The synthesis, characterization, and photovoltaic performance of a series of N-annulated PDI materials is presented. Four novel N-annulated PDI compounds are reported, each of which can be ...synthesized in gram scale without the need for purification using column chromatography. N-Annulation of the PDI chromophore results in a decrease in electron affinity and lowering of the ionization potential, and renders the chromophore insoluble in organic solvents. Installation of an alkyl group improves the solubility. Single crystal X-ray analysis reveals a bowing of the aromatic backbone and compression of phenyl rings adjacent to the N atom. A brominated N-annulated PDI derivate represents a valuable synthon for creating novel multi-PDI chromophore materials. To demonstrate the utility of the new synthon for making electron transporting materials, a dimerization strategy was employed to create a dimeric PDI material. The PDI dimer has excellent solubility and film forming ability along with energetically deep HOMO and LUMO energy levels. X-ray crystal structure analysis reveals that, despite the isotropic nature of the molecule, only 1-D charge transport pathways are formed. Solar cells based on the new PDI dimer with the standard donor polymer PTB7 gave a high power conversion efficiency of 2.21% for this system. Through N-alkyl chain modification this PCE was increased to 3.13%. Further increases in PCE to 5.54% and 7.55% were achieved by using the more advanced donor polymers PTB7-Th and P3TEA, respectively. The simple yet high performance devices coupled with the highly modular and scalable “acceptor” synthesis make fullerene-free organic solar cells an attractive and cost-effective clean energy technology.
C-C bond forming reactions are central to the construction of π-conjugated polymers. Classical C-C bond forming reactions such as the Stille and Suzuki coupling reactions have been widely used in the ...past for this purpose. More recently, direct (hetero)arylation polymerization (DHAP) has earned a place in the spotlight with an increasing number of π-conjugated polymers being produced using this atom-economic and more sustainable chemistry. As semiconductors in organic electronics, the device performances of the polymers made by DHAP are of great interest and importance. This review compares the device performances of some representative π-conjugated polymers made using the DHAP method with those made using the conventional C-C bond forming reactions when they are used as semiconductors in organic thin film transistors (OTFTs) and organic photovoltaics (OPVs).
Charge transport in conjugated polymers depends critically on the chemical structure of the polymer chain, morphology, aggregation, and the complex microstructure in the solid state. Recently, ...molecular planarity and intramolecular electron transport were associated with J-type aggregation, while coplanar stacking and intermolecular hole transport were correlated with H-type aggregation. This fundamental observation suggests that the degree of H- or J-aggregation could be a handle to tune carrier mobility toward desirable device performances. Here, we use a diketopyrrolopyrrole copolymer as a model semiconducting polymer and tune the type and degree of aggregation through film thickness. Optical absorption measurements, grazing incidence wide angle X-ray scattering, and polarized optical microscopy reveal that thin films compose mainly fibrelike J-aggregated structures, and as the films become thicker, the degree of crystallinity and H-aggregation increase. Thickness-dependent charge mobility values, extracted from corresponding organic field effect transistors, confirm that J-aggregated polymer chains are generally preferable for electron mobility, while polymer crystalline H-aggregates support better hole transport. To obtain perfectly balanced ambipolar OFETs, we optimize the microstructure through film thickness and reduce contact resistance by inserting an interlayer of mixed additives at the organic/contact interfaces. A complementary-like voltage inverter combining two identical ambipolar DPP-T-TT OFETs with a common gate as the input voltage and symmetrical performance confirms that DPP copolymers are a promising candidate for applications in ambipolar devices and integrated circuits.
Typical syntheses of conjugated polymers rely heavily on organometallic reagents and metal-catalyzed cross-coupling reactions. Here, we show that an environmentally benign aldol polymerization can be ...used to synthesize poly(bisisoindigo), an analog of polyisoindigo with a ring-fused structural repeat unit. Owing to its extended conjugation length, poly(bisisoindigo) absorbs across the UV/vis/NIR spectrum, with an absorption tail that reaches 1000 nm. Due to the four electron-deficient lactam units on each repeat unit, poly(bisoindigo) possesses a low-lying LUMO, which lies at −3.94 eV relative to vacuum. Incorporation of the ring-fused monomer unit also lowered the overall torsional strain in the polymer backbone (relative to polyisoindigo), and the polymer was successfully used in prototype unipolar n-channel organic thin-film transistors.
A new azine polymer poly(4,4′-didodecyl-2,2′-bithiophene-azine) (PDDBTA) was synthesized in only three steps. PDDBTA showed hole mobilities of up to 4.1 × 10
−2
cm
2
V
−1
s
−1
in organic thin film ...transistors (OTFTs) as a p-channel material. As a donor in organic photovoltaics (OPVs), power conversion efficiencies (PCEs) of up to 2.18% were achieved, which is the first example of using an azine-based polymer for OPVs. These preliminary results demonstrate the potential of bithiophene-azine polymers as a new type of low-cost semiconductor material for OPVs and other organic electronics.
A new azine polymer poly(4,4′-didodecyl-2,2′-bithiophene-azine) (PDDBTA) is synthesized by a simple condensation reaction, which is a promising semiconductor for printed electronics.
N-type organic semiconductors are notoriously unstable in air, requiring the design of new materials that focuses on lowering their LUMO energy levels and enhancing their air stability in organic ...electronic devices such as organic thin-film transistors (OTFTs). Since the discovery of the notably air stable and high electron mobility polymer poly{N,N'-bis (2-octyldodecyl)- naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl-alt-5,5'-(2,29-bisthiophene)} (N2200), it has become a popular n-type semiconductor, with numerous materials being designed to mimic its structure. Although N2200 itself is well-studied, many of these comparable materials have not been sufficiently characterized to compare their air stability to N2200. To further the development of air stable and high mobility n-type organic semiconductors, N2200 was studied in organic thin film transistors alongside three N2200-based analogues as well as a recently developed polymer based on a (3E,7E)-3,7-bis(2-oxoindolin-3-ylidene)benzo1,2-b:4,5-b'difuran-2,6(3 H,7 H)-dione (IBDF) core. This IBDF polymer has demonstrated promising field-effect mobility and air stability in drop-cast OTFTs. While N2200 outperformed its analogues, the IBDF-based polymer displayed superior air and temperature stability compared to N2200. Overall, polymers with more heteroatoms displayed greater air stability. These findings will support the development of new air-stable materials, and further demonstrate the persistent need for the development of novel n-type semiconductors.
An N-annulated perylene diimide dimer, tPDI2N-hex, a graphene model compound with atomic precision, was investigated for luminescence applications. Electrochemiluminescence (ECL) of tPDI2N-hex was ...studied with tri-n-propylamine (TPrA) as a reducing coreactant. ECL-voltage curves along with spooling ECL spectra provided details of light generation mechanisms. The relative ECL quantum efficiency of the Ru(bpy)3(PF6)2/TPrA system was calculated to be 64%, which is superior to that of many other organic molecules because of the desired excited state in the absence of surface states. An organic light-emitting diode (OLED) fabricated with tPDI2N-hex displayed bright orange-red emission with a low color temperature, which is very desirable. It is plausible that the sterically constrained and thus orthogonal aromatic moieties in the tPDI2N-hex structure, with atomic precision graphene layer characteristics, lead to the excellent luminescence performances. The ECL and OLED studies of tPDI2N-hex showcase great application potentials of tPDI2N-hex in both solution-based ECL probes and solid-state light devices.
This study reports on the new and optimized synthesis of an N‐annulated perylene diimide dimer with functional N–H moieties. The presence of two N–H moieties renders the dimer relatively insoluble in ...most organic solvents. The dimer is easily functionalized with electron donating hexyl chains or electron withdrawing tert‐butyloxycarbonyl (tBOC) groups to yield highly soluble materials. The tBOC groups can be thermally cleaved in the thin film to give the parent dimer. The N–H bonds are acidic and interact with volatile organic bases. Deprotonation results in a color change from red to blue. All compounds have utility as electron transport materials in organic field‐effect transistors and green solvent, air processed organic solar cells. Electron mobilities were on the order of about 2–7 × 10–6 cm2/V s. Solar cell power conversion efficiency reached 2 % for those using the tBOC functionalized dimer, 3 % for those using the H‐atom functionalized dimer, and 6 % for those using the hexyl chain functionalized dimer. The performance of the latter is quite impressive considering the simple materials synthesis and greener solar cell processing.
Synthesis of the elusive N‐annulated perylene diimide dimer with pyrrolic N–H bonds is reported. The parent tPDI2NH dimer can be used as an electron transport material in OFETs or non‐fullerene acceptor on OSCs. The N–H bonds can easily be functionalized to incorporate alkyl side chains or cleavable “tBOC” groups. The acidic N–H bonds can be deprotonated to give drastic color changes in solution or as thin films.
A new, easily synthesized diphosphine based on a heterocyclic 1,3,2-diazaphospholidine framework has been prepared. Due to the large, sterically encumbering Dipp groups (Dipp = 2,6-diisopropylphenyl) ...on the heterocyclic ring, the diphosphine undergoes homolytic cleavage of the P–P bond in solution to form two phosphinyl radicals. The diphosphine has been reacted with O2, S8, Se, Te, and P4, giving products that involve insertion of elements between the P–P bond to yield the related phosphinic acid anhydride, sulfide/disulfide, selenide, telluride, and a butterfly-type perphospha-bicyclobutadiene structure with a trans,trans-geometry. All molecules have been characterized by multinuclear NMR spectroscopy, elemental analysis, and single-crystal X-ray crystallography. Variable-temperature EPR spectroscopy was utilized to study the nature of the phosphinyl radical in solution. Electronic structure calculations were performed on a number of systems from the parent diphosphine H2P2 to amino-substituted (H2N)2P2 and cyclic amino-substituted (H2C)2(NH)2P2; then, bulky substituents (Ph or Dipp) were attached to the cyclic amino systems. Calculations on the isolated diphosphine at the B3LYP/6-31+G* level show that the homolytic cleavage of the P–P bond to form two phosphinyl radicals is favored over the diphosphine by ∼11 kJ/mol. Furthermore, there is a significant amount of relaxation energy stored in the ligands (52.3 kJ/mol), providing a major driving force behind the homolytic cleavage of the central P–P bond.
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