Impact of Incorporating Nitrogen Atoms in Naphthalenediimide

Subscriber access provided by Nottingham Trent University

Organic Electronic Devices

Impact of Incorporating Nitrogen Atoms in NaphthalenediimideBased Polymer Acceptors on the Charge Generation, Device Performance and Stability of All-Polymer Solar Cells Sang Woo Kim, Yang Wang, Hoseon You, Wonho Lee, Tsuyoshi Michinobu, and Bumjoon J. Kim ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b12037 • Publication Date (Web): 05 Sep 2019 Downloaded from pubs.acs.org on September 5, 2019

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

ACS Applied Materials & Interfaces

Impact of Incorporating Nitrogen Atoms in NaphthalenediimideBased Polymer Acceptors on the Charge Generation, Device Performance and Stability of All-Polymer Solar Cells Sang Woo Kim, † Yang Wang, ‡ Hoseon You, † Wonho Lee,§ Tsuyoshi Michinobu ‡,*, Bumjoon J. Kim†,*

†

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

and Technology (KAIST), Daejeon 34141, Republic of Korea ‡

Department of Materials Science and Engineering, Tokyo Institute of Technology, Tokyo

152-8552, Japan §

Department of Polymer Science and Engineering, Kumoh National Institute of Technology,

Gumi 39177, Republic of Korea

Keywords: all-polymer solar cells, naphthalenediimide (NDI), polymer acceptor, nitrogen atom, charge generation * E-mail: [email protected], [email protected]

1

ACS Paragon Plus Environment

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 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 24

Abstract Substitution of C atoms in a polymer backbone by N atoms allows for the facile tuning of the energy levels as well as the backbone conformation and packing structures of conjugated polymers. Herein, we report a series of three polymer acceptors (PAs) with N atoms introduced at different positions of the backbone, and investigate how these N atoms affect the device performances of all-polymer solar cells (all-PSCs). The three PAs, namely, P(NDI2DT-BTT), P(NDI2DT-PTT), and P(NDI2DT-BTTz), are composed of naphthalenediimide (NDI) and benzothiadiazole

(BT)-based

derivative

(dithiophene-BT

(BTT),

dithiophene-

thiadiazolepyridine (PTT), and dithiazole-BT (BTTz)) units. The PTT and BTTz units are synthesized by replacing the C atoms in BT and thiophene, respectively, with N atoms, which effectively tune the optical, electrochemical, and charge-transporting properties of the corresponding PAs. The all-PSCs using PBDB-T as a polymer donor and P(NDI2DT-PTT) as the PA exhibit a significantly enhanced power conversion efficiency (PCE) of 6.95%, whereas the all-PSCs based on the other PAs show relatively lower PCEs (6.02% for PBDBT:P(NDI2DT-BTT) and 1.43% for PBDB-T:P(NDI2DT-BTTz)). The high PCE of the PBDBT:P(NDI2DT-PTT) device is due to superior charge transfer and charge dissociation, resulting from the closely-matched energy levels between PBDB-T and P(NDI2DT-PTT), as well as the more favorable BHJ morphology with improved miscibility. Importantly, the P(NDI2DTPTT)-based all-PSC device shows improved air stability compared to the P(NDI2DT-BTT)based device, which is most likely due to a decreased lowest unoccupied molecular orbital level of the PA. Our findings suggest that incorporation of N atoms into the PAs is an effective strategy for improving the efficiency and stability of all-PSCs.

2


Page 3 of 24 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


Introduction All-polymer solar cells (all-PSCs), composed of an electron-donating p-type polymer (PD) and an electron-accepting n-type polymer (PA), have received considerable attention because of the potential advantages of PAs over fullerene derivatives. These advantages include versatility of the molecular design, complementary light absorption, tunable energy levels of PAs, and superior stabilities against mechanical, thermal, and photochemical degradation.1-12 Among various PAs, naphthalenediimide (NDI)-based copolymers are the most widely used, as they possess deep frontier energy levels and strong self-assembly properties, which produce efficient charge generation at PD/PA interfaces and an electron transport ability in bulk heterojunction (BHJ) thin films.13-17 Thus, state-of-the-art all-PSCs of NDI-based PAs have achieved power conversion efficiencies (PCEs) exceeding 10%.18-21 Nevertheless, the PCEs of all-PSCs need to be further improved by addressing several challenges, such as improving light absorption, charge generation and transport in BHJ films. In order to achieve efficient charge generation, it is required to control the packing structure and molecular orientation of PAs relative to the PD/PA interface. A face-to-face stacking of PD and PA is desirable since strong overlapping π-π orbitals leads to efficient charge dissociation and a reduced voltage loss.22-26 Also, suitable energy levels between the PD and PA polymers are the key to facilitating efficient charge transfer.27-29 At the same time, the morphological features of the PD and PA BHJ blend, in terms of the domain spacing, domain connectivity, and domain purity, must be considered to achieve a balanced charge generation and transport, which is also strongly dependent on the miscibility of two components and processing conditions.30,31 As a strategy to overcome the above-mentioned challenges, the introduction of heteroatoms with strong electron affinities (e.g., N, F, or Cl) into the conjugated backbone has received considerable attention.27,32,33 Heteroatom conjugated system is a simple yet effective 3



approach to simultaneously enhancing the coplanarity of a polymer’s backbone and fine-tuning the frontier molecular orbitals.34-36 Compared to the halogen substitutions, examples of introducing the N atoms into the photovoltaic polymers are relatively limited.37-40 Substituting the C-H bonds in the aromatic rings of PA backbones with the sp2-nitrogen (N) atoms stabilizes the frontier molecular orbitals, due to the stronger electronegativity of the N atom compared to a C atom.41,42 Both highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of PAs can be finely tuned by the number and position of N atoms, which leads to the proper energy level alignment for efficient charge dissociation. In addition, the sp2-N atom substitution is effective for improving the molecular planarity through the intermolecular interactions (such as N···S interaction), which are beneficial for the formation of large crystalline domains and charge carrier transport.43 For example, we previously investigated the effects of substituted N atoms on the structural properties and photovoltaic performances of PDs. As the number of N atoms in the benzene ring increased from 0 to 2, the planarity of the main chain backbone and the intermolecular ordering of the PDs were significantly enhanced, which improved the hole mobilities and PCEs.44 Also, Cao and co-workers incorporated the N atom into the electron-rich thiophene rings of benzothiadiazole (BT)-based PAs.45 By substituting the thiophene with the thiazole ring, better miscibility with the PD and a lower LUMO energy level were observed, which led to improved electron mobility. Although the significance of the N atom substitution in semiconducting polymers was recognized, the effects of the N atom substitution into the NDI-containing copolymers on the photovoltaic performances of all-PSCs have not been studied. In this study, we developed a series of NDI-based PAs containing the dithiophenebenzothiadiazole (BTT) and its N atom-substituted derivatives. We initially synthesized P(NDI2DT-BTT) as a reference polymer, which consists of the NDI and BTT units. 4


Page 4 of 24

Page 5 of 24 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


P(NDI2DT-PTT) and P(NDI2DT-BTTz) were then synthesized by using the dithiophenethiadiazolepyridine (PTT) and dithiazole-BT (BTTz) monomers, respectively, to incorporate N atoms at the different positions of BTT. The effects of the incorporated N atoms on the electrochemical, optical, and structural properties of the PAs were systematically investigated, and the photovoltaic performance of the PAs was examined in all-PSC devices. Among the allPSCs

fabricated

with

poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-

b′]dithiophene)-co-(1,3-di(5-thiophene-2-yl)-5,7-bis(2-ethylhexyl)benzo[1,2-c:4,5c′]dithiophene-4,8-dione)] (PBDB-T) as the PD, the device based on P(NDI2DT-PTT) exhibited the best performance with a PCE of 6.95%. This performance was attributed to the appropriate energy levels and enhanced miscibility of the PBDB-T and P(NDI2DT-PTT) compared to the other PAs, resulting in an efficient charge generation and a suppressed charge recombination. In contrast, the all-PSC device based on P(NDI2DT-BTTz) showed a poor performance with a PCE of 1.43%, resulting from a larger HOMO offset of the PD that caused inefficient hole transfer from PA to PD and increased monomolecular recombination and thereby inefficient hole transfer. Furthermore, the P(NDI2DT-PTT)-based device showed better air-stability than the P(NDI2DT-BTT)-based device, which may have been related to the lower LUMO level of the former PA. Thus, we demonstrated the significance of molecular design with respect to the N atom positions in the building blocks and also confirmed the potential of PAs based on the NDI and BT derivatives for the application in efficient all-PSCs.

5



Page 6 of 24

Results and Discussion

Figure 1. (a) Chemical structures of PD and PAs used in this study. (b) Energy diagram and (c) UV-vis absorption spectra of PD and PAs.

Figure 1a presents the chemical structures of the three PAs and the PD used in this study. Electronegative N atoms were introduced into the different positions of the reference PA, P(NDI2DT-BTT), producing P(NDI2DT-PTT) (N incorporated in the BT unit) and P(NDI2DTBTTz) (N incorporated in the thiophene units). Based on these three PAs, we are able to investigate the influence of the N atom position in NDI-based PAs on the performance of allPSCs in terms of charge transfer and recombination. This family of PAs was synthesized by Stille

cross-coupling

polymerizations

between

dibromonaphthalene-1,4:5,8-tetracarboxylic

diimide

N,N′-bis(2-decyltetradecyl)-2,6(NDI

(trimethylstannyl)thienyl)benzo[c][1,2,5]thiadiazole

unit)

and

(BTT),

(trimethylstannyl)thiophen-2-yl)[1,2,5]thiadiazolo[3,4-c]pyridine

(PTT),

4,7-bis(54,7-bis(5-

or

4,7-bis(5-

(tributylstannyl)thiazol-2-yl)benzo[c][1,2,5]thiadiazole (BTTz), according to a previously 6


Page 7 of 24 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


reported procedure.46 The number-average molecular weight (Mn) and polydispersity (Mw/Mn) of each PA were estimated by gel permeation chromatography (GPC) with o-dichlorobenzene (o-DCB) as the eluent by using polystyrene standards. All of the PAs exhibited similar Mn values (52–68 kg mol-1), thus minimizing the molecular-weight effects on various properties. Cyclic voltammetry (CV) measurements were performed to investigate the effect of N atoms on the electrochemical properties (Figure S1). The HOMO/LUMO energy levels decreased from -5.77/-3.78 eV for P(NDI2DT-BTT) to -5.87/-3.81 eV for P(NDI2DT-PTT) and further to -6.01/-3.86 eV for P(NDI2DT-BTTz). The strong electron-withdrawing nature of the N atoms gradually decreased both the LUMO and HOMO levels of the PAs. In particular, the HOMO level of P(NDI2DT-BTTz) was substantially down-shifted compared to that of the other PAs, resulting from the more electron-deficient nature of thiazoles.47 Next, UV-vis absorption spectra of the PD and three PAs as pristine films were collected as shown in Figure 1c and the results are summarized in Table 1. The PA thin films exhibit strong and broad absorption in the visible region, with two distinct absorption bands corresponding to π–π* transitions in the high-energy region (300–400 nm) and intramolecular charge transfer (ICT) in the low-energy region (550–800 nm).48,49 The optical bandgap (Egopt) values of the P(NDI2DT-BTT), P(NDI2DT-PTT), and P(NDI2DT-BTTz) films, as estimated by the absorbance onset, are 1.50, 1.59, and 1.74 eV, respectively, and are consistent with the trend observed for the energy bandgaps determined from CV. The stronger electron-withdrawing properties of the PTT unit than those of the BTT unit can decrease push-pull effect and result in the blue-shifted absorption band of P(NDI2DT-PTT) polymers compared to that of P(NDI2DT-BTT) polymers. And, the thiazole unit in P(NDI2DT-BTTz) can reduce the pushpull effect between the BTTz and NDI units and also induce larger torsion angles along the backbone (see the backbone planarity of PAs suggested by the DFT calculation), resulting in 7



the decrease of the effective conjugation length.50 Both effects may lead to a blue-shift of the ICT band of the P(NDI2DT-BTTz) polymer along with an increase in the bandgap (mainly due to the down-shifted HOMO level) compared to P(NDI2DT-BTT) and P(NDI2DT-PTT). In these regards, the P(NDI2DT-BTT) and P(NDI2DT-PTT) PAs produce better complementary absorption and energy level alignment with PBDB-T PD (Figure 1c). The thermal properties of PAs were investigated using differential scanning calorimetry (DSC) (Figure S2). P(NDI2DT-BTT) and P(NDI2DT-PTT) showed melting temperatures (Tm) at 324 °C and 292 °C, and crystallization temperatures (Tc) at 300 °C and 265 °C, respectively. However, the P(NDI2DT-BTTz) did not showed clear melting or crystallization transitions. The P(NDI2DTBTT) exhibited the higher melting enthalpy (ΔHm) of 11.1 J g-1 compared to that of the P(NDI2DT-PTT) (6.2 J g-1), indicating the higher crystallinity of the P(NDI2DT-BTT). To better understand the effect of the different N substitution patterns on the electrochemical properties of the polymers, theoretical calculations were performed using the density functional theory (DFT) method at the B3LYP/6-31G(d) level with the Spartan 14 package.51 The electron density distributions of the calculated LUMO and HOMO energy levels of the PAs are shown in Figure S3. The LUMO energy levels were mainly localized on the NDI units, whereas the HOMO energy levels were mostly localized on the BTT, PTT, and BTTz units. The calculated HOMO/ LUMO energy levels of P(NDI2DT-BTT), P(NDI2DTPTT), and P(NDI2DT-BTTz) were -5.35/-3.46, -5.52/-3.54, and -5.80/-3.61 eV, respectively, which was consistent with the trend observed in the CV results. We also examined the effect of different N substitution patterns on the backbone planarity of PAs (Figure S4). The reference PA, P(NDI2DT-BTT), had dihedral angles of 9° (θ1) and 10° (θ2). P(NDI2DT-PTT) showed slightly reduced dihedral angles of 3° (θ1) and 3° (θ2), most likely due to N···S non-covalent interactions.43,44 In contrast, the θ1 angle (26°) of P(NDI2DT-BTTz) was considerably larger 8


Page 8 of 24

Page 9 of 24 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


than those of P(NDI2DT-BTT) and P(NDI2DT-PTT), which are caused by the repulsion between the N atoms of the BT and thiazole units. Accordingly, the dihedral angles determined by the DFT simulations revealed that the backbone planarity of these polymers increased in the following order: P(NDI2DT-BTTz) < P(NDI2DT-BTT) < P(NDI2DT-PTT).

Table 1. Basic characteristics of PAs. Polymer acceptor

λmaxa) (nm)

Egopt b)

Mnc) (kg mol-1)

Mwc) (kg mol-1)

Đ

HOMOd) (eV)

LUMOe) (eV)

P(NDI2DT694 1.50 68.1 224.7 3.3 -5.77 -3.78 BTT) P(NDI2DT686 1.59 61.4 141.2 2.3 -5.87 -3.81 PTT) P(NDI2DT620 1.74 51.8 134.7 2.6 -6.01 -3.86 BTTz) a) Determined from UV-vis spectra; b)Calculated from the absorption onset in film; c)Determined from GPC measurements; d)Estimated from the onset oxidation potentials in CV; e)Estimated from the onset reduction potentials in CV.

Figure 2. (a) J–V curves and (b) EQE spectra of P(NDI2DT-BTT), P(NDI2DT-PTT), and P(NDI2DT-BTTz)-based all-PSCs.

9



Table 2. Photovoltaic performances of the P(NDI2DT-BTTz) based all-PSC devices. Voc Jsc Active layer FF (V) (mA cm-2) PD:P(NDI2DT0.90 11.98 0.56 BTT) PD:P(NDI2DT0.88 13.85 0.57 PTT) PD:P(NDI2DT0.68 6.26 0.34 BTTz) a) Average values and their standard deviations b) Determined by SCLC method.

Page 10 of 24

P(NDI2DT-BTT), P(NDI2DT-PTT), and PCEmax µh b) (PCEavg) a) (%) (cm2V-1s-1) 6.02 1.8 × 10-4 (5.89 ± 0.08) 6.95 2.2 × 10-4 (6.73 ± 0.14) 1.43 9.0 × 10-5 (1.39 ± 0.04) were obtained from at least

µe b) (cm2V-1s-1) 2.2 × 10-5 2.5 × 10-5 9.5 × 10-6 ten devices;

P(NDI2DT-BTT), P(NDI2DT-PTT), and P(NDI2DT-BTTz)-based all-PSCs were fabricated using PBDB-T as the PD with a device structure of ITO/poly(3,4ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/active layer/poly[(9,9-bis(3′((N,N-dimethyl)-N-ethylammonium)propyl)-2,7-fluorene)-alt-5,5′-bis(2,2′-thiophene)-2,6naphthalene-1,4,5,8-tetracaboxylic-N,N′-di(2-ethylhexyl)imide]dibromide

(PNDIT-F3N-

Br)/Ag. The PEDOT:PSS and PNDIT-F3N-Br52 were used as a hole-transporting layer and an electron-transporting layer, respectively. The optimized PD:PA blend ratio was 1.5:1.0 (w/w) in chlorobenzene (CB). Details regarding the fabrication of devices can be found in the experimental section of the supporting information. Figure 2a shows the J–V characteristics of the all-PSC devices under AM 1.5G illumination (100 mW cm-2) and Table 2 summarizes device performances. The PBDB-T:P(NDI2DT-BTT) blend, which was used as a control device, showed a PCE of 6.02% with an open-circuit voltage (Voc) of 0.90 V, short-circuit current density (Jsc) of 11.98 mA cm-2 and fill factor (FF) of 0.56. The PCE of the device based on PBDB-T:P(NDI2DT-PTT), in which the C atom of BTT was replaced with the N atom, was improved to 6.95% with a Jsc of 13.85 mA cm-2 and FF of 0.57. However, the Voc value slightly decreased from 0.90 V for the P(NDI2DT-BTT)-based device to 0.88 V for the P(NDI2DTPTT)-based device. The slight change in the VOC is consistent with the down-shifted LUMO 10


Page 11 of 24 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


level of P(NDI2DT-PTT). Alternatively, the performance of the all-PSC based on the PBDBT:P(NDI2DT-BTTz) blend film was very poor with a PCE of 1.43%, Voc of 0.68V, Jsc of 6.26 mA cm-2 and FF of 0.34. All the photovoltaic parameters (Voc, Jsc and FF) of the P(NDI2DTBTTz)-based device significantly decreased as compared with those of the P(NDI2DT-BTT) and P(NDI2DT-PTT)-based devices. Figure 2b shows the external quantum efficiency (EQE) profiles of the all-PSC devices under monochromatic light illumination. The calculated Jsc values from the EQE data were 11.74, 13.48, and 6.10 mA cm−2 for the P(NDI2DT-BTT), P(NDI2DT-PTT), and P(NDI2DT-BTTz) based devices, respectively, within 3% mismatch with those obtained from J–V measurements. The EQE curves of PBDB-T:P(NDI2DT-BTT) and PBDB-T:P(NDI2DT-PTT) showed a broad photoresponse (up to 800 nm) because of the complementary light absorption of P(NDI2DT-BTT) or P(NDI2DT-PTT) and the PD at longer wavelengths. In contrast, the EQE curve of PBDB-T:P(NDI2DT-BTTz) displayed a narrower photoresponse (up to 700 nm). Among the three all-PSCs, the PBDB-T:P(NDI2DT-PTT) device exhibited the highest photoresponse (> 70%) in the range of 500–600 nm. The influence of the N position on the hole and electron mobilities in the pristine and blend films was investigated using the space charge limited current (SCLC) method (Table 2).53,54 The hole mobilities (µh)/electron mobilities (µe) were calculated to be 1.8 × 10-4/2.2 × 10-5 cm2 V-1 s-1, 2.2 × 10-4/2.5 × 10-5 cm2 V-1 s-1, and 9.0 × 10-5/9.5 × 10-6 cm2 V-1 s-1 for the P(NDI2DT-BTT)-, P(NDI2DT-PTT)- and P(NDI2DT-BTTz)-based blend films, respectively. Thus, the P(NDI2DT-BTTz)-based blend film had the lowest mobilities, but the P(NDI2DTBTT) and P(NDI2DT-PTT)-based blend films afforded similar values. The low hole and electron transport ability of the PBDB-T:P(NDI2DT-BTTz) blends may contribute to the reduced Jsc and FF in device.

11



Figure 3. Dependence of (a) Jsc and (b) Voc on light intensities of PBDB-T:P(NDI2DT-BTT), PBDB-T:P(NDI2DT-PTT), and PBDB-T:P(NDI2DT-BTTz) all-PSCs.

To gain a deeper insight into the effect of varying the PAs N substitution pattern on allPSC performance, the charge recombination behavior was investigated by analyzing the light intensity (Plight) dependence of Jsc and Voc (Figure 3). The correlation between Jsc and Plight is plotted based on the following relationship: Jsc ∝ Plightα, where α is an exponential factor.55 All

the devices exhibited α values between 0.88−0.90, which suggests similar bimolecular recombination characteristics (Figure 3a). Under open-circuit conditions, the slope of Voc vs. the natural logarithm of Plight has a value of kBTq-1, where kB, T, and q are the Boltzmann constant, temperature, and elementary charge, respectively. When the monomolecular or trapassisted recombination predominates the loss of free charge carriers, a slope larger than kBTq1

is obtained.55,56 As shown in Figure 3b, the slope (S) of the PBDB-T:P(NDI2DT-PTT) (0.96

kBTq-1) and PBDB-T:P(NDI2DT-BTT) (0.92 kBTq-1) was close to unity, suggesting that the monomolecular or trap-assisted recombination was significantly suppressed; the slope of less than kBTq-1 is attributed to the presence of surface recombination.13,57 In contrast, the PBDBT:P(NDI2DT-BTTz) device (1.61 kBTq-1) exhibited the slope close to 2. This indicates that severe monomolecular recombination is the main reason of poor performances in P(NDI2DT12


Page 12 of 24

Page 13 of 24 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


BTTz)-based devices due to the large HOMO energy level offset, leading to Voc loss and lower Jsc values.58-61

Figure 4. PL spectra (a) P(NDI2DT-BTT) pristine film and PBDB-T:P(NDI2DT-BTT) blend film by exciting at 694 nm; (b) P(NDI2DT-PTT) pristine film and PBDB-T:P(NDI2DT-PTT) blend film by exciting at 686 nm; (c) P(NDI2DT-BTTz) pristine film and PBDB-T:P(NDI2DTBTTz) blend film by exciting at 720 nm. (d) Photocurrent analysis of PBDB-T:P(NDI2DTBTT), PBDB-T:P(NDI2DT-PTT), and PBDB-T:P(NDI2DT-BTTz) all-PSCs.

Next, we investigated the charge transfer and charge dissociation behaviors in order to understand the difference in the device performances between PBDB-T:P(NDI2DT-BTT) and PBDB-T:P(NDI2DT-PTT). First, the photo-induced hole transfer behavior from PAs to PBDBT can be measured by monitoring the photoluminescent (PL) quenching of blended films (Figure 4).27,62 The control blend film, PBDB-T:P(NDI2DT-BTT), showed a moderate PL quenching efficiency (Q.E.) of 75% (Figure 4a). Interestingly, the PL of the PBDB13



T:P(NDI2DT-PTT) blend film was nearly quenched with a 92% Q.E., indicative of an efficient hole transfer process from PA to PD at the donor/acceptor interface (Figure 4b). This supports the difference in Jsc values of the P(NDI2DT-BTT)- and P(NDI2DT-PTT)-based devices. In contrast, the PBDB-T:P(NDI2DT-BTTz) blend film exhibited much lower Q.E. of 21% (Figure 4c). This means that only a portion of the excitons created from P(NDI2DT-BTTz) dissociate to free charges, which agrees with the much lower Jsc value of the corresponding allPSC. The poor Q.E. (inefficient hole transfer) in the PBDB-T:P(NDI2DT-BTTz) blend film could be well explained by the large HOMO offset measured from CV results. In order to quantitatively investigate charge dissociation and collection behavior, the charge dissociation probability (P(E,T)) of the all-PSCs based on P(NDI2DT-BTT), P(NDI2DT-PTT), and P(NDI2DT-BTTz) was compared.63 The P(E,T) value for the PBDB-T:P(NDI2DT-BTT), PBDB-T:P(NDI2DT-PTT) and PBDB-T:P(NDI2DT-BTTz) devices were 0.77, 0.85, and 0.50, respectively. These results agree with the trend observed in the Q.E. values. Therefore, the reduced charge recombination and efficient exciton dissociation behavior of the PBDBT:P(NDI2DT-PTT) blended films contribute to the highest PCE among three different all-PSCs. Additionally, we investigated the blend morphology of all-PSCs using atomic force microscopy (AFM) (Figure S5). The PBDB-T:P(NDI2DT-PTT) blend film shows a more intermixed blend morphology with the smallest root-mean-square (RMS) roughness value compared to PBDB-T:P(NDI2DT-BTT) and PBDB-T:P(NDI2DT-BTTz), which might be beneficial to free charge generation due to the increased donor/acceptor interfacial area. This morphological feature is attributed to the decreased molecular ordering of P(NDI2DT-PTT) caused by the regio-random structure as evidenced by the grazing-incidence X-ray scattering (GIXS) results in Figure S6.64 Although the crystallinity of P(NDI2DT-BTTz) is lower than the other two polymers, the PBDB-T:P(NDI2DT-BTTz) blend film had stronger phase 14


Page 14 of 24

Page 15 of 24 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


separation (as shown in AFM images) probably due to the strong aggregation of P(NDI2DTBTTz) polymers caused by the lower solubility of P(NDI2DT-BTTz) (~ 8 mg mL-1) than the other two PAs (~ 15 mg mL-1) in CB.

Figure 5. Air-stability of PBDB-T:P(NDI2DT-BTT) and PBDB-T:P(NDI2DT-PTT) devices without encapsulation.

In addition to the efficiency of the PA, the air stability should be considered to realize a commercially viable all-PSCs. It is established that lowering the LUMO level of n-type materials can improve the air-stability.65,66 Therefore, we compared the air-stability of the P(NDI2DT-BTT) and P(NDI2DT-PTT)-based all-PSC devices under ambient air condition without encapsulation (with room temperature, relative humidity of ~ 20% and dark condition), and the results are presented in Figure 5. While the PBDB-T:P(NDI2DT-BTT) device exhibited 59% of its initial PCE value after being stored for 400 h, the PBDB-T:P(NDI2DTPTT) device showed relatively better air stability, retaining 74% of its initial PCE value. It is reported that improving the air stability of n-type semiconducting materials requires a lower LUMO energy level and tighter molecular packing, as these can prevent the penetration of oxidants into the active layer.67 Therefore, we hypothesize that ambient oxidation was decreased in the case of the P(NDI2DT-PTT)-based device owing to the relatively lower 15



LUMO energy level of P(NDI2DT-PTT). Overall, the all-PSCs based on P(NDI2DT-PTT) show improved air stability, demonstrating the good potential of this PA for high-efficiency and stable all-PSCs.

Conclusions In summary, we developed a series of PAs based on the NDI and BT derivatives with N substitution at varying positions of the BTT monomer. This allowed for a systematic investigation into the effect of the N position on the photovoltaic performance of all-PSCs. When the number of incorporated N atoms into BTT unit increased, the HOMO and LUMO energy levels were gradually decreased and the polymer planarity was controlled. As a result, the P(NDI2DT-PTT) polymer exhibited the high polymer backbone planarity, appropriate energy level offsets and superior miscibility with the PBDB-T donor polymer in the blend film, which facilitated efficient charge generation and transport. Consequently, the all-PSCs based on PBDB-T:P(NDI2DT-PTT) exhibited the highest photovoltaic performance with a PCE of 6.95%, and also exhibited superior air-stability than the PBDB-T:P(NDI2DT-BTT) device. Our results demonstrated that incorporating N atoms into the backbone of the NDI-based polymer acceptors is a simple and effective way to modulate the energy levels and structural properties of the polymers as well as their photovoltaic performances and stabilities in all-PSCs.

ASSOCIATED CONTENT Supplementary Information. Materials and methods, detail experimental procedures, and additional characterization data. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author 16


Page 16 of 24

Page 17 of 24 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


* E-mail: [email protected] * E-mail: [email protected]

NOTE The authors declare no competing financial interest.

ACKNOWLEDGEMENTS S. W. K., H. Y. and B. J. K. acknowledge the support from the National Research Foundation Grant (2012M3A6A7055540 and 2017M3A7B8065584), provided by the Korean Government. And, Y. W. and T. M. acknowledge the support from JSPS KAKENHI (18KK0157, 19H02786), the Ogasawara Foundation for the Promotion of Science and Engineering, the Yazaki Memorial Foundation for Science and Technology, the Asahi Glass Foundation, the Support for Tokyotech Advanced Researchers and the ASPIRE League Research Grant 2019, Tokyo Tech. We acknowledge Dr. G. S. Collier for the helpful discussions.

17



REFERENCES (1) Wang, G.; Melkonyan, F. S.; Facchetti, A.; Marks, T. J. All-Polymer Solar Cells: Recent Progress, Challenges, and Prospects. Angew. Chem. Int. Ed. 2019, 58, 4129-4142. (2) Xu, X.; Li, Z.; Zhang, W.; Meng, X.; Zou, X.; Di Carlo Rasi, D.; Ma, W.; Yartsev, A.; Andersson, M. R.; Janssen, R. A. J.; Wang, E. 8.0% Efficient All-Polymer Solar Cells with High Photovoltage of 1.1 V and Internal Quantum Efficiency near Unity. Adv. Energy Mater. 2018, 8, 1700908. (3) Kim, W.; Choi, J.; Kim, J.-H.; Kim, T.; Lee, C.; Lee, S.; Kim, M.; Kim, B. J.; Kim, T.-S. Comparative Study of the Mechanical Properties of All-Polymer and Fullerene−Polymer Solar Cells: The Importance of Polymer Acceptors for High Fracture Resistance. Chem. Mater. 2018, 30, 2102-2111. (4) 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, 1700309. (5) Kim, T.; Younts, R.; Lee, W.; Lee, S.; Gundogdu, K.; Kim, B. J. Impact of the PhotoInduced Degradation of Electron Acceptors on the Photophysics, Charge Transport and Device Performance of All-Polymer and Fullerene–Polymer Solar Cells. J. Mater. Chem. A 2017, 5, 22170-22179. (6) 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. (7) Kim, T.; Choi, J.; Kim, H. J.; Lee, W.; Kim, B. J. Comparative Study of Thermal Stability, Morphology, and Performance of All-Polymer, Fullerene–Polymer, and Ternary Blend Solar Cells Based on the Same Polymer Donor. Macromolecules 2017, 50, 6861-6871. (8) Wang, Y.; Yan, Z.; Guo, H.; Uddin, M. A.; Ling, S.; Zhou, X.; Su, H.; Dai, J.; Woo, H. Y.; Guo, X. Effects of Bithiophene Imide Fusion on the Device Performance of Organic Thin-Film Transistors and All-Polymer Solar Cells. Angew. Chem. Int. Ed. 2017, 56, 15304-15308. (9) Kim, H. I.; Kim, M.; Park, C. W.; Kim, H. U.; Lee, H.-K.; Park, T. Morphological Control of Donor/Acceptor Interfaces in All-Polymer Solar Cells Using a Pentafluorobenzene-Based Additive. Chem. Mater. 2017, 29, 6793-6798. (10) 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. (11) Lee, C.; Lee, S.; Kim, G. U.; Lee, W.; Kim, B. J. Recent Advances, Design Guidelines, and Prospects of All-Polymer Solar Cells. Chem. Rev. 2019, 119, 8028-8086. (12) Su, W.; Meng, Y.; Guo, X.; Fan, Q.; Zhang, M.; Jiang, Y.; Xu, Z.; Dai, Y.; Xie, B.; Liu, F.; Zhang, M.; Russell, T. P.; Li, Y. Efficient and Thermally Stable All-Polymer Solar Cells Based on a Fluorinated Wide-Bandgap Polymer Donor with High Crystallinity. J. Mater. Chem. A 2018, 6, 16403-16411. (13) Cho, H.-H.; Kim, S.; Kim, T.; Sree, V. G.; Jin, S.-H.; Kim, F. S.; Kim, B. J. Design of Cyanovinylene-Containing Polymer Acceptors with Large Dipole Moment Change for

18


Page 18 of 24

Page 19 of 24 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


Efficient Charge Generation in High-Performance All-Polymer Solar Cells. Adv. Energy Mater. 2018, 8, 1701436. (14) Genene, Z.; Mammo, W.; Wang, E.; Andersson, M. R. Recent Advances in n-Type Polymers for All-Polymer Solar Cells. Adv. Mater. 2019, 31, 1807275. (15) Lee, W.; Lee, C.; Yu, H.; Kim, D.-J.; Wang, C.; Woo, H. Y.; Oh, J. H.; Kim, B. J. Side Chain Optimization of Naphthalenediimide-Bithiophene-Based Polymers to Enhance the Electron Mobility and the Performance in All-Polymer Solar Cells. Adv. Funct. Mater. 2016, 26, 1543-1553. (16) 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.; Facchetti, A.; Olvera de la Cruz, M.; Marks, T. J. All-Polymer Solar Cell Performance Optimized via Systematic Molecular Weight Tuning of Both Donor and Acceptor Polymers. J. Amer. Chem. Soc. 2016, 138, 1240-1251. (17) Zhou, N.; Facchetti, A. Naphthalenediimide (NDI) polymers for all-polymer photovoltaics. Mater. Today 2018, 21, 377-390. (18) Yao, H.; Bai, F.; Hu, H.; Arunagiri, L.; Zhang, J.; Chen, Y.; Yu, H.; Chen, S.; Liu, T.; Lai, J. Y. L.; Zou, Y.; Ade, H.; Yan, H. Efficient All-Polymer Solar Cells based on a New Polymer Acceptor Achieving 10.3% Power Conversion Efficiency. ACS Energy Lett. 2019, 4, 417-422. (19) Li, Z.; Ying, L.; Zhu, P.; Zhong, W.; Li, N.; Liu, F.; Huang, F.; Cao, Y. A Generic Green Solvent Concept Boosting the Power Conversion Efficiency of All-Polymer Solar Cells to 11%. Energy Environ. Sci. 2019, 12, 157-163. (20) Kolhe, N. B.; Tran, D. K.; Lee, H.; Kuzuhara, D.; Yoshimoto, N.; Koganezawa, T.; Jenekhe, S. A. New Random Copolymer Acceptors Enable Additive-Free Processing of 10.1% Efficient All-Polymer Solar Cells with Near-Unity Internal Quantum Efficiency. ACS Energy Lett. 2019, 4, 1162-1170. (21) Wu, J.; Meng, Y.; Guo, X.; Zhu, L.; Liu, F.; Zhang, M. All-Polymer Solar Cells Based on a Novel Narrow-Bandgap Polymer Acceptor with Power Conversion Efficiency over 10%. J. Mater. Chem. A 2019, 7, 16190-16196. (22) Zhou, K.; Zhang, R.; Liu, J.; Li, M.; Yu, X.; Xing, R.; Han, Y. Donor/Acceptor Molecular Orientation-Dependent Photovoltaic Performance in All-Polymer Solar Cells. ACS Appl. Mater. Interfaces 2015, 7, 25352-25361. (23) Ye, L.; Jiao, X.; Zhou, M.; Zhang, S.; Yao, H.; Zhao, W.; Xia, A.; Ade, H.; Hou, J. Manipulating Aggregation and Molecular Orientation in All-Polymer Photovoltaic Cells. Adv. Mater. 2015, 27, 6046-6054. (24) Lee, C.; Giridhar, T.; Choi, J.; Kim, S.; Kim, Y.; Kim, T.; Lee, W.; Cho, H.-H.; Wang, C.; Ade, H.; Kim, B. J. Importance of 2D Conjugated Side Chains of Benzodithiophene-Based Polymers in Controlling Polymer Packing, Interfacial Ordering, and Composition Variations of All-Polymer Solar Cells. Chem. Mater. 2017, 29, 9407-9415. (25) Schubert, M.; Collins, B. A.; Mangold, H.; Howard, I. A.; Schindler, W.; Vandewal, K.; Roland, S.; Behrends, J.; Kraffert, F.; Steyrleuthner, R.; Chen, Z.; Fostiropoulos, K.; Bittl, R.; Salleo, A.; Facchetti, A.; Laquai, F.; Ade, H. W.; Neher, D. Correlated Donor/Acceptor Crystal Orientation Controls Photocurrent Generation in All-Polymer Solar Cells. Adv. Funct. Mater. 2014, 24, 4068-4081. 19



(26) Jung, J.; Lee, W.; Lee, C.; Ahn, H.; Kim, B. J. Controlling Molecular Orientation of Naphthalenediimide-Based Polymer Acceptors for High Performance All-Polymer Solar Cells. Adv. Energy Mater. 2016, 6, 1600504. (27) Uddin, M. A.; Kim, Y.; Younts, R.; Lee, W.; Gautam, B.; Choi, J.; Wang, C.; Gundogdu, K.; Kim, B. J.; Woo, H. Y. Controlling Energy Levels and Blend Morphology for All-Polymer Solar Cells via Fluorination of a Naphthalene Diimide-Based Copolymer Acceptor. Macromolecules 2016, 49, 6374-6383. (28) Blakesley, J. C.; Neher, D. Relationship between Energetic Disorder and Open-Circuit Voltage in Bulk Heterojunction Organic Solar Cells. Phys. Rev. B 2011, 84, 84. (29) Zhou, K.; Wu, Y.; Liu, Y.; Zhou, X.; Zhang, L.; Ma, W. Molecular Orientation of Polymer Acceptor Dominates Open-Circuit Voltage Losses in All-Polymer Solar Cells. ACS Energy Lett. 2019, 4, 1057-1064. (30) 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. (31) Deshmukh, K. D.; Matsidik, R.; Prasad, S. K. K.; Chandrasekaran, N.; Welford, A.; Connal, L. A.; Liu, A. C. Y.; Gann, E.; Thomsen, L.; Kabra, D.; Hodgkiss, J. M.; Sommer, M.; McNeill, C. R. Impact of Acceptor Fluorination on the Performance of All-Polymer Solar Cells. ACS Appl. Mater. Interfaces 2018, 10, 955-969. (32) Zhang, Q.; Kelly, M. A.; Bauer, N.; You, W. The Curious Case of Fluorination of Conjugated Polymers for Solar Cells. Acc. Chem. Res. 2017, 50, 2401-2409. (33) Fan, Q.; Zhu, Q.; Xu, Z.; Su, W.; Chen, J.; Wu, J.; Guo, X.; Ma, W.; Zhang, M.; Li, Y. Chlorine Substituted 2D-Conjugated Polymer for High-Performance Polymer Solar Cells with 13.1% Efficiency via Toluene Processing. Nano Energy 2018, 48, 413-420. (34) Wang, Y.; Hasegawa, T.; Matsumoto, H.; Michinobu, T. Significant Improvement of Unipolar n-Type Transistor Performances by Manipulating the Coplanar Backbone Conformation of Electron-Deficient Polymers via Hydrogen Bonding. J. Am. Chem. Soc. 2019, 141, 3566-3575. (35) Yum, S.; An, T. K.; Wang, X.; Lee, W.; Uddin, M. A.; Kim, Y. J.; Nguyen, T. L.; Xu, S.; Hwang, S.; Park, C. E.; Woo, H. Y. Benzotriazole-Containing Planar Conjugated Polymers with Noncovalent Conformational Locks for Thermally Stable and Efficient Polymer FieldEffect Transistors. Chem. Mater. 2014, 26, 2147-2154. (36) Reichenbacher, K.; Suss, H. I.; Hulliger, J. Fluorine in Crystal Engineering−"the little atom that could". Chem. Soc. Rev. 2005, 34, 22-30. (37) Sun, B.; Hong, W.; Yan, Z.; Aziz, H.; Li, Y. Record High Electron Mobility of 6.3 cm2 V1 -1 s Achieved for Polymer Semiconductors using a New Building Block. Adv. Mater. 2014, 26, 2636-2642. (38) Xiao, C.; Zhao, G.; Zhang, A.; Jiang, W.; Janssen, R. A.; Li, W.; Hu, W.; Wang, Z. High Performance Polymer Nanowire Field-Effect Transistors with Distinct Molecular Orientations. Adv. Mater. 2015, 27, 4963-4968.

20


Page 20 of 24

Page 21 of 24 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


(39) Ni, Z.; Dong, H.; Wang, H.; Ding, S.; Zou, Y.; Zhao, Q.; Zhen, Y.; Liu, F.; Jiang, L.; Hu, W. Quinoline-Flanked Diketopyrrolopyrrole Copolymers Breaking through Electron Mobility over 6 cm2 V-1 s-1 in Flexible Thin Film Devices. Adv. Mater. 2018, 30, 1704843. (40) Dai, Y. Z.; Ai, N.; Lu, Y.; Zheng, Y. Q.; Dou, J. H.; Shi, K.; Lei, T.; Wang, J. Y.; Pei, J. Embedding Electron-Deficient Nitrogen Atoms in Polymer Backbone Towards High Performance n-Type Polymer Field-Effect Transistors. Chem. Sci. 2016, 7, 5753-5757. (41) Chen, X.-K.; Guo, J.-F.; Zou, L.-Y.; Ren, A.-M.; Fan, J.-X. A Promising Approach to Obtain Excellent n-Type Organic Field-Effect Transistors: Introducing Pyrazine Ring. J. Phys. Chem. C 2011, 115, 21416-21428. (42) Wei, C.; Zhang, W.; Huang, J.; Li, H.; Zhou, Y.; Yu, G. Realizing n-Type Field-Effect Performance via Introducing Trifluoromethyl Groups into the Donor–Acceptor Copolymer Backbone. Macromolecules 2019, 52, 2911-2921. (43) Tian, Y.-H.; Kertesz, M. Ladder-Type Polyenazine Based on Intramolecular S···N Interactions: A Theoretical Study of a Small-Bandgap Polymer. Macromolecules 2009, 42, 6123-6127. (44) Cho, H.-H.; Kang, T. E.; Kim, K.-H.; Kang, H.; Kim, H. J.; Kim, B. J. Effect of Incorporated Nitrogens on the Planarity and Photovoltaic Performance of Donor–Acceptor Copolymers. Macromolecules 2012, 45, 6415-6423. (45) Cao, Y.; Lei, T.; Yuan, J.; Wang, J.-Y.; Pei, J. Dithiazolyl-Benzothiadiazole-Containing Polymer Acceptors: Synthesis, Characterization, and All-Polymer Solar Cells. Polym. Chem. 2013, 4, 5228–5236. (46) Wang, Y.; Hasegawa, T.; Matsumoto, H.; Mori, T.; Michinobu, T. High-Performance nChannel Organic Transistors Using High-Molecular-Weight Electron-Deficient Copolymers and Amine-Tailed Self-Assembled Monolayers. Adv. Mater. 2018, 30, 1707164. (47) Wang, S.; Sun, H.; Erdmann, T.; Wang, G.; Fazzi, D.; Lappan, U.; Puttisong, Y.; Chen, Z.; Berggren, M.; Crispin, X.; Kiriy, A.; Voit, B.; Marks, T. J.; Fabiano, S.; Facchetti, A. A Chemically Doped Naphthalenediimide-Bithiazole Polymer for n-Type Organic Thermoelectrics. Adv. Mater. 2018, 30, 1801898. (48) Schubert, M.; Dolfen, D.; Frisch, J.; Roland, S.; Steyrleuthner, R.; Stiller, B.; Chen, Z.; Scherf, U.; Koch, N.; Facchetti, A.; Neher, D. Influence of Aggregation on the Performance of All-Polymer Solar Cells Containing Low-Bandgap Naphthalenediimide Copolymers. Adv. Energy Mater. 2012, 2, 369-380. (49) Jespersen, K. G.; Beenken, W. J.; Zaushitsyn, Y.; Yartsev, A.; Andersson, M.; Pullerits, T.; Sundstrom, V. The Electronic States of Polyfluorene Copolymers with Alternating DonorAcceptor Units. J. Chem. Phys. 2004, 121, 12613-12617. (50) Wang, Y.; Hasegawa, T.; Matsumoto, H.; Michinobu, T. Significant Difference in Semiconducting Properties of Isomeric All-Acceptor Polymers Synthesized via Direct Arylation Polycondensation. Angew. Chem. Int. Ed. 2019, 58, 11893-11902. (51) Cho, H.-H.; Kim, T.; Kim, K.; Lee, C.; Kim, F. S.; Kim, B. J. Synthesis and Side-Chain Engineering of Phenylnaphthalenediimide (PNDI)-Based n-Type Polymers for Efficient AllPolymer Solar Cells. J. Mater. Chem. A 2017, 5, 5449-5459. 21



(52) 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 HighPerformance Polymer Solar Cells. J. Amer. Chem. Soc. 2016, 138, 2004-2013. (53) Distler, A.; Sauermann, T.; Egelhaaf, H.-J.; Rodman, S.; Waller, D.; Cheon, K.-S.; Lee, M.; Guldi, D. M. The Effect of PCBM Dimerization on the Performance of Bulk Heterojunction Solar Cells. Adv. Energy Mater. 2014, 4, 1300693. (54) Chiguvare, Z.; Dyakonov, V. Trap-Limited Hole Mobility in Semiconducting Poly(3hexylthiophene). Phys. Rev. B 2004, 70, 235207. (55) Cowan, S. R.; Roy, A.; Heeger, A. J. Recombination in Polymer-Fullerene Bulk Heterojunction Solar Cells. Phys. Rev. B 2010, 82, 245207. (56) Kang, H.; Kim, K. H.; Kang, T. E.; Cho, C. H.; Park, S.; Yoon, S. C.; Kim, B. J. Effect of Fullerene Tris-adducts on the Photovoltaic Performance of P3HT:Fullerene Ternary Blends. ACS Appl. Mater. Interfaces 2013, 5, 4401-4408. (57) Brus, V. V. Light Dependent Open-Circuit Voltage of Organic Bulk Heterojunction Solar Cells in the Presence of Surface Recombination. Org. Electron. 2016, 29, 1-6. (58) Menke, S. M.; Ran, N. A.; Bazan, G. C.; Friend, R. H. Understanding Energy Loss in Organic Solar Cells: Toward a New Efficiency Regime. Joule 2018, 2, 25-35. (59) Veldman, D.; Meskers, S. C. J.; Janssen, R. A. J. The Energy of Charge‐Transfer States in Electron Donor–Acceptor Blends: Insight into the Energy Losses in Organic Solar Cells. Adv. Funct. Mater. 2009, 19, 1939-1948. (60) Kang, T. E.; Cho, H.-H.; Cho, C.-H.; Kim, K.-H.; Kang, H.; Lee, M.; Lee, S.; Kim, B.; Im, C.; Kim, B. J. Photoinduced Charge Transfer in Donor–Acceptor (DA) Copolymer: Fullerene Bis-adduct Polymer Solar Cells. ACS Appl. Mater. Interfaces 2013, 5, 861-868. (61) Eisner, F. D.; Azzouzi, M.; Fei, Z.; Hou, X.; Anthopoulos, T. D.; Dennis, T. J. S.; Heeney, M.; Nelson, J. Hybridization of Local Exciton and Charge-Transfer States Reduces Nonradiative Voltage Losses in Organic Solar Cells. J. Am. Chem. Soc. 2019, 141, 6362-6374. (62) Chen, S.; An, Y.; Dutta, G. K.; Kim, Y.; Zhang, Z.-G.; Li, Y.; Yang, C. A Synergetic Effect of Molecular Weight and Fluorine in All-Polymer Solar Cells with Enhanced Performance. Adv. Funct. Mater. 2017, 27, 1603564. (63) Blom, P. W. M.; Mihailetchi, V. D.; Koster, L. J. A.; Markov, D. E. Device Physics of Polymer:Fullerene Bulk Heterojunction Solar Cells. Adv. Mater. 2007, 19, 1551-1566. (64) Wen, W.; Ying, L.; Hsu, B. B.; Zhang, Y.; Nguyen, T. Q.; Bazan, G. C. Regioregular pyridyl[2,1,3]thiadiazole-co-indacenodithiophene Conjugated Polymers. Chem. Commun. 2013, 49, 7192-7194. (65) Schmidt, R.; Oh, J. H.; Sun, Y.-S.; Deppisch, M.; Krause, A.-M.; Radacki, K.; Braunschweig, H.; Konemann, M.; Erk, P.; Bao, Z.; Wurthner, F. High-Performance AirStable n-Channel Organic Thin Film Transistors Based on Halogenated Perylene Bisimide Semiconductors. J. Am. Chem. Soc. 2009, 131, 6215-6228. (66) Zhao, Z.; Yin, Z.; Chen, H.; Zheng, L.; Zhu, C.; Zhang, L.; Tan, S.; Wang, H.; Guo, Y.; Tang, Q.; Liu, Y. High-Performance, Air-Stable Field-Effect Transistors Based on Heteroatom-Substituted Naphthalenediimide-Benzothiadiazole Copolymers Exhibiting Ultrahigh Electron Mobility up to 8.5 cm2 V-1 s-1. Adv. Mater. 2017, 29, 1602410. 22


Page 22 of 24

Page 23 of 24 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


(67) Stolte, M.; Gsanger, M.; Hofmockel, R.; Suraru, S. L.; Wurthner, F. Improved Ambient Operation of n-Channel Organic Transistors of Solution-Sheared Naphthalene Diimide under Bias Stress. Chem. Chem. Phys. 2012, 14, 14181-14185.

23



TOC Graphic

24


Page 24 of 24

Impact of Incorporating Nitrogen Atoms in Naphthalenediimide

Recommend Documents