Poly(naphthalene diimide-alt-bithiophene) Prepared by Direct (Hetero

Subscriber access provided by University of Winnipeg Library

Article

Poly(naphthalene diimide-alt-bithiophene) Prepared by Direct (Hetero)arylation Polymerization for Efficient All-Polymer Solar Cells Amélie Robitaille, Samson A. Jenekhe, and Mario Leclerc Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.8b02160 • Publication Date (Web): 09 Jul 2018 Downloaded from http://pubs.acs.org on July 9, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 11 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

Chemistry of Materials

Poly(naphth oly(naphthalene diimide diimideiimide-alt-bithiophene) Prepared Prepared by Direct (Het(Hetero)arylation Polymerization for Efficient Efficient AllAll-Polymer Solar Cells Amélie Robitaille†‡, Samson A. Jenekhe‡*, Mario Leclerc†* †

Département de Chimie, Université Laval, Québec, QC, G1V 0A6, Canada. Department of Chemical Engineering and Department of Chemistry, University of Washington, Seattle, Washington 98195-1750, USA. ‡

ABSTRACT: A high molecular weight alternating naphthalene diimide-bithiophene copolymer (PNDIOD-T2) has been prepared by direct (hetero)arylation polymerization (DHAP). Its structure and properties were investigated in comparison with the Stille-prepared commercial analog, N2200. It was found that the new DHAP-derived PNDIOD-T2 and known N2200 have similar optical absorption spectra, HOMO/LUMO energy levels, but slightly different 1H NMR spectra. Inverted allpolymer solar cells using PNDIOD-T2 as the acceptor and PCE12 or PCE10 as the donor polymer showed slightly superior performances compared to similar N2200 devices. All-polymer solar cells with 7.3% efficiency could be achieved with PNDIOD-T2 blends without the use of a processing additive. These results demonstrate that low-cost and eco-friendly DHAP-based n-type semiconducting polymers are promising for developing high performance all-polymer solar cells.

INTRODUCTION Over the past few years, extensive research has been carried out on the development of new π-conjugated polymers. Organic conductors and semi-conductors have advantages over their inorganic counterparts such as easily modulated optoelectronic properties, solubility in common solvents as well as the mechanical properties of plastics. This synergy enables the possibility to develop efficient, flexible and lightweight devices using low-cost, simple and large-area roll-to-roll printing techniques for the fabrication of many organic electronics devices such as solar cells, [1-5] field-effect transistors, [6-8] and Li-ion batteries, [9,10] just to name a few. However, some drawbacks remain in most organic electronic devices, mainly due to the synthetic procedures used to obtain such polymers. [11,12] State-of-the-art methods for synthesis of πconjugated alternating copolymers (e.g Migita-Stille and Suzuki-Miyaura couplings) are far from being optimal. Indeed, the synthetic pathways for the preparation of the monomers require numerous synthetic steps and they also call for expensive organometallics reagents, which are most of the time, unstable, hard to purify and even toxic in the case of organostannanes involved in the Stille coupling. [13-15]

Since organic electronic devices should be low-cost and eco-friendly, the choice of the synthetic pathway should be in the same vein. Direct (hetero)arylation polymerization (DHAP) allows the formation of C-C bonds between (hetero)arenes and (hetero)aryl halides without organometallics intermediates reducing the number of synthetic steps. DHAP also enables the synthesis of high molecular weight and high-performing organic materials. [16-18] DHAP has recently lead to low-defect polymers even with the use of thiophene derivative and 2,2’-bithiophene.

[19-21] One of them is one of the most popular n-type πconjugated polymer, PNDIOD-T2 (analog of N2200 active ink which has achieved excellent devices’ performances in OFET [22,23], Li-ion batteries[24] and all-polymer solar cells [25].) realized by Sommers et al. [26] They have shown relatively good molecular weight (31 kDa) that offers electron mobilities of 2.9 cm2/Vs in organic field-effect transistors. This was slightly lower than the 3.2 cm2/Vs from the Stille control (32 kDa). Although this performance is excellent, it is important to know that the commercial N2200 normally has a much higher molecular weight, which could probably explain the slightly better performance and its use to fabricate efficient all-PSCs. All-PSCs have attracted attention since they can overcome the problems of fullerene acceptors such as their weak molar absorption coefficient, their low stability under light, stress and their poor stability over time due to the formation of crystalline domains in the active layer. [27-30] Indeed, using an active layer of two polymers, a donor and an acceptor, provides a better optimization of the energy levels, band gap and absorption spectra as well as a higher molar absorption coefficient. [31-33] All-PSC have already demonstrated a better thermal, mechanical stability and suitability for the roll-to-roll large area with a conversion efficiency (PCE) >5% [34] The effect, in All-PSCs, of the molecular weight of both donor and acceptor polymers has been widely studied [35,36] as well as the effect of crystallinity and regioregularity. [37-41] Additionally, the optimization of the morphology by the utilization of additives, the effect of solvents and different post-treatment and the utilization of ternary blend have allowed an increase of PCE form 2% to 9%. [4248]

ACS Paragon Plus Environment

Chemistry of Materials 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 2 of 11

2 In this paper, we present the synthesis of high-molecular weight PNDIOD-T2 (76 kDa) via DHAP. It has been compared to a commercially available high-molecular weight N2200. All-polymer solar cells have been realized with PNDIOD-T2 and N2200. PNDIOD-T2 has demonstrated slightly better performance than the Stille coupled analog, the commercial N2200. Air aging process of the allpolymer solar cells with PBDB-T: PNDIOD-T2 (DHAP) allows a high-PCE of 7.3%.

EXPERIMENTAL SECTION Materials. Naphthalene-1,4,5,8-tetracarboxylic dianhydride was obtained from TCI America and used without any further purification. 2,2’-Bithiophene was obtained from Sigma-Aldrich and purified by low-pressure distillation. Tris(dibenzylideneacetone)dipalladium (0), Pivalic acid, cesium carbonate as well as other precursors for the preparation of the 2-octyl-1-dodecylamine were obtained from Sigma-Aldrich and used without further purifications. Extra dry chlorobenzene was obtained from Accros Organic and degased with argon for 15 min prior to utilization. Other starting materials were purchased from SigmaAldrich, TCI America or Alfa Aesar. The donor polymer PTB7-Th (PCE10) and the commercial N2200 were obtained from 1-Material (Montréal, Québec, Canada) and PBDT-T (PCE12) was obtained from Brilliant Matters (Québec, Québec, Canada), and were all used without any further purification.

path length quartz cells. A polymeric solution (10 mg/mL in chloroform) was spin coated on untreated glass substrate to perform the solid-state measurements. The optical bandgap was calculated from the onset of the absorption band. Cyclic voltammetry (CV) was performed with a Solartron 1287 potentiostat using platinum electrodes at a scan rate of 10 mV/s and a Ag/Ag+ (0.01 M of AgNO3 in acetonitrile) reference electrode in an anhydrous and argon-saturated solution of 0.1 M of tetrabutylammonium tetrafluoborate (Bu4NBF4) in acetonitrile. In these conditions, the oxidation potential (Eox) of ferrocene was 0.314 V versus Ag/Ag+, whereas the Eox of ferrocene was 0.446 V versus standard calomel electrode (SCE). The HOMO and LUMO energy levels were determined from the oxidation and reduction onset from the voltammogram assuming SCE electrode to be -4.7 eV in vacuum, as reported in the literature. Electrochemical onsets were determined at the position where the current starts to differ from the baseline. [49] Thermogravimetric analyses of the polymers were performed with a TGA/SDTA 851e from Metler-Toledo. The acquisitions were recorded under argon with a 10 °C/min scan rate from 50 to 800 °C. The reported degradation temperatures (DT) correspond to a 5% mass lost.

Number-average (Mn) and weight-average (Mw) molecular weights were determined by size exclusion chromatography (SEC) using a high temperature Varian Polymer Laboratories GPC220 equipped with an RI detector and a PL BV400 HT Bridge Viscometer. The column set consists of 2 PL gel Mixed C (300 x 7.5 mm) columns and a PL gel Mixed C guard column. The flow rate was fixed at 1mL/min using 1,2,4-trichlorobenzene (TCB) (with 0.0125% BHT w/v) as the eluent. The temperature of the system was set to 110 °C. The samples (2 mg) were dissolved in 2 mL of TCB in a 5 mL chromatography vial then stirred and heated to 110 °C for 1 hour for a complete dissolution. Then, a filtration through a 0.45 µm cellulose fiber film in a 5 mL chromatography vial lead to a homogenous polymeric solution. Dissolution of the polymers was performed through a loop of 200 µL with a Varian Polymer Laboratories PL-SP 260VC sample preparation system. The calibration method used to generate the reported data was the classical polystyrene method using polystyrene narrow standards Easi-Vials PS-M from Varian Polymer Laboratories which were dissolved in TCB.

Fabrication and characterization of all-polymer solar cells. Inverted BHJ solar cells were prepared on a commercial ITO coated glass substrate. ITO glass substrates were cleaned sequentially in ultrasonic baths with acetone and isopropyl alcohol for 20 minutes, dried using nitrogen gas, and stored in a glove box. The ITO glass substrate was UV-ozone treated for 2 minutes right before coating the ZnO/PEI layer. The ZnO precursor solution (250 mg of zinc acetate, 0.069 mL of ethanolamine and 2.91 mL of 2-methoxyethanol) was spin-coated onto the ITO glass at 5000 rpm for 40 secs, annealed at 250 °C on a hot plate in air for 1 hr to make 20 – 30 nm thick ZnO layer. A 0.05 wt% polyethylenimine (PEI, Mw ~ 25000, Aldrich 408727) in 2- methoxyethanol solution was spin-coated onto the ZnO layer and dried at 110 °C on a hot plate in air for 10 minutes. Then, the glass/ITO/ZnO/PEI substrate was transferred into an argon filled glove box. The active layer was deposited over the ZnO layer by spin coating the polymer/polymer solution which is then dried at 130 °C for 90 seconds. The blend solutions were prepared by dissolving the polymers in chlorobenzene and stirring the mixtures on a hotplate at 60 °C for 2 hours and then stirred at 40 °C overnight. The different blends used were PTB7Th:PNDIOD-T2 with a 1:1 ratio with a concentration of 15 mg/mL and PBDB-T:PNDIOD-T2 with a 1:1 ratio with a concentration of 10mg/mL. Finally, MoO3 (7.5 nm) and Ag anode (100 nm) were deposited onto the active layer through a shadow mask on top of the active layer by thermal evaporation under high vaccum (1 x 10-7 Torr) onto the active layer. Five pixels, each with an active area of 4 mm2, were fabricated per ITO substrate.

UV vis-NIR absorption spectra were recorded using a Varian Cary 500 UV-vis-NIR spectrophotometer using 1 cm

Characterization of all-polymer solar cells: The photovoltaic cells were tested under AM 1.5 G solar illumination

Measurements. 1H spectra were recorded using a Varian AS400 in deuterated chloroform at 298 K. Chemicals shifts were reported as δ values (ppm) relative to chloroform value of 7.26 ppm. 1H spectra of the polymers were recorded on a Varian Agilent DD2 500 MHz apparatus in 1,1,2,2-tetrachloroethane-D2 at 90 °C.


Page 3 of 11 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


3 at 100 mW/cm2 in ambient condition using a Solar Simulator (model 16S, Solar Light Co., Philadelphia, PA) with a 200 W Xenon Lamp Power Supply (Model XPS 200, Solar Light Co., Philadelphia, PA) calibrated by NREL certified Si photodiode (Model 1787–04, Hamamatsu Photonics K.K., Japan) and a HP4155A semiconductor parameter analyzer (Yokogawa Hewlett-Packard, Japan). After the J-V measurement, the external quantum efficiency (EQE) was measured by using a solar cell quantum efficiency measurement system (Model QEX10, PV Measurements, Inc., Boulder, CO) with a 2 mm2 (2 mm × 1 mm) size masked incident light source and TF Mini Super measurement apparatus for multiple devices in a single substrate. The EQE system was calibrated with a Si photodiode before each measurement.

RESULTS AND DISCUSSION The synthesis of 2,6-dibromonaphthalene-1,4,5,8diimide is a two-step procedure inspired by reported literature, a detailed protocol is available in the supporting information (SI). [50,51] As shown in Scheme 1, to afford a PNDIOD-T2 2,6-dibromonaphthalene-1,4,5,8-diimide has been polymerized with 2,2’-Bithiophene with modified conditions from the literature. [26] The concentration, the polymerization time and the concentration over the polymerization reaction have been modified. Details for the synthesis of Poly{[N,N′-bis(2-octyldodecyl)-

naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′(2,2′-bithiophene)} (PNDIOD-T2 are presented in the SI. Scheme 1. Synthesis of PNDIOD-T2

To fully study the structural and electronic properties, both polymers (PNDIOD-T2 and commercial N2200) have been characterized under the same conditions. 1H NMR spectra of both polymers, PNDIOD-T2 (red) and N2200 (blue), are presented in Figures 1, S2, S3 and S4. The spectra demonstrated that both polymers possess well-defined structures. In the aromatic region, PNDIODT2 showed a 2:4 proton ratio, which corresponds to the desired structure. In the case of N2200, a 2:3.95 proton ratio was observed and the deviation from 2:4 could be associated with homocoupling. Indeed, it is known that stannylated monomers in Stille coupling can undergo homocoupling reactions. [52,53]

Figure 1. 1H NMR of a) aromatic region of PNDIOD-T2 (DHAP) b) aromatic region of N2200 (Stille coupled) c) comparison of PNDIOD-T2 (red) and N2200 (blue) d) comparison of aromatic region of PNDIOD-T2 (red) and N2200 (blue)



Page 4 of 11

4 Results of the characterizations are presented in Table 1 and are detailed in the SI. The number-average molecular weights (Mn) and polydispersity index (PDI) were measured by gel permeation chromatography (GPC) in 1,2,4trichlorobenzene at 110 °C by using polystyrene standards. The HOMO and LUMO levels of the polymers were calculated from the oxidation and reduction potentials of the cyclic voltammetry (CV) measurements. Thermal analysis (TGA and DSC) and OFET have been carried on both polymers and they exhibited essentially similar thermal properties as well as electron mobilities. They are presented in SI. The optical absorption spectra of PNDIOD-T2 and N2200 were recorded in dilute chloroform solutions and as thin films are shown in Figure 2. Both polymers displayed similar UV-visible absorption spectra, each has a characteristic two-bands with a high energy band peak at 391 nm and lower energy band centered at 699 nm due to intramolecular charge transfer (ICT) between the NDI and bithiophene moieties in the backbone. [54] The optical absorption edge bandgap (Egopt) was found to be 1.5 eV for both PNDIOD-T2 and N2200.

PNDIOD-T2 are 0.2-0.6 eV, which are sufficient to drive efficient photoinduced charge transfer and charge photogeneration in the photovoltaic blends. All devices were prepared in a glove box using an inverted configuration: indium tin oxide (ITO)/ ZnO/ polyethylenimine (PEI)/active layer/MoO3/Ag (Figure 3d). The optimized donor:acceptor polymer blend ratios were 1:1 (w/w) and the active layers were spin coated from chlorobenzene (CB) solutions with or without a processing additive. The active area of each cell was 4 mm2 and the current density– voltage (J–V) measurements were carried out in ambient condition under simulated AM1.5 solar illumination calibrated at 100 mW cm-2. Table 1. Molecular Weight, Electronic Structure, and Optical Bandgap of PNDIOD-T2 and N2200. Mn Polymer

PDI

(kDa)

HOMOa.c.

LUMOb.c

Egel

Egoptc.d.

(eV)

(eV)

(eV)

(eV)

PNDIODT2

76

3.2

-5.8

-3.9

1.9

1.5

N2200

76

2.5

-5.8

-3.9

1.9

1.5

PTB7-The

63

3.0

-5.24

-3.7

1.6

1.6

PBDB-Tf

66

1.9

-5.3

-3.5

1.8

1.8

a. From the onset of the oxidation (CV thin film) b. From the onset of the reduction (CV thin film) c. Spin cast film from CHCl3 solution.d. From the edge of the absorption spectra of thin films. e. Data provided by 1-Material f. Data provided by Brilliant Matters

Figure 2. UV-Visible absorption spectra of PNDIOD-T2 (red) and N2200 (blue): {a) solution and (b) thin film.

To further compare the commercial N2200 synthesized by Stille coupling and PNDIOD-T2 synthesized via DHAP, both polymers were investigated in bulk-heterojunction all-polymer solar cells (all-PSCs) with donor polymers PTB7-Th and PBDT-T. These donor polymers have optical absorption spectra that are complementary to that of PNDIOD-T2 (Figure 3). We note that the HOMO/LUMO energy level offsets of the donor polymers with those of

The references solar cells based on the commercial N2200 and donor PTB7-Th gave a PCE of 4.61% with Jsc of 10.63 mA/cm2, Voc of 0.82 V, FF of 0.53 and a maximum EQE of 51%. In contrast, the PBDB-T:N2200 blend system gave a PCE of 5.57% with Jsc of 9.43 mA/cm2, Voc of 0.89 V, FF of 0.67 and maximum EQE of 50%. Compared to the N2200 reference devices, PNDIOD-T2 based all-PSCs gave rise to enhanced photovoltaic performance in both all-PSC blend systems: PCE=4.83%, Jsc=10.90 mA/cm2, Voc= 0.82 V, FF=0.54 and EQEmax=56% for PTB7-Th:PNDIOD-T2; and PCE=6.06%, Jsc=11.87 mA/cm2, Voc= 0.89 V, FF=0.58 and EQEmax=53% for PBDB-T:PNDIOD-T2. Following literature precedence, [55,56] we attempted to use different amounts of processing additives such as 1,8-diiodooctane (DIO), diphenyl ether (DPE) or 1-chloronaphthalene (CN) in the fabrication of the all-PSCs. However, all-PSCs fabricated from PNDIOD-T2 and N2200 with each of the different processing additives resulted in a lower performance. The absence of enhancement from the use of a processing additive means that it is not necessary in these blends systems and it could actually be an advantage in large-scale production.


Page 5 of 11 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


5

Figure 3. (a) Molecular structures of acceptor polymers, PNDIOD-T2 and N2200, and donor polymers, PTB7-Th and PBDB-T. (b) Normalized optical absorption spectra of PNDIOD-T2, N2200, PTB7-Th and PBDB-T. (c) HOMO/LUMO energy levels of the donor and acceptor polymers. (d) Schematic of inverted solar cell configuration used in this work.

Figure 4. J-V characteristics of (a) PTB7-Th-based and (c) PBDB-T based all-PSCs. The corresponding EQE spectra of the all-PSCs (b, d).



Page 6 of 11

6 Table 2. Photovoltaic Parameters of all-PSCs. Film thickness

Additive

Voc

Jsc

(V)

(mA cm-2)

FF

PCEave (PCEmax)

Blend (nm)

(%)

PTB7-Th: PNDIOD-T2

93 ± 6

-

0.81 ± 0.01

11.73 ± 0.35

0.50 ± 0.01

4.71 (4.83)

PTB7-Th: N2200

99 ± 7

-

0.82 ± 0.01

10.17 ± 0.64

0.47 ± 0.03

4.02 (4.61)

PTB7-Th: PNDIOD-T2

101 ± 9

1%DIO

0.82 ± 0.01

10.20 ± 0.28

0.48 ± 0.02

3.99 (4.24)

PTB7-Th: N2200

106 ± 9

1%DIO

0.82 ± 0.01

8.80 ± 0.26

0.48 ± 0.03

3.45 (3.79)

PBDB-T: PNDIOD-T2

66 ± 7

-

0.88 ± 0.02

10.58 ± 0.71

0.59 ± 0.05

5.42 (6.06)

PBDB-T: N2200

63 ± 9

-

0.87 ± 0.01

9.84 ± 0.47

0.58 ± 0.05

4.97 (5.57)

PBDB-T: PNDIOD-T2

65 ± 4

1%DIO

0.88 ± 0.01

8.39 ± 0.39

0.67 ± 0.07

4.68 (5.78)

PBDB-T: N2200

72 ± 2

1%DPE

0.87 ± 0.01

9.27 ± 0.45

0.62 ± 0.02

4.92 (5.66)

Average over 20 cells J-V characteristics of the a) PTB7-Th-based all-PSCs and c) PBDB-T based all-PSCs b), d) The corresponding EQE profiles of the all-PSCs

Our comparative investigation of PNDIOD-T2 and N2200 based all-PSCs, found that PNDIOD-T2–based devices always showed a better performance than the commercial N2200-based devices. The possible influence of molecular weight as a factor to explain the superiority of PNDIOD-T2 is eliminated since both polymers have an identical molecular weight (Mn = 76 kDa). We suggest that the difference in photovoltaic performance of PNDIOD-T2 versus N2200 could be a result of the demonstrated higher structural defects in N2200, which in turn could influence the self-organization and morphology of the two blend systems. Clearly, blend morphology plays a key in achieving efficient exciton dissociation, charge transport, and charge collection in BHJ solar cells. [57-60]

Atomic force microscopy (AFM) topography images of the PBDB-T:PNDIOD-T2 and PBDB-T:N2200 blend films, as shown in Figure 5, reveal a subtle difference in surface morphology. A relatively rougher surface is observed on the PBDB-T:N2200 blend film (root-mean-square (RMS) roughness value of 1.71 nm for PNDIOD-T2 blend film and 2.70 nm for N2200 blend film). Also, a larger phase separation domain is observed in the N2200 blend films. These morphological observations imply that the slightly lower performance of N2200 blend devices is probably caused by the different end groups and bithiophene homocoupling observed in the 1H NMR spectra. [61-63] To further control the self-organization of the polymer: polymer blends, the aging process, previously reported in recent publications,[64,65] was applied to the PBDB-T: PNDIOD-T2 1:1 (w/w) blends. As used here, the aging process involved brief annealing of the spin coated blend active layer at 130 °C for 90 seconds in the glove box and followed by drying of the active layer in a closed box at room temperature (25 °C) in air for various periods (0-4

days). This aging process prior to the deposition of the MO3 interlayer and aluminum electrode presumably facilitated the self-organization of the blend active layers to form the final morphology existing in the all-PSC devices. The resulting photovoltaic parameters of the aged all-PSC devices, including Jsc, Voc, fill factor (FF) and the PCE are summarized in Table 3. The current density-voltage curves, EQE spectra, and aging time dependence of the photovoltaic parameters of the PBDB-T;PNDIOD-T2 devices are presented in Figure 6. The reference devices without any aging gave a PCE of 6.32% (with Jsc = 12.05 mA/cm2, Voc = 0.89 V, FF = 0.59) and maximum EQE of 59%. However, we found the photovoltaic is enhanced with aging in air up to 2 days, reaching a maximum PCE of 7.27% (with Jsc = 12.55 mA/cm2, Voc = 0.90 V, FF = 0.65) and EQE of 62%. These results further highlight the critical role of controlling the phase-separated morphology towards enhancing the efficiency of all-PSCs.

Figure 5. Topographic AFM images (1 x 1 µm2) of all-PSC blend films: (a) PBDB-T:N2200 Height; (b) PBDB-T:N2200 Phase; (c) PBDB-T:PNDIOD-T2 Height ; and (d) PBDBT:PNDIOD-T2 Phase.


Page 7 of 11 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 Table 3. Variation of the Photovoltaic Parameters of PBDB-T: PNDIOD-T2 (1:1 w/w) all-PSCs with Aging Time. Film thickness

Air-aging

Voc

Jsc

FF

PCEave (PCEmax)

(nm)

(days)

(V)

(mA cm-2)

PBDB-T: PNDIOD-T2a)

90 ± 10

0

0.88 ± 0.01

11.34 ± 0.76

0.57 ± 0.04

5.60 (6.32)

PBDB-T: PNDIOD-T2b)

90 ± 5

1

0.88 ± 0.01

12.08 ±0.94

0.58 ± 0.04

6.11 (6.85)

PBDB-T: PNDIOD-T2b)

93 ± 4

2

0.89 ± 0.01

12.36 ±0.59

0.60 ± 0.03

6.58 (7.27)

PBDB-T: PNDIOD-T2b)

91 ± 2

3

0.88 ± 0.01

11.99 ±0.78

0.58 ± 0.04

6.12 (6.80)

PBDB-T: PNDIOD-T2c)

93± 2

4

0.88 ± 0.01

11.60 ±0.12

0.57 ± 0.02

5.87 (6.26)

Blend (%)

a) Average over 40 cells, b) average over 20 cells and c) average over 5 cells

Figure 6. J-V characteristics (a), EQE spectra (b) and photovoltaic parameters Voc (c), FF (d), Jsc (e) and PCE (f) of PBDB-T: PNDIODT2 all-PSCs aged for various times.



Page 8 of 11

8

Figure 7. Topographic AFM images (1 µm2) of PBDB-T:PNDIOD-T2 blend active layer films annealed at 130 oC for 1.5 min and followed by various air-aging times. (Height (top) and Phase (bottom))

To investigate the effect of aging on the morphology of the all-PSCs, we used AFM topographic imaging to observe blend films prepared and aged under identical conditions as the devices. As observed in Figure 7, the AFM topography images (height and phase) of the PBDB-T: PNDIOD-T2 blend ﬁlms (1:1 w/w) clearly show a different topography over aging time. This is supported by the surface rootmean-square (RMS) roughness value of 1.71 nm for the fresh film, 1.81 nm for 1 day aging, 2.03 nm for 2 days aging, 2.99 nm for 3 days aging and 3.10 nm for 4 days aging. These results imply that self-organization of the photovoltaic blend reaches optimal phase-separated morphology at the 2-day aging mark in accord with the observed performance of the PBDB-T: PNDIOD-T2 all-PSCs.

CONCLUSIONS In summary, we have synthesized a high molecular weight PNDIOD-T2 via DHAP and investigated its structural and photovoltaic properties in comparison with the Stille-coupled, commercial, N2200. The commercial N2200 was found to have some bithiophene homocoupling defects, which were not found in the DHAP polymer. The slightly lower performance of N2200-based all-polymer solar cells was partly attributed to such structural defects. PBDB-T: PNDIOD-T2 blend film aging was found to facilitate the achievement of optimal phase-separated morphology, which led to highly efficient all-PSCs with a maximum PCE of 7.3%, Jsc of 12.55 mA/cm2, Voc of 0.90 V, and FF of 0.65. The results of the present comparative study highlight the promise of DHAP towards the synthesis of improved n-type semiconducting polymers for all-PSCs.

ASSOCIATED CONTENT Supporting Information. Detailed experimental procedures and additional characterization data (UV-vis, 1H NMR, TGA, GPC, CV, µe of thin-film OFET and their preparation)

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

Author Contributions The manuscript was written through contributions of all authors.

ACKNOWLEDGMENTS ACKNOWLEDGMENTS The authors acknowledge the Natural Sciences and Engineering Research Council of Canada (NSERC) for their support. We would also like to acknowledge the financial support of the FRQNT international training program via the Centre québecois sur le matériaux fonctionnels (CQMF). Work at the University of Washington was supported by the US NSF (DMR1708450) and the Office of Naval Research (N00014-17-12203). We acknowledge Arthur D. Hendsbee and Prof. Yuning Li from the University of Waterloo for the OFET preliminary tests. We also acknowledge Xiaomei Ding and Nagesh Kolhe for instructions on instruments at UW and for helpful discussions.

REFERENCES (1) Marzano, G.; Carulli, F.; Babudri, F.; Pellegrino, A.; Po, R.; Luzzati, S.; Farinola, G. M. PBDTTPD for Plastic Solar Cells via Pd(PPh3)4 -Catalyzed Direct (Hetero)arylation Polymerization. J. Mater. Chem. A 2016, 4, 17163–17170. (2) Guérette, M.; Najari, A.; Maltais, J.; Pouliot, J.-R.; Dufresne, S.; Simoneau, M.; Besner, S.; Charest, P.; Leclerc, M. New Processable Phenanthridinone-Based Polymers for Organic Solar Cell Applications. Adv. Energy Mater. 2016, 6, 1502094. (3) Hösel, M.; Dam, H. F.; Krebs, F. C. Development of Lab-toFab Production Equipment Across Several Length Scales for Printed Energy Technologies, Including Solar Cells. Energy Technol. 2015, 3, 293–304.


Page 9 of 11 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


9 (4) Etxebarria, I.; Ajuria, J.; Pacios, R. Solution-Processable Polymeric Solar Cells: A Review on Materials, Strategies and Cell Architectures to Overcome 10%. Org. Electron. physics, Mater. Appl. 2015, 19, 34–60. (5) Zhou, H.; Yang, L.; You, W. Rational Design of High Performance Conjugated Polymers for Organic Solar Cells. Macromolecules 2012, 45, 607–632. (6) Kang, I.; Yun, H. J.; Chung, D. S.; Kwon, S. K.; Kim, Y. H. Record High Hole Mobility in Polymer Semiconductors via SideChain Engineering. J. Am. Chem. Soc. 2013, 135, 14896–14899. (7) Li, J.; Zhao, Y.; Tan, H. S.; Guo, Y.; Di, C. A.; Yu, G.; Liu, Y.; Lin, M.; Lim, S. H.; Zhou, Y.; Su, H.; Ong, B. S. A Stable SolutionProcessed Polymer Semiconductor with Record High-Mobility for Printed Transistors. Sci. Rep. 2012, 2, 754, 1–9. (8) Lee, J. S.; Son, S. K.; Song, S.; Kim, H.; Lee, D. R.; Kim, K.; Ko, M. J.; Choi, D. H.; Kim, B. S.; Cho, J. H. Importance of Solubilizing Group and Backbone Planarity in Low Band Gap Polymers for High Performance Ambipolar Field-Effect Transistors. Chem. Mater. 2012, 24, 1316–1323. (9) Robitaille, A.; Perea, A.; Bélanger, D.; Leclerc, M. Poly(5Alkyl-thieno[3,4-C]pyrrole-4,6-Dione): A Study of π-Conjugated Redox Polymers as Anode Materials in Lithium-Ion Batteries. J. Mater. Chem. A 2017, 18088–18094. (10) Liang, Y.; Chen, Z.; Jing, Y.; Rong, Y.; Facchetti, A.; Yao, Y. Heavily N-Dopable π-Conjugated Redox Polymers with Ultrafast Energy Storage Capability. J. Am. Chem. Soc. 2015, 137, 4956– 4959. (11) Kuwabara, J.; Yamazaki, K.; Yamagata, T.; Tsuchida, W.; Kanbara, T.; Wang, F.; Horie, M.; Kanbara, T.; Kanbara, T. The Effect of a Solvent on Direct Arylation Polycondensation of Substituted Thiophenes. Polym. Chem. 2015, 6, 891–895. (12) Po, R.; Bianchi, G.; Carbonera, C.; Pellegrino, A. “All That Glisters Is Not Gold”: An Analysis of the Synthetic Complexity of Efficient Polymer Donors for Polymer Solar Cells. Macromolecules 2015, 48, 453–461. (13) Iizuka, E.; Wakioka, M.; Ozawa, F. Mixed-Ligand Approach to Palladium-Catalyzed Direct Arylation Polymerization: Synthesis of Donor-Acceptor Polymers with Dithienosilole (DTS) and Thienopyrroledione (TPD) Units. Macromolecules 2015, 48, 2989–2993. (14) Berrouard, P.; Najari, A.; Pron, A.; Gendron, D.; Morin, P. O.; Pouliot, J. R.; Veilleux, J.; Leclerc, M. Synthesis of 5-alkyl[3,4C]thienopyrrole-4,6-Dione-Based Polymers by Direct Heteroarylation. Angew. Chemie - Int. Ed. 2012, 51, 2068–2071. (15) Bura, T.; Blaskovits, J. T.; Leclerc, M. Direct (Hetero)arylation Polymerization: Trends and Perspectives. J. Am. Chem. Soc. 2016, 138, 10056–10071. (16) Wakioka, M.; Ichihara, N.; Kitano, Y.; Ozawa, F. A Highly Efficient Catalyst for the Synthesis of Alternating Copolymers with thieno[3,4-C]pyrrole-4,6-Dione Units via Direct Arylation Polymerization. Macromolecules 2014, 47, 626–631. (17) Grenier, F.; Goudreau, K.; Leclerc, M. Robust Direct (Hetero)arylation Polymerization in Biphasic Conditions. J. Am. Chem. Soc. 2017, 139, 2816–2824. (18) Yu, S.; Liu, F.; Yu, J.; Zhang, S.; Cabanetos, C.; Gao, Y.; Huang, W. Eco-Friendly Direct (Hetero)-Arylation Polymerization: Scope and Limitation. J. Mater. Chem. C 2017, 5, 29–40. (19) Bura, T.; Beaupré, S.; Légaré, M.-A.; Quinn, J.; Rochette, E.; Blaskovits, J. T.; Fontaine, F.-G.; Pron, A.; Li, Y.; Leclerc, M. Direct Heteroarylation Polymerization: Guidelines for Defect-Free Conjugated Polymers. Chem. Sci. 2017, 8, 3913–3925. (20) Morin, P. O.; Bura, T.; Sun, B.; Gorelsky, S. I.; Li, Y.; Leclerc, M. Conjugated Polymers à La Carte from Time-Controlled Direct (Hetero)arylation Polymerization. ACS Macro Lett. 2015, 4, 21– 24. (21) Wakioka, M.; Ichihara, N.; Kitano, Y.; Ozawa, F. A Highly Efficient Catalyst for the Synthesis of Alternating Copolymers with

thieno[3,4-C]pyrrole-4,6-Dione Units via Direct Arylation Polymerization. Macromolecules 2014, 47, 626–631. (22) 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. (23) Bucella, S. G.; Luzio, A.; Gann, E.; Thomsen, L.; McNeill, C. R.; Pace, G.; Perinot, A.; Chen, Z.; Facchetti, A.; Caironi, M. Macroscopic and High-Throughput Printing of Aligned Nanostructured Polymer Semiconductors for MHz Large-Area Electronics. Nat. Commun. 2015, 6, 1–10. (24) Liang, Y.; Chen, Z.; Jing, Y.; Rong, Y.; Facchetti, A.; Yao, Y. Heavily N-Dopable π-Conjugated Redox Polymers with Ultrafast Energy Storage Capability. J. Am. Chem. Soc. 2015, 137, 4956– 4959. (25) Zhou, N.; Facchetti, A. Naphthalenediimide ( NDI ) Polymers for All-Polymer Photovoltaics. Mater. Today, 2018, 21, 377-390. (26) Matsidik, R.; Komber, H.; Luzio, A.; Caironi, M.; Sommer, M. Defect-Free Naphthalene Diimide Bithiophene Copolymers with Controlled Molar Mass and High Performance via Direct Arylation Polycondensation. J. Am. Chem. Soc. 2015, 137, 6705–6711. (27) Yang, X.; Duren, J. K. J. Van; Janssen, R. a J.; Michels, M. a J.; Loos, J. Morphology and Thermal Stability of the Active Layer in Poly (p -Phenylenevinylene)/ Methanofullerene Plastic Photovoltaic Devices. Macromolecules 2004, 37, 2151–2158. (28) Cheng, Y. J.; Hsieh, C. H.; Li, P. J.; Hsu, C. S. Morphological Stabilization by in Situ Polymerization of Fullerene Derivatives Leading to Efficient, Thermally Stable Organic Photovoltaics. Adv. Funct. Mater. 2011, 21, 1723–1732. (29) Facchetti, A. Polymer Donor-Polymer Acceptor (AllPolymer) Solar Cells. Mater. Today 2013, 16, 123–132. (30) Wadsworth, A.; Moser, M.; Marks, A.; Little, M. S.; Gasparini, N.; Brabec, C. J.; Baran, D.; McCulloch, I. Critical Review of the Molecular Design Progress in Non-Fullerene Electron Acceptors towards Commercially Viable Organic Solar Cells. Chem. Soc. Rev. 2018. Advance Article (31) Fan, B.; Ying, L.; Zhu, P.; Pan, F.; Liu, F.; Chen, J.; Huang, F.; Cao, Y. All-Polymer Solar Cells Based on a Conjugated Polymer Containing Siloxane-Functionalized Side Chains with Efficiency over 10%. Adv. Mater. 2017, 29, 1–7. (32) Liu, M.; Yang, J.; Yin, Y.; Zhang, Y.; Zhou, E.; Guo, F.; Zhao, L. Novel Perylene Diimide-Based Polymers with Electron-Deficient Segments as the Comonomer for Efficient All-Polymer Solar Cells. J. Mater. Chem. A 2018, 6, 414–422. (33) Balar, N.; Xiong, Y.; Ye, L.; Li, S.; Nevola, D.; Dougherty, D. B.; Hou, J.; Ade, H.; O’Connor, B. T. Role of Polymer Segregation on the Mechanical Behavior of All-Polymer Solar Cell Active Layers. ACS Appl. Mater. Interfaces 2017, 9 , 43886–43892 (34) Gu, X.; Zhou, Y.; Gu, K.; Kurosawa, T.; Guo, Y.; Li, Y.; Lin, H.; Schroeder, B. C.; Yan, H.; Molina-Lopez, F.; et al. Roll-to-Roll Printed Large-Area All-Polymer Solar Cells with 5% Efficiency Based on a Low Crystallinity Conjugated Polymer Blend. Adv. Energy Mater. 2017, 7, 1–13. (35) Deshmukh, K. D.; Matsidik, R.; Prasad, S. K. K.; Connal, L. A.; Liu, A. C. Y.; Gann, E.; Thomsen, L.; Hodgkiss, J. M.; Sommer, M.; McNeill, C. R. Tuning the Molecular Weight of the Electron Accepting Polymer in All-Polymer Solar Cells: Impact on Morphology and Charge Generation. Adv. Funct. Mater. 2018, 28, 1–13. (36) Zhou, N.; Dudnik, A. S.; Li, T. I. N. G.; Manley, E. F.; Aldrich, T. J.; Guo, P.; Liao, H. C.; Chen, Z.; Chen, L. X.; Chang, R. P. H.; et al. All-Polymer Solar Cell Performance Optimized via Systematic Molecular Weight Tuning of Both Donor and Acceptor Polymers. J. Am. Chem. Soc. 2016, 138, 1240–1251. (37) Li, Z.; Xu, X.; Zhang, W.; Meng, X.; Ma, W.; Yartsev, A.; Inganäs, O.; Andersson, M. R.; Janssen, R. A. J.; Wang, E. High Performance All-Polymer Solar Cells by Synergistic Effects of



Page 10 of 11

10 Fine-Tuned Crystallinity and Solvent Annealing. J. Am. Chem. Soc. 2016, 138, 10935–10944. (38) Lee, W.; Lee, C.; Yu, H.; Kim, D. J.; Wang, C.; Woo, H. Y.; Oh, J. H.; Kim, B. J. Side Chain Optimization of NaphthalenediimideBithiophene-Based Polymers to Enhance the Electron Mobility and the Performance in All-Polymer Solar Cells. Adv. Funct. Mater. 2016, 26, 1543–1553. (39) Liu, S.; Kan, Z.; Thomas, S.; Cruciani, F.; Brédas, J.-L.; Beaujuge, P. M. Thieno[3,4- c ]Pyrrole-4,6-Dione-3,4Difluorothiophene Polymer Acceptors for Efficient All-Polymer Bulk Heterojunction Solar Cells. Angew. Chemie 2016, 128, 13190–13194. (40) Kang, H.; Lee, W.; Oh, J.; Kim, T.; Lee, C.; Kim, B. J. From Fullerene-Polymer to All-Polymer Solar Cells: The Importance of Molecular Packing, Orientation, and Morphology Control. Acc. Chem. Res. 2016, 49, 2424–2434. (41) Hendsbee, A. D.; Li, Y. Performance Comparisons of Polymer Semiconductors Synthesized by Direct (Hetero)Arylation Polymerization (DHAP) and Conventional Methods for Organic Thin Film Transistors and Organic Photovoltaics. Molecules 2018, 23, 1255. (42) Guo, Y.; Li, Y.; Awartani, O.; Han, H.; Zhao, J.; Ade, H.; Yan, H.; Zhao, D. Improved Performance of All-Polymer Solar Cells Enabled by Naphthodiperylenetetraimide-Based Polymer Acceptor. Adv. Mater. 2017, 29, 1–6. (43) Li, Z.; Zhang, W.; Xu, X.; Genene, Z.; Di Carlo Rasi, D.; Mammo, W.; Yartsev, A.; Andersson, M. R.; Janssen, R. A. J.; Wang, E. High-Performance and Stable All-Polymer Solar Cells Using Donor and Acceptor Polymers with Complementary Absorption. Adv. Energy Mater. 2017, 7, 1–11. (44) Gao, L.; Zhang, Z. G.; Xue, L.; Min, J.; Zhang, J.; Wei, Z.; Li, Y. All-Polymer Solar Cells Based on Absorption-Complementary Polymer Donor and Acceptor with High Power Conversion Efficiency of 8.27%. Adv. Mater. 2016, 28, 1884–1890. (45) Fan, B.; Ying, L.; Wang, Z.; He, B.; Jiang, X. F.; Huang, F.; Cao, Y. Optimisation of Processing Solvent and Molecular Weight for the Production of Green-Solvent-Processed All-Polymer Solar Cells with a Power Conversion Efficiency over 9%. Energy Environ. Sci. 2017, 10, 1243–1251. (46) Li, Z.; Xu, X.; Zhang, W.; Meng, X.; Genene, Z.; Ma, W.; Mammo, W.; Yartsev, A.; Andersson, M. R.; Janssen, R. A. J.; et al. 9.0% Power Conversion Efficiency From Ternary All-Polymer Solar Cells. Energy Environ. Sci. 2017, 10, 2212–2221. (47) Ye, L.; Jiao, X.; Zhao, W.; Zhang, S.; Yao, H.; Li, S.; Ade, H.; Hou, J. Manipulation of Domain Purity and Orientational Ordering in High Performance All-Polymer Solar Cells. Chem. Mater. 2016, 28, 6178–6185. (48) Lee, W.; Lee, C.; Yu, H.; Kim, D. J.; Wang, C.; Woo, H. Y.; Oh, J. H.; Kim, B. J. Side Chain Optimization of NaphthalenediimideBithiophene-Based Polymers to Enhance the Electron Mobility and the Performance in All-Polymer Solar Cells. Adv. Funct. Mater. 2016, 26, 1543–1553. (49) Thompson, B. C.; Kim, Y. G.; Reynolds, J. R. Spectral Broadening in MEH-PFV:PCBM-Based Photovoltaic Devices via Blending with a Narrow Band Gap Cyanovinylene-Dioxythiophene Polymer. Macromolecules 2005, 38, 5359–5362. (50) Goyindaraju T, Venkata SY, A process for bromination of arylene dianhydrides and a method of synthesis of diimides thereof. WO 2014/188385 A2. November 27th. (51) Sharma, S.; Kolhe, N. B.; Gupta, V.; Bharti, V.; Sharma, A.; Datt, R.; Chand, S.; Asha, S. K. Improved All-Polymer Solar Cell Performance of N-Type Naphthalene Diimide-Bithiophene P(NDI2OD-T2) Copolymer by Incorporation of Perylene Diimide as Coacceptor. Macromolecules 2016, 49, 8113–8125.

(52) Sun, C.-L.; Li, B.-J.; Shi, Z.-J. Pd-Catalyzed Oxidative Coupling with Organometallic Reagents via C–H Activation. Chem. Commun. 2010, 46, 677-685. (53) Espinet, P.; Echavarren, A. M. The Mechanisms of the Stille Reaction. Angew. Chemie - Int. Ed. 2004, 43, 4704–4734. (54) Jenekhe, S. A.; Lu, L.; Alam, M. M. New Conjugated Polymers with Donor-Acceptor Architectures: Synthesis and Photophysics of Carbazole-Quinoline and PhenothiazineQuinoline Copolymers and Oligomers Exhibiting Large Intramolecular Charge Transfer. Macromolecules 2001, 34, 7315– 7324 (55) Li, Z.; Xu, X.; Zhang, W.; Meng, X.; Ma, W.; Yartsev, A.; Inganäs, O.; Andersson, M. R.; Janssen, R. A. J.; Wang, E. High Performance All-Polymer Solar Cells by Synergistic Effects of Fine-Tuned Crystallinity and Solvent Annealing. J. Am. Chem. Soc. 2016, 138, 10935–10944. (56) Guo, Y.; Li, Y.; Awartani, O.; Zhao, J.; Han, H.; Ade, H.; Zhao, D.; Yan, H. A Vinylene-Bridged Perylenediimide-Based Polymeric Acceptor Enabling Efficient All-Polymer Solar Cells Processed under Ambient Conditions. Adv. Mater. 2016, 8483–8489. (57) Lee, C.; Kang, H.; Lee, W.; Kim, T.; Kim, K. H.; Woo, H. Y.; Wang, C.; Kim, B. J. High-Performance All-Polymer Solar Cells via Side-Chain Engineering of the Polymer Acceptor: The Importance of the Polymer Packing Structure and the Nanoscale Blend Morphology. Adv. Mater. 2015, 27, 2466–2471. (58) Kang, H.; Kim, K. H.; Choi, J.; Lee, C.; Kim, B. J. HighPerformance All-Polymer Solar Cells Based on Face-on Stacked Polymer Blends with Low Interfacial Tension. ACS Macro Lett. 2014, 3, 1009–1014. (59) Earmme, T.; Hwang, Y. J.; Murari, N. M.; Subramaniyan, S.; Jenekhe, S. A. All-Polymer Solar Cells with 3.3% Efficiency Based on Naphthalene Diimide-Selenophene Copolymer Acceptor. J. Am. Chem. Soc. 2013, 135, 14960–14963. (60) Szarko, J. M.; Guo, J.; Liang, Y.; Lee, B.; Rolczynski, B. S.; Strzalka, J.; Xu, T.; Loser, S.; Marks, T. J.; Yu, L.; Chen, L. X. When Function Follows Form: Effects of Donor Copolymer Side Chains on Film Morphology and BHJ Solar Cell Performance. Adv. Mater. 2010, 22, 5468–5472. (61) Lombeck, F.; Komber, H.; Fazzi, D.; Nava, D.; Kuhlmann, J.; Stegerer, D.; Strassel, K.; Brandt, J.; de Zerio Mendaza, A. D.; Müller, C.; Thiel, W.; Caironi, M.; Friend, R.; Sommer, M. On the Effect of Prevalent Carbazole Homocoupling Defects on the Photovoltaic Performance of PCDTBT:PC71BM Solar Cells. Adv. Energy Mater. 2016, 6, 1601232, 1–9. (62) Namepetra, A.; Kitching, E.; Eftaiha, A. F.; Hill, I. G.; Welch, G. C. Understanding the Morphology of Solution Processed Fullerene-Free Small Molecule Bulk Heterojunction Blends. Phys. Chem. Chem. Phys. 2016, 18, 12476–12485. (63) Verstappen, P.; Cardinaletti, I.; Vangerven, T.; Vanormelingen, W.; Verstraeten, F.; Lutsen, L.; Vanderzande, D.; Manca, J.; Maes, W. Impact of Structure and Homo-Coupling of the Central Donor Unit of Small Molecule Organic Semiconductors on Solar Cell Performance. RSC Adv. 2016, 6, 32298–32307. (64) Hwang, Y. J.; Earmme, T.; Courtright, B. A. E.; Eberle, F. N.; Jenekhe, S. A. N-Type Semiconducting Naphthalene DiimidePerylene Diimide Copolymers: Controlling Crystallinity, Blend Morphology, and Compatibility Toward High-Performance AllPolymer Solar Cells. J. Am. Chem. Soc. 2015, 137, 4424–4434. (65) Hwang, Y. J.; Courtright, B. A. E.; Ferreira, A. S.; Tolbert, S. H.; Jenekhe, S. A. 7.7% Efficient All-Polymer Solar Cells. Adv. Mater. 2015, 27, 4578–4584.


Page 11 of 11 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


11

Insert Table of Contents artwork here


11

Poly(naphthalene diimide-alt-bithiophene) Prepared by Direct (Hetero

Recommend Documents