A Facile Approach To Fabricate High-Performance Polymer Solar

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A Facile Approach to Fabricate High Performance Polymer Solar Cells with Annealing-Free and Simple Device of Three Layers Xiaotian Hu, Lie Chen, Yong Zhang, Lin Zhang, Yuanpeng Xie, Weihua Zhou, Wen Chen, and Yiwang Chen J. Phys. Chem. C, Just Accepted Manuscript • Publication Date (Web): 05 May 2015 Downloaded from http://pubs.acs.org on May 6, 2015

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The Journal of Physical Chemistry

A Facile Approach to Fabricate High Performance Polymer Solar Cells with Annealing-Free and Simple Device of Three Layers Xiaotian Hua, Lie Chena,b, Yong Zhanga,b, Lin Zhanga, Yuanpeng Xiea, Weihua Zhoua,b, Wen Chenc, Yiwang Chen*a,b a

School of Materials Science and Engineering/Institute of Polymers, Nanchang University, 999 Xuefu Avenue, Nanchang 330031, China

b

Jiangxi Provincial Key Laboratory of New Energy Chemistry, College of Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang 330031, China c

Institute for Advanced Study, Nanchang University, 999 Xuefu Avenue, Nanchang 330031, China

*Corresponding author. Tel.: +86 791 83968703; fax: +86 791 83969561. E-mail: [email protected] (Y. Chen).

ACS Paragon Plus Environment


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Abstract With the rapid development of polymer solar cells research, “annealing-free” and simplifying the device structure become the main problems of commercialization of polymer solar cells (PSCs). To resolve these challenges, a novel, facile approach to develop favorably vertical separation in poly(3-hexylthiophene):(6,6)-phenyl-C61 butyric acid methyl ester : 2,3,5,6-tetrafluoro-7,7,8,8,-tetracyano-quinodimethane (P3HT:PC61BM:F4TCNQ) ternary blend through the interaction between P3HT and F4TCNQ has been demonstrated, consequently high efficient PSCs only with three layers realized. Driven by the low surface energy of F4TCNQ, a spontaneously P3HT-F4TCNQ layer was enriched on the surface of active layer. The device can escape the annealing treatment and interfacial modification due to the well-defined vertical separation and favorable work function gradient in the activelayer. As a result, without thermal annealing and additional interlayer, PSCs only with three layers based on the ternary blend obtain a PCE of up to 4.1%. It also demonstrates good adaptation for all solution processed and flexible method. This simple device structure and “annealing-free” method of efficient polymer solar cells provide an opportunity for large-scale commercial production in the near future.


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Introduction The requirements of the rapid economic growth and the related increase of global warming associated with the burning of fossil non-renewable energy resource are the driving forces for the exploitation of low-cost renewable energy sources.1-2 Low-cost polymer photovoltaic is one of the most potential candidates for the next generation of renewable energy. This has triggered front-burner research into organic solar cells based on conjugated polymer and fullerene mixtures in the recent past years.3-5 For polymer solar cells (PSCs) with a traditional bulk heterojunction (BHJ) device structure, power conversion efficiency (PCE) has been exceed 10% due to the advance on the synthesis of novel polymer donors, optimized device structure, interfacial morphology control and processing improvement.6-9 Despite significant improvements in understanding and optimizing the morphology or performance of BHJ blends, efforts were made to search for alternative new device structure and make the fabrication simple and convenient PSC for commercial production.5,

10-13

For the BHJ active layers, small amount of diiodooctane,

chloronaphthalene, or other additives were used to satisfy the crystallinity requirement and obtain optimal morphology.14-16 For the interfacial engineering, there are plenty of organic or inorganic interfacial layers have been reported during the past ten

years,

such

(PEDOT:PSS),

as

poly(3,4-ethylenedioxythiophene)

poly(styrenesulfonate)

poly[(9,9-dioctyl-2,7-ﬂuorene)-alt-(9,9-bis

(3’-(N,N-dimethylamino)propyl)-2,7-ﬂuorene)] (PFN), C60,

MoO3, ZnO and

TiOx.10-11, 17-18 However, it also has several intrinsic weaknesses to limit performance enhancement such as thermal annealing for BHJ phase separation, poor tolerance for thickness of interfacial layers and complicated process for roll-to-roll method. Therefore, it is urgently desirable to find a new device structure and preparation method to truly realize commercial application. Stimulated by such a practical need, recently, some low band gap polymers have emerged which can improve PCE without thermal annealing treatment.7, 13 Also, there was certain attention focus on optimized the conductivity of interfacial layers for thicker films.19-22 In this work, we report a novel, simple approach to form favorably vertical separation



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in poly(3-hexylthiophene) (P3HT):(6,6)-phenyl-C61 butyric acid methyl ester (PC61BM) blend by skillfully utilize the interaction between P3HT and 2,3,5,6-tetrafluoro-7,7,8,8,-tetracyano-quinodimethane (F4TCNQ) and simplify the device structure for three layers (chemical structure are shown in Figure 1). Through a mix-solvent method to deal with the solubility problem, incorporation of F4TCNQ into the active layer is found to effectively improve the crystallinity of active layer, thus avoiding high temperature annealing. At the same time, due to the spontaneous drive function, the enriched PC61BM on the bottom and enriched F4TCNQ: P3HT on the surface of the BHJ can also serve as interfacial layers to ensure a better energy alignment in the devices for more efficient charge extraction and collection. After an optimization of energy level the PSCs based on P3HT:PC61BM:F4TCNQ (1 wt.%) exhibits as high as a PCE of 4.1%. It also shows nice universality for different electrodes and substrates. Results and Discussion F4TCNQ has been widely introduced in organic optoelectronic devices, however there is few report on its application in organic photovoltaic devices as it can destroy the solubility of active layers and its high crystalline always affects the morphology of BHJ films.23-26 To solve these film-forming problems, a mixed solvent of dichlorobenzene (DCB) and chloroform (CHCl3) was introduced to treat the P3HT:PC61BM:F4TCNQ ternary active blend in this work. A small amount of CHCl3 not only can enhance the solubility of active layer during liquid phase, but also assist vertical separation without thermal annealing during the spin coating and slow drying process. After optimization the ratio of DCB and CHCl3 to 90:10, a smooth and clean surface of the blend film has been obtained. As shown in Figure S1, it is obviously found the surface of active layer become much more smooth and spotless after incorporation of 1 wt% F4TCNQ in P3HT:PC61BM blend. The color of the film turned darker compared to the pristine P3HT:PC61BM film without thermal annealing, which is expected to enhance light absorption in BHJ film. To verify the modification of F4TCNQ in P3HT:PC61BM blend, the X-ray diffraction spectra of the P3HT:PC61BM:F4TCNQ blends with different F4TCNQ concentration


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were presented in Figure 2a, where one intense and sharp diffraction peak assigned to P3HT can be noticed. For the pristine P3HT:PC61BM film without thermal annealing, the intensity of P3HT peak is weak. However, increasing the F4TCNQ content from 0.5 wt.% to 5 wt.%, the reflection peak becomes stronger, signifying the gradually improved crystallinity of P3HT induced by F4TCNQ, which is consistent with the literatures27. Moreover, the grazing incident X-ray diffraction (GIXRD) spectra of the films with different F4TCNQ concentration were shown in Figure 2b. The relative intensity of (100) diffraction peak corresponding to P3HT becomes more distinct upon incorporation of F4TCNQ, even stronger than that of the blends thermal annealed under 150 oC for 10 minutes. It demonstrates that F4TCNQ can induce P3HT from free state to crystalline state, providing an “annealing-free” approach to achieve optimized BHJ morphology. To correlate the X-ray diffraction pattern of the BHJ blend with the morphology of the active layer, the corresponding transmission electron microscopy (TEM) images are shown in Figure S2. For the pristine P3HT:PC61BM, compared with the P3HT:PC61BM:F4TCNQ blend (1 wt.% F4TCNQ), no characteristic morphology could be observed, as shown in Figure S2a. And there is enormous crystalline region in the pure F4TCNQ film due to its high crystallinity of small molecules (Figure S2b). However, for the P3HT:PC61BM:F4TCNQ blend, short nanowires can be clearly detected in Figure S2c, due to strong interaction between P3HT and highly crystallographic F4TCNQ.27 The selected area electron diffraction (SAED) pattern once again certifies the enhancement of crystallinity, as shown in Figure S2d,e,f. UV–Vis absorption of the ternary blends with different F4TCNQ concentration was measured to study the changes in absorption by incorporation of the third component. Figure 2c shows that increasing the F4TCNQ content in the P3HT:PC61BM matrix gradually enhances the absorption from 400 nm to 600 nm. But when the content of F4TCNQ is over 1 wt.%, an evident decline of absorption can be observed. This is because a small content of F4TCNQ can favor crystallization of P3HT:PC61BM matrix, while too much amount of small molecules tends to self-crystallization in active layers, resulting in the damage of P3HT:PC61BM morphology, consistent with



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the TEM results. In addition, the photoluminescence (PL) spectra (Figure 2d) of P3HT:PC61BM shows a strong PL emission peak at 638 nm assigned to the radiative decay of excitons to the ground state. For the PL spectra of P3HT:PC61BM:F4TCNQ films, the emission intensity decreases sharply as the concentration of F4TCNQ increases to 1 wt.%, suggesting that heterojunction interfaces offer located multicharge-transfer-channels for more efficient charge transfer26. However, when the content keep increasing, too severe vertical separation of donor and acceptor makes the emission intensity have a dramatic growth, which also agrees with X-ray diffraction phenomenon. To give a deeper insight on the crystallinity properties of P3HT:PC61BM:F4TCNQ blend,

the

morphology

of

different

depths

of

P3HT:PC61BM

and

P3HT:PC61BM:F4TCNQ active layers with or without thermal annealing treatment were tested. Figure S3 shows the atomic force microscopy (AFM) height images of different depths P3HT:PC61BM films without or with thermal annealing. It can be found that there is no obviously vertical separation in the active layer without thermal treatment. The morphologies of 0 nm deep to 120 nm deep are no big difference, and all of them show mixed and uniform bulk heterojunction phase. However, thermal annealing can give a specific vertical separation in active blend. In Figure S3f-j, we can clearly see abundant enrichment of PC61BM (dark region) at the bottom depth of 120 nm and large amount of P3HT domains on the surface of the blend. After addition of F4TCNQ, F4TCNQ domains can be seen on the surface region of the film (Figure 3), due to the low surface energy of F4TCNQ. The aggregation of F4TCNQ on the surface of the film can also been identified by the changes in the surface energy from 28.1 mN/m (120 nm depth) to 27.8 mN/m (0 nm surface, Figure S4).28 More importantly, comparison of the morphology of the blends with depth from 0 nm to 120 nm, addition of F4TCNQ can directly induce a vertical separation in active layer. Further conducting annealing treatment on the blends does not cause any change in the morphology, indicating that an ordered and stable vertical separation has already developed through F4TCNQ modification. So as to confirm the AFM results, the depth X-ray photoelectron spectroscopy S 2p


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spectrum is presented in Figure 4a. The component of sulfur (S) increases from 7.07% at the 120 nm bottom layer to 8.53% at the surface of P3HT:PC61BM:F4TCNQ 1wt%, while the component of S maintains a balance at the at the top, middle and bottom of P3HT:PC61BM film (0 nm: 7.38%, 50 nm:7.30% and 90 nm: 7.23%; as shown in Figure S5). It is well known that only the thiophene from P3HT contains S element, so the results of XPS depth profiling strongly supports our hypothesis that p type P3HT is apt to migrate to the surface of the active layer owing to the interaction of P3HT with the low surface energy F4TCNQ.26-27 The enrichment of P3HT:F4TCNQ can also be clearly detected by the cross-sectional SEM image, as shown in Figure S6a. A thin layer of P3HT:F4TCNQ can serve as the self-assembled p type interfacial layer between the active layer and metal electrode for efficient charge extraction and collection. On the contrary, there is no obvious stratification in active layer for Glass/ITO-PEIE/P3HT:PC61BM/Au structure (Figure S6b). As for the vertical distribution of the P3HT and F4TCNQ, the work function (WF) of the active layer by UPS also has a vertical change from -4.2 eV (90 nm) to -4.8 eV (0 nm), as shown in Figure 4b. Figure 4c is the schematic energy diagram of each layer involved in the PSCs. From the figure we can see that a simple sandwich PSC only with three layers can be readily realized by employing the P3HT:PC61BM:F4TCNQ 1wt% into the device, if appropriate anode and cathode are evolved. To determine the function of the F4TCNQ on the optoelectronics, the PSCs based on P3HT:PC61BM were fabricated only through a three layers device structure (Electrode/BHJ/Electrode). The electrodes with different work function are precisely selected to evaluate the validity of the F4TCNQ in conventional and inverted device. The work functions of electrodes provided in Figure 4c are measured by Kelvin probe method (Figure S7). The necessity of thermal annealing is firstly studied, and the current density-voltage (J–V) characteristics of inverted cells with various buffer layers under AM 1.5G irradiation at 100 mW·cm−2 are shown in Figure 5a and Table S1. The control Device A (Glass/ITO/P3HT:PC61BM/Al) with conventional structure delivers a PCE of 0.6% with a short-circuit current density (Jsc) of 4.53 mA·cm−2, an open circuit voltage (Voc) of 0.41 V and a fill factor (FF) of 0.32. After thermal



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annealing, the FF of the Device B (Glass/ITO/P3HT:PC61BM/Al (with annealing)) increases to 0.48 together with improved PCE and Jsc, because the annealing treatment promotes the vertical separation of active layer and improve the morphology of the BHJ film. When the 1 wt.% F4TCNQ was added in mix-solvent BHJ, all of the device parameters, e.g. PCE, Jsc, Voc and FF are substantially rise in Device C (Glass/ITO/P3HT:PC61BM:F4TCNQ/Al), resulting from the improved crystallinity and increased light absorption in active layer. The PCE of 2.4% for Device C without annealing is almost equal to that of 2.5% for Device D with annealing. The vertical nanomorphology optimized directly by the addition of F4TCNQ should be responsible for the improved performance. Therefore, the addition of F4TCNQ in P3HT:PC61BM blend can simplify device structure and provide an annealing-free process. To further improve the PCE based on P3HT:PC61BM:F4TCNQ system, different electrodes were introduced in this simple device (Figure 5b and Table S1). A higher WF cathode ITO- CHCl329 (chloroform pretreatment on ITO, -4.9 eV) and a lower WF cathode ITO-PEIE30 (polyethylenimine pretreatment on ITO, -4.2 eV) were replace the bare ITO electrode. Device E based on ITO- CHCl3 exhibits a reduced PCE of 1.4%. From the UPS result, the WF of 90 nm deep active layer (near the bottom) is -4.2 eV due to the bottom enrichment of PC61BM. However, for a favorable energy alignment in the device, the WF of bare ITO is too high to serve as a bottom electrode. Therefore, the bottom electrode was replaced by ITO-PEIE, a popular electrode with WF of 4.2 eV, in such a way that the device is indeed changed from a conventional structure to inverted one. As expected, incorporation of ITO-PEIE cathode into device can dramatically improve the PCE to 2.8%, together with a growing FF of 0.65. The FF originates from the improved interfacial contact through the reduced work function of cathode after PEIE dipping. Note that the anode Al used in Device F does not well match with the active blend, due to the unsuitable WF (Al: 4.2 eV vs top abundant P3HT layer: 4.8 eV). Hence, two metal anode with higher WF (Ag:-4.5 eV and Au:-5.0 eV) were employed in the devices for improving the performance. As shown

in

Figure

5b

and

Table

S1,

the

high


WF

of

Device

H

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(Glass/ITO-PEIE/P3HT:PC61BM:F4TCNQ/Au) emerges a highest PCE of 4.1%, with a Jsc of 10.12 mA·cm−2, a Voc of 0.63 V and a FF of 0.65. The well aligned energy level forms an ohmic contact to enhance the local charge extraction and reduce the charge combination, leading to the improvement in performance.24, 26 In Figure S8 All the Jsc calculated from integration of the IPCE spectrum from 300 nm to 800 nm is in good agreement with the Jsc obtained from J–V curve. To further satisfy the demand of commercial production, we selected a solution processed composite carbon electrode as top anode and changed the ITO substrate to flexible polyethylene glycol terephthalate (PET) in PSCs. The J–V curves of the PSCs based on P3HT:PC61BM:F4TCNQ blend is shown in Figure 5b, and the device parameters

are

listed

in

Table

S1.

semi-transparent

Delightfully, Device

all

solution

processed I

(Glass/ITO-PEIE/P3HT:PC61BM:F4TCNQ/PEDOT:PSS:CNTs31) exhibits a PCE of 2.2% and the low temperature devices based on PET substrate also shows a good adaptability, with the Device J (PET/ITO-PEIE/P3HT:PC61BM:F4TCNQ/Au) and Device K (PET/ITO-PEIE/P3HT:PC61BM:F4TCNQ/PEDOT:PSS:CNTs) obtaining the PCE of 3.4% and 1.6%, respectively. Conclusions In conclusion, P3HT:PC61BM:F4TCNQ ternary blend with vertical phase separation is skillfully and directly prepared by a mix-solvent treatment of dichlorobenzene and chloroform for PSCs. After the incorporation of F4TCNQ with mix-solvent treatment, the interaction between the P3HT and F4TCNQ can not only effectively improve the crystallinity of active layer for charge transportation, but also induce a well vertical phase separation without thermal treatment. More interestingly, the enrichment of PC61BM on the bottom and P3HT:F4TCNQ on the top of active layer causes a favorable energy alignment in devices for efficient charge extraction and collection. As a result, after precise energy level engineering for electrodes, a simple three layers device based on the Glass/ITO-PEIE/P3HT:PC61BM:F4TCNQ/Au shows a highest PCE of 4.1%. It also demonstrates good adaptability for solution processed electrode and flexible substrates. This simple device structure and “annealing-free” method of



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efficient polymer solar cells provide an opportunity for large-scale commercial production in the near future.

Experimental sections Device fabrication The polymer solar cells were fabricated on indium-tin oxide (ITO) coated glass or polyethylene terephthalate (PET) substrates. The ITO electrode was cleaned with sequential ultrasonic treatment in acetone, detergent, deionized water, and isopropanol, the ITO-PEIE electrode was dipped in polyethylenimine solution for 40 minutes; The polyethylenimine, 80% ethoxylated (PEIE; Mw = 70,000 g/mol, was dissolved in H2O with a concentration of 35-40 wt% when received from Aldrich. Then it was further diluted with 2-methoxyethanol to a weight concentration of 0.2 %.); the ITOCHCl3 electrode was dipped in chloroform (CHCl3) solution for 40 minutes. The ITO electrodes were dried by nitrogen flow followed by plasma treatment for 30 seconds. After cleaning, The P3HT:PC61BM (1:1 w/w, 20 mg•mL-1) blends in 1,2 dichlorobenzene (DCB) and the PC61BM:F4TCNQ blends was dissolved in mixed solvent (DCB: CHCl3=90:10) were stirred in glove box at 60 °C overnight, which was spin-cast on top of the ITO electrodes producing a 130 nm thick active layer and dried in the glove box. The devices are annealed at 150 °C for 10 min on hotplate in a glove box after 3 hours drying. Then 100 nm Al and Ag and Au were evaporated through a shadow mask under 6×10-6 Torr. The PEDOT:PSS CNTs electrodes were transferred from PDMS samples.32 During the device fabrication, the samples and active solution always maintain at 60 oC.

Supporting Information The detailed experimental sections and the corresponding characterization are in Supporting Information. This information is available free of charge via the Internet at http://pubs.acs.org


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Acknowledgements This work was financially supported by the National Science Fund for Distinguished Young Scholars (51425304), National Natural Science Foundation of China (51273088, 51263016 and 51473075), and National Basic Research Program of China (973 Program 2014CB260409). Xiaotian Hu and Lie Chen contributed equally to this work.



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References (1) Yu, G.; Gao, J.; Hummelen, J.; Wudl, F.; Heeger, A., Polymer Photovoltaic Cells: Enhanced Efficiencies via a Network of Internal Donor-Acceptor Heterojunctions. Science 1995, 270, 1789-1791. (2) Dou, L.; You, J.; Yang, J.; Chen, C.-C.; He, Y.; Murase, S.; Moriarty, T.; Emery, K.; Li, G.; Yang, Y., Tandem Polymer Solar Cells Featuring a Spectrally Matched Low-Bandgap Polymer. Nat. Photonics 2012, 6, 180-185. (3) Heeger, A. J., 25th Anniversary Article: Bulk Heterojunction Solar Cells: Understanding the Mechanism of Operation. Adv. Mater. 2014, 26, 10-28. (4) Espinosa, N.; García-Valverde, R.; Urbina, A.; Lenzmann, F.; Manceau, M.; Angmo, D.; Krebs, F. C., Life Cycle Assessment of ITO-Free Flexible Polymer Solar Cells Prepared by Roll-to-Roll Coating and Printing. Sol. Energy Mater. Sol. Cells 2012, 97, 3-13. (5) Søndergaard, R.; Manceau, M.; Jørgensen, M.; Krebs, F. C., New Low-Bandgap Materials with Good Stabilities and Efficiencies Comparable to P3HT in R2R-Coated Solar Cells. Adv. Energy Mater. 2012, 2, 415-418. (6) He, Z.; Zhong, C.; Su, S.; Xu, M.; Wu, H.; Cao, Y., Enhanced Power-Conversion Efficiency in Polymer Solar Cells Using an Inverted Device Structure. Nat. Photonics 2012, 6, 591-595. (7) Liu, Y.; Zhao, J.; Li, Z.; Mu, C.; Ma, W.; Hu, H.; Jiang, K.; Lin, H.; Ade, H.; Yan, H., Aggregation and Morphology Control Enables Multiple Cases of High-Efficiency Polymer Solar Cells. Nat. Commun. 2014, 5. (8) Zuo, L.; Chueh, C. C.; Xu, Y. X.; Chen, K. S.; Zang, Y.; Li, C. Z.; Chen, H.; Jen, A. K. Y., Microcavity‐Enhanced Light‐Trapping for Highly Efficient Organic Parallel Tandem Solar Cells. Adv. Mater. 2014, 26, 6778-6784. (9) Lin, Y.; Dam, H. F.; Andersen, T. R.; Bundgaard, E.; Fu, W.; Chen, H.; Krebs, F. C.; Zhan, X., Ambient Roll-to-Roll Fabrication of Flexible Solar Cells Based on Small Molecules. J Mater Chem C 2013, 1, 8007-8010. (10) Chen, K.-S.; Salinas, J.-F.; Yip, H.-L.; Huo, L.; Hou, J.; Jen, A. K.-Y., Semi-Transparent Polymer Solar Cells with 6% PCE, 25% Average Visible Transmittance and a Color Rendering Index Close to 100 for Power Generating Window Applications. Energy Environ. Sci. 2012, 5, 9551-9557. (11) 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. (12) Lu, L.; Xu, T.; Chen, W.; Landry, E. S.; Yu, L., Ternary Blend Polymer Solar Cells with Enhanced Power Conversion Efficiency. Nat. Photonics 2014, 8, 716-722. (13) Gu, Y.; Wang, C.; Liu, F.; Chen, J.; Dyck, O. E.; Duscher, G.; Russell, T. P., Guided Crystallization of P3HT in Ternary Blend Solar Cell Based on P3HT: PCPDTBT: PCBM. Energy Environ. Sci. 2014, 7, 3782-3790. (14) Lloyd, M. T.; Mayer, A. C.; Subramanian, S.; Mourey, D. A.; Herman, D. J.; Bapat, A. V.; Anthony, J. E.; Malliaras, G. G., Efficient Solution-Processed


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Photovoltaic Cells Based on an Anthradithiophene/Fullerene Blend. J. Am. Chem. Soc. 2007, 129, 9144-9149. (15) Ameri, T.; Khoram, P.; Min, J.; Brabec, C. J., Organic Ternary Solar Cells: A Review. Adv. Mater. 2013, 25, 4245-4266. (16) Khlyabich, P. P.; Burkhart, B.; Thompson, B. C., Compositional Dependence of the Open-Circuit Voltage in Ternary Blend Bulk Heterojunction Solar Cells Based on Two Donor Polymers. J. Am. Chem. Soc. 2012, 134, 9074-9077. (17) He, Z.; Wu, H.; Cao, Y., Recent Advances in Polymer Solar Cells: Realization of High Device Performance by Incorporating Water/Alcohol‐Soluble Conjugated Polymers as Electrode Buffer Layer. Adv. Mater. 2014, 26, 1006-1024. (18) Meyer, J.; Hamwi, S.; Kröger, M.; Kowalsky, W.; Riedl, T.; Kahn, A., Transition Metal Oxides for Organic Electronics: Energetics, Device Physics and Applications. Adv. Mater. 2012, 24, 5408-5427. (19) Cai, W.; Gong, X.; Cao, Y., Polymer Solar Cells: Recent Development and Possible Routes for Improvement in the Performance. Sol. Energy Mater. Sol. Cells 2010, 94, 114-127. (20) Liu, J.; Kim, G. H.; Xue, Y.; Kim, J. Y.; Baek, J. B.; Durstock, M.; Dai, L., Graphene Oxide Nanoribbon as Hole Extraction Layer to Enhance Efficiency and Stability of Polymer Solar Cells. Adv. Mater. 2014, 26, 786-790. (21) Liu, J.; Durstock, M.; Dai, L., Graphene Oxide Derivatives as Hole-and Electron-Extraction Layers for High-Performance Polymer Solar Cells. Energy Environ. Sci. 2014, 7, 1297-1306. (22) 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, 441-444. (23) Miller, N. C.; Cho, E.; Gysel, R.; Risko, C.; Coropceanu, V.; Miller, C. E.; Sweetnam, S.; Sellinger, A.; Heeney, M.; McCulloch, I., Factors Governing Intercalation of Fullerenes and Other Small Molecules between the Side Chains of Semiconducting Polymers Used in Solar Cells. Adv. Energy Mater. 2012, 2, 1208-1217. (24) Pingel, P.; Zhu, L.; Park, K. S.; Vogel, J. r.-O.; Janietz, S.; Kim, E.-G.; Rabe, J. r. P.; Brédas, J.-L.; Koch, N., Charge-Transfer Localization in Molecularly Doped Thiophene-Based Donor Polymers. J. Phys. Chem. Lett. 2010, 1, 2037-2041. (25) Duong, D. T.; Phan, H.; Hanifi, D.; Jo, P. S.; Nguyen, T. Q.; Salleo, A., Direct Observation of Doping Sites in Temperature‐Controlled, P‐Doped P3HT Thin Films by Conducting Atomic Force Microscopy. Adv. Mater. 2014, 26, 6069-6073. (26) Pingel, P.; Neher, D., Comprehensive Picture of P-Type Doping of P3HT with the Molecular Acceptor F4TCNQ. Phys. Rev. B 2013, 87, 115209. (27) Deschler, F.; Riedel, D.; Deák, A.; Ecker, B.; von Hauff, E.; Da Como, E., Imaging of Morphological Changes and Phase Segregation in Doped Polymeric Semiconductors. Synth. Met. 2015, 199, 381-387. (28) Wei, Q.; Nishizawa, T.; Tajima, K.; Hashimoto, K., Self‐Organized Buffer Layers in Organic Solar Cells. Adv. Mater. 2008, 20, 2211-2216. (29) Xu, Z.; Li, J.; Yang, J.; Cheng, P.; Zhao, J.; Lee, S.; Li, Y.; Tang, J., Enhanced



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Performance in Polymer Photovoltaic Cells with Chloroform Treated Indium Tin Oxide Anode Modification. Appl. Phys. Lett. 2011, 98, 253303. (30) Zhou, Y., et al., A Universal Method to Produce Low-Work Function Electrodes for Organic Electronics. Science 2012, 336, 327-32. (31) Hu, X.; Chen, L.; Zhang, Y.; Hu, Q.; Yang, J.; Chen, Y., Large-Scale Flexible and Highly Conductive Carbon Transparent Electrodes Via Roll-to-Roll Process and Its High Performance Lab-Scale Indium Tin Oxide-Free Polymer Solar Cells. Chem. Mater. 2014, 26, 6293-6302. (32) Hau, S. K.; Yip, H.-L.; Zou, J.; Jen, A. K.-Y., Indium Tin Oxide-Free Semi-Transparent Inverted Polymer Solar Cells Using Conducting Polymer as Both Bottom and Top Electrodes. Org. Electron. 2009, 10, 1401-1407.


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Figure 1. Chemical structures of the photoactive layer used in the devices fabrication.

Figure 2. (a) X-ray diffraction (XRD) spectra of P3HT:PC61BM blend system with different F4TCNQ concentration. (b) Grazing incident X-ray diffraction (GIXRD) spectra of P3HT:PC61BM blend system with different conditions or F4TCNQ concentration. (c) The UV-vis absorption profiles of P3HT:PC61BM blend films with different F4TCNQ concentration. (d) PL spectra of the thin films of P3HT:PC61BM blend films with different F4TCNQ concentration.



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Figure 3. Tapping-mode atomic force microscopy (AFM) height images (scan range: 5µm×5µm) of different depths P3HT:PC61BM:F4TCNQ 1wt% films without thermal annealing ((a)-(e) for 0 nm, 30 nm, 60 nm, 90 nm and 120 nm, respectively) and different depths P3HT:PC61BM:F4TCNQ films with thermal annealing ((f)-(j) for 0 nm, 30 nm, 60 nm, 90 nm and 120 nm, respectively).

Figure 4. (a) X-ray photoelectron spectroscopy (XPS) S 2p spectra of as-cast P3HT:PC61BM:F4TCNQ 1wt%films without etching, after etching for 30 nm, 60 nm, 90 nm; (b) work function of as-cast P3HT:PC61BM:F4TCNQ films without etching, after etching for 30 nm, 60 nm, 90 nm by Ultraviolet Photoelectron Spectroscopy (UPS); (c) the schematic energy diagram of the electrodes involved in the PSCs.


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Figure 5. (a) and (b) Current (J)–voltage (V) characteristics of cells based on different devices: Device A: Glass/ITO/P3HT:PC61BM/Al Device B: Glass/ITO/P3HT:PC61BM/Al (with annealing) Device C: Glass/ITO/ P3HT:PC61BM:F4TCNQ/Al Device D: Glass/ITO/P3HT:PC61BM:F4TCNQ/Al (with annealing) Device E: Glass/ITO-CHCl3/P3HT:PC61BM:F4TCNQ/Al Device F: Glass/ITO-PEIE/ P3HT:PC61BM:F4TCNQ/Al Device G: Glass/ITO-PEIE/P3HT:PC61BM:F4TCNQ/Ag Device H: Glass/ITO-PEIE/P3HT:PC61BM:F4TCNQ/Au Device I: Glass/ITO-PEIE/P3HT:PC61BM:F4TCNQ/PEDOT:PSS:CNTs Device J: PET/ITO-PEIE/P3HT:PC61BM:F4TCNQ/Au Device K: PET/ITO-PEIE/P3HT:PC61BM:F4TCNQ/PEDOT:PSS:CNTs



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Table of content A Facile Approach to Fabricate High Performance Polymer Solar Cells with Annealing-Free and Simple Device of Three Layers Xiaotian Hu, Lie Chen, Yong Zhang, Lin Zhang, Yuanpeng Xie, Weihua Zhou, Wen Chen, Yiwang Chen* A

novel,

facile

approach

to

develop

poly(3-hexylthiophene):(6,6)-phenyl-C61

favorably butyric

2,3,5,6-tetrafluoro-7,7,8,8,-tetracyano-quinodimethane

vertical acid

separation methyl

in

ester:

(P3HT:PC61BM:F4TCNQ)

ternary blend through the interaction and spontaneous drive function between P3HT and F4TCNQ has been demonstrated. The high efficient PSCs only with three layers have also been realized. This simple and low temperature method for efficient polymer solar cells provides an opportunity for large-scale commercial production in the near future.

Graphical abstract


A Facile Approach To Fabricate High-Performance Polymer Solar

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