p- and n-Channel Photothermoelectric Conversion based on Ultralong

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p- and n-Channel Photothermoelectric Conversion based on Ultralong Near-Infrared Wavelengths Absorbing Polymers Tsukasa Hasegawa, Minoru Ashizawa, Yoshihiro Hayashi, Susumu Kawauchi, Hiroyasu Masunaga, Takaaki Hikima, Takaaki Manaka, and Hidetoshi Matsumoto ACS Appl. Polym. Mater., Just Accepted Manuscript • DOI: 10.1021/acsapm.8b00234 • Publication Date (Web): 08 Feb 2019 Downloaded from http://pubs.acs.org on February 12, 2019

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ACS Applied Polymer Materials

p- and n-Channel Photothermoelectric Conversion based on Ultralong Near-Infrared Wavelengths Absorbing Polymers Tsukasa Hasegawa,† Minoru Ashizawa,* † Yoshihiro Hayashi, ‡ Susumu Kawauchi, ‡ Hiroyasu Masunaga, § Takaaki Hikima, ∥ Takaaki Manaka, ⊥ Hidetoshi Matsumoto* † †

Department of Materials Science and Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8552, Japan ‡

Department of Chemical Science and Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8552, Japan § Japan Synchrotron Radiation Research Institute (JASRI)/SPring-8, 1-1-1 Kouto, Sayo, Sayo 679-5198, Japan ∥ RIKEN SPring-8 Center, 1-1-1 Kouto, Sayo, Sayo 679-5148, Japan ⊥ Department of Electrical and Electronic Engineering, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8552, Japan KEYWORDS. Organic electronics, organic semiconductor material, low-energy gap polymer, photothermoelectric conversion device, NIR-II.

ABSTRACT: Organic materials absorbing near-infrared (NIR) light are very attractive for the fabrication of optoelectronic devices. In this study, we developed an ultralow energy gap copolymer TzQI-TDPP composed of thiadiazoloquinoxalinimide (TzQI) and thiophene-flanked diketopyrrolopyrrole (TDPP) repeat units. TzQI-TDPP has a nearly identical narrow energy gap (0.60 eV) to that of the p-channel thienoisoindigo-based homopolymer PTII. Both polymers exhibit broad and intense optical absorption in the NIR-II light window (1000 – 1700 nm). Examination of charge polarity using field-effect transistors (FETs) indicates p-channel conduction for PTII and n-channel-dominant ambipolar conduction for TzQI-TDPP with moderate mobilities, in which a thin film of TzQI-TDPP displayed air-stable n-channel performance with a persistent mobility of over 0.003 cm2 V-1 s-1 after 30 days. In addition, we explored the photothermal (PT) and thermoelectric (TE) effects in the NIR-II light window by fabricating a photothermoelectric (PTE) device. Both polymers exhibit PT conversion efficiencies of approximately 30%, and the TE effect is observed in p-channel PTII and n-channel TzQI-TDPP. Notably, the PTII and TzQI-TDPP films display excellent photostability during on-off irradiating light cycles, indicating prominent NIR light detection. Our work not only provides a set of p-channel and n-channel-dominant ambipolar polymers with ultralow energy gaps but also demonstrates their underlying structure-property correlations based on electronic structures and their promising potential in applications utilizing NIR-II light.

INTRODUCTION Semiconducting polymers have been extensively studied for use in low-cost electronic devices owing to their modulated electronic conduction with various functionalities.1-4 Potential applications include organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), organic photovoltaic cells (OPVs), and thermoelectric conversion elements (TEs). 513 Additionally, the recent interest in organic electronics, including optical and electronic biosensors, bioimaging, and anticancer and antimicrobial therapies, has been inspired by the biomedical fields.14-22 In these applications, near-infrared (NIR) light has attracted increasing attention because of its high transparency, biopermeability and higher level of maximum permissible exposure (MPE) in the biological environment. In addition, in the field of energy harvesting, NIR light also shows a promising photothermoelectric (PTE) effect, wherein NIR light energy is converted to electricity through a sequence of typical photothermal and thermoelectric conversion. To observe the PTE effect, NIR light absorption with nonemissive decay and a relatively high thermoelectric effect are required. In general, thermoelectric conversion is governed by thermopower and electrical conductivity; however, these

two factors have a trade-off relation in improving the conversion efficiency.23,24 The existence of multiple considerable factors dominating the PTE effect limits material development, and exploration of the underlying principle in PTE conversion is at an initial stage. To date, active inorganic materials, such as carbon nanotubes, graphene and MoS2, that show PTE effects have proved to be potential candidates for photodetection Scheme 1. Chemical structures of (a) thienoisoindigo (TII)based homopolymer (PTII) and (b) thiadiazoloquinoxalineimide (TzQI) and TzQI and thienyldiketopyrrolopyrrole (TDPP)-based copolymer (TzQITDPP). (a)

(b) TzQI-based D-A copolymer

PTII

ACS Paragon Plus Environment

TzQI

TzQI-TDPP

ACS Applied Polymer Materials Scheme 2. Synthesis of TzQI-TDPP.

(a) ΔE = QSE (b)

Quinoid Aromatic 4 3.5

applications.25-33 In contrast, organic materials exhibiting PTE responses are still rare.34-36 The NIR optical window is categorized into the NIR-I re gion covering 750 nm – 1000 nm and the NIR-II region covering 1000 nm – 1700 nm. To achieve optimal NIR light absorption, most efforts have been devoted to reducing the energy gap with donor-acceptor (D-A)-alternating copolymers, which tune the frontier orbitals, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbitals (LUMO).37-52 Another approach to absorbing NIR light is to utilize charge-transfer band absorption by adding any p- or ntype dopant into polymer thin films, which are simultaneously enabled to be conductive.53-55 The D-A copolymers, depending on their frontier orbital levels, exhibit p-channel (hole transport), n-channel (electron transport), and ambipolar (both transport) behavior. Compared with well-established p-channel polymers,39-43,52 n-channel polymers still suffer from a lag in development.44-49,51 In addition, NIR-I absorbing conjugated polymers have been recently developed,56-59 but NIR-II absorbing polymers are still uncommon, and only a few materials have been reported.34-36,60-65 Actually, the D-A alteration is quite effective in reducing the energy gap by elevating the HOMO levels and reducing the LUMO levels. However, when this polymer design is adopted to develop an n-channel polymer achieving NIR-II light absorption, large reductions in both the HOMO and LUMO levels are required along with a narrowing energy gap. Therefore, achieving both n-channel transport and a low-energy-gap to match the NIR-II light window is very challenging. In order to minimize energy gap, well-balanced aromatic and quinoidal character is highly desired, thereby, at the minimum point of the aromatic and quinoidal indexes, the lowest energy gap is determined.66,67 In our previous works, a p-channel thienoisoindigo-based homopolymer (PTII) bearing an ultralow energy gap of 0.66 eV was developed, and PTII had strong absorption in the NIR-II light window (Scheme 1a).68 In addition, we developed a strong electron-accepting building block, thiadiazoloquinoxalinimide (TzQI),69 which proved to be effectively lowered both the HOMO and LUMO levels (Scheme 1b). These results have prompted us to create a TzQI-based nchannel polymer bearing the same ultralow energy gap as that of p-channel PTII (Scheme 1b). To develop this n-channel polymer, we designed a TzQI-based copolymer with a thiophene-flanked diketopyrrolopyrrole (TDPP) unit since DPP is a popular electron-deficient component, producing a rich variety of low-energy-gap copolymers with excellent chargecarrier mobility.70-74 This n-channel polymer design is verified by theoretical estimations, as discussed below. In this study, we designed and synthesized a novel nchannel polymer (TzQI-TDPP) bearing an ultralow energy gap as well as PTII. TzQI-TDPP absorbs the NIR-II light window up to 2200 nm, which originates from an ultralow

Energy gap (eV)

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3

2.5 2 1.5 1

■★

0.5

0 -8

-6

-4

-2

0

2

4

6

8

QSESC (kcal/mol) ■ PTII

★ TzQI-TDPP

● Various homopolymers or copolymers

Figure 1. (a) The homodesmotic reaction of a dimethylated monomer and oligo-acetylene. (b) Calculated QSESC and energy gap of PTII, TzQI-TDPP, and various homopolymers or copolymers. energy gap of 0.60 eV. The thin films of PTII and TzQITDPP exhibit p-channel and n-channel PTE effects, respectively, without any dopant addition. By focusing on charge polarity, we explored photothermal and thermoelectric phenomena from the perspective of polymer structure-function correlation. This study provides a fundamental design in organic electronics utilizing p- and n-channel polymers absorbing long wavelengths far from the NIR-II light window without any dopant molecule. RESULT AND DISCUSSIONS Synthesis and Characterization of Polymers P-channel polymer PTII was prepared according to a method described in our previous report.68 The synthesis of TzQITDPP is outlined in Scheme 2. The key monomer dibromoTzQI was prepared using a similar method in our previous reports.69 TzQI-TDPP was prepared via Stille cross-coupling of dibromo-TzQI with bis(trimethylstannyl)-TDPP. The resulting polymers were precipitated in methanol and purified by Soxhlet extraction using methanol, acetone, and hexane to remove impurities and oligomers. The purified polymers were extracted with chloroform and precipitated in methanol to give the final PTII and TzQI-TDPP. The obtained polymers were characterized by NMR and elemental analyses. The molecular weight of TzQI-TDPP (Mn = 17.8 kDa and PDI = 4.83) was determined by gel permeation chromatography (GPC) using odichlorobenzene against a polystyrene standard at 40 °C (Figure S2). Notably, we could not determine the accurate molecular weight of PTII, probably due to its strong propensity for aggregation during the GPC measurements.68 The thermogravimetric analysis of the two polymers was performed, and PTII and TzQI-TDPP exhibited sufficient thermal stability with


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Table 1. Electrochemical and optical properties of PTII and TzQI-TDPP. EHOMOCV, a [eV]

ELUMOCV, a [eV]

EgCV, b [eV]

λmaxsol, c [nm]

λmaxfilm, d [nm]

λonsetfilm, d [nm]

Egopt, e [eV]

PTII

−4.82

−3.74

1.08

1295

1369

2085

0.66

TzQITDPP

−5.28

−4.17

1.11

1591

1697

2177

0.60

a

Estimated from cyclic voltammetry vs. Fc/Fc+ (EHOMO = −4.80 eV). coated thin films. e Estimated from tauc plot

b

EgCV = ELUMOCV − EHOMOCV. c In CHCl3 solutions. d Spin-

decomposition temperatures (defined as 5 weight % loss temperature) of 330 °C for PTII and 386 °C for TzQI-TDPP (Figure S3(a)). The differential scanning calorimetry (DSC) measurements show that neither polymers has an obvious melting or crystalizing point (Figure S3(b)). Theoretical Calculations At a first glance to evaluate aromatic and quinoidal characters, our original index, quinoidal stabilization energy (QSE), showing aromatic and quinoidal resonance was employed, wherein the energy gap was correlated with aromatic and quinoidal index. The QSE is recently developed by Hayashi et al.,75 and it is defined as the energy change between the homodesmotic reactions between dimethylated monomers and oligo-acetylene from theoretical calculation (Figure 1(a)). The positive QSE value means that polymer consisted of the monomers arranges aromatic form. In the quinoidal case, the QSE becomes negative value. As the QSE approaches 0, the polymer forms well-balanced aromatic and quinoidal structure. In alternating copolymers, the energy gap was correlated with the average of QSE of the two monomers. Therefore, the QSE provides the molecular designs to be considered the balance of aromatic and quinoidal character. The correlation between QSE and energy gap can be improved by using the sizecorrected QSE (QSESC), which can be calculated by the following equation; QSESC = QSE / A (1) , where A is the minimum number of π-electrons along the conjugated main chain. To estimate the QSESC values of PTII and TzQI-TDPP, a density functional theory (DFT) calculation was performed on the ωB97X-D/6-311G(d,p) level76 using Gaussian 09 program.77. The theoretical energy gap was estimated by the B3LYP/6-31G(d,p) level78 under periodic boundary condition. Based on this calculation, it was found that the QSESC of both polymers were very close to 0, and they just plotted on the minimum point of energy gap (Figure 1(b)), indicating that the design of these polymers has well-balanced aromatic and quinoidal resonance. To further understand the structural and electronic features of PTII and TzQI-TDPP, a DFT calculation was performed at the B3LYP/6-31G(d,p) level (Figure S4). For computational simplicity, the calculations were carried out for trimer structures by replacing long alkyl chains with methyl groups. Both polymers exhibit a completely planar molecular geometry. The high coplanarity of their backbone indicates that the conjugation is effectively enlarged, probably beneficial for

Figure 2. UV-vis-NIR absorption spectra of PTII and TzQI-TDPP. reducing the energy gaps. The HOMO and LUMO of PTII are well delocalized over the entire molecular backbone. Meanwhile, the HOMO of TzQI-TDPP is uniformly distributed along the molecular backbone, but the LUMO is mainly on the electron-accepting TzQI unit, implying that a distinct intramolecular charge transfer reduced the energy gap. Electrochemical Properties The frontier molecular orbital (FMO) levels of a semiconducting polymer substantially influence its charge-carrier polarity. Cyclic voltammetry (CV) was carried out on the PTII and TzQI-TDPP films to examine their redox properties, and the results are listed in Table 1. The CV profiles of the two polymers show quasi-reversible oxidation and reduction behaviors (Figure S5). The observed potentials were calibrated with the ferrocene/ferrocenium redox couple (Fc/Fc+), in which the absolute energy level was assumed to be -4.8 eV in vacuum.79 The calculated HOMO/LUMO levels are −4.82/− 3.74 eV for PTII and −5.28/−4.17 eV for TzQI-TDPP. Two polymers have a nearly identical ultranarrow electrochemical energy gap of approximately 1.1 eV. Interestingly, TzQITDPP has a low LUMO level below -4.0 eV, which is a criterion to show air-stable n-channel transport in field-effect transistors (FETs)80; in addition, it achieves an ultranarrow energy gap. In general, typical D-A polymers reduce the energy gap by elevating the HOMO levels and lowering the LUMO levels. When the HOMO and LUMO energy levels of TzQI-TDPP are compared with those of TDPP-based homopolymers,68 the TzQI framework is a strong electron-accepting segment with narrowing energy gap and lowering both the HOMO and LUMO levels


ACS Applied Polymer 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

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Table 2. OFET properties of PTII and TzQI-TDPP. p-channel

PTIIa TzQI-TDPPa

μavg (μmax) [cm2 V-1 s-1]

Vth [V]

Ion/Ioff

μavg (μmax) [cm2 V-1 s-1]

vacuum

7.4×10-3 (8.2×10-3)

N.A.

>101

N.A.

vacuum

1.9×10-2 (2.5×10-2)

−44.3

>101

air

1.2×10-2 (1.3×10-2)

8.55

8.7×10-3 (9.8×10-3)

−33.1

air (after days) a

n-channel

30

Vth [V]

Ion/Ioff

6.7×10-2 (8.7×10-2)

−20.8

>101

>100

4.4×10-2 (5.9×10-2)

3.57

>102

>101

3.9×10-3 (5.8×10-3)

25.9

>101

Calculated from the equation below: gm = (∂ID/∂VG) = (μWCi/L)VD (L = 50 μm, W = 1000 μm).

Optical Properties The UV-vis absorption spectra of the two polymers in chloroform solution and as thin films are shown in Figure 2, and the data are summarized in Table 1. The chloroform solutions of PTII and TzQI-TDPP exhibit intensive and broad optical absorption bands entirely covering the NIR-II light window, wherein the absorption maximum wavelengths (λmaxsol) of PTII and TzQI-TDPP are 1295 nm and 1591 nm, respectively. These long-wavelength absorption bands corresponding to the low-energy absorption range arise from quinoidal resonance, enhancing the -delocalization along the polymer backbone. The absorption profiles of the two polymer thin films are still redshifted, indicating tightly packed aggregation in the solid state, presumably due to the highly planar and rigid polymer backbone. The differences between λmaxsol and the maximum absorption wavelength in thin film (λmaxfilm) of TzQI-TDPP (106 nm) are larger than that of PTII (74 nm), suggesting stronger interchain J-aggregation-like dipole interaction originating from copolymerized structure composed of the TDPP unit and TzQI units. These results indicate that both polymers are very promising NIR-II-absorbing PTE materials. The optical energy gaps estimated from the tauc plot (Figure S6), which is typically utilized to estimate energy gap of semiconducting materials in the thin films81, are extremely small and are determined to be 0.66 eV for PTII and 0.60 eV for TzQI-TDPP. The electrochemical energy gaps are 0.4-0.5 eV larger than those estimated optically, even though this deference is slightly large, this value would be attributed to the exciton-binding energy of the semiconducting polymers estimated to be in the range of 0.3-0.5 eV.82,83 Overall, the electrochemical and optical properties of the two polymers agree with the trend of the theoretical estimations. Field-Effect Transistor Properties The charge transport properties were evaluated for FET devices fabricated with a bottom-gate/top-contact geometry uti-

lizing Au electrodes. The polymer films were spin-coated from chloroform or o-dichlorobenzene solutions onto an octadecyltrimethoxysilane (OTMS)-modified SiO2/Si substrate. The polymer thin films were annealed at 200 °C to improve the thin-film morphology, and measurements were carried out under vacuum and ambient conditions. The extracted FET parameters and transfer and output curves are listed in Table 2 and Figures S8-S10, respectively. Both polymers exhibited normally-on operation with high OFF current probably owing to reduced carrier-injection barrier from Au source electrodes,

(a) Electrode (Au)

Thermocouple 25 μm

(b) Laser OFF

≈ 1 μm

1000 μm 600 μm

Polymer film Glass substrate

Laser ON

Figure 3. (a) An illustration of PTE device configuration. (b) The thin film surface temperature under NIR laser irradiation at the wavelength of 1700 nm. which is basically well associated with ultralow energy gap. As a result, both polymers showed low the on/off current ratios due to their high off currents. Tuning the work function of the electrode materials could further improve the on/off ratio. We, however, could fairly compare carrier-transport properties of both polymers by utilizing carrier mobilities in linear-region. The thin film of PTII displayed p-channel operation with an average mobility of 7.4×10-3 cm2 V-1 s-1. In contrast, the thin film of TzQI-TDPP displayed a typical n-channel-dominant, ambipolar performance with hole and electron mobilities of 1.9×10-2 cm2 V-1 s-1 and 6.7×10-2 cm2 V-1 s-1, respectively. Notably, the TzQI-TDPP device achieved air-stable electron transport with a mobility of 3.9×10-3 cm2 V-1 s-1 under ambient conditions after being kept in air for one month. This air-stable


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ACS Applied Polymer Materials Table 3. NIR-PTE properties of PTII and TzQI-TDPP.

a c

ΔTmaxa [°C]

ηPT [%]

VPTEb [mV]

SPTEc [μV/K]

PFd [μW/mK2]

PTII

11.7

25.1

3.3±0.15

282

0.18

TzQI-TDPP

14.4

30.9

−4.4±0.12

−306

0.013

The wavelength of the NIR laser was 1700 nm. The laser power was 7.8 W cm-2. b The averaged value estimated over 90 points. SPTE = VPTE/ΔTmax. d PF = SPTE2σ (σ is the electrical conductivity of the polymer thin film)

performance is due to the deep LUMO level of TzQI-TDPP, which is less than -4.0 eV, and proves that the LUMO level is a criterion for showing air-stable electron conduction. The microstructures and morphologies of the spin-coated thin films of PTII and TzQI-TDPP were evaluated to gain further insight into carrier transport using grazing incidence wide-angle X-ray scattering (GIWAXS) and tapping-mode atomic force microscopy (AFM) (Figure S11-S12 and Table S3). From the GIWAXS patterns, both polymers displayed (100) diffraction peaks along both the out-of-plane and in-plane directions, corresponding to interlayer distances of ~20 Å for PTII and ~18 Å for TzQI-TDPP. Additionally, both polymers showed (010) diffraction peaks corresponding to π-π stacks along the out-of-plane direction. These results indicate that both polymers adopted face-on and edge-on mixed orientations on the substrate. The shorter π-π stack distance of TzQI-TDPP, 3.57 Å for TzQI-TDPP and 3.71 Å for PTII, suggest stronger π-π intermolecular interactions of TzQI-TDPP. Compared with typical TDPP-based polymers,84 the π-π stack distance of TzQI-TDPP is smaller and close to that of single crystal pentacene,85 implying that balanced aromatic and quinoidal characters delocalizing π-framework contributes to reducing interchain electronic coulombic repulsion, resulting in densely packed microstructure.86 In the AFM images, PTII exhibits interconnected fibril grains, while TzQI-TDPP shows slightly larger granular grains than those of PTII. Considering the results of the GIWAXS and AFM measurements, closer interchain packing and improved thin-film morphology of TzQITDPP are responsible for the improved FET performance of TzQI-TDPP-based devices. Regarding charge polarity, PTII and TzQI-TDPP are hole-transporting and electron-transport predominant ambipolar-transporting polymers, respectively. Photothermoelectric Properties Considering the PT and TE properties arising from the ultralow-energy-gap p-channel and n-channel dominant ambipolar polymers of PTII and TzQI-TDPP, we further studied their PTE conversion characteristics in the NIR-II light window. For the control conditions, a bare glass substrate and poly(3-hexylthiophene) (P3HT) thin film as reference samples were also measured. The experimental details are described in Supporting Information. The polymer thin films were dropcasted on the glass substrate, and their thicknesses were approximately fixed at 1 m. In the GIWAXS profiles of the drop-casted thin films, the diffraction profiles of both polymers are very similar to those of the spin-coated thin films (Figure S13 and Table S4). In the AFM images, both polymers showed large interconnected granular grains, approximately 50 nm in size, with high roughness values (RMS: 3.95 nm for

PTII and 3.47 nm for TzQI-TDPP) (Figure S14). First, the PT conversion performance was evaluated by exposing the polymer thin films to an NIR laser with a wavelength in the range of 1120 nm – 2000 nm in terms of optimizing absorption efficiency. The measurement setting is illustrated in Figure 3(a). Both polymers showed the highest the maximum temperature change (ΔTmax) / laser intensity at the wavelength of 1700 nm (Figure S16). Therefore, 1700 nm wavelength was selected for evaluating the NIR-II PTE conversion performance. For evaluating the PT effect of the polymers, the surface temperatures of the laser-exposed and unexposed areas were directly measured using a thermocouple. Upon exposing the polymer films of PTII and TzQI-TDPP to an NIR laser at wavelength of 1700 nm, the temperature of the exposed area of the polymer film rapidly exhibited a dramatic increase (Figure 3(b)). The NIR-PTE data are summarized in Table 3. The temperature increase (T) was linearly proportional to the laser power, and the maximum temperatures (Tmax) of 101 °C for PTII and 94 °C for TzQI-TDPP were achieved at a laser power of 81 W cm-2 (Figure S17-S18). The excellent laser power dependence for PT effect of both polymers is well associated with high thermal stability, as verified by the TGA analysis. The thin films of PTII and TzQI-TDPP displayed a larger temperature increase than the glass substrate and P3HT thin film. Because the control glass substrate and P3HT do not absorb NIR-II light, the observed PT conversion effects in PTII and TzQI-TDPP should arise from the optical absorption band covering the NIR-II light window of the two polymers. The fast temperature rises and drops, which depend on the balance between light-induced heating and thermal diffusion by the environment, were observed within a few seconds, suggesting that the temperature induced by a given laser power reaches equilibrium in real time. By means of the illumination time being prolonged with turning the light on and off, the PT efficiency (pt) was determined from the following equation:34-36 𝜂𝑃𝑇 =

ℎ𝐴∆𝑇𝑚𝑎𝑥 𝐼(1−10−𝐴𝜆 )

(2)

,where h is the heat transfer coefficient, A is the surface area of the system, Tmax is the maximum temperature increase of the films, I is the laser power, and Ais the absorbance of the polymer film at the corresponding NIR laser wavelengths. The thin films of PTII and TzQI-TDPP exhibited higher pt values of 25.1% and 30.9%, respectively, at the laser power of 7.8 W cm-2, indicating that these values of PTII and TzQITDPP are comparable to those reported for typical organic and inorganic materials showing photothermal conversion. It should be noted that the very long wavelengths in this study



have a great benefit, allowing deeper tissue penetration and higher MPE to light in biomedical applications. Coupling the photothermal (PT) and thermoelectric conversion (TE) effects facilitates PTE conversion in a single device. It is very interesting to explore and compare how the generated heat could be converted into electricity in the PTII and TzQI-TDPP thin films. Next, the PTE effect of the two polymers was evaluated by fabricating PTE devices, and the measurement setup is illustrated in Figure 4(a). To detect the PTE voltage (VPTE), gold electrodes with a channel width of 1000 μm and a channel length of 600 μm were deposited on the thin films, and the surface temperature was measured directly using a thermocouple. The detailed device fabrication procedures are described in Supporting Information. For this measurement, a 1700 nm line-shaped laser with a width of 2000 μm and a length of 50 μm was used at a fixed laser power of 7.8 W cm-2. When the laser light was exposed at position No. 1 (electrode and polymer layer interface), the thin films of PTII and TzQI-TDPP displayed a positive VPTE of 2.8 mV and a negative VPTE of -5.3 mV, suggesting hole transport for PTII and electron transport for TzQI-TDPP. This trend agrees well with the charge polarity observed in FET devices: the pchannel conduction for PTII and n-channel-dominant ambipolar conduction for TzQI-TDPP. Upon moving the exposed area from position No. 1 to No. 2, the VPTE decreases and becomes zero at position No. 2. Then, further moving the position from No. 2 to No. 3 led to the generation of an opposite VPTE value with nearly the same magnitude. This observed behavior is interpreted according to a previous report.35 When the electrode and polymer film interface (No. 1 and No. 3) were exposed to the laser light, the polymer film absorbed light to generate a high-temperature region (PT effect), and the resulting difference in maximum temperature (Tmax) between the electrodes led to a VPTE value with the same magnitude but with an opposite polarity on positions No. 1 and No. 3 (TE effect). In contrast, when the center between the electrodes (position No. 2) was exposed to the laser light, the generated values of VPTE are canceled in all directions (Figure S19). Very clearly, the VPTE profiles of both polymers in Figure 4(b)-(c) are approximately symmetrical in shape within our measurement setting error, which is attributed to the p-channel conduction for PTII and n-channel conduction for TzQI-TDPP. The TE efficiency of materials is determined by the figure-of-merit of ZT as follows: ZT = S2T/

(3)

where S is the Seebeck coefficient, and  are the electrical and thermal conductivity, respectively, and T is the absolute temperature. Herein, in this measurement, we can roughly estimate value of S simply by dividing VPTE by the temperature gradient Tmax generated between the two electrodes. In addition, we can measure the electrical conductivity  of a thin film between two electrodes. The obtained electrical conductivities in the neutral state are 2.2×10-2 S cm-1 for PTII and 1.4×10-3 S cm-1 for TzQI-TDPP. Note that electrical conductivity measurements were conducted under vacuum to eliminate doping in air by small amount of oxygen or some impurities. Additionally, to ensure the undoped state, no noticeable changes in thin film absorption of PTII and TzQI-TDPP were evidenced by treating thin films with hydrazine solution or FeCl3 solution (Figure. S7). Compared with common undoped organic semiconductors utilized in PTE devices, these values are relatively high by two or three orders of magnitude pre-

(a)

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V Laser spot polymer film

(b)

(c) 3

1

1

2

3

2

2 3

0 μm

1

600 μm

Laser irradiated position

(d)

(e)

Figure 4. (a) The illustration of the VPTE measurement setup under NIR laser irradiation at different positions from No. 1 to No. 3. Generated VPTE at different laser-irradiated positions of (b) PTII and (c) TzQI-TDPP. Cycle properties of generated VPTE of (d) PTII and (e) TzQI-TDPP. The interval of the laser on-off cycle was 5 s, and the NIR laser irradiate position was No. 1. sumably owing to low injection barrier from Au electrodes, which is similarly related to high OFF current in FETs. The evaluated TE parameters of S and power factor (PF) S, which are important for evaluating the thermoelectric performance of organic materials because of the difficulty in measuring in-plane thermal conductivity, are 282 μV K-1 and 0.18 μW m-1 K-2, respectively, for PTII and -306 μV K-1 and 0.013 μW m-1 K-2, respectively, for TzQI-TDPP. Overall, these TE properties are comparable to those of self-doped polymers;87 however, the PTE performance is still lower than those of PTE devices utilizing carrier-doped organic materials. Nevertheless, the PTE properties of PTII and TzQI-TDPP should be remarkably improved by electrical or chemical carrier doping. In particular, PTE conversion utilizing a 1700 nm laser is, to the best of our knowledge, observed for the first time with polymers bearing an ultranarrow energy gap. We emphasize that simultaneous achievement of NIR-II light absorption and nchannel conduction in TzQI-TDPP is very significant since compatibility of low-lying FMO levels with maintaining ultralow energy gap is quite challenging in consideration of material design. Additionally, for the practical use of PTE devices, complementary p- and n-channel materials are absolutely in demand. Considering the importance of PTE applications, the cycle properties of the PTII and TzQI-TDPP films leading to heating and cooling processes were evaluated using repeatable light irradiation (Figure 4(d)-(e)). During 20 on-off cycles at 10 second intervals, both polymers showed a fast response for laser on-off switching and the steady state of VPTE remained unchanged. Since both polymers exhibited excellent thermal stability as verified by TGA analysis, prominent cycle stability would be expected. The p-channel and n-channel dominant ambipolar polymers in this study are useful for harvesting energy in NIR-II light windows into electricity. In addition, with carrier doping, both polymers would not only achieve a high conductive state but also enlarge their optical absorption toward the IR light window. Conclusion In addition to using a p-channel polymer (PTII) bearing a very narrow energy gap of 0.66 eV, we successfully designed and synthesized an n-channel polymer (TzQI-TDPP) com-


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posed of strong electron-accepting TzQI and TDPP repeat units. TzQI-TDPP also has the same energy gap (0.60 eV) as PTII. Our original index for evaluating the balance of aromatic and quinoidal resonance, namely QSE, revealed that PTII and TzQI-TDPP form well-balanced aromatic and quinoidal resonance, thus leading to ultralow energy gaps. Both polymers exhibited broad and intensive absorption bands covering the NIR-II light window. As confirmed by their FET performance, the thin films of PTII and TzQI-TDPP displayed p-channel- and n-channel-dominant conductions with moderate mobilities on the order of 10-2 cm2 V-1s-1. In particular, the TzQI-TDPP-based device achieved air-stable electron conduction, maintaining a mobility of 0.003 cm2 V-1s-1 under ambient conditions over 30 days, which is due to a low LUMO level of under -4.0 eV. Notably, the PTII and TzQI-TDPP films show moderate PT efficiency in the NIR-II light as measured at 1700 nm. This excellent PT conversion realized by a very long wavelength was successfully applied to PTE conversion, turning light energy into electricity. As evidenced from the results concerning charge polarity, the thin films of PTII and TzQI-TDPP displayed positive VPTE and negative VPTE, respectively, ensuring hole conduction for PTII and electron conduction for TzQI-TDPP. The presence of pchannel and n-channel materials enables efficient TE modules to be built. In addition, fast response for VPTE during the on-off light cycles was achieved. These findings demonstrate that the ultralow-energy-gap polymers, p-channel PTII and n-channel dominant ambipolar TzQI-TDPP, are promising materials applicable for devices utilizing NIR-II light in fields such as energy harvesting, sensing, imaging, photodetector, and PT therapy. To further obtain the underlying properties, studies on the doping state of PTII and TzQI-TDPP are under investigation.

ASSOCIATED CONTENT Supporting Information The synthesis procedure, elemental analyses, GPC, TGA and DSC profiles and GIWAXS and AFM data of the polymers, information on the instruments and measurements, and the detailed procedures for fabricating the FET and PTE devices are available free of charge via the internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author * [email protected] * [email protected]

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This study was partly supported by the fund for the Development of Human Resources in Science and Technology of the Japan Science and Technology Agency, JST (for H. M.), a Grant-in-Aid for Scientific Research (C) (No. 26410087) from the Ministry of Education, Culture, Sports, Science and Technology (for M.A.), and a Grant-in-Aid for JSPS Research Fellows (No. 17J07292) by JSPS KAKENHI (for T. H.). The authors are thankful to Mr. Hiroshi Iida, at the Center for Advanced Materials Analysis, Tokyo Institute of Technology, for assistance with the GIWAXS measurements. The synchrotron radiation experiments were performed at BL45XU in SPring-8 with the approval of JASRI (Proposal No. 2015B1690). The numerical calculations were carried out on the

TSUBAME3.0 supercomputer at the Tokyo Institute of Technology, Tokyo, Japan, and on the supercomputer at the Research Center for Computational Science, Okazaki, Japan. This computational work was supported by a Grant-in-Aid for Young Scientists (B) (JSPS KAKENHI Grant Number JP17K17720 to Y. H.), a Grant-in-Aid for Specially promoted Research (JSPS KAKENHI Grant Number JP17H06092 to S. K.), and a JST CREST (Grant Number JPMJCR1522 to S. K.). The authors are thankful to Mr. Mahiro Iwasaki, at Tokyo Institute of Technology, for assistance with the theoretical calculations.

REFERENCES (1) Arias, A. C.; MacKenzie, J. D.; McCulloch, I.; Rivnay, J.; Salleo, A. Materials and Applications for Large Area Electronics: SolutionBased Approaches. Chem. Rev., 2010, 110, 3−24. (2) Gelinck, G.; Heremans, P.; Nomoto, K.; Anthopoulos, T. D. Organic Transistors in Optical Displays and Microelectronic Applications. Adv. Mater., 2010, 22, 3778−3798. (3) Sirringhaus, H. 25th Anniversary Article: Organic Field-Effect Transistors: The Path Beyond Amorphous Silicon. Adv. Mater., 2014, 26, 1319−1335. (4) Huang, W.; Besar, K.; LeCover, R.; Rule, A. M.; Breysse, P. N.; Katz, H. E. Highly Sensitive NH3 Detection Based on Organic FieldEffect Transistors with Tris(pentafluorophenyl)borane as Receptor. J. Am. Chem. Soc., 2012, 134, 14650−14653. (5) Reineke, S.; Thomschke, M.; Lüssem, B.; Leo, K. White Organic Light-Emitting Diodes: Status and Perspective. Rev. Mod. Phys., 2013, 85, 1245−1293. (6) Gaspar, D.; Polikarpov, E. OLED Fundamentals: Materials, Devices, and Processing of Organic Light-Emitting Diodes, 1st ed.; CRC Press: Boca Raton, FL, 2015. (7) Tee, B. C.-K.; Chortos, A.; Berndt, A.; Nguyen, A. K.; Tom, A.; McGuire, A.; Lin, Z. C.; Tien, K.; Bae, W.-G.; Wang, H.; Mei, P.; Chou, H.-H.; Cui, B.; Deisseroth, K.; Ng, T. N.; Bao, Z. A SkinInspired Organic Digital Mechanoreceptor. Science, 2015, 350, 313− 316. (8) Facchetti, A. Polymer Donor−Polymer Acceptor (all-polymer) Solar Cells. Mater. Today, 2013, 16, 123−132. (9) Lin, Y.; Zhan, X. Nonfullerene Acceptors for Organic Photovoltaics: an Emerging Horizon. Mater. Horiz., 2014, 1, 470−488. (10) Bubnova, O.; Crispin, X. Towards Polymer-Based Organic Thermoelectric Generators. Energy Environ. Sci., 2012, 5, 9345− 9362. (11) Russ, B.; Robb, M. J.; Brunetti, F. G.; Miller, P. L.; Perry, E. E.; Patel, S. N.; Ho, V.; Chang, W. B.; Urban, J. J.; Chabinyc, M. L.; Hawker, C. J.; Segalman, R. A. Power Factor Enhancement in Solution-Processed Organic N-Type Thermoelectrics Through Mo- lecular Design. Adv. Mater., 2014, 26, 3473−3477. (12) Schlitz, R. A.; Brunetti, F. G.; Glaudell, A. M.; Miller, P. L.; Brady, M. A.; Takacs, C. J.; Hawker, C. J.; Chabinyc, M. L. Solubility-Limited Extrinsic N-Type Doping of a High Electron Mobility Polymer for Thermoelectric Applications. Adv. Mater., 2014, 26, 2825−2830. (13) Russ, B.; Robb, M. J.; Popere, B. C.; Perry, E. E.; Mai, C.-K.; Fronk, S. L.; Patel, S. N.; Mates, T. E.; Bazan, G. C.; Urban, J. J.; Chabinyc, M. L.; Hawker, C. J.; Segalman, R. A. Tethered Tertiary Amines as Solid-State N-Type Dopants for Solution-Processable Organic Semiconductors. Chem. Sci., 2016, 7, 1914−1919. (10) (14) Antaris, A. L.; Chen, H.; Cheng, K.; Sun, Y.; Hong, G.; Qu, C.; Diao, S.; Deng, Z.; Hu, X.; Zhang, B.; Zhang, X.; Yaghi, O. K.; Alamparambil, Z. R.; Hong, X.; Cheng, Z.; Dai, H. A Small-Molecule Dye for NIR-II Imaging. Nat. Mater., 2016, 15, 235−242. (15) Yang, J. P.; Shen, D. K.; Zhou, L.; Li, W.; Li, X. M.; Yao, C.; Wang, R.; El-Toni, A. M.; Zhang, F.; Zhao, D. Y. Spatially Confined Fabrication of Core-Shell Gold Nanocages@Mesoporous Silica for Near-Infrared Controlled Photothermal Drug Release. Chem. Mater., 2013, 25, 3030− 3037. (16) Cheng, L.; Wang, C.; Feng, L.; Yang, K.; Liu, Z. Functional Nanomaterials for Phototherapies of Cancer. Chem. Rev., 2014, 114, 10869−10939.



(17) Qian, Q.; Huang, X.; Zhang, X.; Xie, Z.; Wang, Y. One-step Preparation of Macroporous Polymer Particles with Multiple Interconnected Chambers: A Candidate for Trapping Biomacromolecules. Angew. Chem., Int. Ed., 2013, 52, 10625−10629. (18) Zhang, Y.; Teh, C.; Li, M.; Ang, C. Y.; Tan, S. Y.; Qu, Q.; Korzh, V.; Zhao, Y. Acid-Responsive Polymeric Doxorubicin Prodrug Nano particles Encapsulating a Near-Infrared Dye for Combined Photo- thermal-Chemotherapy. Chem. Mater., 2016, 28, 7039−7050. (19) Geng, J.; Sun, C.; Liu, J.; Liao, L.-D.; Yuan, Y.; Thakor, N.; Wang, J.; Liu, B. Biocompatible Conjugated Polymer Nanoparticles for Efficient Photothermal Tumor Therapy. Small, 2015, 11, 1603−1610. (20) Lyu, Y.;Xie,C.; Chechetka, S. A.;Miyako, E.; Pu, K. Semiconducting Polymer Nanobioconjugates for Targeted Photo-Thermal Activation of Neurons. J. Am. Chem. Soc., 2016, 138, 9049−9052. (21) Lyu, Y.; Fang, Y.; Miao, Q.; Zhen, X.; Ding, D.; Pu, K. Intraparticle Molecular Orbital Engineering of Semiconducting Polymer Nano- particles as Amplified Theranostics for in Vivo Photoacoustic Imaging and Photothermal Therapy. ACS Nano, 2016, 10, 4472−4481. (22) Miao, Q.; Lyu, Y.; Ding, D.; Pu, K. Semiconducting Oligomer Nanoparticles as an Activatable Photoacoustic Probe with Amplified Brightness for In Vivo Imaging of pH. Adv. Mater., 2016, 28, 3662−3668. (23) Bubnova, O.; Khan, Z. U.; Malti, A.; Braun, S.; Fahlman, M.; Berggren, M.; Crispin, X. Optimization of the Thermoelectric Figure of Merit in the Conducting Polymer Poly(3,4ethylenedioxythiophene) Nat. Mater. 2011, 10, 429-433. (24) Zhang, Q.; Sun, Y.; Zhu, D. What To Expect from Conducting Polymers on the Playground of Thermoelectricity: Lessons Learned from Four High-Mobility Polymeric Semiconductors. Macromolecules, 2014, 609-615. (25) Basko, D. A Photothermoelectric Effect in Graphene. Science, 2011, 334, 610-611. (26) Gabor, N. M.; Song, J. C.; Ma, Q.; Nair, N. L.; Taychatanapat, T.; Watanabe, K.; Taniguchi, T.; Levitov, L. S.; Jarollo-Herrero, P. Hot Carrier-Assisted Intrinsic Photoresponse in Graphene. Science, 2011, 334, 648-652. (27) Song, J. C.; Rudner, M. S.; Marcus, C. M.; Levitov, L. S. Hot Carrier Transport And Photocurrent Response in Graphene. Nano Lett. 2011, 11, 4688-4692. (28) Yan, K.; Wu, D.; Peng, H.; Jin, L.; Fu, Q.; Bao, X.; Lin, Z. Modulation-Doped Growth of Mosaic Graphene with Single-Crystalline pn junctions for Efficient Photocurrent Generation. Nat. Commun. 2012, 3, 1280-1286. (29) Liu, C. -H.; Chang, Y. -C.; Norris, T. B.; Zhong, Z. Graphene Photodetectors with Ultra-Broadband And High Responsivity at Room Temperature. Nat. Nanotechnol. 2014, 9, 273-278. (30) Sun, D.; Aivazian, G.; Jones, A. M.; Ross, J. S.; Yao, W.; Cobden, D.; Xu, X. Ultrafast Hot-Charrier-Dominated Photocurrent in Graphene. Nat. Nanotechnol. 2012, 7, 273-278. (31) Wu, C. -C.; Jariwala, D.; Sangwan, V. K.; Marks, T. J.; Hersam, M. C.; Lauhon, L. J. Elucidating the Photoresponse of Ultrathin MoS2 Field Effect Transistors by Scanning Photocurrent Microscopy. J. Phys. Chem. Lett. 2013, 4, 2508-2513. (32) Wu, D.; Yan, K.; Zhou, Y.; Wang, H.; Lin L.; Peng, H.; Liu, Z. Plasmon-Enhanced Photothermoelectric Conversion in Chemical Vapor Deposited Graphene p-n Junctions. J. Am. Chem. Soc. 2013, 135, 10926-10929. (33) Miyako, E.; Hosokawa, C.; Kojima, M.; Yudasaka, M.; Funahashi, R.; Oishi, I.; Hagihara, Y.; Shichiri, M.; Takashima, M.; Nishio, K.; Yoshida, Y. A Photo-Thermal-Electrical Converter Based On Carbon Nanotubes for Bioelectronic Applications. Angew. Chem. Int. Ed., 2011, 50, 12266-12270. (34) Cao, Y.; Dou, J. -H.; Zhao, N. -J.; Zhang, S.; Zhang, S.; Zheng, Y. -Q.; Zhang, J. -P.; Wang, J. -Y.; Pei, J.; Wang, Y. Highly Efficient NIR-II Photothermal Conversion Based on an Organic Conjugated Polymer. Chem. Mater. 2017, 29, 718-725. (35) Huang, D.; Zoo, Y.; Jiao, F.; Zhang, F.; Zang, Y.; Di, C.; Xu, W.; Zhu, D. Inter-located Photothermoelectric Effect of Organic Thermoelectric Materials in Enabling NIR Detection. ACS, Appl. Mater. Interface. 2015, 7, 8968-8973.

Page 8 of 10

(36) Kim, B.; Shin, H.; Park, T.; Park, T.; Lim. H.; Kim, E. NIRSensitive Poly(3,4-ethylenedioxyselenophene) Derivatives for Transparent Photo-Thermo-Electric Converters. Adv. Mater. 2013, 25, 5483–5489 (37) Wang, C.; Dong, H.; Hu, W.; Liu, Y.; Zhu, D. Semiconducting π-Conjugated Systems in Field-Effect Transistors: A Material Odyssey of Organic Electronics. Chem. Rev., 2012, 112, 2208−2267. (38) Mei, J.; Diao, Y.; Appleton, A. L.; Fang, L.; Bao, Z. Integrated Materials Design of Organic Semiconductors for Field-Effect Transistors. J. Am. Chem. Soc., 2013, 135, 6724−6746. (39) Tsao, H. N.; Cho, D. M.; Park, I.; Hansen, M. R.; Mavrinskiy, A.; Yoon, D. Y.; Graf, R.; Pisula, W.; Spiess, H. W.; Müllen, K. Ultrahigh Mobility in Polymer Field-Effect Transistors by Design. J. Am. Chem. Soc. 2011, 133, 2605−2612. (40) Kim, G.; Kang, S.-J.; Dutta, G. K.; Han, Y.-K.; Shin, T. J.; Noh, Y.-Y.; Yang, C. A Thienoisoindigo-Naphthalene Polymer with Ultrahigh Mobility of 14.4 cm2/V·s That Substantially Exceeds Benchmark Values for Amorphous Silicon Semiconductors. J. Am. Chem. Soc., 2014, 136, 9477−9483. (41) Tseng, T.-R.; Phan, H.; Luo, C.; Wang, M.; Perez, L. A.; Patel, S. N.; Ying, L.; Kramer, E. J.; Nguyen, T.-Q.; Bazan, G. C.; Heeger, A. J. High‐Mobility Field‐Effect Transistors Fabricated with Macroscopic Aligned Semiconducting Polymers. Adv. Mater., 2014, 26, 2993−2998. (42) Yi,Z.; Wang,S.; Liu, Y. Design of High-Mobility Diketopyrrolopyrrole-Based π-Conjugated Copolymers for Organic ThinFilm Transistors. Adv. Mater., 2015, 27, 3589−3606. (43) Yamashita, Y.; Hinkel, F.; Marszalek, T.; Zajaczkowski, W.; Pisula, W.; Baumgarten, M.; Matsui, H.; Müllen, K.; Takeya, J. Mobility Exceeding 10 cm2/(V·s) in Donor−Acceptor Polymer Transistors with Band-like Charge Transport. Chem. Mater., 2016, 28, 420−424. (44) Zhao, X.; Zhan, X. Electron Transporting Semiconducting Polymers in Organic Electronics. Chem. Soc. Rev., 2011, 40, 3728−3743. (45) Li, H.; Kim, F. S.; Ren, G.; Jenekhe, S. A. High-Mobility n‑ Type Conjugated Polymers Based on Electron-Deficient Tetraazabenzodifluoranthene Diimide for Organic Electronics J. Am. Chem. Soc. 2013, 135, 14920−14923. (46) Li, H.; Earmme, T.; Ren, G.; Saeki, A.; Yoshikawa, S.; Murari, N. M.; Subramaniyan, S.; Crane, M. J.; Seki, S.; Jenekhe, S. A. Beyond Fullerenes: Design of Nonfullerene Acceptors for Efficient Organic Photovoltaics. J. Am. Chem. Soc., 2014, 136, 14589−14597. (47) Jung, B. J.; Tremblay, N. J.; Yeh, M.-L.; Katz, H. E. Molecular Design and Synthetic Approaches to Electron-Transporting Organic Transistor Semiconductors. Chem. Mater., 2011, 23, 568−582. (48) Sun, B.; Hong, W.; Yan, Z.; Aziz, H.; Li, Y. Record High Electron Mobility of 6.3 cm2 V−1 s−1 Achieved for Polymer Semiconductors Using a New Building Block Adv. Mater., 2014, 26, 2636−2642. (49) Kang, B.; Kim, R.; Lee, S. B.; Kwon, S.-K.; Kim, Y.-H.; Cho, K. Side-Chain-Induced Rigid Backbone Organization of Polymer Semiconductors through Semifluoroalkyl Side Chains. J. Am. Chem. Soc., 2016, 138, 3679−3686. (50) Zhu, C.; Zhao, Z.; Chen, H.; Zheng, L.; Li, X.; Chen, J.; Sun, Y.; Liu, F.; Guo, Y.; Liu, Y. Regioregular Bis-Pyridal[2,1,3]thiadiazoleBased Semiconducting Polymer for High-Performance Ambipolar Transistors. J. Am. Chem. Soc., 2017, 139, 17735−17738. (51) Osaka, I.; Takimiya, K. Naphthobischalcogenadiazole Conjugated Polymers: Emerging Materials for Organic Electronics. Adv. Mater., 2017, 29, 1605218. (52) Chen, H.; Guo, Y.; Yu, G.; Zhao, Y.; Zhang, J.; Gao, D.; Liu, H.; Liu, Y. Highly π-Extended Copolymers with Diketopyrrolopyrrole Moieties for High-Performance Field-Effect Transistors. Adv. Mater., 2012, 24, 4618−4622. (53) Lee, B. H.; Bazan, G. C.; Heeger, A. J. Doping-Induced Carrier Density Modulation in Polymer Field-Effect Transistors. Adv. Mater., 2016, 28, 57−62. (54) Li, W.; Guo, Y.; Shi, J.; Yu, H.; Meng, H. Solution-Processable Neutral Green Electrochromic Polymer Containing Thieno[3,2‑b]thiophene Derivative as Unconventional Donor Units. Macromolecules, 2016, 49, 7211-7219.


Page 9 of 10 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


(55) Li, H.; DeCoster, M. W.; Ireland, R. M.; Song, J.; Hopkins, P. E.; Katz, H. E. Modification of the Poly(bisdodecylquaterthiophene) Structure for High and Predominantly Nonionic Conductivity with Matched Dopants. J. Am. Chem. Soc., 2017, 139, 11149-11157. (56) Xu, L.; Cheng, L.; Wang, C.; Peng, R.; Liu, Z. Conjugated Polymers for Photothermal Therapy of Cancer. Polym. Chem., 2014, 5, 1573−1580. (57) Dou, L.; Liu, Y.; Hong, Z.; Li, G.; Yang, Y. Low-Bandgap NearIR Conjugated Polymers/Molecules for Organic Electronics. Chem. Rev., 2015, 115, 12633−12665. (58) Qian, G.; Wang, Z. Y. Near-Infrared Organic Compounds and Emerging Applications. Chem. - Asian J., 2010, 5, 1006−1029. (59) Liu, F.; Espejo, G. L.; Qiu, S.; Oliva, M. M.; Pina, J.; Seixas de Melo, J. S.; Casado, J.; Zhu, X. Multifaceted Regioregular Oligo(thieno 3,4-b thiophene)s Enabled by Tunable Quinoidization and Reduced Energy Band Gap. J. Am. Chem. Soc., 2015, 137, 10357−10366. (60) Deng, Y.; Sun, B.; He, Y.; Quinn, J.; Guo, C.; Li, Y. ThiopheneS,S-dioxidized Indophenine: A Quinoid-Type Building Block with High Electron Affinity for Constructing n-Type Polymer Semiconductors with Narrow Band Gaps. Angew. Chem., Int. Ed., 2016, 55, 3459−3462. (61) Zhang, C.; Zang, Y.; Gann, E.; McNeill, C. R.; Zhu, X.; Di, C.a.; Zhu, D. Two-Dimensional π-Expanded Quinoidal Terthiophenes Terminated with Dicyanomethylenes as n-Type Semiconductors for High-Performance Organic Thin-Film Transistors. J. Am. Chem. Soc., 2014, 136, 16176−16184. (62) Steckler, T. T.; Henriksson, P.; Mollinger, S.; Sallo, L. A.; Andersson, M. R. Very Low Band Gap Thiadiazoloquinoxaline Donor− Acceptor Polymers as Multi-tool Conjugated Polymers. J. Am. Chem. Soc., 2014, 136, 1190-1193. (63) An, C.; LI, M.; Marzalek, T.; Li, D.; Berger, R.; Pisula, W.; Baumgarten, M. Thiadizoloquinoxaline-Based Low-Bandgap Conjugated Polymers as Ambipolar Semiconductors for Organic Field Effect Transistors. Chem. Mater., 2014, 26, 5923-5929. (64) Steckler, T. T.; Zhang, X.; Hwang, J.; Honeyager, R.; Ohira, S.; Zhang, X. -H.; Grant, A.; Ellinger, S.; Odom, S. A.; Sweat, D.; Tanner, D. B.; Rinzler, A. G.; Barlow, S.; Brédas, B.; Kippelen, B.; Marder, S. R.; Reynold, J. R. A Spray-Processable, Low Bandgap, and Ambipolar Donor-Acceptor Conjugated Polymer J. Am. Chem. Soc., 2009, 131, 2824-2826. (65) Foster, M. E.; Zhang, B. A.; Murtagh, D.; Liu, Y.; Sfeir, M. Y.; Wong, M. B. M.; Azoulay, J. D. Solution ‐ Processable Donor – Acceptor Polymers with Modular Electronic Properties and Very Narrow Bandgaps. Macromol. Rapid. Commun. 2014, 35, 1516-1521. (66) Dou, L.; Liu, Y.; Hong, Z.; Li, G.; Yang, Y. Low-Bandgap NearIR Conjugated Polymers/Molecules for Organic Electronics. Chem. Rev., 2015, 115, 12633-12665. (67) Kertesz, M.; Choi, C. H.; Yang, S. Conjugated Polymers and Aromaticity. Chem. Rev., 2005, 105, 3448-3481. (68) Hasegawa, T.; Ashizawa, M.; Hiyoshi, J.; Kawauchi, S.; Mei, J.; Bao, Z.; Matsumoto, H. An Ultra-narrow Bandgap Derived from Thienoisoindigo Polymers: Structural Influence on Reducing Bandgap and Self-Organization. Polym. Chem., 2016, 7, 1181-1190. (69) Hasegawa, T.; Ashizawa, M.; Aoyagi, K.; Masunaga, H.; Hikima, T.; Matsumoto, H. Thiadiazole-fused Quinoxalineimide as an Electron-Deficient Building Block for N-Type Organic Semiconductors. Org. Lett., 2017, 3275-3278. (70) Nielsen, C. B.; Turbiez, M.; McCulloch, I. Recent Advances in the Development of Semiconducting DPP-Containing Polymers for Transistor Applications. Adv. Mater., 2013, 25, 1859−1880. (71) Yi, Z.;Wang, S.;Liu,Y.Design of High-Mobility Diketopyrrolopyrrole-Based π-Conjugated Copolymers for Organic ThinFilm Transistors. Adv. Mater., 2015, 27, 3589−3606. (72) Yao, J.; Yu, C.; Liu, Z.; Luo, H.; Yang, Y.; Zhang, G.; Zhang, D. Significant Improvement of Semiconducting Performance of the Diketopyrrolopyrrole−Quaterthiophene Conjugated Polymer through Side-Chain Engineering via Hydrogen-Bonding. J. Am. Chem. Soc., 2016, 138, 173−185.

(73) Bronstein, H.; Chen, Z.; Ashraf, R. S.; Zhang, W.; Du, J.; Durrant, J. R.; Tuladhar, P. S.; Song, K.; Watkins, S. E.; Geerts, Y.; Wienk, M. M.; Janssen, R. A.; Anthopoulos, T.; Sirringhaus, H.; Heeney, M.; McCulloch, I. Thieno[3,2-b]thiophene-Diketopyrrolopyrrole-Containing Polymers for High-Performance Organic FieldEffect Transistors and Organic Photovoltaic Devices. J. Am. Chem. Soc., 2011, 133, 3272−3275. (74) Han, A. R.; Dutta, G. K.; Lee, J.; Lee, H. R.; Lee, S. M.; Ahn, H.; Shin, T. J.; Oh, J. H.; Yang, C. ε-Branched Flexible Side Chain Substituted Diketopyrrolopyrrole-Containing Polymers Designed for High Hole and Electron Mobilities. Adv. Funct. Mater., 2015, 25, 247− 254. (75) Ootsuki, K.; Hayashi, Y.; Kawauchi, S. Development and Assessment of Quinoidal Index for Designing of Low Band Gap Polymers. J. Comput. Chem. Jpn., 2017, 16, 5, 123-125. (76) Chai, J.-D.; Head-Gordon, M. Long-Range Corrected Hybrid Density Functionals with Damped Atom-Atom Dispersion Corrections. Phys. Chem. Chem. Phys., 2008, 10, 6615–6620. (77) Gaussian 09, Revision D.01, Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Moroku-ma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian, Inc., Wallingford CT, 2009. (78) Becke, A. D. Density-Functional Thermochemistry. III. The Role of Exact Exchange. J. Chem. Phys., 1993, 98, 5648. (79) Pommerehne, J.; Vestweber, W.; Guss, W.; Mark, R. F.; Bӓssles, H.; Porsch, M.; Daub, J. Efficient Two Layer Leds on a Polymer Blend Basis. Adv. Mater. 1995, 7, 551-554. (80) Takimiya, K.; Osaka, I.; Nakano, M. π‑Building Blocks for Organic Electronics: Revaluation of “Inductive”and “Resonance” Effects of π‑Electron Deficient Units. Chem. Mater., 2014, 26, 587593. (81) Viezbicke, B. D.; Patel, S.; Davis, B. E.; Birnie lll, D. P. Evaluation of the Tauc Method for Optical Absorption Edge Determination: ZnO Thin Films as a Model System. Phys. Status. Solidi. B, 2015, 252, 1700-1710. (82) Bhatta, R. S.; Tsige, M. Chain Length and Torsional Dependence of Exciton Binding Energies in P3HT and PTB7 Conjugated Polymers: A First-Principles Study. Polymer, 2014, 55, 2667-2672. (83) Li, Y. Molecular Design of Photovoltaic Materials for Polymer Solar Cells: Toward Suitable Electronic Energy Levels and Broad Absorption. Acc. Chem. Res. 2012, 45, 723-733 (84) Pietro, R. D.; Erdmann, T.; Carpenter, J. H.; Wang, N.; Shivhara, R. R.; Formanek, P.; Heintze, C.; Voit, B.; Neher, D.; Ade, H.; Kiriy, A. Synthesis of High-Crystallinity DPP Polymers with Balanced Electron and Hole Mobility. Chem. Mater., 2017, 29, 10220-10232. (85) Curtis, M. D.; Cao, J.; Kampf, J. W. Solid-State Packing of Conjugated Oligomers: From π-Stacks to the Herringbone Structure. J. Am. Chem. Soc., 2004, 126, 4318-4328. (86) Kim, Y.; Hwang, H.; Kim, N.-K.; Hwang, K.; Park, J.-J.; Shin, G.-I.; Kim, D.-Y. π-Conjugated Polymers Incorporating a Novel Planar Quinoid Building Block with Extended Delocalization and High Charge Carrier Mobility. Adv. Mater., 2018, 30, 1706557. (87) Mai, C. –K.; Schlitz, R. A.; Su, G. M.; Spitzer, D.; Wang, X.; Fronk, S. L.; Cahill, D. G.; Chabinyc, M. L.; Bazan, G. C. Side-Chain Effects on Conductivity, Morphology, and Thermoelectric Properties of Self-Doped Narrow-Band-Gap Conjugated Polyelectrolytes. J. Am. Chem. Soc. 2014, 136, 13478-13481.



Insert Table of Contents artwork here

Ultralong near-infrared wavelengths absorbing polymers λmaxfilm = 1369 nm

λmaxfilm = 1697 nm

Egopt = 0.66 eV

Egopt = 0.60 eV

PTII(p-type)

TzQI-TDPP(n-type)

NIR-II light (1700 nm) PTII: positive VPTE TzQI-TDPP: negative VPTE V

NIR-II-photo-thermo-electric conversion


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p- and n-Channel Photothermoelectric Conversion based on Ultralong

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