Molecule Organic Solar Cells Based on Porphyrin Donors

Subscriber access provided by - Access paid by the | UCSB Libraries

Article

Near Infrared Harvesting Fullerene-Free All-SmallMolecule Organic Solar Cells Based on Porphyrin Donors Wisnu Tantyo Hadmojo, Dajeong Yim, Septy Sinaga, Wooseop Lee, Du Yeol Ryu, Woo-Dong Jang, In Hwan Jung, and Sung-Yeon Jang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b00010 • Publication Date (Web): 01 Mar 2018 Downloaded from http://pubs.acs.org on March 1, 2018

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

ACS Sustainable Chemistry & Engineering 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 26 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 Sustainable Chemistry & Engineering

Near Infrared Harvesting Fullerene-Free All-SmallMolecule Organic Solar Cells Based on Porphyrin Donors

Wisnu Tantyo Hadmojo, †,§ Dajeong Yim, ‡,§ Septy Sinaga, † Wooseop Lee,∥ Du Yeol Ryu,∥WooDong Jang,* ‡ In Hwan Jung,*† Sung-Yeon Jang*†

†

Department of Chemistry, Kookmin University, 77 Jeongneung-ro, Seongbuk-gu, Seoul 02707,

Republic of Korea. ‡

Department of Chemistry, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul, Republic of

Korea. ∥

Department of Chemical and Biomolecular Engineering, Yonsei University, 50 Yonsei-ro,

Seodaemun-gu, 03722 Seoul, Republic of Korea

1 ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 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

ABSTRACT: Fullerene-free all-small-molecule organic photovoltaic cells (SM-OPVs) have

attracted considerable attention because of well-defined molecular structures with low batch-tobatch variation. Porphyrin derivatives are recently emerged as one of promising conjugated building blocks for the small-molecule (SM) donors. Herein, we first report fullerene-free SMOPVs employing porphyrin-based donors. Three zinc porphyrin (PZn)-based SM donors, which have strong bimodal absorption in visible region and near infrared region, are synthesized. Constructing bulk-heterojunction (BHJ) active layers using the PZn donors and a SM acceptor, IDIC, which have complementary absorption, achieved panchromatic photon-to-currentconversion from 400 to 900 nm. The manipulation of side chains in the PZn donors considerably influenced the molecular ordering and nanomorphology of the BHJ active layers. The PZn based fullerene-free SM-OPV devices with a promising power conversion efficiency of 6.13% was achieved, which also offers a crucial guidance for developing fullerene-free OPVs using porphyrin derivatives.

Keywords: Organic solar cell, Porphyrin donor, All-small-molecule solar cell, Fullerene free, Panchromatic absoprtion

INTRODUCTION Organic photovoltaics (OPVs) have been considered as a promising low-cost power generator because they can be fabricated by solution process, and applicable to printed and/or portable electronics.1-6 During the last decade, the power conversion efficiency (PCE) of OPVs has continuously improved due to intensive investigation into active materials and device engineering. Early interest was focused on the synthesis of donor polymers with narrow 2 ACS Paragon Plus Environment

Page 2 of 26

Page 3 of 26 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


bandgaps needed to match the energy levels of fullerene acceptors because fullerene derivatives were considered as the best energy acceptors.7-12 Recently, several nonfullerene-based smallmolecule (SM) organic acceptors have emerged. The design of SM organic acceptors having complimentary absorption to donor polymers with appropriate energy levels can synergistically improve the PCE of OPVs through broadband light absorption and energy loss reduction.13-18 Although polymeric donor based OPVs have recently demonstrated the PCE of >12%,13, 19-20 the development of SM donors has become an emerging solution for further improvement of PCE because well-defined molecular structures possibly reduce the morphological complexity in OPV devices.21-25 In the design of SM organic donors, a π-extended conjugated backbone is largely necessary to achieve proper bandgaps and good absorption of the solar flux. However, most of the current SM organic donors possess the limited absorption in near infrared (NIR) region.14, 2628

Thus, the development of SM donors possessing broader absorption range is highly important

for the harvesting of lower energy photons. Porphyrin derivatives have recently emerged as efficient narrow bandgap SM donor materials for OPVs because of their broad optical absorption and excellent charge transport properties.29-32 The OPV devices based on porphyrin donors and fullerenes have demonstrated sufficiently high PCE (>8%).29 However, there has been no report on the devices using porphyrin donors with nonfullerene acceptors because the fulfillment for high-efficiency devices such as complimentary absorption, favorable molecular ordering and nanomorphology was difficult to achieve. Thus, the development of new porphyrin donors that possess constructive properties with nonfullerene acceptors are highly important. The porphyrin derivatives generally have peculiar bimodal absorption characteristics; one is the transition from the ground state (S0) to the second excited state (S2), called as Soret band, and



the other is from the ground state (S0) to the first excited state (S1), called as Q band.33 The extension of π-conjugation length along the porphyrin backbone red-shifts the absorption of Q band to the NIR area, while the Soret band is located in visible regime. Thus, the absorption of porphyrin derivatives can readily cover from visible to NIR regime. However, the strong bathochromic shift of Q band may enhance the apart between absorption maxima of Q and Soret band, resulting in the absorption loss in the wavelengths between the two bands. Thus, the proper selection of acceptor materials exhibiting complimentary absorption to the porphyrin donor materials can realize the panchromatic absorption in the active layer. In our earlier report, we synthesized new zinc porphyrin (PZn) based acceptor which has bimodal absorption in visible and NIR regime. Panchromatic photon-to-current conversion was successfully achieved by choosing an appropriate donor polymer, PTB7-Th34, which can cover the gap between Soret band and NIR Q band absorption.35 In this work, we fabricated fullerene-free all-small-molecule OPV (SM-OPV) devices using NIR absorbing PZn donors and a nonfullerene acceptor, IDIC.5 The NIR absorption of PZn donors was achieved by incorporation of a red dye, diketopyrrolopyrrole (DPP), to extend conjugation. The complimentary absorption and appropriate energy levels between three PZn donors and IDIC successfully achieved panchromatic photon-to-current conversion from 400 to 900 nm. The meso substituents of the PZn donors, p-octoxyphenyl, p-(2-ethyl)hexoxyphenyl, and 5-(2ethyl)hexylthiophenyl groups, considerably influenced the performance of SM-OPV. The alkoxybenezene-substituted PZn donors showed higher PCE than the alkylthiophene-substituted PZn donor. The PZn donors with twisted benzene substituents at meso-position substituents assisted preferential molecular ordering of IDIC in the blend films. To the best of our knowledge,


Page 4 of 26

Page 5 of 26 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


this work is the first time report on the porphyrin based fullerene-free OPVs with a promising PCE of 6.13%.

RESULTS AND DISCUSSION Three PZn derivatives containing various meso substituents were synthesized as SM donors. The synthetic procedures of PZn donors are outlined in Scheme 1 and summarized in Supporting Information (SI) in detail. Briefly, 5,15-disubstituted porphyrin 6 (or 9) was synthesized by acidcatalyzed cross-condensation and successive oxidation reactions of dipyrrolomethane and corresponding substituted aldehydes. The Zn incorporated porphyrin ring 8 (or 11) was obtained via the metalation

using zinc acetate and

the meso-bromination

reactions

using

bromosuccinimide (NBS). Trimethylsilyl acetylene was introduced to the PZn derivatives through the Sonogashira coupling reaction, and this reaction was followed by the removal of the trimethylsilyl group to give the ethynyl-bearing PZn 14 (or 15). The PZn derivative 16 was synthesized according to the literature procedure.36 Finally, PZn donor 1, 2 and 3 were synthesized using the DPP-Br and the ethynyl-bearing PZn, 14, 15 and 16, respectively, by Sonogashira coupling. The molecular structures of the synthesized PZn SMs were identified by 1

H NMR and matrix-assisted laser desorption ionization time-of-flight mass spectrometry

(MALDI-TOF-MS), which were recorded in SI. Figure 1a-b shows the absorption spectra of the PZn donors in solution and film states. All three of them showed strong Soret and Q band absorption at visible (400 – 600 nm) and NIR (700 – 900 nm) regimes, respectively, owing to the extended π-conjugation and strong intramolecular charge transfer (ICT) within the donor molecules. Compared to the PZn donors in a solution state, the Q band absorption of the three in a film state showed strong bathochromic shifts, indicating



the formation of J-type aggregates.37 The full-width-half-maximum (FWHM) of the Q band absorption by the PZn donors in film was ~30 nm higher than those in a solution state, implying that intermolecular interactions among the PZn donors were very strong in a film state. Because DPP units and focal porphyrin are connected via ethyne bridges, all PZn donors possibly have planar backbone structures. Thus, high planarity would have contributed to strong molecular π-π interactions. The absorption spectra of IDIC film is shown in Figure 1b. We chose IDIC as the electron acceptor because its strong absorption in the range of 600 – 700 nm afforded an ideal complementary absorption to the PZn donors with bimodal absorption (Figure 1b). The absorption property of IDIC promised the panchromatic absorption covering all of the wavelengths between 400 and 900 nm when it combines with the three PZn donors. To evaluate the matching of energy levels between the PZn donors and IDIC, the highest occupied molecular orbital (HOMO) energy levels and the lowest unoccupied molecular orbital (LUMO) energy levels of PZn donors were determined using cyclic voltammetry (CV, Figure 1c) and optical bandgap values.38 These results are summarized in Table 1. As shown in Figure 1c, the oxidation potential of PZn donors 1, 2, and 3 were -0.52, -0.53, and -0.58, respectively, which corresponded to HOMO energy levels of −5.22, −5.23, and −5.28, respectively. The HOMO energy levels of PZn donors 1 and 2 were slightly higher than that of PZn donor 3. The electron donating meso-p-alkoxyphenyl groups raised the HOMO energy levels of the PZn donors. The optical bandgaps of PZn donors 1, 2, and 3 were determined as 1.37, 1.37, and 1.41 eV, respectively, by the onset of the absorption spectra of their films. Thus, the LUMO energy levels of the PZn donors 1, 2, and 3 were calculated to be −3.85, −3.86, and −3.87 eV, respectively. The LUMO energy levels of the three are quite similar because it contains identical electron withdrawing DPP moiety. We also measured the energy levels of IDIC using identical methods.


Page 6 of 26

Page 7 of 26 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


The HOMO and LUMO energy levels of IDIC were −5.69 and −4.10 eV, respectively. The energy levels of the PZn donors and IDIC are summarized in Figure 1d. The energy levels of three PZn donors were appropriate to collect holes from IDIC and to transfer electrons to IDIC. We fabricated fullerene-free bulk-heterojunction (BHJ) SM-OPV devices using the PZn donors and IDIC. The current density-voltage (J-V) characteristics and external quantum efficiency (EQE) spectra of the PZn donor:IDIC based SM-OPV devices are shown in Figure 2, and the results are summarized in Table 2. Although the three PZn donors had the same molecular backbone structures except for the meso substituents, the PCEs of the devices exhibited large deviation. The SM-OPV devices fabricated from meso-alkoxyphenyl-substituted donors (PZn donors 1 and 2) showed higher PCEs with improved JSC and FF values than that from an ethylhexylthiophene-substituted donor (PZn donor 3). In addition, linear alkyl chain substituted PZn donor 1 showed the better performance than the branched one (PZn donor 2). Thus, PZn donor 1:IDIC device attained the highest PCE of 6.13%, JSC of 15.46 mA cm-2, and FF of 0.56. As shown in the energy diagram (Figure 1d) and the absorption spectra of the active layers (Figure 2b), the optical and energetic properties of three BHJ active layers are not considerably different, therefore the variation in device performance is probably attributable to the alteration in both (either) charge transport properties and (or) donor/acceptor nanomorphology. The hole and electron mobilities of the BHJ active layers were measured using the steady-state space-charge-limited current (SCLC) method (Figure S4). Hole- and electron-dominant devices were fabricated with the configurations of ITO/PEDOT:PSS/active layer/MoOx/Ag and ITO/ZnO/active layer/ZnO/Al, respectively. The mobility was determined by Mott-Gurney law, in the SCLC trap free regime, by using the slope of J1/2 vs V.39 The hole mobilities of PZn donors 1, 2, and 3 were 1.12 × 10-3, 0.49 × 10-3, and 0.22 × 10-3 cm-2V-1s-1, respectively, and the



corresponding electron mobilities were 1.11 × 10-3, 0.70 × 10-3, and 0.19 × 10-3 cm-2V-1s-1, respectively. The hole and electron mobilities increased in the order of PZn donor 1 > PZn donor 2 > PZn donor 3, which was consistent with the EQE values. Because the same composition of IDIC was used in all BHJ samples, the highest electron mobility in PZn donor 1 based BHJ films is attributable to favorable nanomorphology. Moreover, the PZn donor 1 based BHJ films exhibited most balanced hole/electron mobility ratio (1.01). The highest hole/electron mobility with balanced ratio are responsible for the highest photovoltaic performance in PZn donor 1:IDIC device among the studied devices. The molecular ordering and nanomorphology of the active layers were revealed by twodimensional grazing-incidence X-ray diffraction (2D-GIXD) measurements and patterns shown in Figure 3. The pristine PZn donor films mainly showed long-range orderings. Among the three PZn donors, the highest ordering was observed in PZn donor 3 (Figure 3a and c), which can be explained by the orientation of its thiophene moieties. The meso-phenyl group of porphyrin should have been perpendicularly oriented to the plane of the porphyrin ring due to steric repulsion. However, the thiophene moiety was able to make a planar structure with the focal porphyrin, and thus several short-distance orderings were observable for PZn donor 3. In the case of IDIC, strong molecular ordering was observed due to its planar structure with strong intermolecular π-π interactions, especially the very strong out-of-plane (Qz) peak at 1.51 Å−1 assignable to the intermolecular π–π distance of 4.15 Å. The blend films of PZn donor 1:IDIC and PZn donor 2:IDIC showed a strong out-of-plane (Qz) peak at 1.51 Å−1, whereas PZn donor 3:IDIC showed a very weak Qz peak at 1.50 Å−1 (Figure 3b and d). Therefore, we expect that PZn donor 3 diminished the intermolecular stacking of the IDIC domains in face-on mode. On the other hand, IDIC maintained sizable face-on orientation even in the blend film with meso-


Page 8 of 26

Page 9 of 26 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


alkoxyphenyl-substituted PZn donors 1 and 2. Thus, the maintained face-on orientation of IDIC in the PZn donor 1- and 2-based BHJ films might have facilitated efficient vertical charge transport in OPV devices.40-41 In the region of long-distance ordering, (100) peaks at around 0.3 Å−1 in the PZn donor:IDIC blend films were attributed to the PZn donor domains because the positions of these peak were almost similar with those of the (100) peaks of pristine PZn donor film. Thus, we investigated the azimuthal scan at the (100) peaks11 of the PZn donor:IDIC blend films to reveal the orientation of the PZn donor in them. As shown in Figure 3e-f, PZn donor 1 was oriented largely in face-on mode, but PZn donors 2 and 3 showed a higher population in edge-on mode. As a result, the PZn donor 1:IDIC blend film predominantly had face-on oriented donor domains as well as acceptor domains. Thus, both PZn donor 1 and IDIC could facilitate vertical charge transport in the devices, resulting in the highest JSC and PCE. In the case of PZn donor 2:IDIC, the IDIC domain showed strong face-on orientation whereas PZn donor 2 displayed relatively weak face-on orientation. Because the intermolecular stacking of IDIC and PZn donor 3 could have interfered with each other, the device made with them showed the lowest JSC and PCE. For comparison, we also fabricated fullerene based OPV devices using PC70BM and the PZn donors. Interestingly, the PCEs of the fullerene based devices showed a different trend compared to nonfullerne based devices (Figure S5). The PCE of device using donor 3 showed the highest value (6.26%), while that using donor 2 exhibited the lowest value (2.98%). The PCEs of the fullerene based devices were strongly correlated with the molecular ordering of PZn donors; the PZn donors with higher ordering (Figure 3c) exhibited higher PCEs (3>1>2). This is quite a different result compared to the nonfullerene based devices, in which the high ordering of PZn donors is not always favorable because of the high intermolecular stacking of IDIC. The twisted



benzene substituent in the meso-position of PZn (PZn donor 1) exhibited the preferential molecular ordering with IDIC, resulting in the highest charge collection efficiency and PCE in nonfullerene based OPV devices.

CONCLUSION Near Infrared harvesting PZn based fullerene-free OPVs were developed. Three PZn based SM donors having strong absorption in both the visible (400 – 600 nm) and NIR (700 – 900 nm) region were synthesized. The appropriate absorption characteristics and energy levels of the PZn donors enabled to achieve efficient photon-to-current-conversion from 400 – 900 nm by constructing BHJ active layers with a nonfullerene acceptor, IDIC. Depending on the side chains on the PZn donors, the nanomorphologies of the BHJ layers were effectively modified, and the PZn donor 1:IDIC film achieved the PCE of 6.13% owing to the most face-on-preferred donor and acceptor domains. To the best of our knowledge, this is the first example of a PZn donorbased fullerene-free OPV device. Currently, the molecular behavior and photovoltaic properties of a PZn donor in a blend with a nonfullerene acceptor are unexplored, thus our study can offer a crucial guidance for developing porphyrin-based fullerene-free OPVs.

EXPERIMENTAL Synthesis 1: 14 (237 mg, 0.286 mmol), DPP-Br (380 mg, 0.629 mmol) and Pd(PPh3)2Cl2 (0.01 eq.) were placed in a 100 mL two-neck round-bottomed flask. The flask was degassed under high vacuum and back-filled with N2 three times. TEA (3.00 mL), THF (9.00 mL) and CuI (0.01 eq.) were added to the flask, and the reaction was refluxed overnight. The reaction mixture was extracted


Page 10 of 26

Page 11 of 26 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


with CH2Cl2 and the combined organic layer was evaporated in vacuo. The residue was purified by silica gel column chromatography and recycling SEC with THF. After recrystallization from CH2Cl2/hexanes, 1 was obtained as a black solid (222 mg, 41%): 1H NMR (400 MHz, THF-d8, 25 oC) δ (ppm) = 9.52-9.51 (d, 4 H, J = 4.4 Hz), 9.07-9.06 (d, 2 H, J = 4.0 Hz), 9.03 (m, 2 H), 8.89-8.88 (d, 4 H, J = 4.4 Hz), 8.19-8.17 (d, 4 H, J = 8.0 Hz), 7.85-7.84 (d, 2 H, J = 4.0 Hz), 7.76-7.75 (d, 2 H, J = 4.0 Hz), 7.40-7.38 (d, 4 H, J = 8.0 Hz), 7.32-7.30 (t, 2 H, J = 4.0 Hz), 4.35-4.32 (t, 4 H, J = 6.4 Hz), 4.02-3.94 (m, 8 H), 2.07-2.00 (m, 4 H), 1.97 (m, 4 H), 1.52-1.29 (m, 52 H), 0.99-0.90 (m, 30 H). MALDI-TOF-MS: m/z: calcd. for C112H128N8O6S4Zn: 1872.81 [M] +; found 1876.64. 2: 2 was synthesized from 15 (457 mg, 0.550 mmol), DPP-Br (793 mg, 1.32 mmol), TEA (5.00 mL) and THF (10.0 mL). The procedure was similar to that for 1, and a black solid was obtained (285 mg, 28%): 1H NMR (400 MHz, THF-d8, 25 oC) δ (ppm) = 9.55-9.54 (d, 4 H, J = 4.4 Hz), 9.07-9.06 (d, 2 H, 4.0 Hz), 9.03 (m, 2 H), 8.91-8.89 (d, 4 H, J = 4.4 Hz), 8.19-8.17 (d, 4 H, J = 8.0 Hz), 7.85-7.84 (d, 2 H, J = 4.8 Hz), 7.77 (m, 2 H), 7.41-7.39 (d, 4 H, J = 8.0 Hz), 7.32-7.30 (t, 2 H, 4.8 Hz), 4.26-4.24 (d, 4 H, J = 8.0 Hz), 4.02-4.00 (m, 8 H), 1.98 (m, 6 H), 1.52-1.28 (m, 48 H), 1.16-1.12 (t, 6 H, J = 7.2 Hz), 1.07-1.03 (t, 6 H, J = 7.2 Hz), 0.99-0.90 (m, 24 H). MALDITOF-MS: m/z: calcd. for C112H128N8O6S4Zn: 1872.81 [M] +; found 1875.14. 3: 3 was synthesized from 16 (134 mg, 0.166 mmol), DPP-Br (210 mg, 0.348 mmol), TEA (2.00 mL) and THF (10.0 mL). The procedure was similar to that for 1, and a black solid was obtained (130 mg, 42%): 1H NMR (400 MHz, THF-d8, 25 oC) δ (ppm) = 9.46-9.45 (d, 4 H, J = 4.4 Hz), 9.13-9.12 (d, 6 H, J = 4.4 Hz), 9.02 (s, 2 H), 7.84-7.83 (m, 4 H), 7.68 (s, 2 H), 7.32-7.30 (m, 4 H), 4.05 (m, 8 H), 3.20-3.18 (d, 4 H, J = 8.0 Hz), 1.95-1.93 (m, 6 H), 1.53-1.29 (m, 48 H), 1.17-1.13



(t, 6 H, J = 8.0 Hz), 1.08-1.04 (t, 6 H, J = 8.0 Hz), 0.99-0.91 (m, 24 H). MALDI-TOF-MS: m/z: calcd. for C108H124N8O4S6Zn: 1852.74 [M] +; found 1855.95.

Device Fabrication OPV devices were fabricated with an inverted structure (ITO/ZnO/BHJ/MoOx/Ag). ZnO (30 nm) act as electron transport layer and was prepared following the reported procedure. Zinc acetate dehydrate ([Zn(CH3COO)2·2H2O], Sigma Aldrich, 99.9%, 5 g) and ethanolamine (NH2CH2CH2OH, Sigma Aldrich, 99.5%, 1.35 mL) in 2-methoxyethanol (CH3OCH2CH2OH, Sigma Aldrich, 99.8%, 50 mL) were prepared to make a precursor solution. ZnO was spin-coated at 4000 rpm for 15 s in ambient environment, followed by thermal anneal treatment by gradually increasing the temperature to 200°C. Bulk heterojunction as active layers were achieved by mixing various PZn as electron donor and IDIC (purchased from Sunatech) (1:1.2 w/w) with DIO (TCI) (0.8 v/v %) and pyridine (Sigma Aldrich) (0.5 v/v %) as additives. The active materials were dissolved in chloroform and stirred for 2 hours in ambient environment. The donor concentration was 7.5 mg/ml. The thickness of active layer was 100 nm. MoOx (8 nm) as hole transport layer and Ag (100 nm) as electrode were deposited using thermal evaporation at low pressure (10-6 bar). The active area was measured to be 0.707 cm2.

Device Analysis The J-V characteristics of devices were measured by using a Keithley 2401 and a solar simulator with a 150 W Xenon lamp (Newport) as light source. Measurements were done by adjusting the light intensity to 1.5G and calibrated by using a monosilicon standard purchased from the National Renewable Energy Laboratory. The external quantum efficiency (EQE) spectra were


Page 12 of 26

Page 13 of 26 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


obtained by passing the 400W Xenon lamp as light source to a monochromator using the appropriate wavelength filter. The EQE values were collected using frequency of 5 Hz and measured from 300 to 950 nm. Space charge limited current (SCLC) was used to measure the charge mobilities of active layers. Hole mobility was measured by using hole only device (ITO/PEDOT:PSS/Active layer/MoOx/Ag). Electron mobility was measured by using electron only device (ITO/ZnO/Active layer/ZnO/Al). The mobility was calculated by using Mott-Gurney law in SCLC trap-free regime.

Two Dimensional Grazing-Incidence X-Ray Diffraction (2D-GIXD) 2D-GIXD measurements were performed at the 9A beamline at Pohang Light Source Accelerator, Korea. The samples were prepared on top of ZnO-modified Si substrates under the same condition that used for fabrication of OPV devices. The wavelength of X-ray source was 1.12 A, the incident angle was 0.12° and the irradiation times was 15 s. The 2D-GIXD images from the films were analyzed based on the relationship between the scattering vector (q) and the d spacing (q = 2π/d).

ASSOCIATED CONTENT Supporting Information The detailed synthetic procedures of the materials, 1H NMR, MALDI-TOF MS and SCLC mobility of hole-only and electron-only devices are provided in detail. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION 13 ACS Paragon Plus Environment


Corresponding author * W.-D. Jang ([email protected]), *I. H. Jung ([email protected]), * S.-Y. Jang ([email protected]) Author Contributions §

The authors are contributed equally.

ACKNOWLEDGMENTS The authors gratefully acknowledge support from the New and Renewable Energy Core Technology Program of the Korea Institute of Energy Technology Evaluation and Planning (KETEP), granted financial resources from the Ministry of Trade, Industry and Energy, Republic of Korea (No. 20163030013960), the National Research Foundation (NRF) Grant funded by the Korean Government (MSIP, No.2016R1A5A1012966), and the Global Scholarship Program for Foreign Graduate Students at Kookmin University in Korea.

REFERENCES 1. Scharber, M. C.; Sariciftci, N. S., Efficiency of bulk-heterojunction organic solar cells. Prog. Polym. Sci. 2013, 38 (12), 1929-1940. 2. Søndergaard, R.; Hösel, M.; Angmo, D.; Larsen-Olsen, T. T.; Krebs, F. C., Roll-to-roll fabrication of polymer solar cells. Mater. Today 2012, 15 (1), 36-49. 3. Lipomi, D. J.; Tee, B. C. K.; Vosgueritchian, M.; Bao, Z., Stretchable Organic Solar Cells. Adv. Mater. 2011, 23 (15), 1771-1775.


Page 14 of 26

Page 15 of 26 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


4. Kim, T.; Kim, J.-H.; Kang, T. E.; Lee, C.; Kang, H.; Shin, M.; Wang, C.; Ma, B.; Jeong, U.; Kim, T.-S.; Kim, B. J., Flexible, highly efficient all-polymer solar cells. Nat. Commun. 2015, 6, 8547. 5. Lin, Y.; Zhao, F.; Wu, Y.; Chen, K.; Xia, Y.; Li, G.; Prasad, S. K. K.; Zhu, J.; Huo, L.; Bin, H.; Zhang, Z.-G.; Guo, X.; Zhang, M.; Sun, Y.; Gao, F.; Wei, Z.; Ma, W.; Wang, C.; Hodgkiss, J.; Bo, Z.; Inganäs, O.; Li, Y.; Zhan, X., Mapping Polymer Donors toward High-Efficiency Fullerene Free Organic Solar Cells. Adv. Mater. 2017, 29 (3), 1604155. 6. Ha, Y.-H.; Lee, J. E.; Hwang, M.-C.; Kim, Y. J.; Lee, J.-H.; Park, C. E.; Kim, Y.-H., A New BDT-Based Conjugated Polymer with Donor-Donor Composition for Bulk Heterojunction Solar Cells. Macromol. Res. 2016, 24 (5), 457-462 7. Zhao, J.; Li, Y.; Yang, G.; Jiang, K.; Lin, H.; Ade, H.; Ma, W.; Yan, H., Efficient organic solar cells processed from hydrocarbon solvents. Nat. Energy 2016, 1, 15027. 8. Huo, L.; Liu, T.; Sun, X.; Cai, Y.; Heeger, A. J.; Sun, Y., Single-Junction Organic Solar Cells Based on a Novel Wide-Bandgap Polymer with Efficiency of 9.7%. Adv. Mater. 2015, 27 (18), 2938-2944. 9. He, Z.; Xiao, B.; Liu, F.; Wu, H.; Yang, Y.; Xiao, S.; Wang, C.; Russell, T. P.; Cao, Y., Single-junction polymer solar cells with high efficiency and photovoltage. Nat. Photonics 2015, 9, 174. 10. Liu, Y.; Zhao, J.; Li, Z.; Mu, C.; Ma, W.; Hu, H.; Jiang, K.; Lin, H.; Ade, H.; Yan, H., Aggregation and morphology control enables multiple cases of high-efficiency polymer solar cells. Nat. Commun. 2014, 5, 5293.



11. Vohra, V.; Kawashima, K.; Kakara, T.; Koganezawa, T.; Osaka, I.; Takimiya, K.; Murata, H., Efficient inverted polymer solar cells employing favourable molecular orientation. Nat. Photonics 2015, 9, 403. 12. Nam, S.; Song, M.; Kim, H.; Bradley, D. D. C.; Kim, Y., Thickness Effect of Bulk Heterojunction Layers on the Performance and Stability of Polymer:Fullerene Solar Cells with Alkylthiothiophene-Containing Polymer. ACS Sustainable Chem. Eng. 2017, 5 (10), 9263-9270. 13. Zhao, W.; Li, S.; Yao, H.; Zhang, S.; Zhang, Y.; Yang, B.; Hou, J., Molecular Optimization Enables over 13% Efficiency in Organic Solar Cells. J. Am. Chem. Soc. 2017, 139 (21), 71487151. 14. Badgujar, S.; Song, C. E.; Oh, S.; Shin, W. S.; Moon, S.-J.; Lee, J.-C.; Jung, I. H.; Lee, S. K., Highly efficient and thermally stable fullerene-free organic solar cells based on a small molecule donor and acceptor. J. Mater. Chem. A 2016, 4 (42), 16335-16340. 15. Hadmojo, W. T.; Wibowo, F. T. A.; Ryu, D. Y.; Jung, I. H.; Jang, S.-Y., Fullerene-Free Organic Solar Cells with an Efficiency of 10.2% and an Energy Loss of 0.59 eV Based on a Thieno[3,4-c]Pyrrole-4,6-dione-Containing Wide Band Gap Polymer Donor. ACS Applied Mater. Interfaces 2017, 9 (38), 32939-32945. 16. Lin, Y.; Wang, J.; Zhang, Z.-G.; Bai, H.; Li, Y.; Zhu, D.; Zhan, X., An Electron Acceptor Challenging Fullerenes for Efficient Polymer Solar Cells. Adv. Mater. 2015, 27 (7), 1170-1174. 17. Lopez, S. A.; Sanchez-Lengeling, B.; de Goes Soares, J.; Aspuru-Guzik, A., Design Principles and Top Non-Fullerene Acceptor Candidates for Organic Photovoltaics. Joule, DOI 10.1016/j.joule.2017.10.006.


Page 16 of 26

Page 17 of 26 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


18. Li, Y.; Zhong, L.; Gautam, B.; Bin, H.-J.; Lin, J.-D.; Wu, F.-P.; Zhang, Z.; Jiang, Z.-Q.; Zhang, Z.-G.; Gundogdu, K.; Li, Y.; Liao, L.-S., A near-infrared non-fullerene electron acceptor for high performance polymer solar cells. Energy Environ. Sci. 2017, 10 (7), 1610-1620. 19.

Wang, Y.; Zhang, Y.; Qiu, N.; Feng, H.; Gao, H.; Kan, B.; Ma, Y.; Li, C.; Wan, X.;

Chen, Y., A Halogenation Strategy for over 12% Efficiency Nonfullerene Organic Solar Cells. Advanced Energy Materials, DOI: 10.1002/aenm.201702870. 20.

Xu, X.; Yu, T.; Bi, Z.; Ma, W.; Li, Y.; Peng, Q., Realizing Over 13% Efficiency in

Green-Solvent-Processed Nonfullerene Organic Solar Cells Enabled by 1,3,4-Thiadiazole-Based Wide-Bandgap Copolymers. Advanced Materials 2018, 30 (3), 1703973. 21. Bin, H.; Yang, Y.; Zhang, Z.-G.; Ye, L.; Ghasemi, M.; Chen, S.; Zhang, Y.; Zhang, C.; Sun, C.; Xue, L.; Yang, C.; Ade, H.; Li, Y., 9.73% Efficiency Nonfullerene All Organic Small Molecule Solar Cells with Absorption-Complementary Donor and Acceptor. J. Am. Chem. Soc. 2017, 139 (14), 5085-5094. 22. Qiu, B.; Xue, L.; Yang, Y.; Bin, H.; Zhang, Y.; Zhang, C.; Xiao, M.; Park, K.; Morrison, W.; Zhang, Z.-G.; Li, Y., All-Small-Molecule Nonfullerene Organic Solar Cells with High Fill Factor and High Efficiency over 10%. Chem. Mater. 2017, 29 (17), 7543-7553. 23. Li, M.; Liang, Q.; Zhao, Q.; Zhou, K.; Yu, X.; Xie, Z.; Liu, J.; Han, Y., A bi-continuous network structure of p-DTS(FBTTh2)2/EP-PDI via selective solvent vapor annealing. J. Mater. Chem. C 2016, 4 (42), 10095-10104. 24. Ni, W.; Li, M.; Kan, B.; Liu, F.; Wan, X.; Zhang, Q.; Zhang, H.; Russell, T. P.; Chen, Y., Fullerene-free small molecule organic solar cells with a high open circuit voltage of 1.15 V. Chem. Commun. 2016, 52 (3), 465-468.



25. Xin, R.; Feng, J.; Zeng, C.; Jiang, W.; Zhang, L.; Meng, D.; Ren, Z.; Wang, Z.; Yan, S., Nonfullerene-Acceptor All-Small-Molecule Organic Solar Cells Based on Highly Twisted Perylene Bisimide with an Efficiency of over 6%. ACS Applied Mater. Interfaces 2017, 9 (3), 2739-2746. 26. Wang, J.-L.; Xiao, F.; Yan, J.; Liu, K.-K.; Chang, Z.-F.; Zhang, R.-B.; Wu, H.-B.; Cao, Y., Toward high performance indacenodithiophene-based small-molecule organic solar cells: investigation of the effect of fused aromatic bridges on the device performance. J. Mater. Chem. A 2016, 4 (6), 2252-2262. 27. Li, M.; Ni, W.; Wan, X.; Zhang, Q.; Kan, B.; Chen, Y., Benzo[1,2-b:4,5-b[prime or minute]]dithiophene (BDT)-based small molecules for solution processed organic solar cells. J. Mater. Chem. A 2015, 3 (9), 4765-4776. 28. Zhou, J.; Zuo, Y.; Wan, X.; Long, G.; Zhang, Q.; Ni, W.; Liu, Y.; Li, Z.; He, G.; Li, C.; Kan, B.; Li, M.; Chen, Y., Solution-Processed and High-Performance Organic Solar Cells Using Small Molecules with a Benzodithiophene Unit. J. Am. Chem. Soc. 2013, 135 (23), 8484-8487. 29. Gao, K.; Li, L.; Lai, T.; Xiao, L.; Huang, Y.; Huang, F.; Peng, J.; Cao, Y.; Liu, F.; Russell, T. P.; Janssen, R. A. J.; Peng, X., Deep Absorbing Porphyrin Small Molecule for High-Performance Organic Solar Cells with Very Low Energy Losses. J. Am. Chem. Soc. 2015, 137 (23), 72827285. 30. Kesters, J.; Verstappen, P.; Kelchtermans, M.; Lutsen, L.; Vanderzande, D.; Maes, W., Porphyrin-Based Bulk Heterojunction Organic Photovoltaics: The Rise of the Colors of Life. Adv. Energy Mater. 2015, 5 (13), 1500218.


Page 18 of 26

Page 19 of 26 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


31. Gao, K.; Zhu, Z.; Xu, B.; Jo, S. B.; Kan, Y.; Peng, X.; Jen, A. K. Y., Highly Efficient Porphyrin-Based OPV/Perovskite Hybrid Solar Cells with Extended Photoresponse and High Fill Factor. Adv. Mater. 2017, 29 (47), 1703980. 32. Xiao, L.; Chen, S.; Gao, K.; Peng, X.; Liu, F.; Cao, Y.; Wong, W.-Y.; Wong, W.-K.; Zhu, X., New Terthiophene-Conjugated Porphyrin Donors for Highly Efficient Organic Solar Cells. ACS Applied Mater. Interfaces 2016, 8 (44), 30176-30183. 33. Hashimoto, T.; Choe, Y.-K.; Nakano, H.; Hirao, K., Theoretical Study of the Q and B Bands of Free-Base, Magnesium, and Zinc Porphyrins, and Their Derivatives. J. Phys. Chem. A 1999, 103 (12), 1894-1904. 34. Lu, L.; Chen, W.; Xu, T.; Yu, L., High-performance ternary blend polymer solar cells involving both energy transfer and hole relay processes. Nat. Commun. 2015, 6, 7327. 35. Hadmojo, W. T.; Yim, D.; Aqoma, H.; Ryu, D. Y.; Shin, T. J.; Kim, H. W.; Hwang, E.; Jang, W.-D.; Jung, I. H.; Jang, S.-Y., Artificial light-harvesting n-type porphyrin for panchromatic organic photovoltaic devices. Chem. Sci. 2017, 8 (7), 5095-5100. 36. Lee, H.; Jeong, Y.-H.; Kim, J.-H.; Kim, I.; Lee, E.; Jang, W.-D., Supramolecular Coordination Polymer Formed from Artificial Light-Harvesting Dendrimer. J. Am. Chem. Soc. 2015, 137 (38), 12394-12399. 37. D'Urso, A.; Fragala, M. E.; Purrello, R., From self-assembly to noncovalent synthesis of programmable porphyrins' arrays in aqueous solution. Chem. Commun. 2012, 48 (66), 81658176. 38. Eom, S. H.; Nam, S. Y.; Do, H. J.; Lee, J.; Jeon, S.; Shin, T. J.; Jung, I. H.; Yoon, S. C.; Lee, C., Dark current reduction strategies using edge-on aligned donor polymers for high detectivity and responsivity organic photodetectors. Polym. Chem. 2017, 8 (23), 3612-3621.



Page 20 of 26

39. Hadmojo, W. T.; Nam, S. Y.; Shin, T. J.; Yoon, S. C.; Jang, S.-Y.; Jung, I. H., Geometrically controlled organic small molecule acceptors for efficient fullerene-free organic photovoltaic devices. J. Mater. Chem. A 2016, 4 (31), 12308-12318. 40.

Lin, Y.; He, Q.; Zhao, F.; Huo, L.; Mai, J.; Lu, X.; Su, C.-J.; Li, T.; Wang, J.; Zhu, J.;

Sun, Y.; Wang, C.; Zhan, X., A Facile Planar Fused-Ring Electron Acceptor for As-Cast Polymer Solar Cells with 8.71% Efficiency. J. Am. Chem. Soc. 2016, 138 (9), 2973-2976. 41. Hou,

Kan, B.; Feng, H.; Wan, X.; Liu, F.; Ke, X.; Wang, Y.; Wang, Y.; Zhang, H.; Li, C.; J.;

Chen,

Y.,

Small-Molecule

Acceptor

Based

on

the

Heptacyclic

Benzodi(cyclopentadithiophene) Unit for Highly Efficient Nonfullerene Organic Solar Cells. J. Am. Chem. Soc. 2017, 139 (13), 4929-4934.


Page 21 of 26 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


Scheme 1. Synthetic procedure of PZn donors, and the structure of IDIC.



Figure 1. Absorption spectra a) in solution (chloroform) and b) solid film, c) cyclic voltammograms, and d) estimated energy levels of the three PZn donors and IDIC as the acceptor


Page 22 of 26

Page 23 of 26 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


Figure 2. a) Current density-voltage (J-V) curves and b) external quantum efficiency (EQE) spectra of the PZn donor:IDIC based all-small-molecule OPV devices (solid lines) and absorption spectra of the PZn donor:IDIC active layers (dot lines).




Page 24 of 26

Page 25 of 26 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


Figure 3. Out of plane intensity of a) pristine PZn donor and acceptor films and b) PZn donor and IDIC blend films. 2D GIXD spectra of c) pristine PZn donor films and d) their IDIC blend films. e) Azimuthal ling-cut extracted from the long-distance ordering at around 0.3 Å−1 in blend films and f) the ratio of the face-on (Axy) to edge-on (Az) orientation

Table 1. Optical and electrochemical properties λmax (nm)

Donor

[a]

solution

film

[b]

Egopt (eV)[c]

EHOMO (eV)[d]

ELUMO (eV)[e]

1

450, 557, 713, 742

462, 573, 811

1.37

-5.22

-3.85

2

440, 557, 705, 752

465, 572, 808

1.37

-5.23

-3.86

3

446, 566, 724

477, 575, 800

1.41

-5.28

-3.87

[a]

Dilute chloroform solution; [b] film on a quartz plate; [c] bandgap calculated from the film-state absorption onset wavelength; [d] HOMO levels determined from the Eonset of the first oxidation potential; [e] LUMO levels determined from the EHOMO and Egopt. Table 2. Summary of photovoltaic and morphological properties SCLC mobility JSC (×10-3 cm2 V-1s-1) Donor:I VOC PCE (mA FF DIC (V) (%) µh / µe -2 cm ) µh[a] µe [b] [c]

2DGIXD Axy /Az [d]

1

0.71 ±0.01

15.46 ±0.19

0.56 ±0.00

6.13 ±0.08

1.12

1.11

1.01

16.3

2

0.71 ±0.01

14.03 ±0.34

0.53 ±0.02

5.21 ±0.10

0.49

0.70

0.70

2.68

3

0.70 ±0.01

11.46 ±0.01

0.51 ±0.01

4.08 ±0.02

0.22

0.19

1.16

1.58

[a]

hole (µh) and [b] electron (µe) mobility, [c] µh/µe charge balance, and [d] face-on/edge-on ratio of Figure 3f



Near infrared harvesting fullerene-free all-small-molecule organic photovoltaic cells are developed achieved by combining Zn porphyrin donors and a nonfullerene acceptor.


Page 26 of 26

Molecule Organic Solar Cells Based on Porphyrin Donors

Recommend Documents