Alcohol-Soluble Conjugated Polymers with

Mar 6, 2018 - Naphthalene diimide (NDI) and perylene diimide (PDI) based polymeric semiconductors with high mobility have shown great promise as ...
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Article Cite This: Macromolecules XXXX, XXX, XXX−XXX

N‑Type Self-Doped Water/Alcohol-Soluble Conjugated Polymers with Tailored Energy Levels for High-Performance Polymer Solar Cells Jianchao Jia, Baobing Fan, Manjun Xiao, Tao Jia, Yaocheng Jin, Yuan Li, Fei Huang,* and Yong Cao Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, P. R. China S Supporting Information *

ABSTRACT: Naphthalene diimide (NDI) and perylene diimide (PDI) based polymeric semiconductors with high mobility have shown great promise as electron transport materials (ETMs) in applications such as highperformance polymer solar cells (PSCs) and other optoelectronic devices. However, these NDI and PDI semiconductors usually have limited adjustment of the lowest unoccupied molecular orbital (LUMO) energy levels, which hinders their further use in the organic electronic device. Here, by using various degrees of esterification instead of imide groups, three perylenetetracarboxylic acid derivatives based, self-doped, n-type water/ alcohol-soluble conjugated polymers (n-WSCPs) were developed, which can act as electron transport layers (ETLs) to produce high-performance PSCs. Owing to the distinct electron-deficient nature of the backbones, these nWSCPs exhibited different optoelectronic properties. The relationships between doping effects, charge-transporting capabilities, interfacial modifications, and structures of n-WSCPs were systematically investigated. When these n-WSCPs were used as ETLs, highperformance PSCs with the efficiencies of near 9% and over 10% were achieved in the combinations of poly[[2,6-4,8-di(5ethylhexylthienyl)benzo[1,2-b;3,3-b]dithiophene]-[3-fluoro-2[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7-Th)/ [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) and poly(2,5-thiophene-alt-5,5′-(5,10-bis(4-(2-octyldodecyl)thiophen-2yl)naphtho[1,2-c:5,6-c′]bis([1,2,5]thiadiazole)) (PNTT)/PC71BM, respectively. The device of PNTT/PC71BM still exhibited a high PCE of 9.37% when the thickness of ETL was increased to 50 nm. Our results demonstrate the identical importance of energy level alignment and electron transporting in the design of n-WSCPs used for thickness-insensitive ETLs in PSCs for large area practical applications.

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INTRODUCTION Bulk-heterojunction polymer solar cells (PSCs) have attracted extensive attention due to their enormous potential applications in flexible, lightweight, and large-area devices through low-cost solution processing.1−4 Especially, appreciable achievements have been made in improving the device performance, with the power conversion efficiencies (PCEs) reaching higher than 14% in PSCs.5,6 The main endeavors to boost the efficiencies were involved in the use of the novel donor/acceptor materials, optimization of morphology, and device configuration engineering.7−13 However, it is noteworthy that interface engineering shows critical importance to improve the performance of solar cells, which plays a key role in modulating the energy level alignments between the active layer and electrodes, enhancing charge selectivity and extraction and thereby promoting the PCEs.14−25 Among the different types of interfacial materials, water/ alcohol-soluble conjugated polymers (WSCPs), such as poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7(9,9-dioctylfluorene)] (PFN), have been proven to be a very promising candidate for cathode modification and have been © XXXX American Chemical Society

generally used in the state-of-the-art polymer and perovskite solar cells.26−35 However, due to the poor electron transport properties of those PFN type polymers, they can only be used as efficient cathode interlayer when they are ultrathin, which limits their use for large area printing process.36 Recently, in order to overcome the electron transport problem, n-type WSCPs (n-WSCPs), as new electron transport layers (ETLs), have been developed for the application of highly efficient polymer solar cells and attracted enormous attention due to their superiorities.37−41 N-WSCPs are composed of electrondeficient conjugated backbone and highly polar side chains. The electron-deficient conjugated backbone endows it good electron transporting property and can adjust the energy level alignment between active layer and cathode electrode in PSCs. The highly polar side chains provide good solubility in highly polar solvents for n-WSCPs, assuring the fabrication of multilayer solar cell devices without the interface erosion. In Received: January 18, 2018 Revised: February 27, 2018

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DOI: 10.1021/acs.macromol.8b00126 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules Scheme 1. Synthetic Route of PIF-PTE-N, PFI-PMIDE-N, and PIF-PDI-N

paramagnetic resonance studies indicate that PIF-PDI-N displayed the strongest n-type doping effects, and PIFPMIDE-N and PIF-PTE-N exhibited similar signal intensities due to the low-lying HOMO and LUMO energy levels of the polymers. The parallel work functions (WFs) of modified Ag electrode revealed their similar interface modified capabilities. The space-charge-limited current study shows the charge mobilities are correlated with their doping behaviors and backbone structures. When these n-WSCPs were applied as electron transport layers (ETLs) in PSCs, the excellent photovoltaic efficiencies of near 9% and over 10% were achieved in the combinations of poly[[2,6-4,8-di(5-ethylhexylthienyl)benzo[1,2-b;3,3-b]dithiophene]-[3-fluoro-2[(2ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7-Th)/ [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) and poly(2,5-thiophene-alt-5,5′-(5,10-bis(4-(2-octyldodecyl)thiophen-2-yl)naphtho[1,2-c:5,6-c′]bis([1,2,5]thiadiazole)) (PNTT)/PC71BM, respectively. Even when the thickness of ETL (for PIF-PDI-N) was increased to 50 nm, the device based on PNTT/PC71BM still remained a high PCE over 9%, implying its promise as ETLs in fabrication of large-area PSC devices.

addition, the polar side chain can reduce the work functions of metal/metal oxide electrodes, induce interface doping, and trap holes in the cathode interfaces of polymer solar cells.28,42 Furthermore, different from PFN type polymers, the aminebased n-WSCPs showed self-doping effects from electrondonating amine to the electron-deficient backbone, thereby leading to a better electron conductive capability, which allows the roll-to-roll (R2R) processing of PSCs. Self-doping effects are commonly relevant with the molecular energy levels; however, these n-WSCPs contain electron-deficient naphthalene diimide (NDI) and perylene diimide (PDI) units in the backbones, which fix the LUMO energy levels of the polymers and are not able to effectively tune LUMO values.43,44 Therefore, it is still challenging to study the correlation of self-doping behavior and the molecular energy levels to develop preferable self-doped n-WSCPs for high-performance polymer solar cells. In this paper, by using various degrees of esterification instead of imide groups, we designed and synthesized three perylenetetracarboxylic acid derivatives based, self-doped nWSCPs (namely PIF-PTE-N, PIF-PMIDE-N, and PIF-PDI-N). The chemical structures are shown in Scheme 1. On one hand, the multifused backbone can give polymers large backbone coplanarity to facilitate the π-orbital overlap, thus improving the intermolecular charge transporting.45 On the other hand, the perylenetetracarboxylic acid derivatives with large electron affinities can endow the resulting polymers good electron transport properties, and the structure derivatives of PDIs can be used to adjust the energy levels and thereby facilitate the study about the correlation of self-doping behavior and the energy levels of the polymers and help to develop preferable cathode interfacial materials with high electron transport properties.46−48 The results of optical absorptions and electrochemical characterization show that these n-WSCPs possess tunable electronic and electrical properties due to the variable intramolecular charge transfer process. Electron

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RESULTS AND DISCUSSION The synthetic route of PIF-PTE-N, PFI-PMIDE-N, and PIFPDI-N is shown in Scheme 1. They were prepared by a Pdcatalyzed Suzuki coupling polymerization between the diboronated monomer 8 and the corresponding dibromated monomers including 15, 16, and 17. The synthesis of the monomers is outlined in the Supporting Information (Scheme S1). First, the 6- and 12-positions of compound 3 were substituted by protected side chains to form compound 4, which was through deprotection, bromination, amination, and palladium-catalyzed coupling to yield the diboronated monomer 8. Then, the intermediate 10 was obtained primarily via two-step reaction of esterification, bromination, and it was B

DOI: 10.1021/acs.macromol.8b00126 Macromolecules XXXX, XXX, XXX−XXX

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Figure 1. UV−vis absorption spectra of the n-WSCPs in chloroform solution (a) and as thin films (b).

Table 1. UV−Vis Absorption and Electrochemical Properties of the Polymers λmax (nm) polymers

solution

film

Egopt (eV)

Eox (V)

Ere (V)

EHOMO (eV)

ELUMO (eV)

PIF-PTE-N PIF-PMIDE-N PIF-PDI-N

406, 536 408, 480, 589 408, 518, 630

406, 537 410, 484, 576 410, 533, 630

1.87 1.68 1.52

0.48 0.49 0.56

−1.20 −1.05 −0.82

−5.28 −5.29 −5.36

−3.60 −3.75 −3.98

PIF-PMIDE-N and PIF-PDI-N could be attributed to perylene3,4,9,10-tetracarboxymonoimide dibutyl ester (PMIDE) and perylene-3,4,9,10-tetracarboxylic diimide (PDI)-centered transition, respectively.49,50 The optical bandgaps (Egopt) of these polymers, estimated from the absorption onsets of their corresponding thin films, were determined to be 1.87, 1.68, and 1.52 eV, respectively. Cyclic voltammetry (CV) measurements were conducted to evaluate the frontier molecular orbital energy levels of these polymers. The CV curves are shown in Figure 2. PIF-PTE-N,

through elimination of butanol and amidation to afford compound 12. After further Stille coupling reaction and bromination, compounds 10 and 12 can be converted into tetrabutyl 1,7-di(5-bromothiophen-2-yl)perylene-3,4,9,10-tetracarboxylate (15) and N-(2-ethylhexyl)-1,7-di(5-bromothiophen-2-yl)perylene-3,4,9,10-tetracarboxymonoimide dibutyl ester (16) in high yields, respectively. The chemical structures of these n-WSCPs were determined with 1H NMR spectroscopy, and their molecular weights were estimated to be 12.4 kDa for PIF-PTE-N, 11.0 kDa for PIF-PMIDE-N, and 9.3 kDa for PIF-PDI-N. All the polymers possess good solubility in common organic solvents, such as chloroform and toluene, and they can be soluble in methanol (∼20 mg/mL) by adding a trace amount of acetic acid, making them good candidates for the fabrication of multilayer polymer solar cells from orthogonal solvents. Their thermal properties were evaluated by differential scanning chromatography (DSC) and thermogravimetric analysis (TGA). As shown in Figure S4, PIF-PTE-N, PIF-PMIDE-N, and PIF-PDI-N exhibited the decomposition temperatures (5% weight loss) at 258, 270, and 353 °C, respectively, and DSC study results did not show any distinct exothermal transition for these copolymers over the temperature range of 40−200 °C, implying that there are no formation of crystals and phase change when they were in the heating or cooling runs. The UV−vis absorptions of these polymers in chloroform solution and as thin films are shown in Figure 1, with the relevant data summarized in Table 1. As shown in Figure 1, the three polymers, which possess different electron-deficient blocks in the backbone, exhibited the distinct absorption characteristic. PIF-PTE-N displayed two absorption bands, while PIF-PMIDE-N and PIF-PDI-N possessed three absorption bands. The mutual band at ca. 330−470 nm can be ascribed to π−π* transition absorption among them, while the lowest energy band can be assigned to a transition with significant intramolecular charge transfer (ICT) character for the three polymers. Interestingly, the ICT absorption bands showed the red-shift from PIF-PTE-N to PIF-PMIDE-N and then to PIF-PDI-N, implying that the electron-accepting capability of acceptor units in the backbones increased in above order. In addition, the bands at ca. 484 and 533 nm for

Figure 2. Cyclic voltammetry curves of the n-WSCPs films coated on a glassy-carbon electrode.

PIF-PMIDE-N, and PIF-PDI-N exhibit the reversible oxidation process with the anodic peaks at 0.80, 0.67, and 1.33 V, respectively, which are relevant to the oxidation of orbithybridized donor parts in the backbones. Besides, three polymers show the reversible two-electron reduction process in the scanning range of voltage, and their one/two electron cathodic peaks are located at −1.36/−1.66 V for PIF-PTE-N, −1.15/−1.40 V for PIF-PMIDE-N, and −0.96/−1.17 V for PIF-PDI-N, which are similar to those of the PDI-based polymers.51 The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels were calculated according to the equations EHOMO = C

DOI: 10.1021/acs.macromol.8b00126 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules −e(Eox + 4.80) eV and ELUMO = −e(Ere + 4.80) eV, in which Eox/Ere denote the onset oxidation/reduction potentials. The results are shown in Table 1. One can observe that the Eox/Ere of PIF-PTE-N, PIF-PMIDE-N, and PIF-PDI-N are 0.48/−1.20 V, 0.49/−1.05 V, and 0.56/−0.82 V, respectively, corresponding to their HOMO/LUMO energy levels of −5.28/−3.60 eV, −5.29/−3.75 eV, and −5.36/−3.98 eV, respectively. Note that the LUMO levels varied from −3.60 eV for PIF-PTE-N to −3.75 eV for PIF-PMIDE-N and then to −3.98 eV for PIFPDI-N, consistent with the strength of electron-deficient acceptors, which is in favor of modulating doping process from the polar side chain to backbone to study the relationship between doping process and molecular energy levels. Electron paramagnetic resonance (EPR) spectroscopy was used to study the interaction of pendant amino groups with the polymer backbone since amino groups are proved to be able to donate electrons to electron-deficient conjugated groups under the trigger of light, leading to substantial doping behavior.48,52−54 Quantitative tests of three n-WSCPs samples were implemented, and the resulting curves are presented in Figure 3. PIF-MIDE-N and PIF-PTE-N exhibit relatively low EPR

Scanning Kelvin probe microscopy was implemented to verify the modification capability of these n-WSCPs on Ag electrode, and the results of work function (WF) change are summarized in Table 2. The WF of the bare Ag was measured Table 2. Scanning Kelvin Probe Microscopy Characterization of Ag Electrode Modified with Different nWSCPs n-WSCPs/Ag Ag PIF-PTE-N/Ag PIF-PMIDE-N/Ag PIF-PDI-N/Ag

thickness/work function 4.57 eV 5 nm/4.23 eV 5 nm/4.24 eV 5 nm/4.30 eV

50 nm/4.08 eV 50 nm/4.03 eV 50 nm/4.07 eV

to be 4.57 eV, and after deposition of an ultrathin layer (5 nm) of PIF-PTE-N, PIF-PMIDE-N, and PIF-PDI-N, the WFs were decreased to 4.23, 4.24, and 4.30 eV, respectively. The changes in WF of n-WSCP modified Ag electrode mainly resulted from the interfacial dipole induced by the pendant polar groups on the n-WSCPs, leading to a better ohmic contact at the cathode. When the thickness of n-WSCPs on Ag electrode were increased to 50 nm, the work functions were further decreased to 4.08, 4.03, and 4.09 eV for PIF-PTE-N, PIF-PMIDE-N, and PIF-PDI-N, respectively, which is similar to the previous reports.55 The results imply that the reduced work functions of Ag electrode can lead to a more suitable energy level alignment, which are beneficial to collect electrons in PSC devices.55−58 The electron mobility was investigated using the electrononly device with the configuration of ITO/Al/n-WSCPs/Al, and it was extracted by fitting the data using the space-chargelimited current (SCLC) model.59 Figure S5 shows the J−V curves of these polymers, and the electron mobilities are summarized in Table S1. Notably, PIF-PDI-N exhibits the highest electron mobility of 6.26 × 10−5 cm2 V−1 s−1, which could be assigned to its stronger doping behavior and larger conjugated plane of intermolecular π-electron overlap.60,61 The value of PIF-PTE-N is 5.61 × 10−5 cm2 V−1 s−1, while PIFPMIDE-N displays the lowest value of 7.92 × 10−6 cm2 V−1 s−1. In spite of the larger coplanarity of PIF-PMIDE-N than PIFPTE-N, the asymmetry of PMIDE units in the backbone may disturb well-organized stack of the conjugated blocks, which affects the intermolecular charge transporting, thus leading to the lower electron mobility. Because of the higher electron mobility of PIF-PDI-N, it might be possible to allow a thicker ETLs used in photovoltaic devices without significantly sacrificing device performance.

Figure 3. Electron paramagnetic resonance spectra of three n-WSCPs in the solid state.

signal with similar g value of ∼2.005. In contrast, PIF-PDI-N shows higher EPR signal with a g value of ∼2.003. These results imply that self-doping may occur in all the n-WSCPs. However, PIF-MIDE-N and PIF-PTE-N exhibit the similar EPR intensities, while the signal intensity of PIF-PDI-N is 6 times higher than those of PIF-MIDE-N and PIF-PTE-N. This phenomenon can be rationalized by their different HOMO and LUMO energy levels. The doping process in amine-functionalized n-WSCPs involves the electron transfer from amine to the HOMO level of the photoexcited polymers. Since the amine contains an electron lone pair and the oxidation potential of amine (∼5.1 eV) is commonly smaller than HOMO levels of the excited polymers, electron transfer from amine to the HOMO of polymers is energetically favorable. As a result, a free electron remains in the LUMO of the polymer and is stable by the positively charged ammonium.39 The similar HOMO levels of PIF-MIDE-N and PIF-PTE-N are only 0.19 and 0.18 eV larger than that of amine, respectively, which means less drive force for the electron transfer. In contrast, PIF-PDI-N possesses deeper HOMO and LUMO levels, which is more favorable to the n-doping process. It is noteworthy that PIF-PDI-N exhibits strongest n-doping effect, which may be beneficial for the charge transporting since effective doping can improve the carrier density in the film.

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PHOTOVOLTAIC PROPERTIES To evaluate the performance of these n-WSCPs as ETLs in PSCs, the devices were investigated by fabricating and evaluating the conventional PSCs with the configuration of ITO/PEDOT:PSS/active layer/n-WSCPs/Ag (Figure 4), where PTB7-Th and PC71BM were used as the donor and acceptor, respectively. The J−V curves and relevant parameters are shown in Figure 5a and Table 3, respectively, with EQE curves displayed in Figure S6. When 5 nm n-WSCPs are used as ETLs, the devices derived from PIF-PTE-N, PIF-PMIDE-N, and PIF-PDI-N exhibit the similarly improved photovoltaic efficiency of 8.56%, 8.90%, and 8.66%, respectively, in comparison with the value of device without interlayers (6.79%),62 demonstrating that these n-WSCPs are a promising type of ETLs. The increased performance of these devices can D

DOI: 10.1021/acs.macromol.8b00126 Macromolecules XXXX, XXX, XXX−XXX

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to the device with the 5 nm interlayer. But the PCEs of PIFPTE-N and PIF-PMIDE-N-based devices were decreased rapidly to 0.18% and 5.06%, respectively. Similar to that in the device with PTB7-Th as the donor material, the inferior PCE of 50 nm PIF-PTE-N-based device is equally attributed to the unfavorable electron barrier induced by its high-lying LUMO energy level, which can also be indicated by its huge series resistance (Rs). However, the lowered efficiency of 50 nm PIF-PMIDE-N based device are mainly caused by the sharp decrease of fill factor, which could be assigned to its lower electron mobility in comparison with that of the active layer, thus depressing the electron collection and transporting and resulting in the more recombination loss.65 The results suggest the identical importance of energy levels and electron mobility in the design of n-WSCPs used for thickness-insensitive ETLs in PSCs.

Figure 4. Device structure of the conventional PSC and the chemical structures of PTB7-Th, PNTT, and PC71BM used for active layer in devices.

be assigned to the better energy level alignment at the interface of active layer/Ag, hole blocking, as well as the doping from the polar group of these n-WSCPs to PC71BM at the active layer/ ETLs interface, which can enhance the electron collections in the PSC device.39 Next, when the thickness of ETLs are increased to 50 nm, the devices with PIF-PTE-N, PIF-PMIDEN, and PIF-PDI-N showed decreased efficiencies of 3.85%, 7.02%, and 7.36%, respectively, which corresponded to a 55%, 21%, and 15% loss of PCE with respected to the PSCs based on 5 nm ETLs. Note that PIF-PTE-N-based device showed a sharp decrease in PCEs, even though it has a high electron mobility close to that of PIF-PDI-N. The main reason may lie in the high-lying LUMO energy levels. As the LUMO energy level of PIF-PTE-N is 0.3 eV higher than that of PC71BM,63 it could form an electron barrier that blocks electrons from reaching the cathode; thus, the Jsc and FF drop quickly with the increase of thickness.64 Another active material, PNTT (shown in Figure 4),65 which enables high-performance PSCs with active layer thickness over 280 nm, was also used as a donor polymer to fabricate PSCs. The performance parameters are presented in Figure 5b and Table 4, and EQE curves are presented in Figure S7. As shown in Figure 5b, the devices with 5 nm ETLs of PIF-PTE-N, PIFPMIDE-N, and PIF-PDI-N can produce the very excellent PCEs of 10.31%, 10.21%, and 10.49%, respectively, with the high Jsc near 20 mA cm−1 and high FFs of approximately 0.70. The results suggest these n-WSCPs are likely to be used as a commonly used ETLs to improve the interface contact in polymer solar cells with different active materials. In addition, when the thicknesses of ETLs are increased to 50 nm, these devices exhibit very distinct photovoltaic performance. For the PIF-PDI-N-based device, it still remained a PCE of 9.37%, with a high Jsc of 18.07 mA cm−2 and FF of 0.69, which is much close

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CONCLUSION

In summary, by using various degrees of esterification instead of imide groups, we designed and synthesized three perylenetetracarboxylic acid derivatives based, self-doped n-WSCPs (namely PIF-PTE-N, PIF-PMIDE-N, and PIF-PDI-N). Because of the distinct nature of these electron-deficient blocks in their backbones, these n-WSCPs exhibit tunable absorptions and energy levels. The results of EPR spectroscopy indicate that the doping intensity can be adjusted with the variation of HOMO and LUMO energy levels in these n-WSCPs. Further SCLC characterization suggests that the n-doping effects and favorable main-chain stacking result in the higher electron mobility of PIF-PDI-N. Because of their good interfacial modification capabilities, high-performance PSCs with the efficiencies of near 9% or over 10% were achieved by using ultrathin n-WSCPs as ETLs in the both combinations of PTB7-TH/PC71BM and PNTT/PC71BM, respectively. When three n-WSCPs as ETLs were increased to 50 nm, the PIF-PDI-N based device with the active layer of PNTT/PC71BM still remained a high PCE over 9%, implying a possibility to fabricate large-area PSCs via the R2R method. Conversely, the PIF-PTE-N and PIF-PMIDE-N based device results are unsatisfactory because of their mismatched energy levels and electron mobility, respectively. It suggests the equivalent importance of suitable energy levels and efficient electron transporting in the design of n-WSCPs used for thickness-insensitive ETLs in PSCs.

Figure 5. J−V curves of the conventional PSCs based on the active layer of PTB7-Th/PC71BM (a) and PNTT/PC71BM (b) with different ETLs in various thicknesses. E

DOI: 10.1021/acs.macromol.8b00126 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules Table 3. Device Parameters of the PSCs Based on PTB7-Th/PC71BM with 5 and 50 nm ETLs Voc (V)

Jsc(mA cm−2)

FF (%)

PCEa (%)

best PCE (%)

0.79 ± 0.00 0.80 ± 0.00

16.66 ± 0.27 13.29 ± 0.07

64.87 ± 0.39 32.90 ± 3.66

8.49 ± 0.10 3.48 ± 0.36

8.56 3.85

0.79 ± 0.00 0.80 ± 0.00

16.55 ± 0.45 14.30 ± 0.48

67.16 ± 0.29 60.84 ± 2.06

8.78 ± 0.18 6.96 ± 0.10

8.90 7.02

0.78 ± 0.00 0.79 ± 0.00

16.62 ± 0.41 13.60 ± 0.37

65.20 ± 0.79 66.09 ± 0.79

8.44 ± 0.17 7.06 ± 0.27

8.66 7.36

ETLs PIF-PTE-N 5 nm 50 nm PIF-PMIDE-N 5 nm 50 nm PIF-PDI-N 5 nm 50 nm a

The PCE values are obtained from eight devices.

Table 4. Device Parameters of the PSCs Based on PNTT/PC71BM with 5 and 50 nm ETLs ETLs none PIF-PTE-N 5 nm 50 nm PIF-PMIDE-N 5 nm 50 nm PIF-PDI-N 5 nm 50 nm a

Voc (V)

Jsc (mA cm−2)

FF (%)

PCEa (%)

best PCE (%)

0.70 ± 0.00

19.67 ± 0.22

54.70 ± 1.37

7.51 ± 0.17

7.72

9.8

0.75 ± 0.00 0.78 ± 0.00

19.44 ± 0.26 1.32 ± 0.28

69.86 ± 1.25 13.08 ± 0.65

10.19 ± 0.11 0.14 ± 0.04

10.31 0.18

6.2 3747.0

0.75 ± 0.00 0.76 ± 0.00

19.48 ± 0.34 17.86 ± 0.28

68.51 ± 0.66 30.49 ± 6.92

10.06 ± 0.13 4.16 ± 1.01

10.21 5.06

4.4 111.9

0.75 ± 0.00 0.76 ± 0.00

19.73 ± 0.28 17.84 ± 0.32

68.96 ± 0.89 68.73 ± 0.09

10.24 ± 0.19 9.28 ± 0.13

10.49 9.37

3.6 10.7

Rsb (Ω·cm2)

The PCE values are obtained from eight devices. bDefined from the J−V curves at V = Voc.

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(3) Li, G.; Zhu, R.; Yang, Y. Polymer Solar Cells. Nat. Photonics 2012, 6, 153−161. (4) Ameri, T.; Li, N.; Brabec, C. J. Highly Efficient Organic Tandem Solar Cells: A Follow up Review. Energy Environ. Sci. 2013, 6, 2390− 2413. (5) Cui, Y.; Yao, H. F.; Yang, C. Y.; Zhang, S. Q.; Hou, J. H. Organic Solar Cells with an Efficiency Approaching 15%. Acta Polym. Sin. 2017, DOI: 10.11777/j.issn1000-3304.2018.17297. (6) Xiao, Z.; Jia, X.; Ding, L. M. Ternary Organic Solar Cells Offer 14% Power Conversion Efficiency. Sci. Bull. 2017, 62, 1562−1564. (7) Yao, H. F.; Ye, L.; Zhang, H.; Li, S. S.; Zhang, S. Q.; Hou, J. H. Molecular Design of Benzodithiophene-Based Organic Photovoltaic Materials. Chem. Rev. 2016, 116, 7397−7457. (8) Li, Y. F. Molecular Design of Photovoltaic Materials for Polymer Solar Cells: Toward Suitable Electronic Energy Levels and Broad Absorption. Acc. Chem. Res. 2012, 45, 723−733. (9) Wu, J. S.; Cheng, S. W.; Cheng, Y. J.; Hsu, C. S. Donor-Acceptor Conjugated Polymers Based on Multifused Ladder-Type Arenes for Organic Solar Cells. Chem. Soc. Rev. 2015, 44, 1113−1154. (10) Lin, Y. Z.; Zhan, X. W. Oligomer Molecules for Efficient Organic Photovoltaics. Acc. Chem. Res. 2016, 49, 175−183. (11) Cai, Y. H.; Huo, L. J.; Sun, Y. M. Recent Advances in WideBandgap Photovoltaic Polymers. Adv. Mater. 2017, 29, 1605437. (12) Chen, L. M.; Hong, Z. R.; Li, G.; Yang, Y. Recent Progress in Polymer Solar Cells: Manipulation of Polymer:Fullerene Morphology and the Formation of Efficient Inverted Polymer Solar Cells. Adv. Mater. 2009, 21, 1434−1449. (13) Liu, F.; Gu, Y.; Jung, J. W.; Jo, W. H.; Russell, T. P. On the Morphology of Polymer-Based Photovoltaics. J. Polym. Sci., Part B: Polym. Phys. 2012, 50, 1018−1044. (14) Ma, H.; Yip, H. L.; Huang, F.; Jen, A. K. Y. Interface Engineering for Organic Electronics. Adv. Funct. Mater. 2010, 20, 1371−1388. (15) Duarte, A.; Pu, K. Y.; Liu, B.; Bazan, G. C. Recent Advances in Conjugated Polyelectrolytes for Emerging Optoelectronic Applications. Chem. Mater. 2011, 23, 501−515.

ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.8b00126. Synthetic details, measurement and characterization, fabrication and characterization of PSCs, 1H NMR of these polymers, TGA and DSC curves, J−V curves for electron-only devices, EQE curves, etc. (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (F.H.). ORCID

Yuan Li: 0000-0002-7931-9879 Fei Huang: 0000-0001-9665-6642 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The work was financially supported by the Natural Science Foundation of China (No. 21634004, 21490573, and 51521002), the Ministry of Science and Technology (No. 2014CB643501), and the Science and Technology Program of Guangzhou, China (No. 201707020019).

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REFERENCES

(1) Yu, G.; Gao, J.; Hummelen, J. C.; Wudl, F.; Heeger, A. J. Polymer Photovoltaic Cells: Enhanced Efficiencies Via a Network of Internal Donor-Acceptor Heterojunctions. Science 1995, 270, 1789−1791. (2) Lu, L.; Zheng, T. Y.; Wu, Q. H.; Schneider, A. M.; Zhao, D. L.; Yu, L. P. Recent Advances in Bulk Heterojunction Polymer Solar Cells. Chem. Rev. 2015, 115, 12666−12731. F

DOI: 10.1021/acs.macromol.8b00126 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules (16) Dou, L. T.; You, J. B.; Hong, Z. R.; Xu, Z.; Li, G.; Street, R. A.; Yang, Y. 25th Anniversary Article: A Decade of Organic/Polymeric Photovoltaic Research. Adv. Mater. 2013, 25, 6642−6671. (17) Yin, Z. G.; Wei, J. J.; Zheng, Q. D. Interfacial Materials for Organic Solar Cells: Recent Advances and Perspectives. Adv. Sci. 2016, 3, 1500362. (18) Hu, Z. C.; Huang, F.; Cao, Y. Layer-by-Layer Assembly of Multilayer Thin Films for Organic Optoelectronic Devices. Small Methods 2017, 1, 1700264. (19) Oh, S. H.; Na, S. I.; Jo, J.; Lim, B.; Vak, D.; Kim, D. Y. WaterSoluble Polyfluorenes as an Interfacial Layer Leading to CathodeIndependent High Performance of Organic Solar Cells. Adv. Funct. Mater. 2010, 20, 1977−1983. (20) Zhou, Y. H.; Hernandez, C. F.; Shim, J.; Meyer, J.; Giordano, A. J.; Li, H.; Winget, P.; Papadopoulos, T.; Cheun, H.; Kim, J.; Fenoll, M.; Dindar, A.; Haske, W.; Najafabadi, E.; Khan, T. M.; Sojoudi, H.; Barlow, S.; Graham, S.; Brédas, J. L.; Marder, S. R.; Kahn, A.; Kippelen, B. A Universal Method to Produce Low−Work Function Electrodes for Organic Electronics. Science 2012, 336, 327−332. (21) Liu, F.; Page, Z. A.; Duzhko, V. V.; Russell, T. P.; Emrick, T. Conjugated Polymeric Zwitterions as Efficient Interlayers in Organic Solar Cells. Adv. Mater. 2013, 25, 6868−6873. (22) Zhong, S.; Wang, R.; Mao, H. Y.; He, Z. C.; Wu, H. B.; Chen, W.; Cao, Y. Interface Investigation of the Alcohol-/Water-Soluble Conjugated Polymer PFN as Cathode Interfacial Layer in Organic Solar Cells. J. Appl. Phys. 2013, 114, 113709. (23) Zhang, W. J.; Wu, Y. L.; Bao, Q. Y.; Gao, F.; Fang, J. F. Morphological Control for Highly Efficient Inverted Polymer Solar Cells Via the Backbone Design of Cathode Interlayer Materials. Adv. Energy Mater. 2014, 4, 1400359. (24) Zhang, Z. G.; Qi, B. Y.; Jin, Z. W.; Chi, D.; Qi, Z.; Li, Y. F.; Wang, J. Z. Perylene Diimides: A Thickness-Insensitive Cathode Interlayer for High Performance Polymer Solar Cells. Energy Environ. Sci. 2014, 7, 1966−1973. (25) Liu, Z. Y.; Ouyang, X. H.; Peng, R. X.; Bai, Y. Q.; Mi, D. B.; Jiang, W. G.; Facchetti, A.; Ge, Z. Y. Efficient Polymer Solar Cells Based on the Synergy Effect of a Novel Non-Conjugated SmallMolecule Electrolyte and Polar Solvent. J. Mater. Chem. A 2016, 4, 2530−2536. (26) Duan, C. H.; Zhang, K.; Zhong, C. M.; Huang, F.; Cao, Y. Recent Advances in Water/Alcohol-Soluble Π-Conjugated Materials: New Materials and Growing Applications in Solar Cells. Chem. Soc. Rev. 2013, 42, 9071−9104. (27) Chueh, C. C.; Li, C. Z.; Jen, A. K. Y. Recent Progress and Perspective in Solution-Processed Interfacial Materials for Efficient and Stable Polymer and Organometal Perovskite Solar Cells. Energy Environ. Sci. 2015, 8, 1160−1189. (28) Liu, Y.; Duzhko, V. V.; Page, Z. A.; Emrick, T.; Russell, T. P. Conjugated Polymer Zwitterions: Efficient Interlayer Materials in Organic Electronics. Acc. Chem. Res. 2016, 49, 2478−2488. (29) He, Z. C.; Zhong, C. M.; Su, S. J.; Xu, M.; Wu, H. B.; Cao, Y. Enhanced Power-Conversion Efficiency in Polymer Solar Cells Using an Inverted Device Structure. Nat. Photonics 2012, 6, 591−595. (30) You, J. B.; Yang, Y.; Hong, Z. R.; Song, T. B.; Meng, L.; Liu, Y. S.; Jiang, C. Y.; Zhou, H. P.; Chang, W. H.; Li, G.; Yang, Y. Moisture Assisted Perovskite Film Growth for High Performance Solar Cells. Appl. Phys. Lett. 2014, 105, 183902. (31) Andersen, T. R.; Dam, H. F.; Hösel, M.; Helgesen, M.; Carlé, J. E.; Larsen-Olsen, T. T.; Gevorgyan, S. A.; Andreasen, J. W.; Adams, J.; Li, N.; Machui, F.; Spyropoulos, G. D.; Ameri, T.; Lemaître, N.; Legros, M.; Scheel, A.; Gaiser, D.; Kreul, K.; Berny, S.; Lozman, O. R.; Nordman, S.; Välimäki, M.; Vilkman, M.; Søndergaard, R. R.; Jørgensen, M.; Brabec, C. J.; Krebs, F. C. Scalable, Ambient Atmosphere Roll-to-Roll Manufacture of Encapsulated Large Area, Flexible Organic Tandem Solar Cell Modules. Energy Environ. Sci. 2014, 7, 2925−2933. (32) Zhang, Q.; Kan, B.; Liu, F.; Long, G. K.; Wan, X. J.; Chen, X. Q.; Zuo, Y.; Ni, W.; Zhang, H. J.; Li, M. M.; Hu, Z. C.; Huang, F.; Cao, Y.;

Liang, Z. Q.; Zhang, M. T.; Russell, T. P.; Chen, Y. S. Small-Molecule Solar Cells with Efficiency over 9%. Nat. Photonics 2015, 9, 35−41. (33) Zuo, L. J.; Chang, C. Y.; Chueh, C. C.; Zhang, S. H.; Li, H. Y.; Jen, A. K. Y.; Chen, H. Z. Design of a Versatile Interconnecting Layer for Highly Efficient Series-Connected Polymer Tandem Solar Cells. Energy Environ. Sci. 2015, 8, 1712−1718. (34) Liang, N. N.; Sun, K.; Zheng, Z.; Yao, H. F.; Gao, G. P.; Meng, X. Y.; Wang, Z. H.; Ma, W.; Hou, J. H. Perylene Diimide Trimers Based Bulk Heterojunction Organic Solar Cells with Efficiency over 7%. Adv. Energy Mater. 2016, 6, 1600060. (35) Li, M. M.; Gao, K.; Wan, X. J.; Zhang, Q.; Kan, B.; Xia, R. X.; Liu, F.; Yang, X.; Feng, H. R.; Ni, W.; Wang, Y. C.; Peng, J. J.; Zhang, H. T.; Liang, Z. Q.; Yip, H.-L.; Peng, X. B.; Cao, Y.; Chen, Y. S. Solution-Processed Organic Tandem Solar Cells with Power Conversion Efficiencies > 12%. Nat. Photonics 2017, 11, 85−90. (36) Liu, S. J.; Zhang, K.; Lu, J. M.; Zhang, J.; Yip, H. L.; Huang, F.; Cao, Y. High-Efficiency Polymer Solar Cells Via the Incorporation of an Amino-Functionalized Conjugated Metallopolymer as a Cathode Interlayer. J. Am. Chem. Soc. 2013, 135, 15326−15329. (37) Zhang, K.; Hu, Z. C.; Sun, C.; Wu, Z. H.; Huang, F.; Cao, Y. Toward Solution-Processed High-Performance Polymer Solar Cells: From Material Design to Device Engineering. Chem. Mater. 2017, 29, 141−148. (38) Liu, Y.; Page, Z. A.; Russell, T. P.; Emrick, T. Finely Tuned Polymer Interlayers Enhance Solar Cell Efficiency. Angew. Chem., Int. Ed. 2015, 54, 11485−11489. (39) Wu, Z. H.; Sun, C.; Dong, S.; Jiang, X. F.; Wu, S. P.; Wu, H. B.; Yip, H. L.; Huang, F.; Cao, Y. N-Type Water/Alcohol-Soluble Naphthalene Diimide-Based Conjugated Polymers for High-Performance Polymer Solar Cells. J. Am. Chem. Soc. 2016, 138, 2004−2013. (40) Hu, Z. C.; Chen, Z. M.; Zhang, K.; Zheng, N. N.; Xie, R. H.; Liu, X.; Yang, X. Y.; Huang, F.; Cao, Y. Self-Doped N-Type Water/ Alcohol Soluble-Conjugated Polymers with Tailored Backbones and Polar Groups for Highly Efficient Polymer Solar Cells. Sol. RRL 2017, 1, 1700055. (41) Liu, H. M.; Huang, L. Q.; Cheng, X. F.; Hu, A. F.; Xu, H. T.; Chen, L.; Chen, Y. W. N-Type Self-Doping of Fluorinate Conjugated Polyelectrolytes for Polymer Solar Cells: Modulation of Dipole, Morphology, and Conductivity. ACS Appl. Mater. Interfaces 2017, 9, 1145−1153. (42) Hu, Z. C.; Zhang, K.; Huang, F.; Cao, Y. Water/Alcohol Soluble Conjugated Polymers for the Interface Engineering of Highly Efficient Polymer Light-Emitting Diodes and Polymer Solar Cells. Chem. Commun. 2015, 51, 5572−5585. (43) Takimiya, K.; Osaka, I.; Nakano, M. Π-Building Blocks for Organic Electronics: Revaluation of “Inductive” and “Resonance” Effects of Π-Electron Deficient Units. Chem. Mater. 2014, 26, 587− 593. (44) Ding, Z. C.; Long, X. J.; Dou, C. D.; Liu, J.; Wang, L. X. A Polymer Acceptor with an Optimal Lumo Energy Level for AllPolymer Solar Cells. Chem. Sci. 2016, 7, 6197−6202. (45) Guo, X. G.; Facchetti, A.; Marks, T. J. Imide- and AmideFunctionalized Polymer Semiconductors. Chem. Rev. 2014, 114, 8943−9021. (46) Mai, C. K.; Schlitz, R. A.; Su, G. M.; Spitzer, D.; Wang, X. J.; Fronk, S. L.; Cahill, D. G.; Chabinyc, M. L.; Bazan, G. C. Side-Chain Effects on the Conductivity, Morphology, and Thermoelectric Properties of Self-Doped Narrow-Band-Gap Conjugated Polyelectrolytes. J. Am. Chem. Soc. 2014, 136, 13478−13481. (47) Shi, K.; Zhang, F. J.; Di, C. A.; Yan, T. W.; Zou, Y.; Zhou, X.; Zhu, D. B.; Wang, J. Y.; Pei, J. Toward High Performance N-Type Thermoelectric Materials by Rational Modification of BDPPV Backbones. J. Am. Chem. Soc. 2015, 137, 6979−6982. (48) Russ, B.; Robb, M. J.; Popere, B. C.; Perry, E. E.; Mai, C. K.; Fronk, S. L.; Patel, S. N.; Mates, T. E.; Bazan, G. C.; Urban, J. J.; Chabinyc, M. L.; Hawker, C. J.; Segalman, R. A. Tethered Tertiary Amines as Solid-State N-Type Dopants for Solution-Processable Organic Semiconductors. Chem. Sci. 2016, 7, 1914−1919. G

DOI: 10.1021/acs.macromol.8b00126 Macromolecules XXXX, XXX, XXX−XXX

Article

Macromolecules (49) Sengupta, S.; Dubey, R. K.; Hoek, R. W. M.; van Eeden, S. P. P.; Gunbas, D. D.; Grozema, F. C.; Sudholter, E. J. R.; Jager, W. F. Synthesis of Regioisomerically Pure 1,7-Dibromoperylene-3,4,9,10Tetracarboxylic Acid Derivatives. J. Org. Chem. 2014, 79, 6655−6662. (50) Zhan, X. W.; Tan, Z. A.; Zhou, E. J.; Li, Y. F.; Misra, R.; Grant, A.; Domercq, B.; Zhang, X. H.; An, Z. S.; Zhang, X.; Barlow, S.; Kippelen, B.; Marder, S. R. Copolymers of Perylene Diimide with Dithienothiophene and Dithienopyrrole as Electron-Transport Materials for All-Polymer Solar Cells and Field-Effect Transistors. J. Mater. Chem. 2009, 19, 5794−5803. (51) Ma, W. T.; Qin, L. Q.; Gao, Y.; Zhang, W. Q.; Xie, Z. Q.; Yang, B.; Liu, L. L.; Ma, Y. G. A Perylene Bisimide Network for HighPerformance N-Type Electrochromism. Chem. Commun. 2016, 52, 13600−13603. (52) Li, C. Z.; Chueh, C. C.; Ding, F. Z.; Yip, H. L.; Liang, P. W.; Li, X. S.; Jen, A. K. Y. Doping of Fullerenes Via Anion-Induced Electron Transfer and Its Implication for Surfactant Facilitated High Performance Polymer Solar Cells. Adv. Mater. 2013, 25, 4425−4430. (53) Jia, T.; Sun, C.; Xu, R. G.; Chen, Z. M.; Yin, Q. W.; Jin, Y. C.; Yip, H. L.; Huang, F.; Cao, Y. Naphthalene Diimide Based N-Type Conjugated Polymers as Efficient Cathode Interfacial Materials for Polymer and Perovskite Solar Cells. ACS Appl. Mater. Interfaces 2017, 9, 36070−36081. (54) Wang, Z. F.; Zheng, N. N.; Zhang, W. Q.; Yan, H.; Xie, Z. Q.; Ma, Y. G.; Huang, F.; Cao, Y. Self-Doped, N-Type Perylene Diimide Derivatives as Electron Transporting Layers for High-Efficiency Polymer Solar Cells. Adv. Energy Mater. 2017, 7, 1700232. (55) Page, Z. A.; Liu, Y.; Duzhko, V. V.; Russell, T. P.; Emrick, T. Fulleropyrrolidine Interlayers: Tailoring Electrodes to Raise Organic Solar Cell Efficiency. Science 2014, 346, 1255826. (56) Yip, H. L.; Jen, A. K. Y. Recent Advances in Solution-Processed Interfacial Materials for Efficient and Stable Polymer Solar Cells. Energy Environ. Sci. 2012, 5, 5994−6011. (57) Zhang, K.; Zhong, C. M.; Liu, S. J.; Mu, C.; Li, Z. K.; Yan, H.; Huang, F.; Cao, Y. Highly Efficient Inverted Polymer Solar Cells Based on a Cross-Linkable Water-/Alcohol-Soluble Conjugated Polymer Interlayer. ACS Appl. Mater. Interfaces 2014, 6, 10429−10435. (58) Zhang, Q.; Zhang, D. W.; Li, X. D.; Liu, X. H.; Zhang, W. J.; Han, L.; Fang, J. F. Neutral Amine Based Alcohol-Soluble Interface Materials for Inverted Polymer Solar Cells: Realizing High Performance and Overcoming Solvent Erosion. Chem. Commun. 2015, 51, 10182−10185. (59) Mihailetchi, V. D.; Wildeman, J.; Blom, P. W. M. Space-Charge Limited Photocurrent. Phys. Rev. Lett. 2005, 94, 126602. (60) Kim, J.; Khim, D.; Baeg, K.; Park, W.; Lee, S.; Kang, M. J.; Noh, Y.; Kim, D. Systematic Study of Widely Applicable N-Doping Strategy for High-Performance Solution-Processed Field-Effect Transistors. Adv. Funct. Mater. 2016, 26, 7886−7894. (61) Kularatne, R. S.; Sista, P.; Magurudeniya, H. D.; Hao, J.; Nguyen, H. Q.; Biewer, M. C.; Stefan, M. C. Donor-Acceptor Semiconducting Polymers Based on Pyromellitic Diimide. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1617−1622. (62) Jia, T.; Zheng, N. N.; Cai, W. Q.; Ying, L.; Huang, F. Naphthalene Diimide-Based Polymers Consisting of Amino Alkyl Side Groups:Three-Component One-Pot Polymerization and Their Application in Polymer Solar Cells. Acta Chim. Sinica 2017, 75, 808−818. (63) Zhang, G. C.; Zhang, K.; Yin, Q. W.; Jiang, X. F.; Wang, Z. Y.; Xin, J. M.; Ma, W.; Yan, H.; Huang, F.; Cao, Y. High-Performance Ternary Organic Solar Cell Enabled by a Thick Active Layer Containing a Liquid Crystalline Small Molecule Donor. J. Am. Chem. Soc. 2017, 139, 2387−2395. (64) Sun, C.; Wu, Z. H.; Hu, Z. H.; Xiao, J. Y.; Zhao, W. C.; Li, H. W.; Li, Q. Y.; Tsang, S. W.; Xu, Y. X.; Zhang, K.; Yip, H. L.; Hou, J. H.; Huang, F.; Cao, Y. Interface Design for High-Efficiency Non-Fullerene Polymer Solar Cells. Energy Environ. Sci. 2017, 10, 1784−1791. (65) Jin, Y. C.; Chen, Z. M.; Xiao, M. J.; Peng, J. J.; Fan, B. B.; Ying, L.; Zhang, G. C.; Jiang, X. F.; Yin, Q. W.; Liang, Z. Q.; Huang, F.; Cao, Y. Thick Film Polymer Solar Cells Based on Naphtho[1,2-C:5,6-

C]Bis[1,2,5]Thiadiazole Conjugated Polymers with Efficiency over 11%. Adv. Energy Mater. 2017, 7, 1700944.

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