Solar Cell and Transistor Applications of Naphthodithiophene-Based Polymers (original) (raw)
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3,8-Dialkoxynaphthodithiophene based copolymers for efficient polymer solar cells
Solar Energy Materials and Solar Cells, 2013
A new donor unit viz. 3,8-bis(2-butyloctyloxy)naphtho[3,2-b:7,6-b 0 ]dithiophene (NDT) was developed for a novel donor-acceptor semiconducting polymer. And the new NDT-based polymers (PNDTTT-C and PNDTTT-CF) with thienothiophene units were synthesized. The polymers showed deep HOMO levels of À 5.44 eV and À 5.51 eV with the optical band gap of $ 1.6 eV. The electrochemical as well as optical and photovoltaic properties of these polymers were studied. The OPV devices fabricated from the blends of polymer PNDTTT-C/PNDTTT-CF: PC 71 BM were afforded a high power conversion efficiency of 4.49% and 5.16%, respectively. The optimization of device fabrication included different solvents, different weight ratios and usage of solvent processing additive. To obtain the high PCE a typical processing additive 1,8-diiodooctane was used. The effect of processing additive was studied using AFM analysis. In addition, the field-effect hole mobilities of 3.5 Â 10 À 4 cm 2 V À 1 s À 1 and 5.7 Â 10 À 4 cm 2 V À 1 s À 1 were observed for the polymers PNDTTT-C and PNDTTT-CF, respectively. Since we have developed the synthetic process of the 3,8-bis(2-butyloctyloxy)-naphtho [3,2-b:7,6-b 0 ]dithiophene(NDT) monomer, the NDT unit will play an important role in future research on conjugated polymer and small molecule design for high-performance organic semiconducting material.
For years, scientists are relying on fullerene-free acceptors because of their prominent role in tuning and improving the optoelectronic characteristics and efficiency of photovoltaic cells. To improve the PCE of non-fullerene based OSCs, four new molecules based on AD A pattern substituted with different acceptor groups namely NDT1 (malononitrile), NDT2 (methyl-2cyanoacrylate), NDT3 (2-(5,6-difluoro-3-oxo-2,3-dihydroinden-1-ylidene) malononitrile), and NDT4 (2-(3-methyl-4-oxothiazolidin-2-ylidene) malononitrile) have been designed. All constructed structures have a common central unit, naphtho-dithiophene which is attached to various acceptor groups at the peripheral position. A detailed computational study of optical and electronic properties of designed molecules in comparison to reference molecule NDT shows that NDT3 possesses maximum absorption (473.9 nm) and smallest bandgap (5.26 eV), while NDT1 exhibits the highest Voc (3.17 eV). TDM analysis has been performed which shows efficient charge density transition from core to acceptor groups. Besides that, because of their low reorganization energy values, larger dipole moments, and higher values of Voc, these constructed molecules are considered superior scaffolds for designing of SM-OSCs. Hence, the molecules under scrutiny are likely to be successful acceptors for the fabrication of photovoltaic cells in the future. 1. Introduction Energy is a basic need for the social and economic progress of a country. There is no way to improve a country's economy and people's living conditions until adequate energy is available in convenient and affordable forms [1]. Global energy demand is estimated to be increased twice by the start of 2050, and more than thrice by the end of this decade. If existing power networks are only strengthened incrementally, they will not be able to satisfy this demand in a sustainable manner [2]. Seeking suitable sources of clean energy for the future is one of society's most difficult challenges. Probably the most abundant carbon-free energy supply is solar energy. The Earth receives more energy from the sun in an hour (4.3 × 10 20 J) than it is needed per year. The use of the sun as an energy source is a convincing alternative to our desire for sustainable and reliable energy. Sunlight is easy to use, clean, unobtrusive, abundant, long-lasting, and consistent. Solar power is a viable choice for meeting the world's growing power needs as a consequence of population growth and infrastructure creation for these advantages. Photovoltaic (PV) systems transform solar energy into electrical energy, and solar energy is among the most promising possible renewable energy sources [3].
ACS Applied Materials & Interfaces, 2019
In this research, we developed six new selenophene-incorporated naphthobisthiadiazole-based D-A polymers PNT2Th2Se-OD, PNT2Se2Th-OD, PNT4Se-OD, PNT2Th2Se-DT, PNT2Se2Th-DT and PNT4Se-DT. The structure-property relationships have been systematically established through the comparison of their structural variations: (1) isomeric biselenophene/bithiophene arrangement between PNT2Th2Se and PNT2Se2Th polymers, (2) biselenophene/bithiophene and quarterselenophene donor units between PNT2Th2Se/PNT2Se2Th and PNT4Se polymers, (3) side-chain modification between the OD-and DT-series polymers. The incorporation of selenophene unit in the copolymers induces stronger charge transfer to improve the light-harvesting capability while maintaining the strong intermolecular interactions to preserve the intrinsic crystallinity for high carrier mobility. The OFET device using PNT2Th2Se-OD achieved a high hole-mobility of 0.36 cm 2 V-1 s-1 with an on/off ratio of 1.9×10 5. The solar cells with PNT2Th2Se-OD:PC 71 BM exhibited a power conversion efficiency (PCE) of 9.47% with an V oc of 0.68 V, an FF of 67 %, and an impressive J sc of 20.69 mAcm-2 .
Dyes and Pigments, 2017
Two new small molecules, composed of naphthodithiophene (NDT) donor core and thienopyrroledione (TPD) group acceptor group end-capped with and without an alkyl-bithiophene, defined as NDT(TPD) 2 and NDT(TPDTT) 2 were designed and synthesized by stille coupling reactions. The thermal and electrochemical analyses carried out for both the small molecules revealed good thermal stability along with high decomposition temperature (>350 C). NDT(TPD) 2 showed a deep HOMO level (À5.38 eV), compared to slightly upshifted HOMO (À5.26 eV) of NDT(TPDTT) 2. While X-ray diffractometry suggests crystalline and amorphous nature of NDT(TPD) 2 and NDT(TPDTT) 2 respectively, the space charge limited current analysis revealed high hole mobility in the former and appreciable charge balance in the later. The conventional organic solar cell (OSC) devices fabricated using NDT(TPD) 2 and NDT(TPDTT) 2 as donor show power conversion efficiency (PCE) of 0.26% and 0.8% respectively. While NDT(TPDTT) 2 device after blending with additive, owing to the improved D-A heterojunction yielded maximum PCE of 1.31% resulting from enhanced J sc 3.32 mA/cm 2 , V oc 0.75 V and FF of 52.44.
bulk-heterojunction (BHJ) devices facilitate efficient exciton diffusion, charge separation, and carrier collection, giving rise to high power-conversion efficien-cies (PCE). The appealing properties of solution-processed BHJ PSCs include low cost, light weight, mechanical flexibility, and promise of facile large-area fabrications. [1-4] Up to date, PSCs containing hole-transporting polymers as the donor, with fullerene or organic small molecules as the acceptor, have demonstrated impressive performance, with the state-of-the-art PCE values reaching >10%. [5-12] Compared to fullerene-and small molecule-based devices, all-PSCs offer additional merits of high morphological stability, superior mechanical properties, and suitability for printing-related fabrication techniques. [13-20] The bottleneck that limits the advancement of all-PSCs is currently the properties of polymer acceptors. With extensive research efforts spent on new acceptor designs and device optimizations, [21-26] the record PCE of all-PSCs was pushed to 8.27%, as reported by Li and co-workers. This high PCE was accomplished by a widely studied low-bandgap naphthalene-diimide (NDI) based polymer acceptor N2200, along with a medium-bandgap donor polymer. Due to their well-complemented absorption spectra, a high short-circuit current density (J sc) of 14.18 mA cm −2 was obtained. [23] Recently, we also reported that, by implementing an acceptor of perylenediimide (PDI) polymer with vinylene linkers (PDI-V, Figure 1), a high PCE of 7.57% can be obtained, [27] which was the best performance achieved for PDI-based polymer acceptors. In the current contribution, we report our further endeavors at improving the PCE of all-PSCs to a new record of 8.59%. This is realized by designing a new polymer acceptor, NDP-V, featuring a backbone of naphthodiperylenetetraimide and vinylene units. The design rationale is to reduce the conforma-tional disorder of the previous PDI-V acceptor. By covalently fusing half of the vinylene linkers in PDI-V backbone to the bay region of adjacent PDI units on both sides, larger, shape-persistent NDP units are obtained, based on which a new polymer (NDP-V) featuring a poly(NDP-vinylene) backbone is designed and synthesized (Figure 1). We anticipate that, by reducing the number rotatable CC bonds in the backbone and incorporating larger polycyclic NDP units, the chain flexibility of the polymer is tuned and the molecular packing behaviors of the A new polymer acceptor, naphthodiperylenetetraimide-vinylene (NDP-V), featuring a backbone of altenating naphthodiperylenetetraimide and vinylene units is designed and applied in all-polymer solar cells (all-PSCs). With this polymer acceptor, a new record power-conversion efficiencies (PCE) of 8.59% has been achieved for all-PSCs. The design principle of NDP-V is to reduce the conformational disorder in the backbone of a previously developed high-performance acceptor, PDI-V, a perylenediimide-vinylene polymer. The chemical modifications result in favorable changes to the molecular packing behaviors of the acceptor and improved morphology of the donor-acceptor (PTB7-Th:NDP-V) blend, which is evidenced by the enhanced hole and electron transport abilities of the active layer. Moreover, the stronger absorption of NDP-V in the shorter-wavelength range offers a better complement to the donor. All these factors contribute to a short-circuit current density (J sc) of 17.07 mA cm −2. With a fill factor (FF) of 0.67, an average PCE of 8.48% is obtained, representing the highest value thus far reported for all-PSCs. Polymer Solar Cells As an emerging technology for harnessing solar energy, polymer solar cells (PSCs) have received extensive attention during the past decade. With a binary active layer formed by interpenetrating electron donor and acceptor, the
RSC Advances, 2012
A series of donor-acceptor (D-A) copolymers from a benzodithiophene (BDT) donor unit and a naphtho[2,3-c]thiophene-4,9-dione (NTDO) acceptor unit with different side chains, PBDTNTDO-C1, PBDTNTDO-C2 and PBDTNTDO-C3, were synthesized by a standard Stille cross-coupling polymerization. The thermal, optical and electrochemical properties of the copolymers were well investigated. Preliminary investigations of the copolymers based on the device structure of ITO/ PEDOT : PSS/polymer: PC 71 BM (1 : 2)/Ca/Al showed power conversion efficiencies (PCEs) of 1.96% for PBDTNTDO-C1, 1.01% for PBDTNTDO-C2 and 2.21% for PBDTNTDO-C3 under the illumination of AM1.5, 100 mW cm 22 .
Journal of Polymer Science Part A: Polymer Chemistry, 2015
The synthesis and characterization of two low band gap copolymers (P1 and P2) incorporating benzo[1,2-b:4,5b']dithiophene unit substituted with octylsulfanylthienyl groups (OSBT) are here reported. These materials, designed to be employed in polymer solar cells (PSCs), were obtained from alternating OSBT and bithiophene (P1) or thienothiophene (P2) units. Their structural electrochemical and photophysical properties were investigated. They are thermally stable and soluble in organic solvents from which they easily form films. They also form p-stacks in solution, in film and display a moderate solvatochromism. These polymers were tested with [70]PCBM in bulk-heterojunction (BHJ) PSCs where they act as donor materials and [70]PCBM is the electron acceptor. The best device, obtained using a 1:3 weight ratio for the P1:[70]PCBM blend, shows a PCE around 1.5%. A broad response from 350 to 700 nm is also observed in the external quantum efficiency (EQE) curves, wider for P1 with respect to P2. V
Chemistry of Materials, 2012
An isomerically pure anti-anthradithiophene (aADT) arranged in an angular shape is developed. Formation of the framework of aADT incorporating four lateral alkyl substituents was accomplished by a one-pot benzannulation via multiple Suzuki coupling. This newly designed 2,8-stannylated aADT monomer was copolymerized with a ditheniodiketopyrrolopyrrole (DPP) unit and a bithiophene unit, respectively, to furnish an alternating donor−acceptor copolymer poly(anthradithiophene-alt-dithienyldiketopyrrolopyrrole) (PaADTDPP) and a thiophene-rich poly(anthradithiophene-alt-bithiophene) (PaADTT). PaADTT with crystalline nature achieved a high FET mobility of 7.9 × 10 −2 cm 2 V −1 s −1 with an on−off ratio of 1.1 × 10 7. The photovoltaic device based on the PaADTDPP:PC 71 BM (1:2.5, w/w) blend exhibited a V oc of 0.66 V, a J sc of 9.49 mA/cm 2 , and a FF of 58.4%, delivering a power conversion efficiency (PCE) of 3.66%. By adding 1.5 vol % 1-chloronaphthalene (CN) as a processing additive, the PCE can be improved to 4.24%. We demonstrated that these angular-shaped and alkylated aADT-based polymers have better organic photovoltaic (OPVs) and fieldeffect transistor (FETs) characteristics than the linear-shaped ADT-containing polymers.