Toward Solution-Processed High-Performance Polymer Solar Cells

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Toward Solution-Processed High-Performance Polymer Solar Cells: from Material Design to Device Engineering Kai Zhang, Zhicheng Hu, Chen Sun, Zhihong Wu, Fei Huang, and Yong Cao Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.6b02802 • Publication Date (Web): 08 Sep 2016 Downloaded from http://pubs.acs.org on September 8, 2016

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Chemistry of Materials

Toward Solution-Processed High Performance Polymer Solar Cells: from Material Design to Device Engineering *

Kai Zhang, Zhicheng Hu, Chen Sun, Zhihong Wu, Fei Huang and Yong Cao Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, P. R. China ABSTRACT: With the rapid development of polymer solar cells (PSCs), the manufacture of high-performance large area PSC modules is becoming a critical issue in commercial applications. However, most of the reported light absorption materials and interfacial materials are quite thickness sensitive, with optimal thicknesses of around 100 nm and 5 nm, respectively. The thickness need to be precisely controlled, otherwise, a small variation in thickness can often lead to a sharp decrease in device performance, especially for interfacial materials. This increases the difficulty of apply these materials in the production of large area PSCs. To avoid the shortcomings of thickness-sensitive materials and achieve high-performance large area PSC modules, we designed and synthesized a series of high mobility donor materials and cathode interfacial materials. These materials exhibited excellent device performance at their optimal thicknesses and maintained high performance even with large thickness variations, thus providing a solution to the bottleneck problem in manufacturing PSC modules and enhancing the device reproducibility. We also developed a simple and efficient approach for achieving a large area cathode interlayer with controlled film composition, uniformity, and thickness at the nanometer-scale using an electrostatic layer-by-layer self-assembly (eLbL) process. The eLbL films exhibited excellent cathode modification ability and can be integrated into the current large area device processing techniques. Thus, our approaches from both material design to device engineering provide new solutions for preparing high-performance large area PSC modules.

Introduction Polymer solar cells (PSCs), which mainly consist of polymer light absorption active materials sandwiched between two electrodes, have received considerable attention in both academic and industrial fields in recent decades.1,2 The organic nature of polymer active materials gives PSCs several distinct advantages, such as light weight, good mechanical flexibility, excellent solution processability, and low cost compared with other photovoltaic technologies.3 After decades of development, appreciable achievements have been made in improving the performance of PSCs, with the power conversion efficiencies (PCEs) reaching more than 11% for single junction devices.4-6 As the performance of PSCs continues to increase, the manufacture of high-performance large area PSC modules is becoming a critical issue for commercial applications. Many efforts have been put into pursuing large area PSCs, including the design of large area high conductive electrode,7,8 developing of new technique that used to process large area uniform films,9,10 control of active layer morphology during the device processing11 and so on. And some encouraging progresses have been made in realizing PSCs module. However, some other challenges are still remained to be settled in realizing high-performance large area PSCs. For instance, to achieve high-performance PSCs, multilayer device structures with the active layer and interfacial layer stacked together are often used. It was well recognized that the insertion of the interfacial layer between the electrode and the active layer can tune the work function of the electrode and improve the charge selection and extraction.12,13 However, before the construction

of solution processed multilayer device, the interface mixing/erosion problems between active layer and interfacial layer need to be overcame.14 Again for example, materials and device processing that are optimized for small area devices have been shown a low translation efficiency from champion devices of laboratory to large area manufacturing.15 One of the main reasons for this difficult translation is that most of the reported light absorption and interfacial materials are quite thickness sensitive. The thickness needs to be precisely controlled during the process, otherwise, a small variation in thickness can lead to a sharp decrease in device performance, which is not favorable for large area device processing and the device reproducibility.16 To overcome these challenges, our groups started from both material design and device engineering. On one hand, we have developed a series of water/alcohol soluble conjugated polymer (WSCP) interfacial materials for solutionprocessed high-performance multilayer PSCs. On the other hand, we have designed both thickness insensitive active and interfacial materials as potential candidates for solutionprocessed large area module devices. These materials will ensure us the possibility of achieving high performance large area PSC modules.

WSCPs for the interface engineering of high performance PSCs Orthogonal solvent processing and cross-linking are the most commonly used strategies for overcoming the interface mixing/erosion problems when constructing solutionprocessed multilayer devices. Since most of the reported high-

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the amine-group was found to act as hole trap preventing holes from migrating to the cathode and finally resulted in a reduced bimolecular recombination at the electrode;23,24 d) the small surface energy difference between PFN and PCBM favored the formation of vertical phase separation in the bulk heterojunction film and facilitated the achievement of ohmic contact with the active layer.25 As a result, great improvements in performance were achieved for PSC devices with PFN as the cathode interface material.26-28 Moreover, reports showed that PFN can work as efficient cathode interfacial materials in high performance small molecular organic solar cells,29,30 which meant PFN can be used as universal interfacial material for cathode modification in organic solar cells. Note that the hydrophilic amine-group was found to be critical for enhancing the device performance, which provides guidelines for the future development of cathode interface materials.

_

performance active materials are soluble in non-polar solvents, such as chlorobenzene, toluene and chloroform, which provides an opportunity of using polar solvent to process interfacial material for constructing multi-layer PSC devices. Based on this evaluation, we developed WSCP interface materials for PSCs. In general, WSCPs are composed of two key structural components: π-conjugated backbones and surfactant-like side groups (such as the amino, dihydroxyethylamino, phosphate, carboxyl, quaternary ammonium, anionic carboxyl, sulfonic, and zwitterionic groups).13,17 The π-conjugated backbones determine the intrinsic optoelectronic properties of WSCPs, such as their absorption, emission spectra, band structures, and charge transport characteristics.18 The surfactant-like side groups endow WSCPs with unique solubility in highly polar solvents. These structural traits and unique properties give WSCPs a series of advantages. First, the extraordinary solubility of WSCPs in highly polar solvents is desirable for fabricating multilayer devices without interface mixing through the deposition of different layers using orthogonal solvents. In addition, the environmentally friendly solvent we used to process the WSCPs is an ideal choice for industrial highthroughput manufacturing. Moreover, the surfactant-like side groups are found to endow the WSCPs with excellent interface modification functions. Finally, we are able to manipulate the desired optoelectronic properties of the WSCPs, such as their photophysics properties, solubility, and charge transport ability, by tailoring their π-conjugated backbone structures and side chains.

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Dope PCBM

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Scheme 1. Chemical structures of the WSCPs discussed in this work Poly[9,9-bis(6’-(N,N-diethylamino)propyl)-fluorene](PFN) (Scheme 1) is an early designed neutral WSCP with an aminefunctionalized side chain, which can be dissolved in alcohol with the addition of a tiny amount of acetic acid.19 PSC devices with thin-layer PFN as the cathode interlayer exhibited much better performance than the devices without the PFN. A working mechanism study showed that PFN fulfilled the following functions (shown in Figure 1): a) interfacial dipoles were formed between the PFN and the electrode, which can effectively lower the work function of metal/metal oxide, leading to better energy alignment for electron collecting from the active layer;20,21 b) an interfacial doping effect between the amine-group and fullerene acceptor was also found to contribute greatly to improving the current density in the devices;22 c)

Figure 1. Working mechanism of PFN in PSCs

Although PFN has become a standard prototype for interface studies, the solubility of PFN in non-polar solvent, such as chlorobenzene or toluene, makes it unsuitable for cathode modification in inverted PSCs, which has been shown to be an efficient structure for improving device performance and stability. To broaden the application of PFN-type WSCPs in inverted PSCs, cross-linkable PFNs were developed to form cross-linked films on the electrode to resist the solvent erosion. Poly[9,9-bis(6’-(N,Ndiethylamino)propyl)-fluorene-alt-9,9bis(3-ethyl(oxetane-3-ethyloxy)-hexyl) fluorene] (PFN-OX) (Scheme 1) is a cross-linkable WSCP with the oxetane and amine groups on its side chain.31 The oxetane groups can be thermally cross-linked with annealing at 150°C for 15 min, which results in an insoluble film on the ITO. The cross-linked WSCP film can smooth the surface of the electrode (such as the ITO), improve the interface contact, and lower the work function of the electrode. As a result, inverted PSCs with PFNOX as the cathode interface material achieved much higher performance than the control devices.22,32 However, when PFN-OX was further examined, it was found that the relatively high thermal crosslinking temperature of PFN-OX made it not compatible with the flexible substrate. Moreover, the long crosslinking time meant it was not an ideal choice for future high throughput processing. Thus, it is of vital importance to develop a highly efficient crosslinking PFNs that can be crosslinked under low activation energy, while bearing a fast reac-


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tion rate of the functional groups to reduce the crosslinking time. Click chemistry has been extensively investigated due to its advantages of high selectivity, mild reaction conditions, easy purification, and can give a wide range of molecular systems with high yields.33 It is well-established that the “click” reaction of the thiols and enes groups are very efficient and can be completed within tens of seconds.34 Most importantly, the reaction can be easily triggered by directly exciting the thiol-groups upon the irradiation of UV-light.35 To take the advantage of the “click” reaction, we designed a light induced crosslinkable WSCP, poly[9,9-bis(6(N,Ndiethylamino)propyl)fluorene-alt-9,9-bis(hex-5-en-1-yl)fluorene] (PFN-V) (Scheme 1) that bears vinyl groups on its side chain and can further react with the mercapto groups upon light irradiation. The crosslinking was carried out by UVcuring within only 5 seconds in the presence of ODT based on an efficient thiol/ene “click” reaction. With the crosslinked PFN-V layer as the cathode interlayer, the fabricated PSCs exhibited obviously increased photovoltaic performance.25 More importantly, the fast crosslinking process highlighted the great potential of this polymer as a cathode interface material for high throughput R2R processing. The incorporation of the interfacial material between the active layer and the electrodes in constructing multilayer devices was shown to be very successful in achieving highperformance small area PSCs. However, in most cases, the charge mobility of the interfacial material is around 10-6 ~ 10-7 cm2 V-1 S-1.36 Thus, the optimal thickness of most of the interlayers is less 10 nm, and a small thickness variation can lead to a sharp decrease in device performance. One way to overcome this problem is to develop a new interfacial material with high mobility/conductivity to achieve a thickness insensitive interlayer that can work well within a wide range of thicknesses without significantly sacrificing performance.37 In addition to the well-known excellent charge transport property, the inter chain packing of the resulting polymer films is also identified as one of the main reason for avoid performance decrease at relatively high thickness. Metal-based polymers/molecules have attracted immense interest in the materials field due to their intriguing spectroscopic, luminescence, and electrical properties, and their propensity for exhibiting metal−metal (M−M) interactions that can provide additional means for manipulating the structural order and electronic coupling in organometallic compounds.38 By tuning the molecular structures and M−M interactions, several groups have successfully constructed highly ordered organometallic nanostructures for field-effect transistors with comparably high electron and hole mobilities.39,40 Based on this body of work, we developed an amino-functionalized conjugated metallopolymer PFEN-Hg (Scheme 1).41 In designing this polymer, we aimed to develop several important properties that are required by an efficient interlayer, i.e., insoluble in a non-polar solvent, good film forming ability, effective work function tuning ability, low optical absorption, good electron selectivity, and good electron transport properties. The resulting polymer PFEN-Hg has excellent solubility in tetrahydrofuran (THF) and 1,4-dioxane, but is almost insoluble in chlorobenzene (CB) and dichlorobenzene (o-DCB), making it a suitable interfacial material for the inverted PSC applications because the upper photoactive layer is typically processed from CB or o-DCB. Inverted PSCs with an

ITO/PFEN-Hg/PTB7:PC71BM/MoO3/Al device structure exhibited encouraging PCE values of 9.11%, with an optimized PFEN-Hg thickness of 13 nm, and good device performance was also achieved when the interlayer varied over a wide range of thicknesses. Doping is another strategy for designing an interlayer with excellent charge transport ability. Poly(3,4ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a widely used hole transport layer, which is p-doped by a proton transfer mechanism and stabilized by the PSS polyanions. The doping concentration can be tuned to obtain films with varying conductivity.42 A similar strategy was used to design new n-type semiconductors with high charge transport properties in our group, where the n-type πconjugated backbone or molecule was believed to be ideal choice for thick interlayer application.43 Two novel naphthalene diimide (NDI) based n-type WSCPs, poly[(9,9-bis(3’(N,Ndimethylamino)propyl)-2,7-fluorene)-alt-5,5’-bis(2,2’thiophene)-2,6-naphthalene-1,4,5,8-tetracaboxylic-N,N’-di(2ethylhexyl)imide] (PNDIT-F3N) and poly[(9,9-bis(3’-((N,Ndimethyl)-N-ethylammonium)propyl)-2,7-fluorene)-alt-5,5’bis(2,2’-thiophene)-2,6-naphthalene-1,4,5,8-tetracaboxylicN,N’-di(2-ethylhexyl)imide]dibromide (PNDIT-F3N-Br) (Scheme 1) were designed to work as ETLs in PSCs.44 The high electron affinity of the NDI unit was introduced into the main chain to achieve good electron mobility and appropriate energy level alignment,45 which is desirable for ETLs. The amino or ammonium functionalized side chains endow the polymers with good processability in alcohol. The resulting polymers exhibited excellent solubility in methanol (> 15mg mL-1), allowing the WSCPs to be processed in a broad thickness range with the polar solvent. The LUMO values of the polymers were estimated to be -3.91 eV and -4.18 eV for PNDIT-F3N and PNDIT-F3N-Br, respectively, and the corresponding HOMO values were -5.55 eV and -5.47eV. The lowlying LUMOs of the polymers facilitate electron transportation from the fullerene acceptor to the cathode side, while the lowlying HOMO levels give the polymers hole-blocking properties with respect to the various donor materials in the photovoltaic devices. The mobility of PC71BM was obviously improved after deposition of the ETLs and the electron transfer from the amino groups or bromide anions to PC71BM was also supported by the electron spin resonance spectroscopy (ESR) tests. In addition to the doping effect between the ETLs and PC71BM, self-doping occurred in both of the WSCPs as the weak ESR signals from the unpaired electrons were clearly shown in the ESR spectra. However, PNDIT-F3N and PNDITF3N-Br displayed different self-doping mechanisms, which were caused by their different pendant side-chain groups. PNDIT-F3N-Br exhibited the same high conductivity in both the dark and illuminated conditions, whereas PNDIT-F3N displayed distinct photo conductivity and exhibited further enhanced conductivity under light soaking (see Figure 2). For PSCs with PffBT4T-2OD/PC71BM as an active layer, a high PCE of 10.11% was obtained for 5 ~ 10 nm PNDIT-F3N-Br, and remained at 8.04% when the ETL thickness reached 100 nm (Figure2). Further applications of these WSCPs in perovskite solar cells and tandem organic solar cells were also demonstrated.46,47 The results showed that these new types of WSCPs are potential candidates for application in future rollto-roll processing of large multilayer devices, and provided



new insights into the design of novel thickness-insensitive ETLs. C10H21

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Figure 2. Chemical structures of the polymers PNDIT-F3N and PNDIT-F3N-Br; Dark and illuminated J−V characteristics of the Schottky junction devices of the(a) PNDIT-F3N and (b)PNDITF3N-Br film; (c)Device structure of the PffBT4T-2OD:PC71BM BHJ based PSCs; (d)J−V curves of the PSC devices using PffBT4T-2OD:PC71BM as the active layer with different ETLs of various thickness. Reproduced with permission from ref. 44. Copyright 2016American Chemical Society. Table 1 Device performance with different thickness of WSCPs as ETL. ETL (thickness)

Active layer

PFN-OX

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0.74

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tion, architecture, and properties at the nanometer scale.48 The technique is particularly suitable for the preparation of conjugated polyelectrolyte (CPE) films. CPE is one of the most effective cathode interlayer materials. The ionic nature of CPEs means that they can potentially be processed by the eLbL assembly.18 To realize eLbL-assembly film, we designed and synthesized a complementary pair of cationic and anionic CPEs, namely, poly[(9,9-bis(3’-((N,N-dimethyl)-Nethylammonium)-propyl)-2,7-fluorene)-alt-2,7-(9,9dioctylfluorene)] (PFN+Br-) and poly[9,9-bis(4’butanoatel)fluorene-co-alt-2,7-(9,9-dioctylfluorene)]sodium salt (PFCOO-Na+), and used the eLbL self-assembly process to prepare a cathode interlayer with tunable thickness and surface functionality (see Figure 3). The brief self-assembly process involved immersing the negatively charged ITO in the cationic polyelectrolyte PFN+Br- solution to accomplish the electrostatic absorption of the first monolayer, and then in the anionic polyelectrolyte PFCOO-Na+ solution to form the first bilayer. As PFN+ has a net positive charge and PFCOO- has a net negative charge, alternation of the immersion steps between the cationic and anionic materials led to the formation of the PFN+/PFCOO- multilayers with a controllable number of layers. Inverted polymer solar cells based on a thickness optimized eLbL cathode interlayer exhibited promising performance with power conversion efficiencies as high as 9.41%.49 More importantly, this technique is quite suitable for depositing large area films. We also demonstrated the potential application of the eLbL cathode interlayer in a large area device by replacing the 1.5 × 1.5 cm2 substrate with a 7.5 × 7.5 cm2 one. The quality of the eLbL films deposited on the large area substrate was equal to that of the small area substrate, suggesting that this technique could be applied in the module fabrication of large-area PSCs. +

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Figure 3. The eLbL assembly procedure and eLbL films on the 7.5 × 7.5 cm2 ITO substrate.

41 nm

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In addition to develop new thickness insensitive interfacial materials that can be applied in the production of highperformance large area PSC modules, an alternative strategy for overcoming the coating problem of the thin interlayer film is to develop a new deposition technique that allows the formation of uniform and pinhole-free thin films for the preparation of an efficient interlayer for large area PSC modules. Electrostatic layer-by-layer (eLbL) self-assembly is usually conducted through alternating adsorption of oppositely charged substances on pre-charged substrates. This is a simple and efficient approach for producing controlled film composi-

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Scheme 2. Newly designed electron-withdrawing building blocks with high planarity for donor polymers Most of the currently used light absorption materials are quite thickness sensitive, with an optimal thickness of around 100 nm. As the same situation in interfacial materials, a small thickness variation in the active material can lead to a sharp


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decrease in device performance, which is not favorable for large area device processing and the device reproducibility. Thus, developing high-mobility conjugated polymers that can work well within a wide range of thicknesses without significantly sacrificing performance is an efficient way to overcome this problem.37 However, only a few donor polymers can provide efficient PSCs with thicknesses greater than 250 nm.50-53 To achieve high mobility donor polymers, rigid and high planar backbones should be introduced into materials. The rigid coplanar structures are important because efficient intrachain charge-carrier transport rely on planar and straight polymer chains, while efficient interchain charge-carrier transport needs closely π-stacked polymer aggregates.37 Thus, rigid and high planar backbones can affect the intermolecular stacking and can significantly enhance the charge carrier mobility of the resulting donor polymers. We have synthesized a series of conjugated donor polymers based on a newly designed electron-withdrawing building block (shown in Scheme 2), including naphtho[1,2-c:5,6-c]bis[1,2,5]thiadiazole,54-57 [1,2,5]thiadiazolo[3,4-f]benzotriazole,58,59 naphtho[1,2-c:5,6-

c]bis(2-octyl-[1,2,3]triazole),60,61 dibenzo-[a,c]phenazine,62 Pyrrolo[3,4-f]benzotriazole-5,7-dione,63 and acenaphtho[1,2b]quinoxaline diimides.64 Of these, the naphtho[1,2-c:5,6c]bis[1,2,5]-thiadiazole (NT) unit based polymers showed good performance in thick-film PSCs as they benefited from the large planar aromatic structure of the two fused 1,2,5thiadiazole rings contained in the NT unit, which facilitated the inter chain packing and improved the charge mobility of the resulting polymers. As a result, the polymer PBDT-DTNT (shown in Figure 4), comprised of NT and benzodithiophene (BDT) units, showed a PCE of 8.62% in an inverted device with an active layer thickness of 280 nm. The hole mobility of this polymer was estimated to be 1.1 × 10-3 cm2 V-1 s-1 with single-carrier devices, indicating that the polymer possessed good charge transport properties, and thus resulting in reduced charge-carrier recombination in the devices. More importantly, with further thickness optimization and morphology control, a PCE of 7.20% was obtained from the inverted cells with an active thickness of around 1000 nm (see Figure 4).65

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Figure 4. (a) Inverted device architecture and molecular structures; (b) Energy-level diagram of the inverted PSCs; (c) Device performance of the inverted PSCs with various active layer thicknesses. Reproduced with permission from ref. 65. Copyright 2014 Wiley-VCH Verlag GmbH &KGaA

Furthermore, it was found that the side chain substitution on the conjugated donor-acceptor polymer had a significant effect on the electronic, morphological, and photovoltaic properties. The side chain density affected the structure order of the resulting polymers especially in the lamellar packing direction. Moreover, the change of the side chain from branch to linear substitution enhanced the co-facial π–π stacking of the conjugated polymer chains, which helped promote the structural order. Based on these design outlines, we designed a new NT copolymer with linear substitution on the thiophene spacer units and dilinear substitution on the BDT thiophene units,

which also exhibited excellent photovoltaic properties.66 Benefiting from the high planarity of the NT unit, a novel NT based narrow band gap π-conjugated polymer NT812 with PCE over 10% are newly developed. What’s more attractive is the PCE exhibited a weak dependent on the BHJ layer thickness. As the film thickness increases from 190 to 1000 nm, remarkable PCE of 10.25% can be achieved with the film thickness of 340 nm, and the PCE remains 8.35% with a BHJ film thickness of 1000 nm, which is among the highest PCE so far reported single-junction OPVs with a BHJ film thickness of about 1000 nm.67 Moreover, this approach provides a solution to the bot-



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tleneck problem in manufacturing PSC modules with a lowcost and high throughput large area coating technique. In the meantime, the successful application of the NT unit in donor polymers has evoked great interest among the other research groups in this field.51,52 To achieve high-performance large area PSCs, we started our investigation using a device with an active area of 96 mm2. The interlayer was processed according to the developed eLbL process, while the active layer was processed using the spincoating process. For a device with PCE10:PC71BM as an active layer, the open-circuit voltage (Voc) of the PSC was found to remain at 0.79 V, while the short-circuit current density (Jsc), fill factor (FF), and PCE decreased to 16.1 mA cm-2, 60%, and 7.6%, respectively (see Figure 3).49 The decrease in PCE was mainly due to the ohmic loss from the transparent ITO electrode. It has been widely reported that the relatively high sheet resistance of ITO is a limiting factor in maintaining good performance PSCs when the device size is increased.68,69 This problem is yet to be solved, and will probably require new transparent electrodes with higher conductivity and advanced module design.70 However, as we have developed a series of thickness insensitive active materials and interfacial materials, a number of works based on these materials have been made to fabricate large area PSC modules using blade coating processing, and some encouraging results have been obtained. Thus, we can expect to obtain high-performance large area devices in the near future.

Conclusion and outlook In conclusion, to obtain solution processed highperformance, low-cost large area PSC devices, we started with the materials design and device engineering. For the interfacial materials, WSCPs were successfully synthesized to work as an efficient cathode interlayer in both the conventional and inverted high-performance PSCs. Furthermore, new thickness insensitive interfacial materials, which can maintain excellent device performance even when the thickness reached 100 nm, were developed. To fulfill the requirements for processing large area devices, such as blade coating and roll-to-roll coating, we developed a simple and efficient approach for preparing cathode interlayers with controlled film composition, uniformity, and thickness at the nanometer scale, using an electrostatic layer-by-layer self-assembly process. In terms of active layer materials, a series of electron-withdrawing group based polymers with excellent charge carrier properties and inter chain packing were developed. Of these, the NT based polymers exhibited high PCEs with thicknesses between 300 and 1000 nm, and thus are quite suitable for blade coating and roll-to-roll coating. The design of high-performance active layer material and interfacial material is a critical point for achieving high performance PSCs. However, to realize the commercialization of PSCs, more works should be done besides material design and synthesis. For example, large area electrodes with high conductivity are needed to guarantee efficient charge collection. Active layer morphology should be precisely controlled during the process by new coating technique to obtain optimal morphology. Besides, halogen-free solvent that used to process the active layer should be developed to increase the feasibility of industrial producing. Moreover, the stability of PSCs should

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also be further improved by using new encapsulation technique. These efforts will contribute to high-performance module devices and finally speed up the commercialization of PSC devices.

AUTHOR INFORMATION Corresponding Author E-mail: [email protected].

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT The work was financially supported the Ministry of Science and Technology (No. 2014CB643501), the Natural Science Foundation of China (No. 21520102006and 21490573), the Guangdong Natural Science Foundation (Grant No. S2012030006232), and the China Postdoctoral Science Foundation (NO. 2016M590773).

REFERENCES (1) Yu, G.; Gao, J.; Hummelen, J. C.; Wudl, F.; Heeger, A. J. Polymer Photovoltaic Cells: Enhanced Efficiencies via a Network of Internal Donor-Acceptor Heterojunctions. Science 1995, 270, 17891791. (2) Kippelen, B.; Bredas, J.-L. Organic Photovoltaics. Energy Environ. Sci. 2009, 2, 251-261. (3) Krebs, F. C.; Gevorgyan, S. A.; Alstrup, J. A Roll-to-Roll Process to Flexible Polymer Solar Cells: Model Studies, Manufacture and Operational Stability Studies. J. Mater. Chem. 2009, 19, 5442-5451. (4) 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. (5) 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. (6) 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. (7) Choi, S.; Zhou, Y.; Haske, W.; Shim, J.; Fuentes-Hernandez, C.; Kippelen, B. ITO-Free Large-Area Flexible Organic Solar Cells with an Embedded Metal Grid. Org. Electron. 2015, 17, 349-354. (8) Zuo, L.; Zhang, S.; Li, H.; Chen, H. Toward Highly Efficient Large-Area ITO-Free Organic Solar Cells with a ConductanceGradient Transparent Electrode .Adv. Mater. 2015, 27, 6983-6989. (9) Tsai P.-T.; Yu, K.-C.; Chang, C.-J.; Horng, .S.-F.; Meng, H.-F. Large-Area Organic Solar Cells by Accelerated Blade Coating. Org. Electron. 2015, 22, 166-172. (10) Zhang, T.; Chen, Z.; Yang, D.; Wu, F.; Zhao, X.; Yang, X. Fabricating High Performance Polymer Photovoltaic Modules by Creating Large-Scale Uniform Films. Org. Electron. 2016, 32, 126133. (11) Huang, Y.-C.; Cha, H.-C.; Chen, C.-Y.; Tsao, C.-S. Morphological Control and Performance Improvement of Organic Photovoltaic Layer of Roll-to-Roll Coated Polymer Solar Cells. Sol. Energy Mater. Sol. Cells 2016, 150, 10-18. (12) Yip, H.-L.; Jen, A. K. Y. Recent Advances in SolutionProcessed Interfacial Materials for Efficient and Stable Polymer Solar Cells. Energy Environ. Sci. 2012, 5, 5994-6011. (13) Duan, C.; Zhang, K.; Zhong, C.; Huang, F.; Cao, Y. Recent Advances in Water/Alcohol-Soluble π-conjugated Materials: New Materials and Growing Applications in Solar Cells. Chem. Soc. Rev. 2013, 42, 9071-9104. (14) Zhong, C.; Duan, C.; Huang, F.; Wu, H.; Cao, Y. Materials and Devices towards Fully Solution Processable Organic LightEmitting Diodes. Chem. Mater. 2011, 23, 326-340.


Page 7 of 9

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


(15) Krebs, F. C. Polymer Solar Cell Modules Prepared Using Roll-to-Roll Methods: Knife-over-Edge Coating, Slot-die Coating and Screen Printing. Sol. Energy Mater. Sol. Cells 2009, 93, 465-475. (16) Armin, A.; Hambsch, M.; Wolfer, P.; Jin, H.; Li, J.; Shi, Z.; Burn, P. L.; Meredith, P. Efficient, Large Area, and Thick Junction Polymer Solar Cells with Balanced Mobilities and Low Defect Densities. Adv. Energy Mater. 2014, 5, 1401221. (17) Hu, Z.; Zhang, K.; Huang, F.; Cao, Y. Water/Alcohol Soluble Conjugated Polymers for the Interface Engineering of Highly Efficient Polymer Light-Emitting Diodes and Polymer Solar Cells. Chem. Commun. 2015, 51, 5572-5585. (18) Hoven, C. V.; Garcia, A.; Bazan, G. C.; Nguyen, T.-Q. Recent Applications of Conjugated Polyelectrolytes in Optoelectronic Devices. Adv. Mater. 2008, 20, 3793-3810. (19) Huang, F.; Wu, H.; Wang, D.; Yang, W.; Cao, Y. Novel Electroluminescent Conjugated Polyelectrolytes Based on Polyfluorene. Chem. Mater. 2004, 16, 708-716. (20) He, Z.; Zhong, C.; Huang, X.; Wong, W.-Y.; Wu, H.; Chen, L.; Su, S.; Cao, Y. Simultaneous Enhancement of Open-Circuit Voltage, Short-Circuit Current Density, and Fill Factor in Polymer Solar Cells. Adv. Mater. 2011, 23, 4636-4643. (21) 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. Photon. 2012, 6, 591-595. (22) Zhang, K.; Zhong, C.; Liu, S.; Mu, C.; Li, Z.; Yan, H.; Huang, F.; Cao, Y. Highly Efficient Inverted Polymer Solar Cells Based on a Cross-linkable Water-/Alcohol-Soluble Conjugated Polymer Interlayer. ACS Appl. Mater. Interfaces 2014, 6, 10429-10435. (23) Duan, C.; Cai, W.; Hsu, B. B. Y.; Zhong, C.; Zhang, K.; Liu, C.; Hu, Z.; Huang, F.; Bazan, G. C.; Heeger, A. J.; Cao, Y. Toward Green Solvent ProcessablePhotovoltaic Materials for Polymer Solar Cells: The Role of Highly Polar Pendant Groups in Charge Carrier Transport and Photovoltaic Behavior. Energy Environ. Sci. 2013, 6, 3022-3034. (24) Cai, W.; Zhong, C.; Duan, C.; Hu, Z.; Dong, S.; Cao, D.; Lei, M.; Huang, F.; Cao, Y. The Influence of Amino Group on PCDTBTbased and P3HT-based Polymer Solar Cells: Hole Trapping Processes. Appl. Phys. Lett. 2015, 106, 233302. (25) 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, 6, 1502563. (26) 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. Photon. 2015, 9, 174-179. (27) Zuo, L.; Chang, C.-Y.; Chueh, C.-C.; Zhang, S.; Li, H.; Jen, A. K. Y.; Chen, H. Design of a Versatile Interconnecting Layer for Highly Efficient Series-Connected Polymer Tandem Solar Cells. Energy Environ. Sci. 2015, 8, 1712-1718. (28) Zheng, Z.; Zhang, S.; Zhang, J.; Qin, Y.; Li, W.; Yu, R.; Wei, Z.; Hou, J. Over 11% Efficiency in Tandem Polymer Solar Cells Featured by a Low-Band-Gap Polymer with Fine-Tuned Properties. Adv. Mater. 2016, 28, 5133-5138. (29) Zhang, Q.; Kan, B.; Liu, F.; Long, G.; Wan, X.; Chen, X.; Zuo, Y.; Ni, W.; Zhang, H.; Li, M.; Hu, Z.; Huang, F.; Cao, Y.; Liang, Z.; Zhang, M.; Russell, T. P.; Chen, Y. Small-Molecule Solar Cells with Efficiency over 9%. Nat. Photon. 2015, 9, 35-41. (30) Gao, K.; Li, L.; Lai, T.; Xiao, L.; Huang, Y.; Huang, F.; Peng, J.; Cao, Y.; Liu, F.; Russell, T.; Janssen, R.; Peng, X. Deep Absorbing Porphyrin Small Molecule for High-Performance Organic Solar Cells with Very Low Energy Losses. J. Am. Chem. Soc. 2015, 137, 72827285. (31) Liu, S.; Zhong, C.; Zhang, J.; Duan, C.; Wang, X.; Huang, F. A Novel Crosslinkable Electron Injection/Transporting Material for Solution Processed Polymer Light-Emitting Diodes. Sci. China Chem. 2011, 54, 1745-1749. (32) Guo, X.; Zhang, M.; Ma, W.; Ye, L.; Zhang, S.; Liu, S.; Ade, H.; Huang, F.; Hou, J. Enhanced Photovoltaic Performance by Modu-

lating Surface Composition in Bulk Heterojunction Polymer Solar Cells Based on PBDTTT-C-T/PC71BM. Adv. Mater. 2014, 26, 40434049. (33) Moses, J. E.; Moorhouse, A. D. The Growing Applications of Click Chemistry. Chem. Soc. Rev. 2007, 36, 1249-1262. (34) Cramer, N. B.; Scott, J. P.; Bowman, C. N. Photopolymerizations of Thiol−Ene Polymers without Photoinitiators. Macromolecules 2002, 35, 5361-5365. (35) Tasdelen, M. A.; Yagci, Y. Light-Induced Click Reactions. Angew. Chem. Int. Ed. 2013, 52, 5930-5938. (36) Zhang, Z.-G.; Qi, B.; Jin, Z.; Chi, D.; Qi, Z.; Li, Y.; Wang, J. Perylene Diimides: A Thickness-Insensitive Cathode Interlayer for High Performance Polymer Solar Cells. Energy Environ. Sci. 2014, 7, 1966-1973. (37) Duan, C.; Huang, F.; Cao, Y. Solution Processed Thick Film Organic Solar Cells. Polym. Chem. 2015, 6, 8081-8098. (38) Ho, C.-L.; Wong, W.-Y. Metal-Containing Polymers: Facile Tuning of Photophysical Traits and Emerging Applications in Organic Electronics and Photonics. Coord. Chem. Rev. 2011, 255, 24692502. (39) Yuen, M.-Y.; Roy, V. A. L.; Lu, W.; Kui, S. C. F.; Tong, G. S. M.; So, M.-H.; Chui, S. S.-Y.; Muccini, M.; Ning, J. Q.; Xu, S. J.; Che, C.-M. Semiconducting and Electroluminescent Nanowires SelfAssembled from Organoplatinum(II) Complexes. Angew. Chem. Int. Ed. 2008, 47, 9895-9899. (40) Chen, Y.; Li, K.; Lu, W.; Chui, S. S.-Y.; Ma, C.-W.; Che, C.M. Photoresponsive Supramolecular Organometallic Nanosheets Induced by PtII⋅⋅⋅PtII and CH⋅⋅⋅π Interactions. Angew. Chem. In. Ed. 2009, 48, 9909-9913. (41) Liu, S.; Zhang, K.; Lu, J.; Zhang, J.; Yip, H.-L.; Huang, F.; Cao, Y. High-Efficiency Polymer Solar Cells via the Incorporation of an Amino-Functionalized Conjugated Metallopolymer as a Cathode Interlayer. J. Am. Chem. Soc. 2013, 135, 15326-15329. (42) Heywang, G.; Jonas, F. Poly(alkylenedioxythiophene)s—New, Very Stable Conducting Polymers. Adv. Mater. 1992, 4, 116-118. (43) Bao Q.; Liu, X.; Wang, E.; Fang, J.; Gao, F.; Braun, S.; Fahlman, M. Regular Energetics at Conjugated Electrolyte/Electrode Modifier for Organic Electronics and their Implications on Design Rules. Adv. Mater. Interfaes 2015, 2, 1500204. (44) Wu, Z.; Sun, C.; Dong, S.; Jiang, X.-F.; Wu, S.; Wu, H.; Yip, H.-L.; Huang, F.; Cao, Y. n-Type Water/Alcohol-Soluble Naphthalene Diimide-Based Conjugated Polymers for High-Performance Polymer Solar Cells. J. Am. Chem. Soc. 2016, 138, 2004-2013. (45) Yan, H.; Chen, Z.; Zheng, Y.; Newman, C.; Quinn, J. R.; Dotz, F.; Kastler, M.; Facchetti, A. A High-Mobility Electron-Transporting Polymer for Printed Transistors. Nature 2009, 457, 679-686. (46) Sun, C.; Wu, Z.; Yip, H.-L.; Zhang, H.; Jiang, X.-F.; Xue, Q.; Hu, Z.; Hu, Z.; Shen, Y.; Wang, M.; Huang, F.; Cao, Y. AminoFunctionalized Conjugated Polymer as an Efficient Electron Transport Layer for High-Performance Planar-Heterojunction Perovskite Solar Cells. Adv. Energy Mater. 2015, 6, 1501534. (47) 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 Employing a New nType Conjugated Polymer as an Interconnecting Layer. Adv. Mater. 2016,28, 4817-4823. (48) Decher, G. Fuzzy Nanoassemblies: Toward Layered Polymeric Multicomposites. Science 1997, 277, 1232-1237. (49) Zhang, K.; Hu, Z.; Xu, R.; Jiang, X.-F.; Yip, H.-L.; Huang, F.; Cao, Y. High-Performance Polymer Solar Cells with Electrostatic Layer-by-Layer Self-Assembled Conjugated Polyelectrolytes as the Cathode Interlayer. Adv. Mater. 2015, 27, 3607-3613. (50) Price, S. C.; Stuart, A. C.; Yang, L.; Zhou, H.; You, W. Fluorine Substituted Conjugated Polymer of Medium Band Gap Yields 7% Efficiency in Polymer−Fullerene Solar Cells. J. Am. Chem. Soc. 2011, 133, 4625-4631. (51) Vohra, V.; Kawashima, K.; Kakara, T.; Koganezawa, T.; Osaka, I.; Takimiya, K.; Murata, H. Efficient Inverted Polymer Solar



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

Cells Employing Favourable Molecular Orientation. Nat. Photon. 2015, 9, 403-408. (52) 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. (53) Ma, Z.; Dang, D.; Tang, Z.; Gedefaw, D.; Bergqvist, J.; Zhu, W.; Mammo, W.; Andersson, M. R.; Inganäs, O.; Zhang, F.; Wang, E. A Facile Method to Enhance Photovoltaic Performance of Benzodithiophene-Isoindigo Polymers by Inserting Bithiophene Spacer. Adv Energy Mater. 2014, 4, 1301455. (54) Wang, M.; Hu, X.; Liu, P.; Li, W.; Gong, X.; Huang, F.; Cao, Y. Donor–Acceptor Conjugated Polymer Based on Naphtho[1,2c:5,6-c]bis[1,2,5]thiadiazole for High-Performance Polymer Solar Cells. J. Am. Chem. Soc. 2011, 133, 9638-9641. (55) Wang, M.; Hu, X.; Liu, L.; Duan, C.; Liu, P.; Ying, L.; Huang, F.; Cao, Y. Design and Synthesis of Copolymers of Indacenodithiophene and Naphtho[1,2-c:5,6-c]bis(1,2,5-thiadiazole) for Polymer Solar Cells. Macromolecules 2013, 46, 3950-3958. (56) Ma, W.; Tumbleston, J. R.; Wang, M.; Gann, E.; Huang, F.; Ade, H. Domain Purity, Miscibility, and Molecular Orientation at Donor/Acceptor Interfaces in High Performance Organic Solar Cells: Paths to Further Improvement. Adv. Energy Mater. 2013, 3, 864-872. (57) Liu, L.-Q.; Zhang, G.-C.; Liu, P.; Zhang, J.; Dong, S.; Wang, M.; Ma, Y.-G.; Yip, H.-L.; Huang, F. Donor–Acceptor-Type Copolymers Based on a Naphtho[1,2-c:5,6-c]bis(1,2,5-thiadiazole) Scaffold for High-Efficiency Polymer Solar Cells. Chem. Asian J. 2014, 9, 2104-2112. (58) Dong, Y.; Cai, W.; Hu, X.; Zhong, C.; Huang, F.; Cao, Y. Synthesis of Novel Narrow-Band-Gap Copolymers Based on [1,2,5]Thiadiazolo[3,4-f]benzotriazole and Their Application in BulkHeterojunction Photovoltaic Devices. Polymer2012, 53, 1465-1472. (59) Dong, Y.; Cai, W.; Wang, M.; Li, Q.; Ying, L.; Huang, F.; Cao, Y. [1,2,5]Thiadiazolo[3,4-f]benzotriazoleBased Narrow Band Gap Conjugated Polymers with Photocurrent Response up to 1.1 µm. Org. Electron. 2013, 14, 2459-2467. (60) Dong, Y.; Hu, X.; Duan, C.; Liu, P.; Liu, S.; Lan, L.; Chen, D.; Ying, L.; Su, S.; Gong, X.; Huang, F.; Cao, Y. A Series of New Medium-Bandgap Conjugated Polymers Based on Naphtho[1,2-c:5,6-

Page 8 of 9

c]bis(2-octyl-[1,2,3]triazole) for High-Performance Polymer Solar Cells. Adv. Mater. 2013, 25, 3683-3688. (61) Lan, L.; Zhang, G.; Dong, Y.; Ying, L.; Huang, F.; Cao, Y. Novel Medium Band Gap Conjugated Polymers Based on Naphtho[1,2-c:5,6-c]bis[1,2,3]triazole for Polymer Solar Cells. Polymer 2015, 67, 40-46. (62) Lan, L.; Chen, Z.; Li, Y.; Ying, L.; Huang, F.; Cao, Y. DonorAcceptor Conjugated Polymers Based on Cyclic Imide Substituted Quinoxaline or Dibenzo[a,c]phenazine for Polymer Solar Cells. Polym. Chem. 2015, 6, 7558-7569. (63) Lan, L.; Chen, Z.; Hu, Q.; Ying, L.; Zhu, R.; Liu, F.; Russell, T. P.; Huang, F.; Cao, Y. High-Performance Polymer Solar Cells Based on a Wide-Bandgap Polymer Containing Pyrrolo[3,4f]benzotriazole-5,7-dione with a Power Conversion Efficiency of 8.63%. Adv. Sci. 2016, 1600032 (64) Lan, L.; Chen, Z.; Ying, L.; Huang, F.; Cao, Y. Acenaphtho[1,2-b]quinoxaline Diimides Derivative as a Potential Small Molecule Non-Fullerene Acceptor for Organic Solar Cells. Org. Electron. 2016, 30, 176-181. (65) Hu, X.; Yi, C.; Wang, M.; Hsu, C.-H.; Liu, S.; Zhang, K.; Zhong, C.; Huang, F.; Gong, X.; Cao, Y. High-Performance Inverted Organic Photovoltaics with Over 1-µm Thick Active Layers. Adv. Energy Mater. 2014, 4,1400378. (66) Liu, P.; Dong, S.; Liu, F.; Hu, X.; Liu, L.; Jin, Y.; Liu, S.; Gong, X.; Russell, T. P.; Huang, F.; Cao, Y. Optimizing LightHarvesting Polymers via Side Chain Engineering. Adv. Funct. Mater. 2015, 25, 6458-6469. (67) 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:5,6c']bis([1,2,5]thiadiazole) based Narrow Bandgap π-Conjugated Polymer with Power Conversion Efficiency Over 10%. Adv. Mater. 2016, DOI: 10.1002/adma.201603178. (68) Jeong, W.-I.; Lee, J.; Park, S.-Y.; Kang, J.-W.; Kim, J.-J. Reduction of Collection Efficiency of Charge Carriers with Increasing Cell Size in Polymer Bulk Heterojunction Solar Cells. Adv. Funct. Mater. 2011, 21, 343-347. (69) Choi, S.; Potscavage, W. J.; Kippelen, B. Area-Scaling of Organic Solar Cells. J. Appl. Phys. 2009, 106, 054507. (70) Das, A. J.; Narayan, K. S. Retention of Power Conversion Efficiency – From Small Area to Large Area Polymer Solar Cells. Adv. Mater. 2013, 25, 2193-2199.


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Toward Solution-Processed High-Performance Polymer Solar Cells

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