Locking-In Optimal Nanoscale Structure Induced by

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Locking-In Optimal Nanoscale Structure Induced by Naphthalenediimide-Based Polymeric Additive Enables Efficient and Stable Inverted Polymer Solar Cells Kwang Hyun Park, Yujin An, Seungon Jung, Hyesung Park, and Changduk Yang ACS Nano, Just Accepted Manuscript • Publication Date (Web): 22 Jun 2017 Downloaded from http://pubs.acs.org on June 22, 2017

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Locking-In Optimal Nanoscale Structure Induced by Naphthalenediimide-Based Polymeric Additive Enables Efficient and Stable Inverted Polymer Solar Cells Kwang Hyun Park, †,§ Yujin An, †,§ Seungon Jung, †,§ Hyesung Park, †,* Changduk Yang†,* †

Department of Energy Engineering, School of Energy and Chemical Engineering, Low

Dimensional Carbon Materials Center, Perovtronics Research Center, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Ulju-gun, Ulsan, 44919, Republic of Korea.

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ABSTRACT: Operational stability and high performance are the most critical issues that must be addressed in order to propel and advance the current polymer solar cell (PSC) technology to the next level such as manufacturing and mass production. Herein, we report a high power conversion efficiency (PCE) of 11.2% together with an excellent device stability in PTB7Th:PC71BM-based PSCs in the inverted structure by introducing the n-type P(NDI2OD-T2) macromolecular additive (>75% PCE retention at high temperature up to 120 °C, >97% PCE retention after 6 months in inert conditions, >93% PCE retention after 2 months in air with encapsulation, and >80% PCE retention after 140 h in air without encapsulation). The PCE is the highest value ever reported in the single-junction systems based on PTB7 family and is also comparable to the previously reported highest PCE of inverted PSCs. These promising results are attributed to the efficient optimization and stabilization of the blend film morphology in the photoactive layer, achieved using the P(NDI2OD-T2) additive. From the perspective of manufacturing, our studies demonstrate a promising pathway for fabricating low-cost PSCs with high efficiency as well as long-term stability.

KEYWORDS: inverted structure, macromolecular additive, n-type conjugated polymer, polymer solar cells, thermal stability


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Bulk-heterojunction polymer solar cells (PSCs) comprising semiconducting polymers as the electron donors and fullerene derivatives as the electron acceptors have been extensively studied due to their great potential for realizing light-weight, flexible, and cost-effective solar cells, advancing past the current silicon-based photovoltaic technology.1-5 While in the past few years, various research efforts in the design of new semiconducting polymers and device fabrication techniques have led to PSCs with power conversion efficiencies (PCEs) exceeding 10%,6-22 these values are still not sufficiently high to enable the wide commercial use of PSCs. In addition to the improvement of the PCE, device stability is another key issue for the commercial viability of PSCs. Currently, emerging strategies for improving the stability of PSCs include (i) isolation of high-quality polymers to reduce an abrupt burn-in degradation during the device operation,23,24 (ii) use of air-stable electrodes such as Ag or Au, so-called inverted PSCs, in order to avoid the use of the corrosive and hygroscopic hole-transporting layer and low-workfunction metal cathodes,25,26 and (iii) use of materials that can form either cross-linking or hydrogen bonding in the active layers in order to stabilize the blend morphology.7, 27-30 In line with these research directions, we have recently demonstrated a simple and effective approach for simultaneously improving and stabilizing the performance of conventional-type PSCs based on poly[(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-bˊ]dithiophene-2,6diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)] (PTB7Th):[6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) photoactive layer via the addition of a high-quality n-type macromolecular additive poly[(N,Nˊ-bis(2-octyldodecyl)-naphthalene1,4,5,8-bis(dicarboximide)-2,6-diyl)-alt-5,5-(2,2-bithiophene)], P(NDI2OD-T2).31 The NDIbased n-type polymer, P(NDI2OD-T2), is one of the representative acceptor materials studied in the development of all-polymer solar cells due to its favorable properties such as high electron


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mobility, small optical bandgap, and suitable energy level alignment with commonly used p-type polymers.32,33 Recently, application of P(NDI2OD-T2) as the additive component has also been investigated in the ternary blend organic photovoltaics system.34,35 We expect that a more thorough elucidation of the underlying mechanism and role of P(NDI2OD-T2) in the active layer should help achieve commercially viable PCE values while satisfying the stability requirements. Therefore, in this study, we focus on the effect of P(NDI2OD-T2) in the “inverted PSCs” using PTB7-Th:PC71BM as the model system for the investigation of the issues described above. An exceptional PCE of 11.20% (PCEavg = 10.96%) was achieved for the P(NDI2OD-T2) additiveprocessed device, outperforming the corresponding non-additive control device. This value is one of the best results reported for the inverted PSCs. Moreover, the P(NDI2OD-T2) additiveprocessed device demonstrated a remarkably improved device stability (>75% PCE retention at high temperature up to 120 °C, >97% PCE retention after 6 months in inert conditions, >93% PCE retention after 2 months in air with encapsulation, and >80% PCE retention after 140 h in air without encapsulation). The demonstration of the P(NDI2OD-T2) additive for inverted PSCs with enhanced device performance successfully satisfies the important criteria for ultimately producing highly efficient and operationally stable organic photovoltaic modules.

RESULTS AND DISCUSSION Figure 1a illustrates the inverted device architecture (ITO/ZnO/active layer/MoO3/Ag) and chemical structures of PTB7-Th, PC71BM, and P(NDI2OD-T2). The high-quality P(NDI2ODT2) was prepared using the previously reported marginal solvent-soaking technique.31 In addition, the flat-band energy diagrams of the materials employed in the device are shown in Figure 1b. The fabrication conditions for the active layer in the inverted PSCs were adopted from


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the previously reported optimized processes;31 Briefly, PTB7-Th:PC71BM (1:1.7 wt%, 21.3 mg mL−1) in chlorobenzene (CB):1,8-diiodooctane (DIO) (97:3 vol%) was blended with 0.8 wt% P(NDI2OD-T2) (0.17 mg) based on the total weight of the active materials. A detailed description of the fabrication and testing conditions is provided in the Experimental Section. Figure 1c shows the current density−voltage (J−V) characteristics under simulated AM 1.5G illumination of 100 mW cm−2. The corresponding photovoltaic performance parameters are summarized in Table 1. The PTB7-Th:PC71BM control device without the P(NDI2OD-T2) additive exhibited a PCE of 10.36% (PCEavg = 9.87%) with a short-circuit current density (JSC) of 19.5 ± 0.2 mA cm−2, an open-circuit voltage (VOC) of 0.75 ± 0.02 V, and a fill factor (FF) of 66% ± 2%. To the best of our knowledge, this is one of the very few studies that demonstrate a power efficiency of greater than 10% for inverted single-junction PSCs based on the PTB7-Th system. Introduction of 0.8 wt% P(NDI2OD-T2) into the active layer led to simultaneous improvements in the JSC, VOC, and FF as previously observed in the conventional device architecture.31 Consequently, the best PCE that was as high as 11.20% with JSC of 20.3 ± 0.2 mA cm−2, VOC of 0.78 ± 0.01 V, and a FF of 69% ± 2 (PCEavg = 10.96%), was achieved for the P(NDI2OD-T2) additive-processed device, which is comparable to the best inverted PSCs reported previously.10-20, 36-39 The integrated JSC values obtained from the external quantum efficiency spectra were 20.3 and 18.6 mA cm−2 for the PTB7-Th:PC71BM devices with and without P(NDI2OD-T2), respectively (Figure 1d), in good agreement with the current obtained from the J−V measurements. Furthermore, we also observed that the recombination process is weaker in the P(NDI2OD-T2) additive-processed device compared to that for the non-additive control device, as evidenced by light-intensity-dependent JSC and VOC measurements (Figure S1). For example, the fitted curves from the light intensity dependence of the JSC and VOC for the


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devices with and without the additive yield α = 1.00 (with) and α =0.96 (without), and 1.13 kT/q (with) and 1.77 kT/q (without), respectively. Such higher α value in the power-law dependence (JSC ∝ Iα, I is the illumination intensity) and smaller 1.13 kT/q (where k is the Boltzmann constant, T is the temperature, and q is the elementary charge) corroborates less molecular recombination is involved for the devices with P(NDI2OD-T2) additive compared to the nonadditive control device. These observations partially explain the higher efficiency of the P(NDI2OD-T2) additive-processed device relative to that of the control device. In the following discussion, we explore several aspects of the PSCs stability issue such as the thermal and operation stabilities. Figure 2 shows the data for the evaluation of the effect of the thermal treatments on inverted PSCs based on PTB7-Th:PC71BM with and without P(NDI2OD-T2), wherein the devices were examined at various temperatures (30, 60, 80, 100, and 120 °C) for 10 min in an inert atmosphere. The corresponding photovoltaic parameters and J−V characteristics are listed in Table 1 and shown in Figure S2. Although the increase in the temperature leads to decreased values of all photovoltaic parameters in both the devices, degradation of the solar cell performance was significantly suppressed for the P(NDI2OD-T2) additive-processed device relative to the control device. For example, upon annealing at the evaluated temperature (120 °C), the PCE of P(NDI2OD-T2) additive-processed device retains >75% of its initial value, while the non-additive control device exhibits a sharp decrease in the PCE from 9.79% to 4.57%. Furthermore, we note that the PCE value for the P(NDI2OD-T2) additive-processed device remains almost unchanged (merely decreasing from 10.44% to 10.42%) at the mild temperature annealing (60 °C) conditions, whereas the control device shows a significant decrease in the PCE (from 9.79% to 8.15%). The observed thermal stability at these temperatures is important


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because typical solar cells are expected to reach this temperature range in the practical operational conditions. To gain further insight into the effect of the P(NDI2OD-T2) additive on the active layer, investigations of charge recombination dynamics and film morphologies for various thermal treatment conditions were performed using light-intensity-dependence measurements of J−V characteristics, atomic force microscopy (AFM), transmission electron microscopy (TEM), and grazing-incidence wide-angle X-ray diffraction (GIWAXD). As shown in Figure S3, the α values remain constant for all P(NDI2OD-T2) additive-processed devices, whereas the slope of kT/q gradually increases with increasing temperature, suggesting that geminate recombination loss rather than a bimolecular recombination mechanism is responsible for the decrease in the device performance at the evaluated temperatures. Figure 3 shows the AFM height images of the PTB7-Th:PC71BM blend films with and without P(NDI2OD-T2) exposed to different temperatures. The blend films without P(NDI2ODT2) show relatively rough surface morphologies with large root-mean square (RMS) roughness values. With the addition of P(NDI2OD-T2), the surface roughness of the corresponding blend films becomes smoother, resulting in reduced RMS values. Note that with increasing temperatures (30, 60, 80, 100, and 120 °C), the RMS values of the non-additive control films gradually increase (2.16 ± 0.5, 2.20 ± 0.5, 2.31 ± 0.5, 3.03 ± 0.6, and 3.20 ± 0.4 nm), whereas those from the P(NDI2OD-T2) additive-processed films show only negligible changes with the temperature (1.73 ± 0.2, 1.74 ± 0.2 and 1.79 ± 0.3, 1.84 ± 0.3, and 1.87 ± 0.3 nm). This indicates that with the aid of the P(NDI2OD-T2) additive, the surface morphology of the photoactive blend layer is less affected in the elevated temperature environment, leading to the thermally robust film formation. This is an important factor for the commercial applications of organic


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photovoltaics. Moreover, the TEM images (Figure S4) of the films with P(NDI2OD-T2) exhibit finer phase separation with fibril-like microstructures relative to the control films wherein the morphological features in the blend film after various thermal treatments follow trends that are similar to those observed by AFM; i.e., the P(NDI2OD-T2) in the active layer plays a key role in suppressing the morphological fluctuations. Figure 4 shows the GIWAXD patterns and the corresponding line-cut profiles qz (out-ofplane) and qxy (in-plane)) of the blend films at different annealing temperatures.40,41 The crystallographic parameters are summarized in Table S1 (Supporting Information). The PTB7Th:PC71BM film without P(NDI2OD-T2) at low temperature (30 °C) exhibits a ring-like (100) peak at q = ~0.28 Å-1, corresponding to lamellar d-spacing of ~22.2 Å and a broad (010) peak at qz = 1.61 ± 0.08 Å-1, which is associated with π-π stacking d-spacing of 3.9 ± 0.2 Å. This is in agreement with previous reports of face-on conformation in the PTB7-Th:PC71BM blend films.14,37 Although the addition of P(NDI2OD-T2) into the blend film at 30 °C does not cause noticeable changes in patterns and shifts of the (100) lamellar peaks, the π-π stacking peaks become fainter. Interestingly, as the temperature increases, the intensity of the (100) lamellar peak from the PTB7-Th:PC71BM film without P(NDI2OD-T2) is gradually reduced, whereas only slight change is observed for the PTB7-Th:PC71BM film with P(NDI2OD-T2). This stabilization of the horizontal crystallites of PTB7-Th:PC71BM film with P(NDI2OD-T2) is directly correlated with an improved stability of PSCs since it is generally believed that the horizontal film composition is more favourable for photovoltaic devices because of its vertical charge transportation channel.15 Besides, we also observe that the crystalline correlation length (CCL100) values for P(NDI2OD-T2) additive films are somewhat smaller than those of the corresponding non-additive films annealed up to 100 °C, but both the films at a higher


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temperature (120 °C) possess the same CCL values (131.6 Å) (Table S1 in Supporting Information). Taken together, we conclude that the use of the P(NDI2OD-T2) additive allows the photoactive blend film morphology to be “locked,” affording improved thermal stability in the P(NDI2OD-T2) additive-processed device. This conclusion is also corroborated by the AFM and TEM results discussed above. In addition to the thermal stability, the long-term stability of the PSCs was examined for 6 months at room temperature in inert conditions. The J−V measurements of the test devices were periodically recorded, as shown in Figure 5a and Figure S5. The P(NDI2OD-T2) additiveprocessed device retains more than 97% of the PCE (from 11.1% to 10.8%) after 6 months. This compares with the non-additive control device for which the PCE is reduced by more than 63% (from 9.87% to 3.63%) during the same measurement period. Besides, we encapsulated the inverted devices using the well-known epoxy-glass technique, as explained in Experimental Section. Then, we conducted the device aging test under an ambient atmosphere at room temperature and collected the J−V data under continuous air exposure. As shown in Figure 5b and Figure S6, the non-additive control device exhibits a large decline of the PCE from 9.60% to 5.88% during 2-months measurement, whereas a PCE as high as 9.16% is still maintained for (NDI2OD-T2) additive-processed device. Moreover, as a part of the representative actual-use tests, the devices were also assessed in an air environment without any encapsulation. In contrast to the sharp PCE decrease observed for the non-additive control device, the P(NDI2OD-T2) additive-processed device again demonstrates a remarkable air stability (>80% PCE retention after 140 h of air exposure) (Figure 5c and Figure S7). Collectively, the above stability data clearly indicate that P(NDI2OD-T2) additive plays a crucial role to enhance simultaneously thermal and long-term stabilities of bulk-heterojunction PSCs.


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CONCLUSIONS We demonstrate that the simple addition of P(NDI2OD-T2) into PTB7-Th:PC71BM-based inverted PSCs offers a significant prospect for applications in highly efficient and stable PSCs. The beneficial effects originate from the crucial role played by P(NDI2OD-T2) in not only further optimizing the blend morphology but also in the locking-in of the optimal nanoscale structure. In addition to the notable PCE that is as high as 11.20% observed for the P(NDI2ODT2) additive-processed device, herein we emphasize the excellent stability properties of this device such as (i) >75% PCE retention at high temperature up to 120 °C, (ii) >97% PCE retention after 6 months in inert conditions, (iii) >93% PCE retention after 2 months in air with encapsulation, and (iv) >80% PCE retention after 140 h in air without encapsulation. Therefore, the results in this study clearly demonstrate that the inverted PSCs processed with P(NDI2ODT2) show a great potential for advancing not only the current PSC technology for practical applications but also the understanding of the photovoltaic mechanisms.

EXPERIMENTAL SECTION Materials. The detailed synthesis and characterization of P(NDI2OD-T2) can be found in the Supplementary Materials and our previous work.31 All other commercial reagents, including solvents used in this study were purchased from Aldrich Co., Alfa Aesar, and TCI Co. used without further purification. Solar Cell Characterization. Inverted device was selected to evaluate the performance of PTB7-Th:PC71BM-based OSCs by P(NDI2OD-T2) additive. The device architecture was glass/ITO/ZnO nanoparticle/photoactive materials/MoO3/Ag. First, ITO coated on glass and was


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cleaned using deionized water, acetone and isopropyl alcohol, then the substrates were dried in an oven. ZnO nanoparticle was spin-coated on the substrates at 2500 rpm for 1 min and baked at 80 °C for 10 min and 120 °C for 5 min, respectively. The substrate was moved into the glove box under nitrogen environment. PTB7-Th, and PC71BM, were dissolved in chlorobenzene/1,8diiodooctane solvent (97:3 vol%) with concentrations of 12 and 40 mg mL-1, respectively. Then, blend solution with PTB7-Th:PC71BM (2:1 vol%) with addition of the 0.8 wt% P(NDI2OD-T2) (0.17 mg) was prepared. The blend solution was spin-coated at 900 rpm for 2 min onto the ZnO nanoparticle. Subsequently, MoO3 (20 nm) and Ag (100 nm) counter electrode was thermally evaporated under vacuum (~10-6 Torr), which defines the device area of 13 mm2. Device measurements were conducted in the glove box by a Xenon arc lamp solar simulator. J−V characteristics were measured under AM 1.5G illumination (100 mW cm-2) with a Keithley 2635A source measurement unit, and EQE measurement was performed under ambient conditions using a QE system (Model QEX7) by PV measurements Inc. (Boulder, Colorado). For the long-term operation lifetime tests, the devices were encapsulated within glass slides of ~1 mm in thickness using a two-part epoxy resin (Loctite Instant Mix 5 Minute Epoxy). Light intensity dependent JSC and VOC were measured with neutral density filters. Characterizations. The optical properties of composite films were analyzed using a UV-vis spectrophotometer (Agilent Carry 5000). Agilent 5500 scanning probe microscope (SPM) running with a Nanoscope V controller was used to obtain AFM images of polymer thin films. AFM images were recorded in high-resolution tapping mode under ambient conditions. The GIWAXD measurements were conducted at PLS-II 9A U-SAXS beamline of the Pohang Accelerator Laboratory in Korea. X-rays coming from the in-vacuum undulator (IVU) were monochromated (wavelength λ = 1.10994 Å) using a double crystal monochromator and focused


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both horizontally and vertically (450 (H) × 60 (V) µm2 in FWHM @sample position) using K-B type mirrors. The GIWAXD sample stage was equipped with a 7-axis motorized stage for the fine alignment of sample, and the incidence angle of X-ray beam was set to be 0.13º to 0.135º for neat polymer films and blended films. The GIWAXD patterns were recorded with a 2D CCD detector (Rayonix SX165) and X-ray irradiation time was 6-9 s, dependent on the saturation level of the detector. Diffraction angles were calibrated using a sucrose standard (Monoclinic, P21, a = 10.8631 Å, b = 8.7044 Å, c = 7.7624 Å, β = 102.938º) and the sample-to-detector distance was ~231 mm.


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Figure 1. Chemical structures and device characteristics of PTB7-Th:PC71BM-based OSCs with macromolecular additives. (a) Device structure and molecular structures of donors (PTB7-Th), acceptor (PC71BM), and macromolecular additive (P(NDI2OD-T2)). (b) Schematic flat energy band diagram. (c) J–V characteristics. (d) EQE spectra of devices fabricated with/without P(NDI2OD-T2) additive.


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Figure 2. Device stability of PTB7-Th:PC71BM based OSCs with/without 0.8 wt% P(NDI2ODT2) additive to exposure at different temperatures (30, 60, 80, 100, and 120 °C). (a) Short-circuit current density (JSC). (b) Open-circuit voltage (VOC). (c) Fill factor (FF). (d) Power conversion efficiency (PCE).


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Figure 3. AFM images of PTB7-Th:PC71BM based OSCs with/without 0.8 wt% P(NDI2OD-T2) additive to exposure at different temperatures (30, 60, 80, 100, and 120 °C). (a) Phase images, RMS: root-mean square roughness.


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Figure 4. 2D GIWAXD characterizations of PTB7-Th:PC71BM with/without 0.8 wt% P(NDI2OD-T2) additive exposed to different temperatures (30, 60, 80, 100, and 120 °C). (a) GIWAXD images. (b) In-plane and (c) Out-of-plane profiles.


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Figure 5. Long-term stability of PTB7-Th:PC71BM with/without 0.8 wt% P(NDI2OD-T2) additive under nitrogen environment (a) and ambient air condition ((b) with and (c) without encapsulation).


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Table 1. Device performances of PTB7-Th:PC71BM based OSCs with/without 0.8 wt% P(NDI2OD-T2) additive in inverted device.

w/o P(NDI2OD-T2), 30 °C 60 °C 80 °C 100 °C 120 °C 0.8 wt% P(NDI2OD-T2), 30 °C 60 °C 80 °C 100 °C 120 °C

JSC (mA cm-2)

VOC (V)

FF (%)

19.5±0.2 19.0±0.2 16.4±0.3 15.8±0.5 13.1±0.5 20.3±0.2 20.1±0.2 18.9±0.3 17.8±0.4 16.3±0.5

0.75±0.02 0.72±0.02 0.70±0.02 0.68±0.03 0.65±0.03 0.78±0.01 0.77±0.01 0.77±0.01 0.76±0.01 0.74±0.01

60±2 51±2 46±2 41±2 32±5 69±2 66±2 57±1 56±2 54±4

a

PCE (%) max./avg. 10.4/9.87±0.3a 8.15/7.95±0.5b 7.05/6.88±0.6b 5.14/4.94±0.6b 4.57/4.32±0.8b 11.2/11.0±0.2a 10.8/10.4±0.2b 9.82/9.39±0.4b 9.02/8.67±0.4b 8.32/7.82±0.5b

The average values obtained from at least 50 devices with the standard deviation; average values obtained from at least 20 devices with the standard deviation

b

The


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ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge. J−V characteristics and light intensity dependence of JSC and VOC on PTB7-Th:PC71BM based OSCs in inverted devices with/without 0.8 wt% P(NDI2OD-T2) additive; TEM images of PTB7Th:PC71BM blends with/without 0.8 wt% P(NDI2OD-T2) additive; (PDF)

AUTHOR INFORMATION Corresponding Author *Prof. Hyesung Park, E-mail: [email protected], *Prof. Changduk Yang, E-mail: [email protected] Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. §These authors contributed equally. Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (2015R1A2A1A10053397). This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (2015R1D1A1A0105791). GIWAXD


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measurements at PLS-II 6D UNIST-PAL beamline and 9A beamline were supported in part by MEST, POSTECH, and UNIST UCRF.

REFERENCES (1)

Günes, S.; Neugebauer, H.; Sariciftci, N. S. Conjugated Polymer-Based Organic Solar Cells. Chem. Rev. 2007, 107, 1324-1338.

(2)

Sariciftci, N. S.; Smilowitz, L.; Heeger, A. J.; Wudl, F. Photoinduced Electron Transfer from a Conducting Polymer to Buckminsterfullerene. Science 1992, 258, 1474-1476.

(3)

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.

(4)

Sirringhaus, H.; Brown, P. J.; Friend, R. H.; Nielsen, M. M.; Bechgaard, K.; LangeveldVoss, B. M. W.; Spiering, A. J. H.; Janssen, R. A. J.; Meijer, E. W.; Herwig, P.; de Leeuw, D. M. Two-Dimensional Charge Transport in Self-Organized, High-Mobility Conjugated Polymers. Nature 1999, 401, 685-688.

(5)

Yan, H.; Chen, Z.; Zheng, Y.; Newman, C.; Quinn, J. R.; Dötz, F.; Kastler, M.; Facchetti, A. A High-Mobility Electron-Transporting Polymer for Printed Transistors. Nature 2009, 457, 679-686.

(6)

Kan, B.; Zhang, Q.; Li, M.; Wan, X.; Ni, W.; Long, G.; Wang, Y.; Yang, X.; Feng, H.; Chen, Y. Solution-Processed Organic Solar Cells Based on Dialkylthiol-Substituted Benzodithiophene Unit with Efficiency near 10%. J. Am. Chem. Soc. 2014, 136, 1552915532.


20

Page 21 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(7)

ACS Nano

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, 5293.

(8)

Yang, Y. M.; Chen, W.; Dou, L.; Chang, W.-H.; Duan, H.-S.; Bob, B.; Li, G.; Yang, Y. High-Performance Multiple-Donor Bulk Heterojunction Solar Cells. Nat. Photonics 2015, 9, 190-198.

(9)

Qin, T.; Zajaczkowski, W.; Pisula, W.; Baumgarten, M.; Chen, M.; Gao, M.; Wilson, G.; Easton, C. D.; Müllen, K.; Watkins, S. E. Tailored Donor–Acceptor Polymers with an A– D1–A–D2 Structure: Controlling Intermolecular Interactions to Enable Enhanced Polymer Photovoltaic Devices. J. Am. Chem. Soc. 2014, 136, 6049-6055.

(10) Zhao, J.; Li, Y.; Yang, G.; Jiang, K.; Lin, H.; Ade, H.; Ma, W.; Yan, H. Efficient Organic Solar Cells Processed from Hydrocarbon Solvents. Nat. Energy 2016, 1, 15027. (11) Yan, Y.; Cai, F.; Yang, L.; Li, J.; Zhang, Y.; Qin, F.; Xiong, C.; Zhou, Y.; Lidzey, D. G.; Wang, T. Light-Soaking-Free Inverted Polymer Solar Cells with an Efficiency of 10.5% by Compositional and Surface Modifications to a Low-Temperature-Processed TiO2 ElectronTransport Layer. Adv. Mater. 2017, 29, 1604044. (12) Liu, X.; Li, X.; Li, Y.; Song, C.; Zhu, L.; Zhang, W.; Wang, H.-Q.; Fang, J. HighPerformance Polymer Solar Cells with PCE of 10.42% via Al-Doped ZnO Cathode Interlayer. Adv. Mater. 2016, 28, 7405-7412. (13) Huang, J.; Carpenter, J. H.; Li, C.-Z.; Yu, J.-S.; Ade, H.; Jen, A. K.-Y. Highly Efficient Organic Solar Cells with Improved Vertical Donor–Acceptor Compositional Gradient via an Inverted Off-Center Spinning Method. Adv. Mater. 2016, 28, 967-974.


21

ACS Nano

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 27

(14) Wan, Q.; Guo, X.; Wang, Z.; Li, W.; Guo, B.; Ma, W.; Zhang, M.; Li, Y. 10.8% Efficiency Polymer Solar Cells Based on PTB7-Th and PC71BM via Binary Solvent Additives Treatment. Adv. Funct. Mater. 2016, 26, 6635-6640. (15) He, Z.; Xiao, B.; Liu, F.; Wu, H.; Yang, Y.; Xiao, S.; Wang, C.; Russell, T. P.; Cao, Y. Single-Junction Polymer Solar Cells with High Efficiency and Photovoltage. Nat. Photonics 2015, 9, 174-179. (16) Nam, S.; Seo, J.; Woo, S.; Kim, W. H.; Kim, H.; Bradley, D. D. C.; Kim, Y. Inverted Polymer Fullerene Solar Cells Exceeding 10% Efficiency with Poly(2-ethyl-2-oxazoline) Nanodots on Electron-Collecting Buffer Layers. Nat. Commun. 2015, 6, 8929. (17) Geraghty, P. B.; Lee, C.; Subbiah, J.; Wong, W. W. H.; Banal, J. L.; Jameel, M. A.; Smith, T. A.; Jones, D. J. High Performance p-type Molecular Electron Donors for OPV Applications via Alkylthiophene Catenation Chromophore Extension. Beilstein J. Org. Chem. 2016, 12, 2298-2314. (18) Zhang, G.; Zhang, K.; Yin, Q.; Jiang, X.-F.; Wang, Z.; Xin, J.; 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, 23872395. (19) Jin, Y.; Chen, Z.; Dong, S.; Zheng, N.; Ying, L.; Jiang, X. F.; Liu, F.; Huang, F.; Cao, Y. A Novel Naphtho[1,2-c:5,6-c']Bis([1,2,5]Thiadiazole)-Based Narrow-Bandgap π-Conjugated Polymer with Power Conversion Efficiency Over 10%. Adv. Mater. 2016, 28, 9811-9818. (20) Zhang, K.; Gao, K.; Xia, R.; Wu, Z.; Sun, C.; Cao, J.; Qian, L.; Li, W.; Liu, S.; Huang, F.; Peng, X.; Ding, L.; Yip, H.-L.; Cao, Y. High-Performance Polymer Tandem Solar Cells


22

Page 23 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Nano

Employing a New n-Type Conjugated Polymer as an Interconnecting Layer. Adv. Mater. 2016, 28, 4817-4823. (21) Bin, H.; Gao, L.; Zhang, Z.-G.; Yang, Y.; Zhang, Y.; Zhang, C.; Chen, S.; Xue, L.; Yang, C.; Xiao, M.; Li, Y. 11.4% Efficiency Non-Fullerene Polymer Solar Cells with Trialkylsilyl Substituted 2D-Conjugated Polymer as Donor. Nat. Commun. 2016, 7, 13651. (22) Yang, Y.; Zhang, Z.-G.; Bin, H.; Chen, S. Gao, L.; Xue, L.; Yang, C.; Li. Y. Side-Chain Isomerization on an n-type Organic Semiconductor ITIC Acceptor Makes 11.77% High Efficiency Polymer Solar Cells. J. Am. Chem. Soc. 2016, 138, 15011-15018. (23) Peters, C. H.; Sachs-Quintana, I. T.; Mateker, W. R.; Heumueller, T.; Rivnay, J.; Noriega, R.; Beiley, Z. M.; Hoke, E. T.; Salleo, A.; McGehee, M. D. The Mechanism of Burn-in Loss in a High Efficiency Polymer Solar Cell. Adv. Mater. 2012, 24, 663-668. (24) Heumueller, T.; Mateker, W. R.; Sachs-Quintana, I. T.; Vandewal, K.; Bartelt, J. A.; Burke, T. M.; Ameri, T.; Brabec, C. J.; McGehee, M. D. Reducing Burn-in Voltage Loss in Polymer Solar Cells by Increasing the Polymer Crystallinity. Energy Environ. Sci. 2014, 7, 29742980. (25) White, M. S.; Olson, D. C.; Shaheen, S. E.; Kopidakis, N.; Ginley, D. S. Inverted BulkHeterojunction Organic Photovoltaic Device Using a Solution-Derived ZnO Underlayer. Appl. Phys. Lett. 2006, 89, 143517. (26) Chen, L.-M.; Hong, Z.; 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. (27) Derue, L.; Dautel, O.; Tournebize, A.; Drees, M.; Pan, H.; Berthumeyrie, S.; Pavageau, B.; Cloutet, E.; Chambon, S.; Hirsch, L.; Rivaton, A.; Hudhomme, P.; Facchetti, A.; Wantz, G.


23

ACS Nano

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Page 24 of 27

Thermal Stabilisation of Polymer–Fullerene Bulk Heterojunction Morphology for Efficient Photovoltaic Solar Cells. Adv. Mater. 2014, 26, 5831-5838. (28) Png, R.-Q.; Chia, P.-J.; Tang, J.-C.; Liu, B.; Sivaramakrishnan, S.; Zhou, M.; Khong, S.-H.; Chan, H. S. O.; Burroughes, J. H.; Chua, L.-L.; Friend, R. H.; Ho, P. K. H. HighPerformance Polymer Semiconducting Heterostructure Devices by Nitrene-Mediated Photocrosslinking of Alkyl Side Chains. Nat. Mater. 2010, 9, 152-158. (29) Yau, C. P.; Wang, S.; Treat, N. D.; Fei, Z.; Tremolet de Villers, B. J.; Chabinyc, M. L.; Heeney, M. Investigation of Radical and Cationic Cross-Linking in High-Efficiency, Low Band Gap Solar Cell Polymers. Adv. Energy Mater. 2015, 5, 1401228. (30) Griffini, G.; Douglas, J. D.; Piliego, C.; Holcombe, T. W.; Turri, S.; Fréchet, J. M.; Mynar, J. L. Long-Term Thermal Stability of High-Efficiency Polymer Solar Cells Based on Photocrosslinkable Donor-Acceptor Conjugated Polymers. Adv. Mater. 2011, 23, 16601664. (31) Park, K. H.; An, Y.; Jung, S.; Park, H.; Yang, C. The Use of an n-type Macromolecular Additive as a Simple yet Effective Tool for Improving and Stabilizing the Performance of Organic Solar Cells. Energy Environ. Sci. 2016, 9, 3464-3471. (32) Zhou, N.; Lin, H.; Lou, S. J.; Yu, X.; Guo, P.; Manley, E. F.; Loser, S.; Hartnett, P.; Huang, H.; Wasielewski, M. R.; Chen, L. X.; Chang, R. P. H.; Facchetti, A.; Marks, T. J. Morphology-Performance Relationships in High-Efficiency All-Polymer Solar Cells. Adv. Energy Mater. 2014, 4, 1300785. (33) Facchetti, A. Polymer Donor–Polymer Acceptor (All-Polymer) Solar Cells. Mater. Today 2013, 16, 123-132. (34) Benten, H.; Nishida, T.; Mori, D.; Xu, H.; Ohkita, H.; Ito, S. High-Performance Ternary Blend All-Polymer Solar Cells with Complementary Absorption Bands from Visible to Near-Infrared Wavelengths. Energy Environ. Sci. 2016, 9, 135-140.


24

Page 25 of 27

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Nano

(35) Su, W.; Fan, Q.; Guo, X.; Guo, B. Li, W.; Zhang, Y.; Zhang, M.; Li. Y. Efficient Ternary Blend All-Polymer Solar Cells with a Polythiophene Derivative as a Hole-Cascade Material. J. Mater. Chem. A 2016, 4, 14752-14760. (36) Lee, S.; Kong, J.; Lee, K. Air-Stable Organic Solar Cells Using an Iodine-Free Solvent Additive. Adv. Energy Mater. 2016, 6, 1600970. (37) Wang, J.; Lin, K.; Zhang, K.; Jiang, X. F.; Mahmood, K.; Ying, L.; Huang, F.; Cao, Y. Crosslinkable Amino-Functionalized Conjugated Polymer as Cathode Interlayer for Efficient Inverted Polymer Solar Cells . Adv. Energy Mater. 2016, 11, 1502563. (38) Zhang, C.; Mumyatov, A.; Langner, S.; Perea, J. D.; Kassar, T.; Min, J.; Ke, L.; Chen, H.; Gerasimov, K. L.; Anokhin, D. V.; Ivanov, D. A.; Ameri, T.; Osvet, A.; Susarova, D. K.; Unruh, T.; Li, N.; Troshin, P.; Brabec, C. J. Overcoming the Thermal Instability of Efficient Polymer Solar Cells by Employing Novel Fullerene-Based Acceptors. Adv. Energy Mater. 2016, 7, 1601204. (39) 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. Influence of Processing Parameters and Molecular Weight on the Morphology and Properties of High-Performance PffBT4T-2OD:PC71BM Organic Solar Cells. Adv. Energy Mater. 2015, 5, 1501400. (40) Müller‐Buschbaum, P. The Active Layer Morphology of Organic Solar Cells Probed with Grazing Incidence Scattering Techniques. Adv. Mater. 2014, 26, 7692-7709. (41) Wang, W.; Schaffer, C. J.; Song, L.; Körstgens, V.; Pröller, S.; Indari, E. D.; Wang, T.; Abdelsamie, A.; Bernstorff, S.; Müller-Buschbaum, P. In Operando Morphology Investigation of Inverted Bulk Heterojunction Organic Solar Cells by GISAXS . J. Mater. Chem. A 2015, 3, 8324-8331.


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Locking-In Optimal Nanoscale Structure Induced by

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