Efficient Approach for Improving the Performance of Nonhalogenated

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An Efficient Approach for Improving the Performance of Non-Halogenated Green Solvent-Processed Polymer Solar Cells via Ternary-Blend Strategy Kakaraparthi Kranthiraja, Um Kanta Aryal, Vijaya Gopalan Sree, Kumarasamy Gunasekar, Changyeon Lee, Minseok Kim, Bumjoon J. Kim, Myungkwan Song, and Sung-Ho Jin ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b19548 • Publication Date (Web): 14 Mar 2018 Downloaded from http://pubs.acs.org on March 15, 2018

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ACS Applied Materials & Interfaces

An Efficient Approach for Improving the Performance of Non-Halogenated Green SolventProcessed Polymer Solar Cells via Ternary-Blend Strategy Kakaraparthi Kranthiraja,† Um Kanta Aryal,† Vijaya Gopalan Sree,† Kumarasamy Gunasekar,† Changyeon Lee,§ Minseok Kim,§ Bumjoon J Kim,§ Myungkwan Song*,∥ and Sung-Ho Jin*,† †

Department of Chemistry Education, Graduate Department of Chemical Materials, Institute for

Plastic Information and Energy Materials, Pusan National University, Busan, 46241, South Korea §

Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science

and Technology (KAIST), Daejeon, 305-701, South Korea ∥Surface

Technology Division, Korea Institute of Materials Science, Changwon 641-831, South

Korea

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ABSTRACT: The ternary blend approach has the potential to enhance the power conversion efficiencies (PCEs) of polymer solar cells (PSCs) by providing complementary absorption and efficient charge generation. Unfortunately, most PSCs are processed with toxic halogenated solvents, which are harmful to human health and the environment. Herein, we report the addition of a non-fullerene electron acceptor (ITIC) to a binary blend (P1:PC71BM, PCE = 8.07%) to produce an efficient non-halogenated green solvent-processed ternary PSC system with a high PCE of 10.11%. The estimated wetting coefficient value (0.086) for the ternary blend suggests that ITIC could be located at the P1:PC71BM interface, resulting in efficient charge generation and charge transport. In addition, the improved current density, sustained open-circuit voltage and PCE of the optimized ternary PSCs were highly correlated with their better external quantum efficiency response and flat-band potential value obtained from Mott-Schottky analysis. In addition, the ternary PSCs also showed excellent ambient stability over 720 h. Therefore, our results demonstrate that the combination of fullerene and non-fullerene acceptor in ternary blend as an efficient approach to improve the performance of eco-friendly solvent processed PSCs with long-term stability. KEYWORDS: non-halogenated solvent, ternary polymer solar cells, wetting coefficient, MottSchottky analysis, long-term ambient stability

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INTRODUCTION The power conversion efficiency (PCE) of solution-processable polymer solar cells (PSCs) has exceeded the 12% benchmark, which moves the focus of development to improving the processing solvents and conditions in order to enhance large-scale production for practical industrial applications.1,2 One of the major concerns is to search for environmentally friendly solvents for large area printing of PSC devices.3 To date, the prevalent use of common solvents and additives used for making state-of-the-art PSCs is chlorobenzene, 1,2-dichlorobenzene, 1,8diiodooctane, and chloronaphthalene, which are energy intensive and adversely impact on the environment and human health.4,5 Moreover, these halogenated external additives increase the device optimization time and raise the production cost, which limit commercialization.6,7 Therefore, chlorinated solvents are unfit as the processing solvents for large-scale manufacturing of PSCs. Thus, there is an immediate need to search for better non-halogenated solvents, additive alternatives and green solvent-processable photoactive materials to fabricate high performance PSCs.8 However, achieving high photovoltaic performance from non-halogenated solvents is a challenging task, since most of the photoactive materials show poor solubility, large aggregation and poor miscibility with counter acceptor materials in green solvents, resulting in moderate efficiency.9,10 Despite a few newly designed photoactive materials with improved solubility in non-halogenated solvents, their performances have remained moderate.11,12 Recently, among non-halogenated solvents, high performance was achieved for a few engineered photoactive materials in PSCs, but they required a high temperature of over 60-100 oC for processing, which is a hurdle for practical applications and which limits compatibility on flexible substrates.13,14 Therefore, it is necessary to develop room temperature non-halogenated solvent-processable high performance photoactive materials for commercial applications.15-19 3



Despite the great potential of conventional PSCs, their weak light harvesting capacity, high thermalization losses and low charge carrier mobility are key limitations for their advancement.20 These limitations associated with conventional PSCs can be overcome by developing multi-junction PSCs21-23 or low-band-gap photoactive materials with near-infrared (NIR) complementary absorption profiles.24 However, the complex fabrication process, premeditated control of the interfacial layer and optimization of each cell of multi-junction PSCs limit their practical applications. In this regard, ternary PSCs have become the best alternative to address the aforementioned issues due to their inherent potential advantages of single junction and tandem cells.20 Importantly, incorporating the appropriate third component (either donor or acceptor material) into an optimized binary system can apparently strengthen the absorption of the photoactive layer to better harvest light irradiation, and can also fine-tune the active layer morphology.25,26 Among the various types of ternary PSCs reported, most feature alterations to the third component among the two donors and one acceptor.27-29 The system of two polymer donors and one acceptor is very complicated due to the lack of entropic driving force for mixing the two polymer chains with strong intermolecular interactions.30 In contrast, the easy optimization and potential morphological advantages of one donor/two acceptor systems effectively improving the performance of PSCs.30-38 To the best of our knowledge, all the previously reported ternary PSCs (irrespective of third component) were processed from chlorinated solvents, which may be unsuitable for large-scale industrial production. Furthermore, most of them possess an additional supplementary interlayer in their typical device architecture for realizing efficient charge extraction.30-38 However, it is a highly challenging task to achieve high performance in non-halogenated green solvent-processed ternary PSCs with limited solubility and the strong aggregation property of photoactive layer materials. 4


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Therefore, to address these challenges, herein, we report an efficient non-halogenated solvent-processed ternary PSC system, by combining a side-chain fluorinated conjugated polymer

poly[4,8-bis(2-(4-(2-ethylhexyloxy)3-fluorophenyl)-5-thienyl)benzo[1,2-b:4,5-

b']dithiophene-alt-1,3-bis(4-octylthien-2-yl)-5-(2-ethylhexyl)thieno[3,4-c]pyrrole-4,6-dione] (P1), [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) and 3,9-bis(2-methylene- (3-(1,1dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2',3'-d']-sindaceno[1,2-b:5,6-b']dithiophene) (ITIC) as donor, acceptor and third component, respectively. Upon addition of an optimized amount of ITIC into a binary blend (P1:PC71BM), PCE was improved from 8.07% to 10.11% for the resulting ternary PSCs (P1:PC71BM:ITIC), which were processed from an optimized non-halogenated solvent system (toluene:diphenyl ether (DPE)). In addition to their high performance ternary PSCs also showed long-term stability over 720 h. Furthermore, we also probed the binary and ternary systems with electrochemical impedance spectroscopy (EIS), two-dimensional grazing wide angle incidence X-ray scattering (2DGIWAXS), transient photoluminescence (TRPL), and water contact angle measurements (WCAM) in order to understand the differences in the photovoltaic properties induced by the tiny amount of third component in ternary PSCs. Eventually, the reduced bulk resistance, balanced π-π packing, reduced life time, and wetting coefficient (ω) of the ternary blends were well matched with the obtained results. Finally, our study results not only highlighted the efficient non-halogenated solvent-processed binary and ternary PSCs, but also demonstrated the effective use of alloy acceptor (PC71BM and ITIC) for improving the performance of nonhalogenated solvent-processed PSCs with long-term stability. Furthermore, our high PCE of 10.11% is one of the best reported performances for benzodithiophene-based polymer donors processed from non-halogenated green solvents. 5



RESULTS AND DISCUSSION The molecular structures, UV-vis absorption spectra and energy levels of the donor polymer P1, acceptors PC71BM and ITIC are shown in Figure 1. The potential features of polymer P1, including the appropriate highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels, the strong face on orientation, and the good solubility in organic solvents prompted us to extend its application in non-halogenated processed PSCs.39 Further, we adopted ITIC as the third component in the fabrication of ternary PSCs due to its compatible energy levels with P1 so that PC71BM was expected to reduce the energy loss and also contribute more photons from its strengthened absorption spectra to cover up the NIR region (Figure 1b and Figure S1a (Supporting Information (SI))). The dramatic impact of the third component was revealed by the blend absorption profiles shown in Figure S1b (SI). The ternary blend films showed superior absorption profiles to those of binary blends due to the complementary absorption provided by ITIC. Further, the energy levels of P1, PC71BM and ITIC components from Figure 1c clearly indicates that presence of cascade-like energy level alignment, which further established an effective electron transporting pathway. The HOMO of P1, and LUMOs of PC71BM, ITIC were measured via cyclic voltammetry (Figure 1c,d, SI). And P1 LUMO and PC71BM and ITIC HOMOs were calculated with addition of their optical band gap values (Egopt). The Egopt of the P1, ITIC and PC71BM are 1.82, 1.51 and 1.62 eV respectively. The calculated The ITIC broadened the light absorption and acted as a bridge to ensure suitable energy level matching the charge transfer.34-36 The potential use of low toxic, halogen free, non-aromatic solvents and alcohols are the effective alternatives to the present widely used hazardous solvents.3 Although water and alcohols are the best green alternatives, the poor solubility of photoactive materials, requirements 6


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of special synthetic design strategies and poor efficiencies have limited their use in PSCs.40 In addition, the presence of polar functional groups in the photoactive materials for improving their solubility in alcohols would also act as charge trapping sites in the photoactive layer and thereby enhance the recombination. In addition, these polar groups can also migrate and seriously degrade the stability of PSCs.41 Thus, herein, we choose widespread industrial compatible nonhalogenated solvents (toluene, o-xylene and anisole) that are relatively less toxic for processing the photoactive layers. Bulk heterojunction (BHJ) binary PSCs were fabricated with invertedtype device architecture of (ITO/ZnO/P1:PC71BM:ITIC (1:1:0)/MoO3/Ag) by employing nonhalogenated solvents (Figure 2a). Since it is difficult to get favorable photoactive layer morphology for a PSC blend from non-halogenated solvents due to the limited solubility and strong tendency of aggregation of photoactive materials, the non-halogenated solvent must be carefully chosen. In the present study, we fabricated the binary PSCs with different nonhalogenated solvents (toluene, o-xylene and anisole) to achieve best possible nanoscale photoactive layer morphology. Among all, the pristine anisole-processed devices showed high performance, which is well correlated with their improved photovoltaic properties, i.e., shortcircuit current density (Jsc) and fill factor (FF), and their respective photoactive layer morphological behaviors (Figure S2, SI). Upon addition of a small amount of halogen-free DPE to the above optimized blends, the device performance was dramatically improved with a maximum PCE of 7.48 and 8.07% for o-xylene:DPE and toluene:DPE, respectively. This dramatic improvement in the performance of o-xylene:DPE and toluene:DPE blends is well attributed to the enhanced Jsc and better EQE responses. Furthermore, the absorption coefficient spectra of toluene and toluene:DPE blends (Figure S1b, SI) are well aligned with their EQE spectra. Surprisingly, the addition of DPE to the anisole-processed blends showed poor 7



performance (PCE=1.55%) due to the formation of unfavorable photoactive layer morphology (Figure S2, SI). The detail photovoltaic properties are summarized in Table S1 (SI) and the current-density-voltage (J-V) and external quantum efficiency (EQE) curves are shown in Figure 2b,c and Figure S3 (SI). In addition, Figure 2d also reveals an important correlation of PCE versus non-halogenated solvent. These observations confirmed that toluene:DPE is a very appropriate choice for the present system. Furthermore, we conducted atomic-force microscopy (AFM) and photoluminescence (PL) quenching of the toluene and toluene:DPE-processed binary photoactive layers. As shown in Figure 2e (AFM height and phase images), a dramatic change in the photoactive layer morphology was observed for toluene and toluene:DPE processed films. Especially, toluene:DPE processed films (AFM height images) showed finely mixed surface morphology with a large reduction in root mean square (RMS) roughness of 3.17 nm compared to toluene-processed films with high RMS of 41.25 nm. Similarly, the toluene:DPE-processed films (AFM phase images) also showed a smooth BHJ morphology with better donor/acceptor intermixing than the toluenebased films. Furthermore, the toluene:DPE-processed blend showed more complete PL quenching than that of the toluene-processed blends, indicating the better charge transfer between the donor and acceptor materials (Figure S4a, SI). Altogether, the enhanced performance of the toluene:DPE was attributed to its excellent compatibility of P1 with PC71BM and its well organized photoactive layer morphology. In order to improve the performance of the non-halogenated solvent-processed binary system with a maximum PCE of 8.07%, a minute amount of ITIC was incorporated as the third component to produce an efficient ternary blend. Different amounts of ITIC were added to the control optimized binary blend while either varying or not varying the PC71BM composition. The 8


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detail optimized photovoltaic parameters, open-circuit voltage (Voc), Jsc, FF, and PCE of the ternary blends are shown in Table 1. The J-V and EQE spectra of the optimized devices are shown in Figure 3a,b. The addition of a tiny amount of non-fullerene ITIC into the binary PSCs dramatically improved the performance of the resulting ternary blends, which is well correlated with the high Jsc of the ternary blends. The optimized ternary blends P1:PC71BM:ITIC (1:1:0.1) and P1:PC71BM:ITIC (1:0.9:0.1) showed maximum PCEs of 10.11 and 8.44%, respectively, compared to 8.07% for the binary blends. Further increase in the amount of ITIC in the ternary blends resulted in poor Jsc, FF due to the reduced charge transport properties and poor morphology, thereby lowering the PCE. Especially, the P1:PC71BM:ITIC (1:1:0.1) ternary blend showed the greatest performance improvement (PCE=10.11%) mainly due to its higher Jsc (17.71 mA/cm2). Figure 3c shows the histogram of the optimized ternary PSCs P1:PC71BM:ITIC (1:1:0.1) with consistent PCE over 10%. The increment of Jsc was be ascribed to the incorporation of ITIC, which allowed more photons to be absorbed in the range of 550-800 nm. Even though the Voc values of the ternary blends were sustained, their FF values were poor with respect to the control binary blends, due to the low carrier mobility of ITIC.29 In addition, the EQE spectra of the binary blends was also heavily modulated by the addition of the third component ITIC. As shown in Figure 3b the EQE spectra of ternary PSCs were better at 550-800 nm compared to that of optimized binary blends (limited to 700 nm), which contributed to the improved Jsc values. In particular, the optimized ternary blend P1:PC71BM:ITIC (1:1:0.1) showed a higher maximum EQE response than the binary blends, which agreed well with obtained high Jsc value. Moreover, the integrated Jsc values of the optimized binary and ternary blends were within the error range of 5%.42

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In order to explore the charge transport properties of the binary and ternary blends, we measured the hole mobilities of blend films by employing the space-charge-limited current (SCLC) method using the device structure of ITO/PEDOT:PSS/binary/ternary active layer/MoO3/Al. The J-V curves of the SCLC hole mobilities are shown in Figure 3d. The SCLC hole mobilities of the P1:PC71BM:ITIC (1:1:0), P1:PC71BM:ITIC (1:0.9:0.1), P1:PC71BM:ITIC (1:1:0.1), and P1:PC71BM:ITIC (1:0:1) were 9.26 × 10-4, 1.16 × 10-3, 1.05 × 10-3, and 8.01 × 10-4 cm2 V-1 s-1, respectively. Next, SCLC electron mobility of the P1:PC71BM:ITIC (1:1:0), P1:PC71BM:ITIC (1:0.9:0.1), P1:PC71BM:ITIC (1:1:0.1), and P1:PC71BM:ITIC (1:0:1) blends were found to be 2.06 × 10-4, 2.93 × 10-4, 3.43 × 10-4, and 1.65 × 10-4 cm2 V-1 s-1, respectively (Figure S5, SI).

The relatively balanced charge transport behaviors of the ternary blends

compared to that of the binary blends were well correlated with the obtained Jsc values of the respective blends. The favorable photoactive layer morphologies and well organized molecular packing were expected for the ternary blends.5 The enhanced photovoltaic performance of the ternary blends (i.e., impact of the addition of a tiny amount of ITIC) into the binary blends was further assessed by EIS. The Nyquist plots of P1:PC71BM:ITIC (1:1:0), P1:PC71BM:ITIC (1:0.9:0.1), P1:PC71BM:ITIC (1:1:0.1), and P1:PC71BM:ITIC (1:0:1) are shown represented in Figure 3e and the inset shows the equivalent circuit. The bulk resistance of the blends increased in the order P1:PC71BM:ITIC (1:1:0) (197 Ω cm2) < P1:PC71BM:ITIC (1:1:0.1) (244 Ω cm2) < P1:PC71BM:ITIC (1:0.9:0.1) (271 Ω cm2) < P1:PC71BM:ITIC (1:0:1) (312 Ω cm2), which is well aligned with the corresponding Jsc and FF values. Next, we also performed Mott-Schottky (M-S) analysis (Figure 3f) with capacitancevoltage measurements to understand the impact of the third component ITIC on the flat-band potential (VFB) and in turn on Voc, along with the overall device performance. The obtained VFB 10


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values were very closely related to the built-in potential (VBI) for an identical photoactive layer and a positive variation of VFB is the result of an increased VBI. The increase in VFB matched with the Voc values in the binary and ternary blends in Table 2, which clearly indicates that the higher value of VFB strengthens the built-in field within the PSCs device and in turn positively affects the other parameters (Jsc and FF).42 As a result, more efficient charge extraction and reduction of charge recombination process can be realized. The morphology of the non-halogenated solvent-processed binary and ternary blends and the impact of ITIC on the blend morphology were carefully analyzed by AFM, transmission electron microscopy (TEM) and 2D-GIWAXS measurements. As shown in Figure S6a (SI), the ternary blends P1:PC71BM:ITIC (1:0.9:0.1) (RMS=2.18 nm) and P1:PC71BM:ITIC (1:1:0.1) (RMS=1.27 nm) with a tiny amount of ITIC also exhibited a more finely mixed nanoscale morphology than that of the binary blend P1:PC71BM:ITIC (1:1:0) (RMS=3.17 nm). In contrast, the P1:PC71BM:ITIC blend (1:0:1) showed a relatively rough surface with large separated domains with high RMS (4.63 nm) due to the apparent aggregation of the ITIC effect on the overall blend film formation.29 Furthermore, the TEM results (Figure S6b, SI) supported the AFM results as the optimized binary and ternary blends showed finely mixed morphologies. In particular, the ternary blends showed relatively better organized and finely mixed textures than that of the binary blends P1:PC71BM:ITIC (1:1:0) and P1:PC71BM:ITIC (1:0:1). Next, we conducted PL quenching experiments (Figure S4 and S7a, SI) with the optimized binary and ternary blends to understand the extent of charge transfer behavior between the donor and acceptor units. As shown in Figure S4 (SI), the pristine polymer (P1) film showed a high intensity PL emission (600-800 nm), which was completely quenched for the optimized binary blends (P1:PC71BM:ITIC (1:1:0) and P1:PC71BM:ITIC (1:0:1)). Similarly, a significant PL 11



quenching was observed (Figure S7a, SI) for the ternary blend films with respect to P1. Interestingly, the PL emission of ITIC was partially reduced for PC71BM:ITIC (Figure S7b, SI), indicating that the excitons generated in ITIC can be partially separated into free charges by transferring electrons from the LUMO orbitals of ITIC to the LUMO orbitals of PC71BM or by transferring the holes from the HOMO orbitals of ITIC to the HOMO orbital of PC71BM.43 Next, we measured the TRPL for P1 and the binary (P1:PC71BM:ITIC (1:1:0)) and ternary (P1:PC71BM:ITIC (1:1:0.1)) blends in order to examine the charge transfer processes from donor to acceptor. The TRPL curves of P1, P1:PC71BM:ITIC (1:1:0) and P1:PC71BM:ITIC (1:1:0.1) are shown in Figure S8 (SI). The reduced charge extraction time (0.19 ns) of the ternary blend compared to that of the binary blend (0.44 ns) and the pristine polymer film (0.95 ns) indicates more efficient charge extraction from the photoactive layer, which is favorable for the efficient improvement of current density and thus the overall photovoltaic performance. These results reveal that a high degree of self-organization occurred in the best ternary blend, which could have hampered the proper cascade effect that also separates the electron and hole transport.44 2D-GIWAXS measurements45 were carried out to examine the molecular packing and orientation of active materials in the optimized binary and ternary blend films processed from the non-halogenated solvents (Figure 4). The toluene-processed pristine polymer (P1) films without solvent additive (DPE) showed lamellar spacing of 30.3 Å (q = 0.21 Å−1) in the qxy direction. The π–π stacking peak (010) for P1 was observed in the qz direction at 1.67 Å−1 (d-spacing = 3.76 Å), which indicated strong ‘face-on’ orientation (Figure S9, SI). Interestingly, the P1:PC71BM binary and P1:PC71BM:ITIC ternary blends showed almost identical X-ray diffraction patterns (Figure 4). The diffraction patterns of the ternary blend films with various amounts of ITIC exhibit lamellar and π–π stacking spacings of 28.4 Å and 1.67 Å, which are 12


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similar to those observed from the control binary blends without ITIC, 28.4 Å and 1.68 Å, respectively. These results reveal the minute changes in the packing structure of donor polymer in the ternary blends that contain ITIC.46 However, the P1:ITIC binary blends presented diffraction patterns with a different aspect in the qz direction. We observed a prominent scattering peak at 0.45 Å−1 of q, which originated from the large aggregation of ITIC in the blend film. Nevertheless, this peak was not shown in the ternary blends. Collectively, the addition of an optimized amount of ITIC to the binary blends preserved the molecular packing structure and face-on structure of the P1 polymers in the blends. This apparent effect on the blend morphologies was well matched with the AFM and TEM results. Therefore, it could be concluded that the morphological properties of the binary and ternary blend films might not explain the dramatically improved photovoltaic performance of the ternary blends. Hence, we conducted ω calculations to predict the location of the third component of the ternary blend. The location of the third component (ITIC) in the ternary blend is a crucial factor for attaining efficient charge generation and charge transport to the respective electrodes via the formation of dominating charge carrier channels. Thus, we measured the WCA (Figure 5a) of each individual component to calculate the surface energies via Fowkes model.47 The estimated surface energies of the active components of the photoactive layer (P1, PC71BM and ITIC) were 17.58, 24.26 and 19.17 mJ/m2, respectively (Table 3). The surface energy of the photoactive layer components not only affects the vertical phase separation but is also a vital parameter for determining ω. Next, we estimated ω for the ternary blends by employing Young’s equation. 25,39 When -1 10%. Adv. Mater. 2016, 28, 10008-10015.

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Page 24 of 33

Table 1. Optimized Photovoltaic Properties of Binary and Ternary blends. Voc Jsc (mA/cm2) (V) P1:PC71BM:ITIC 1:1:0 0.90±0.01 12.60±0.12 P1:PC71BM:ITIC 1:0.9:0.1 0.91±0.03 14.81±0.16 P1:PC71BM:ITIC 1:0.8:0.2 0.92±0.01 14.87±0.20 P1:PC71BM:ITIC 1:1:0.1 0.90±0.02 17.71±0.09 P1:PC71BM:ITIC 1:1:0.2 0.91±0.01 14.23±0.12 P1:PC71BM:ITIC 1:0:1 0.91±0.02 10.91±0.24 a The PCE values are obtained from over ten devices. Blend

Ratio

24


FF (%) 70.64±0.05 62.45±0.10 59.21±0.13 63.67±0.12 63.24±0.18 51.34±0.12

PCEave.a (%) 8.07±0.06 8.44±0.10 8.01±0.12 10.11±0.10 8.22±0.14 5.15±0.16

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Table 2. M-S Analysis of Optimized Binary and Ternary Blends for Voc Study. Blend

Ratio

Voc (V)

VFB (V)

P1:PC71BM:ITIC

1:1:0

0.90

0.92

P1:PC71BM:ITIC

1:0.9:0.1

0.91

0.93

P1:PC71BM:ITIC

1:1:0.1

0.90

0.93

P1:PC71BM:ITIC

1:0:1

0.91

0.90

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Page 26 of 33

Table 3. WCA and Surface Energy Study for P1, PC71BM and ITIC. Component

Angle

Surface energy (mJ/m2)

P1

105.9º

17.58

PC71BM

82.2º

24.26

ITIC

92.8º

19.17

P1:PC71BM:ITIC (1:0:1)

102.0º

18.16


87.7º

20.07


102.6º

22.36

P1: PC71BM:ITIC (1:1:0.1)

101.9º

25.38

P1: PC71BM:ITIC (1:0.9:0.1)

102.0º

26.03

26


Page 27 of 33 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


Figure 1. (a) Molecular structure of P1, PC71BM and ITIC. (b) UV-visible absorption spectra of P1, PC71BM and ITIC in thin film state. (c) Energy levels of P1, PC71BM and ITIC.

27


ACS Applied Materials & Interfaces 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

Figure 2. (a) Inverted PSC device structure. (b, c) Optimized J-V and EQE curves of binary PSCs (P1:PC71BM:ITIC (1:1:0)) processed from toluene and toluene:DPE. (d) Comparison chart of PCE and non-halogenated solvents of binary PSCs (P1:PC71BM:ITIC (1:1:0)). (e) AFM height and phase images of binary blends P1:PC71BM:ITIC (1:1:0) processed from toluene and toluene:DPE. 28


Page 28 of 33

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Figure 3. (a, b) Optimized J-V and EQE curves of binary and ternary PSCs. (c) Histogram of PCE of optimized ternary blend (P1:PC71BM:ITIC (1:1:0.1)). (d, e, f) SCLC hole mobilities, Nyquist plots, and M-S plots of optimized binary and ternary blends [P1:PC71BM:ITIC (1:1:0), P1:PC71BM:ITIC (1:0.9:0.1), P1:PC71BM:ITIC (1:1:0.1) and P1:PC71BM:ITIC (1:0:1)].

29



30


Page 30 of 33

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Figure 4. (a) GIWAXS patterns of the optimized binary and ternary blends. (b) In-plane linecuts (qxy) and c) out-of-plane linecuts (qz) collected from the images [P1:PC71BM:ITIC (1:1:0), P1:PC71BM:ITIC (1:1:0.1), P1:PC71BM:ITIC (1:0.9:0.1) and P1: PC71BM:ITIC (1:0:1)].

31



Page 32 of 33

(b) (d) (a)

(c)

Figure 5. (a) Surface energy of P1:ITIC (red circle) and PC71BM:ITIC (black circle) blend films plotted against the ITIC content. (b, c) TEM-EDX elemental mapping of binary (P1:PC71BM:ITIC (1:1:0)) and ternary (P1:PC71BM:ITIC (1:1:0.1)) blends. (d) Long-term stability of ternary PSC blend P1:PC71BM:ITIC (1:1:0.1) under ambient condition without encapsulation.

32


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Table of Contents

33


Efficient Approach for Improving the Performance of Nonhalogenated

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