Unusual Performance Increase in Polymer Solar Cells by Cooling a

Research Article Cite This: ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

www.acsami.org

Unusual Performance Increase in Polymer Solar Cells by Cooling a Hot Donor/Acceptor Ink in a Good Solvent Han Yan,*,†,‡,§ Shuyang Ye,†,§ and Dwight S. Seferos*,† †

Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario M5S 3H6, Canada State Key Laboratory for Mechanical Behavior of Materials, College of Material Science and Engineering, Xi’an Jiaotong University, Xi’an 710049, P. R. China

‡

S Supporting Information *

ABSTRACT: Post processing is widely used to improve the photovoltaic performance of organic solar cells. However, high-temperature and long-time release of halogenated solvents are incompatible with future printing manufacturing. Inspired by the dependence of donor/acceptor optical properties on “ink” temperature, we designed a study to test its effect on photovoltaic performance. We utilize the newly reported nonfullerene ink, poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl)benzo[1′,2′c:4′,5′-c′]dithiophene-4,8-dione))]/3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′d′]-s-indaceno[1,2-b:5,6-b′]dithiophene as a model system, and find that device performance can be improved by heating and then cooling the ink in a specific temperature range. Careful analysis reveals that device improvement comes from the optimized phase miscibility and has a negligible effect on charge-transport properties. We further propose that heating and cooling the ink optimizes the phase formation time, phase distribution, and interphase diffusion in the blend films. Finally, the general nature of this process is demonstrated using a more typical polymer/fullerene system. These findings are important because this effect could potentially lead to progress in organic solar cell manufacturing. KEYWORDS: organic solar cell, solution temperature, temperature-dependent spectrum, morphology evolution, bulk-heterojunction formation, nonfullerene

■

INTRODUCTION Power conversion efficiency (PCE) of polymer solar cell has increased from 5 to 13% over the last decade.1,2 Understanding and then rationally modifying the morphology plays a key role in this progress. Morphology optimization usually involves tuning the crystallinity, domain size, phase purity, and molecular orientation.3−6 To achieve this goal, methodologies including thermal annealing,7,8 solvent annealing,9 and solvent additives with selective solubility10,11 have been developed. From an industrial printing-based manufacturing perspective, the “ink”, that is, the donor/acceptor solution, as well as any post deposition processes require careful consideration. Hightemperature thermal annealing is potentially problematic for flexible plastic substrates. Solvent annealing takes considerable time, and this, combined with the use of halogenated solvents, may be harmful to the environment and the device performance.12 It is imperative to develop a process that satisfies the requirements for future printing manufacturing without these drawbacks. An ideal strategy is to directly modify the morphology from the ink without post processing. Preassembly, in which a poor solvent is chosen to induce polymer aggregation in a solution, is commonly used in polymer solar cell fabrication to facilitate © XXXX American Chemical Society

molecular stacking and hence extend the photon absorption range as well as charge carrier mobility. This strategy has been successfully used in poly(3-alkylthiophene) (P3AT) systems13−15 and its corresponding derivatives such as poly(3alkylselenophene) and polythiophene−polyselenophene statistical polymers.16−18 However, there are several limitations: first, preassembly is difficult to apply to high-performance polymers because they are intrinsically much more amorphous than P3AT; second, poor solvents usually lead to the overgrowth of high-purity phases in the active layer, which decreases the probability of charge separation within the active layer. These drawbacks have limited the application of preassembly to only certain classes of conjugated polymers, and not those that are now achieving record performances.

■

RESULTS AND DISCUSSION Recently, it has been reported that high-performance polymers demonstrate a notable change in their absorption spectra at varying temperatures.19−21 This is the result of intramolecular Received: October 5, 2017 Accepted: December 13, 2017

A

DOI: 10.1021/acsami.7b15113 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Research Article

ACS Applied Materials & Interfaces

Figure 1. (a) Solution absorption spectra of PBDB-T. (b) Corresponding PL spectra; the inset is the corresponding chemical structure. (c) Photovoltaic performances of PBDB-T/ITIC. (d) Photograph J−V curves of PBDB-T/ITIC.

Table 1. Photovoltaic Performance of PBDB-T/ITIC and Corresponding Photograph J−V Parameters temperature (°C)

Jsc (mA/cm2)

Voc (V)

FF (%)

PCE (%)

40 60 60−40 80 80−40

13.9 14.5 16.0 13.5 14.1

0.88 0.89 0.89 0.88 0.88

63.1 61.5 60.4 56.9 57.1

7.7 7.9 8.6 6.8 7.1

PCEavg (%)

Jsat (mA/cm2)

P (%)

± ± ± ± ±

14.6 15.0 16.8 14.0 14.8

93 94 94 94 94

7.5 7.6 8.4 6.4 6.9

0.1 0.2 0.2 0.2 0.1

We next study the effect of solution temperature on photovoltaic performance. Inverted polymer solar cells are fabricated by spin-coating from solutions at 40, 60, and 80 °C. At these deposition temperatures, the PCE increases from 7.7 to 7.9%, and then falls to 6.8% (Figure 1c and Table 1). It seems that mild molecular twisting and modest aggregation can slightly increase the photovoltaic performance. To exclude the effect of solvent evaporation rate, we cool the hotter solution down to 40 °C before spin-coating. Surprisingly, we find that PCE can be improved to as high as 8.6% when cooling the solution from 60 to 40 °C. This observation stands in contrast to previous knowledge in the field. Specifically, the cooled solution should lead to the same device performance as the 40 °C solution. The unusual increase after cooling is similar to the self-assembly of linear conjugated polymers, where cooling induces assembly of nanostructures that extend the absorption in the red and enhance the charge mobility.13−18 We then examine the cooling effect on molecular arrangement. From the overlapping absorption spectra (Figure S2), we conclude that the degree of intramolecular twisting is recovered as the solution is cooled. However, according to the PL spectra (Figure S3), the PL intensity after cooling process is not fully recovered to the initial value, demonstrating the intermolecular aggregation differences remain. It is important to note that the cooling process increases the short-circuit current (Jsc), whereas the open-circuit voltage

twisting or intermolecular aggregation. Therefore, controlling the ink temperature may provide an opportunity to directly modify the blend morphology before deposition. Inspired by this, we have designed a study to directly test the effect of ink temperature on photovoltaic performance. We utilize the newly reported nonfullerene poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene))-alt-(5,5(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl)benzo[1′,2′-c:4′,5′-c′]dithiophene-4,8-dione))] (PBDB-T) and 3,9-bis(2-methylene(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene (ITIC),22−24 as a model high-performance system (insets of Figure 1a and Scheme S1). Chlorobenzene is used as a good solvent. The temperature-dependent evolution of the absorption spectra is first confirmed in PBDB-T alone (Figure 1a). Heating the solution results in a decrease in longwavelength absorption, presumably due to decreased π−π stacking caused by intramolecular distortion. The solution photoluminescence (PL) spectra are measured to examine the intermolecular aggregation (Figure 1b). The PL intensity increases when the solution is heated and the relative intensity of the π−π stacking emission shoulder decreases. The trends observed in the absorption and PL spectra in the PBDB-T:ITIC blend solution are consistent with the pure polymer (Figure S1), demonstrating that PBDB-T plays a major role in the spectral evolution. B


Research Article


Figure 2. (a) Film absorption spectra of PBDB-T/ITIC. (b, c) Film photoluminescence spectra of PBDB-T/ITIC: (b) excited at 570 nm; (c) excited at 670 nm. (d−f) Atomic force microscopy (AFM) phase images of PBDB-T/ITIC blend films (2 μm × 2 μm) spin-coating at various solution temperatures: (d) 40 °C; (e) 60 °C; (f) 60−40 °C. (g−i) Wide-angle X-ray scattering (WAXS) plots of PBDB-T/ITIC blend films spincoating at various solution temperatures: (g) 40 °C; (h) 60 °C; (i) 60−40 °C.

(Voc) and fill factors (FF) are almost unchanged. The Jsc increase is further supported by the external quantum efficiency (EQE) measurements (Figure S4). Similar behavior is observed when cooling the solution from 80 to 40 °C, albeit to a lesser extent. We then measure the photocurrent density (Jph) versus effective voltage curves (V0−V, in which V0 is the built-in voltage, and V is the applied voltage) (Figure 1d). We extract the saturated current density (Jsat) at 3 V, which is consistent with the Jsc. The charge extraction probability (P) is also calculated as Jsc/Jsat: the constant value indicates a remarkable consistency between Jsc and Jsat. Detailed recombination measurements (Figure S5) demonstrate that there is no effect of temperature on charge-transport behavior in the range of temperatures examined. Although cooling the solution increases Jsc, we suspect this is different from the preassembly in a solution based on the absorption spectra and unchanged charge-transport behavior. To better understand the solution temperature effects on device performance, we investigate the blend films directly. The improved photocurrent may come from better photon absorption or charge separation. We observe enhanced

absorption peaks at both 633 and 708 nm when deposited at elevated temperature (Figure 2a), which are assigned to the absorption of PBDB-T and ITIC, respectively (Figure S6). Interestingly, when cooling the solution back to 40 °C, the ITIC absorbance is maintained, whereas the polymer absorbance decreases slightly (Figure 2a). Thin-film PL spectroscopy is measured to characterize and quantify charge separation efficiency. We excite the blend film at 570 and 670 nm (Figure 2b,c), which correspond to the PBDB-T and ITIC absorption maximum, respectively. The thin films possess a higher PL intensity when cast from highertemperature solutions, indicating less efficient charge separation. An exception occurred when cooling the 60 °C solution to 40 °C. Here, we observe the largest amount of PL quenching when excited at 670 nm, which is consistent with the higher Jsc in this condition. Compared with the use of poor solvents or low temperature,13−18 it appears that heating the solution in a good solvent can induce ordered molecular stacking in the blend film, in contrast to the existing preassembly methods. This difference distinguishes our work from the traditional preassembly methods. C


Research Article

ACS Applied Materials & Interfaces To further examine the impact of blend morphology on charge separation, we characterize films cast from 40, 60, to 60−40 °C solutions using the atomic force microscopy (AFM). Phase images are presented in Figure 2d−f (corresponding height images can be found in Figure S7) and are used to estimate the domain size and phase purity through particle analysis and examination of the phase contrast peak at full width at half-maximum (FWHM) (Table 2). Heating the Table 2. AFM and WAXS Data of PBDB-T/ITIC Blend Films temperatures (°C)

domain size (nm)

FWHM (deg)

d-spacing (Å)

π−π distance (Å)

coherence length (Å)

40 60 60−40

42.8 51.7 45.8

4.34 7.95 5.32

20.89 20.12 20.09

3.90 3.82 3.86

56.64 59.05 56.66

Figure 3. (a−c) Proposed mechanism of heating and cooling roles on the blend film morphology. The red ellipsoids represent PBDB-T aggregates; the gray arrows represent ITIC-rich solution flow; the gray spheres represent ITIC aggregates. (d−f) The heating and cooling process is also schemed on the time scale. The solid lines represent the materials’ precipitation under initial and heating conditions; the dashed line represent the polymer’s precipitation after cooling process.

solution from 40 to 60 °C leads to domain growth from 42.8 to 51.7 nm. Subsequent cooling lowers the domain size to an intermediate value, 45.8 nm. Similarly, the smallest FWHM value is found in the film cooled from 60 to 40 °C, indicative of better phase miscibility (Figure S8). The AFM results are therefore consistent with the PL results. The combined heating and cooling process is an effective method to control the domain size and phase purity in blend films that cannot be achieved at a single deposition temperature. To fully understand the blend film morphology, we use a wide-angle X-ray scattering (WAXS) to examine the molecular stacking. We observe the (100) and (020) peaks for PBDB-T, which represent the alkyl chain and π−π stacking respectively, whereas no obvious diffraction signal is recorded for ITIC (Figure S9). The WAXS plots of blend films are shown in Figure 2g−i. A prominent (100) diffraction ring in blend films deposited from 60 and 60 to 40 °C solutions is observed. This indicates that these blend films have more multidirectional organization, which may enhance the three-dimensional charge transport. We calculate the corresponding alkyl chain and π−π stacking distances (Table 2). Heating the solution to 60 °C induces a close packing for PBDB-T, which persists after cooling the solution back to 40 °C. The coherence length is summarized in Table 2. Heating the solution induces a larger polymer stacking length, which decreases upon cooling. According to the WAXS data, the combined heating and cooling process leads to close packing of polymer chain while maintaining the crystalline size. Our analysis shows that changes in morphology are responsible for improvements in device performance. Here, we propose the further role of heating and cooling on the morphology. The blend film formation can be divided into three steps: PBDB-T precipitates first due to relatively poor solubility, forming polymer networks (the solubility of PBDB-T and ITIC is 14 and 64 mg/mL, respectively, at 40 °C) (Figure 3a); then, the ITIC-rich solution infiltrates into the networks forming mixed phases (Figure 3b); finally, ITIC precipitates into pure domains (Figure 3c). The whole process occurs on a relative time scale (Figure 3d−f). The time between PBDB-T and ITIC phase formation corresponds to the ITIC solution diffusion time. The heating and subsequent cooling changes diffusion time of ITIC by tuning the solubility, thus modifying the mixed and pure ITIC phase. We find that the solubility of PBDB-T shows a greater temperature dependence, increasing from 19 mg/mL (60 °C) to 24 mg/mL (80 °C), whereas the

solubility of ITIC changes slightly, from 65 to 67 mg/mL. Due to the shorter ITIC diffusion time, less mixed phase is present in the blend and, thus, the purity of PBDB-T and ITIC phase increases. Cooling from 60 to 40 °C causes some of the PBDBT to reaggregate, which is supported by our PL results, thus PBDB-T precipitates on a longer time scale than when directly spin-coated at 60 °C, forming a multiscale morphology with ITIC. The multiscale phase successfully improves the phase miscibility. When cooling from 80 °C, the polymer required more time to reaggregate, thus it did not lead to better morphology and device performance than spin-coating at 40 °C. Based on the analysis, we propose that the roles of heating and cooling in solution are tuning the phase formation time, phase distribution, and interphase diffusion in the blend films. To further examine our proposed mechanism, we test the general nature of this approach. We fabricate devices using poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b :4,5b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene)-2-carboxylate-2,6-diyl] (PCE10) and [6,6]phenyl-C71-butyric acid methyl ester (PC71BM) system (insets of Figure 4a and Scheme S1), which is a well-studied fullerene material system. We observed a largely temperature-dependent absorption and PL spectra of PCE10 (Figure 4a,b), and the temperature-dependent photovoltaic performance (Figure 4c,d and Table 3). Although the best PCE is from 40 °C solution, the largest Jsc still comes from the cooling solution, which is consistent with the results for PBDB-T/ITIC. The unimproved PCE points out that the ink temperature effect is material system dependent. The morphology evolution is confirmed by the AFM in Figure S10.

■

CONCLUSIONS In conclusion, we have studied the effect of ink solution temperature on the performance of a nonfullerene and a fullerene material system for organic solar cells. In both cases, the solution temperature-dependent PCEs are observed. Cooling the hot solution effectively optimizes the blend film morphology with negligible effect on charge transport. We feel that these findings are important because the dependence of polymer solar cell performance on processing temperature has broad significance. This effect of the solution temperature likely extends to other systems and could be combined with other D


Research Article


Figure 4. (a) Solution absorption spectra of PCE10. (b) Corresponding PL spectra; the inset is the corresponding chemical structure. (c) J−V curves of PCE10/PC71BM. (d) Corresponding EQE curves.

Author Contributions

Table 3. Photovoltaic Performances of PCE10/PC71BM temperatures (°C)

Jsc (mA/cm2)

Voc (V)

FF (%)

PCE (%)

40 60 60−40 80 80−40

17.10 17.21 17.42 16.70 17.24

0.80 0.80 0.80 0.80 0.80

66.81 57.74 62.64 57.56 61.92

9.1 8.0 8.7 7.7 8.5

The manuscript was written through contributions of all of the authors. All of the authors have given approval to the final version of the manuscript.

PCEavg (%) 8.9 7.8 8.4 7.5 8.3

± ± ± ± ±

0.2 0.1 0.1 0.1 0.2

Funding

This work was supported by the NSERC of Canada, the Canadian Foundation for Innovation and the Ontario Research Fund. Notes

The authors declare no competing financial interest.

■

morphology optimization methods, leading to progress in organic solar cell manufacturing.

■

ACKNOWLEDGMENTS The authors thank Joseph Manion for carefully reading and providing feedback on the manuscript.

ASSOCIATED CONTENT

■

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.7b15113. Further details on experiments and analysis, including device fabrication, chemical structures, absorption spectra, PL spectra, WAXS, EQE plots, measured Jsc and Voc of PBDB-T/ITIC plotted against light intensity, film absorption spectra, AFM height images, phase contrast curves (PDF)

■

ABBREVIATIONS

PCE, power conversion efficiency; P3AT, poly(3-alkylthiophene); P3AS, poly(3-alkylselenophene); PBDB-T, poly[(2,6(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2ethylhexyl)benzo[1′,2′-c:4′,5′-c′]dithiophene-4,8-dione))]; ITIC, 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′d′]-s-indaceno[1,2-b:5,6-b′]dithiophene; PL, photoluminescence; Jsc, short-circuit current; Voc, open-circuit voltage; FF, fill factors; EQE, external quantum efficiency; Jph, photocurrent density; Jsat, saturated current density; AFM, atomic force microscopy; FWHM, full width at half-maximum; 2D-XRD, two-dimensional X-ray diffraction; PCE10, poly[4,8-bis(5-(2ethylhexyl)thiophen-2-yl)benzo[1,2-b :4,5-b′]dithiophene-2,6diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene)-2carboxylate-2,6-diyl)]; PC71BM, [6,6]-phenyl-C71-butyric acid methyl ester

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (H.Y.). *E-mail: [email protected] (D.S.S.). ORCID

Dwight S. Seferos: 0000-0001-8742-8058 Author Contributions §

H.Y. and S.Y. contributed equally to this work. E


Research Article


■

(20) Ma, W.; Yang, G.; Jiang, K.; Carpenter, J. H.; Wu, Y.; Meng, X.; McAfee, T.; Zhao, J.; Zhu, C.; Wang, C.; Ade, H.; Yan, H. Organic Solar Cells: Influence of Processing Parameters and Molecular Weight on the Morphology and Properties of High-Performance PffBT4T2OD:PC71BM Organic Solar Cells. Adv. Energy Mater. 2015, 5, No. 1501400. (21) Ma, T.; Jiang, K.; Chen, S.; Hu, H.; Lin, H.; Li, Z.; Zhao, J.; Liu, Y.; Chang, Y.-M.; Hsiao, C.-C.; Yan, H. Efficient Low-Bandgap Polymer Solar Cells with High Open-Circuit Voltage and Good Stability. Adv. Energy Mater. 2015, 5, No. 1501282. (22) Bin, H.; Zhang, Z.-G.; Gao, L.; Chen, S.; Zhong, L.; Xue, L.; Yang, C.; Li, Y. Non-Fullerene Polymer Solar Cells Based on Alkylthio and Fluorine Substituted 2D-Conjugated Polymers Reach 9.5% Efficiency. J. Am. Chem. Soc. 2016, 138, 4657−4664. (23) Lin, Y.; Zhao, F.; He, Q.; Huo, L.; Wu, Y.; Parker, T. C.; Ma, W.; Sun, Y.; Wang, C.; Zhu, D.; Heeger, A. J.; Marder, S. R.; Zhan, X. High-Performance Electron Acceptor with Thienyl Side Chains for Organic Photovoltaics. J. Am. Chem. Soc. 2016, 138, 4955−4961. (24) Zhao, W.; Qian, D.; Zhang, S.; Li, S.; Inganäs, O.; Gao, F.; Hou, J. Fullerene-Free Polymer Solar Cells with over 11% Efficiency and Excellent Thermal Stability. Adv. Mater. 2016, 28, 4734−4739.

REFERENCES

(1) Zhao, W.; Li, S.; Yao, H.; Zhang, S.; Zhang, Y.; Yang, B.; Hou, J. Molecular Optimization Enables over 13% Efficiency in Organic Solar Cells. J. Am. Chem. Soc. 2017, 139, 7148−7151. (2) Cui, Y.; Yao, H.; Gao, B.; Qin, Y.; Zhang, S.; Yang, B.; He, C.; Xu, B.; Hou, J. Fine-Tuned Photoactive and Interconnection Layers for Achieving over 13% Efficiency in a Fullerene-Free Tandem Organic Solar Cell. J. Am. Chem. Soc. 2017, 139, 7302−7309. (3) Dou, L.; You, J.; Hong, Z.; 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. (4) Lu, L.; Zheng, T.; Wu, Q.; Schneider, A. M.; Zhao, D.; Yu, L. Recent Advances in Bulk Heterojunction Polymer Solar Cells. Chem. Rev. 2015, 115, 12666−12731. (5) Hedley, G. J.; Ruseckas, A.; Samuel, I. D. W. Light Harvesting for Organic Photovoltaics. Chem. Rev. 2017, 117, 796−837. (6) Xiao, S.; Zhang, Q.; You, W. Molecular Engineering of Conjugated Polymers for Solar Cells: An Updated Report. Adv. Mater. 2017, 29, No. 1601391. (7) Li, G.; Shrotriya, V.; Huang, J.; Yao, Y.; Moriarty, T.; Emery, K.; Yang, Y. High-efficiency solution processable polymer photovoltaic cells by self-organization of polymer blends. Nat. Mater. 2005, 4, 864− 868. (8) Ma, W.; Yang, C.; Gong, X.; Lee, K.; Heeger, A. J. Thermally Stable, Efficient Polymer Solar Cells with Nanoscale Control of the Interpenetrating Network Morphology. Adv. Funct. Mater. 2005, 15, 1617−1622. (9) Li, G.; Yao, Y.; Yang, H.; Shrotriya, V.; Yang, G.; Yang, Y. “Solvent Annealing” Effect in Polymer Solar Cells Based on Poly(3hexylthiophene) and Methanofullerenes. Adv. Funct. Mater. 2007, 17, 1636−1644. (10) Liao, H.-C.; Ho, C.-C.; Chang, C.-Y.; Jao, M.-H.; Darling, S. B.; Su, W.-F. Additives for morphology control in high-efficiency organic solar cells. Mater. Today 2013, 16, 326−336. (11) Dang, M. T.; Wuest, J. D. Using volatile additives to alter the morphology and performance of active layers in thin-film molecular photovoltaic devices incorporating bulk heterojunctions. Chem. Soc. Rev. 2013, 42, 9105−9126. (12) Wang, W.; Guo, S.; Herzig, E. M.; Sarkar, K.; Schindler, M.; Magerl, D.; Philipp, M.; Perlich, J.; Müller-Buschbaum, P. Investigation of Morphological Degradation of P3HT:PCBM Bulk Heterojunction Films Exposed to Long-Term Host Solvent Vapor. J. Mater. Chem. A 2016, 4, 3743. (13) Berson, S.; De Bettignies, R.; Bailly, S.; Guillerez, S. Poly(3hexylthiophene) Fibers for Photovoltaic Applications. Adv. Funct. Mater. 2007, 17, 1377−1384. (14) Xin, H.; Kim, F. S.; Jenekhe, S. A. Highly Efficient Solar Cells Based on Poly(3-butylthiophene) Nanowires. J. Am. Chem. Soc. 2008, 130, 5424−5425. (15) Yu, Z.; Fang, J.; Yan, H.; Zhang, Y.; Lu, K.; Wei, Z. SelfAssembly of Well-Defined Poly(3-hexylthiophene) Nanostructures toward the Structure−Property Relationship Determination of Polymer Solar Cells. J. Phys. Chem. C 2012, 116, 23858−23863. (16) Gao, D.; Hollinger, J.; Seferos, D. S. Selenophene−Thiophene Block Copolymer Solar Cells with Thermostable Nanostructures. ACS Nano 2012, 6, 7114−7121. (17) Yan, H.; Hollinger, J.; Bridges, C. R.; McKeown, G. R.; AlFaouri, T.; Seferos, D. S. Doping Poly(3-hexylthiophene) Nanowires with Selenophene Increases the Performance of Polymer-Nanowire Solar Cells. Chem. Mater. 2014, 26, 4605−4611. (18) Yan, H.; Song, Y.; McKeown, G. R.; Scholes, G. D.; Seferos, D. S. Adding Amorphous Content to Highly Crystalline Polymer Nanowire Solar Cells Increases Performance. Adv. Mater. 2015, 27, 3484−3491. (19) 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, No. 5293. F


Unusual Performance Increase in Polymer Solar Cells by Cooling a

Recommend Documents