate. Because this reaction is clean and shows no by-products, the resulting product 3 was directly used for the next step without further purification. For the fourth step of Friedel–Crafts acylation, a dichloromethane solution of compound 3 was added dropwise to that of aluminum trichloride and 2-bromobenzoyl chloride. Immediately, a crude product of 4a was solidified by filtering and washed with methanol due to a high reaction yield and purity, thereby ensuring that further purification was not necessary. A total yield of 50% for the presented four steps was achieved. The fifth step involves successive intramolecular cyclization and Knoevenagel condensation. We selected Pd-catalyzed C–H activation for intramolecular cyclization in consideration of its great potential for a green, sustainable, and atom-efficient synthesis at large scale.56 After reacting for 15 min, the crude product was directly used for the next condensation without any purification as a result of the efficient nature of C–H-activated cyclization. A different reaction than the condensation occurred in INCN-type NFAs, and this condensation was completed in an extremely short time (<5 min) at room temperature. Finally, the target molecule F11 was purified by recrystallization in dichloromethane/petroleum ether after passing through diatomite. It is noteworthy that the whole synthetic process eliminates the need for column chromatography, which is perfectly manageable at the laboratory scale yet very expensive or even impossible at the industrial scale.57 Finally, all these synthetic advantages throughout the whole procedure helped achieve the goal of the large-scale preparation of acceptors, in which over 10 g of F11 was obtained in the lab. A total yield of 33% was produced despite a certain waste of products caused by recrystallization, equivalent to >80% yield for each step. Moreover, the synthetic process takes an extremely short time for the rapid preparation of NFAs at a large scale, while most NFAs take more than one week.7 The synthetic process of F13 was similar to that of F11, and F11 and F13 were fully characterized by using 1H NMR, 13C NMR, matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and elemental analysis, as shown in Supporting Information Figures S21–S30. We believe that such a facile and efficient synthetic process can also be transferred to kg-scale industrial production. Figure 2 | Depiction of quick and macroscopic preparation of the all-fused-ring acceptors, F11 and F13. Reagents and conditions: (a) Pd2(dba)3, P(o-tol)3, tributyl(thieno[3,2-b]thiophen-2-yl)stannane, toluene; (b) PPh3, o-dichlorobenzene (c) HD-Br, K2CO3, N,N-dimethylformamide, HD = 2-hexyldecanyl; (d) AlCl3, o-bromoaryl chloride, dichloromethane; (e) K2CO3, Download figure Download PowerPoint We the single-crystal of F11 by X-ray The of F11, without for are shown in Figure displaying the dodecacyclic In to the reported acceptors, the of all-fused-ring F11 presents a and Figure the two of between the of with the stacking of and In are and and a a with molecular in the is by the J-aggregation and as shown in Figure In comparison with the one-dimensional stacking of ITYM, the 3D of F11 shown in Figure which a is for charge in multiple Figure 3 | (a) The of F11, without for (b) The between F11 (c) The single-crystal of one from different (d) The 3D of Download figure Download PowerPoint analysis We the costs of F11 and F13 based on macroscopic only the cost of and solvents used in the whole synthetic procedure, we the total costs of F11 and F13 to and the are in Supporting Information Compared with the reported for other organic photovoltaic F11 and F13 have low with a of for F11 and for F13, which are lower than other NFAs and are almost at the as as in Figure 4a and Supporting Information It be that these cost values be further reduced on an industrial mass The extremely low costs of our acceptors are because of the of the purification especially the of column to the the costs of purification with column in most NFAs for over even to 50% of the total as a result of large of and In the design and of o-bromoaryl chloride as is also an for the cost the material such as Supporting Information o-bromoaryl chloride costs 3 based on a which is with INCN It be that costs that are by the for a large of the total cost in industrial production. The scalable preparation of F11 and F13 was within extremely short thus In we the synthetic complexity (SC) of our F-acceptors with Y6, ITIC, and detailed is shown in Supporting Information Figures and and F11 and F13 show notably lower SC values for F11 and for than that of and even lower SC values than other low-cost NFAs, which is with the low costs of Figure | (a) of material costs for the different photovoltaic materials costs are from the for our (b) of high PCEs for typical non-INCN photovoltaic acceptors Supporting Information Download figure Download PowerPoint and molecular stacking properties Figure shows the of F11, F13, and ITYM in The absorption of F11 and F13 are which are by in comparison to that of The optical are both for F11 and F13 with the main absorption located in the near-infrared region, which is smaller than for The orbital energy of F11 and F13 were by Supporting Information Figure and Figure In comparison with ITYM, the of F11 and F13 are and and the lowest molecular orbital energy are and for F11 and F13, We the energy of F13 than F11, especially the to the of the Figure 5 | (a) absorption (b) Energy of ITYM, F11, and F13. (c) and (d) the and of Download figure Download PowerPoint The molecular stacking of F11, F13, ITYM, and in were by X-ray and of are shown in Supporting Information Figure Figure shows and Figure shows of the and of different It is that ITYM in shows a molecular stacking and the of F11 and F13 exhibit a favorable with in the at and F13 a = from the and the smaller = for than those of F11 = and = a higher of the F13 which be by the photochemical, and thermal stability work that and double bonds the stability of the the chemical and photochemical stability of F11 and F13 were and two typical acceptors based on the ITIC and Y6, were for Chemical stability were by the absorption of four acceptors and after with in the corresponding THF are shown in Supporting Information Figure Figure the absorption of acceptors at the corresponding after the addition of (100 a Supporting Information Figure and of absorption occurred in and ITIC no of the absorption of F11 and F13 was found, even 12 h after However, of and for and ITIC, were the absorption at to a different which can be to of the Figure | The absorption of acceptors at the corresponding the (a) in v/v) of NFAs is at while that of is and (b) in Download figure Download PowerPoint of materials under an role in OSCs. we the photochemical stability of the four acceptors F13, ITIC, and for and Supporting Information Figure the of absorption in THF and in with After for 10 min under at the absorption of ITIC solution in the the was The absorption of at in the while over for F11 and F13. all higher in than in as a result of molecular in the and of water and To the of we a of in In the