ZKC

Although conventional laser ablation (CLA) method has widely been used in patterning of organic semiconductor thin films, its quality control still remains unsatisfied due to the ambiguous photochemical and photothermal processes. Based on industrial available near-infrared laser source, herein, a novel “layer-filter threshold” (LFT) technique is proposed, which involves the decomposition of targeted “layer-filter” and subsequent explosive evaporation process to purge away the upper layers instead of layer-by-layer ablation. For photovoltaic device with structure of metal/blend/PEDOT:PSS/ITO/glass, the PEDOT:PSS layer as the “layer-filter” is first demonstrated to be effective, and then the merged P1–P2 line and metal electrode layer are readily patterned through the “self-aligned” effect and regulation of ablation direction, respectively. The correlation between laser fluence and explosive ablation efficacy is also investigated. Finally, photovoltaic modules based on classical P3HT:PC₆₁BM and low-bandgap PBDT-TFQ:PC₇₁BM systems are separately fabricated following the LFT technique. It is found that over 90% of geometric fill factor is achieved while device performances maintain in a limited change with increased number of series cells. In comparison to conventional laser ablation methods, the LFT technique does not require sophisticated instruments but reaches comparable processing accuracy, which shows promising potential in the fabrication and commercialization of organic semiconductor thin-film devices.

Layer-filter threshold (LFT) technique based on near-infrared laser is proposed and demonstrated, which enables the patterning strategy through an interlayer explosion effect with high precision and easily reachable operating conditions. Thus obtained organic photovoltaic modules reach geometric fill factors exceeding 90% and maintain the performances with increasing number of interconnected cells, which verifies the potential of LFT technique in the patterning of organic semiconductor devices.

In this work, the application of an aluminum (Al)/multiwall carbon nanotube (MWCNT)/Al, multilayered electrode to flexible, high-efficiency, alternating current driven organic electroluminescent devices (AC-OEL), is reported. The electrode is fabricated by sandwiching a spray-cast nanonetwork film of MWCNTs between two evaporated layers of Al. The resulting composite film facilitates a uniform charge distribution across a robust crack-free electrode under various bending angles. It is demonstrated that these composite electrodes stabilize the power efficiency of flexible devices for bending angles up to 120°, with AC-OEL device power efficiencies of ≈22 lm W⁻¹ at luminances of ≈4000 cd m⁻² (using no output coupling). Microscopic examination of the Al/MWCNTs/Al electrode after bending of up to 1300 cycles suggests that the nanotubes significantly enhance the mechanical properties of the thin Al layers while providing a moderate modification to the work function of the metal. While the realization of robust, high-brightness, and high-efficiency AC-OEL devices is potentially important in their future lighting applications, it is anticipated that this to also have significant impact in standard organic light emitting diodes lighting applications.

Nanocomposite cathode structures—in this case metals together with multiwalled nanotubes—with the aim of combining mechanical and electronic properties to achieve better performance in an organic flexible are examined. A flexible high-efficiency alternating current (AC) driven field-induced polymer electroluminescent) device is chosen as the platform system with the understanding that this approach to organic devices clearly points to organic light emitting diodes, organic thin-film transistors, and other flexible systems.

A comparison study of photovoltaic properties of an oligomer and a polymer based on the same backbone structure is conducted to show that high-efficiency small molecules can be developed from breaking down polymers. The oligomer attains high-efficiency as a result of the high-degree molecular ordering and the excellent intrinsic phase separation with [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM).

A five-step procedure to develop solvent systems for thin film photovoltaic materials is described on page 3393 by P. Heremans and co-workers. A combination of wettability studies, toxicological insights, and Hansen solubility parameters analysis lead to suitable inks. Organic photovoltaic devices are blade coated from several new diketopyrrolopyrrole-based inks, and achieve equal performance to those from halogenated solvents.

Top-illuminated flexible organic solar cells with a high power conversion efficiency (≈6.75%) are fabricated using a dielectric/metal/polymer (DMP) electrode. Employing a polymer layer (n = 1.49) makes it possible to show the high transmittance, which is insensitive to film thickness, and the excellent haze induced by well-ordered nanopatterns on the DMP electrode, leading to a 28% of enhancement in efficiency compared to bottom cells.

Highly transparent and nanostructured nickel oxide (NiO) films through pulsed laser deposition are introduced for efficient CH₃NH₃PbI₃ perovskite solar cells. The (111)-oriented nanostructured NiO film plays a key role in extracting holes and preventing electron leakage as hole transporting material. The champion device exhibits a power conversion efficiency of 17.3% with a very high fill factor of 0.813.

On page 3266, S. A. Jenekhe and co-workers present a series of new tetraazabenzodifluoranthene diimide dimers with arylene linkers allowing the 3D molecular structure of these nonfullerene electron acceptors to be tuned, which results in a dramatic variation of the power conversion efficiency from 2.6% to 6.4% as the twist angle between the monomeric building blocks in the dimer is varied. The design illustrates background rainbow sunlight illuminating a polymer solar cell active layer composed of conjugated donor polymer chains and these new nonfullerene electron-acceptor molecules, resulting in electricity generation that flows through connecting wires to power a light bulb.

Energetic disorder, an important parameter affecting the performance of organic photovoltaics, is significantly decreased upon the addition of processing additives in a highly efficient benzodithiophene-based copolymer blend (PBDTTT-C-T:PC₇₁BM). Wide-angle and small-angle X-ray scattering measurements suggest that the origin of this reduced energetic disorder is due to increased aggregation and a larger average fullerene domain size together with purer phases.

Complex materials are defined as nanostructured materials with combinations of structure and/or composition that lead to performance surpassing the sum of their individual components. There are many methods that can create complex materials; however, atomic layer deposition (ALD) is uniquely suited to control composition and structural parameters at the atomic level. The use of ALD for creating complex insulators, semiconductors, and conductors is discussed, along with its use in novel structural applications.

Complex materials combine structure and/or composition leading to performances surpassing the sum of their individual components. Atomic layer deposition (ALD) is uniquely suited to create complex materials, able to control composition and structural parameters at the atomic level. The use of ALD for creating complex insulators, semiconductors, and conductors, is discussed, along with its use in novel structural applications.

Functionalized graphene nanoflakes (GNFs) are used as an electron-cascade acceptor material in air-processed organic ternary bulk heterojunction solar cells. The functionalization is realized via the attachment of the ethylenedinitrobenzoyl (EDNB) molecule to the GNFs. Simulation and experimental results show that such nanoscale modification greatly influences the density of states near the Fermi level. Consequently, the GNF-EDNB blend presents favorable highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels to function as a bridge structure between the poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) and the [6,6]-phenyl-C71-butyric-acid-methyl-ester (PC₇₁BM). The improved exciton dissociation and charge transport are associated with the better energy level alignment of the ternary blend and the high electrical conductivity of the GNFs, which act as additional electron transport channels within the photoactive layer. The resulting PCDTBT/GNF-EDNB/PC₇₁BM ternary organic solar cells, fabricated entirely under ambient conditions, exhibit an average power conversion efficiency enhancement of ≈18% as compared with the binary blend PCDTBT/PC₇₁BM.

Graphene nanoflakes functionalized with 3,5-dinitrobenzoyl with tunable energy levels are used as an electron-cascade acceptor in air-processed ternary organic solar cells (OSCs). Ternary OSCs exhibit an efficiency of 6.41%, 18% higher than the binary blend and one of the highest for air-processed OSCs.

A series of tetrafluorine-substituted small molecules with a D₁-A-D₂-A-D₁ linear framework based on indacenodithiophene and difluorobenzothiadiazole is designed and synthesized for application as donor materials in solution-processed small-molecule organic solar cells. The impacts of thiophene π-bridge and multiple fluorinated modules on the photophysical properties, the energy levels of the highest occupied molecular orbitals (HOMO) and lowest unoccupied molecular orbitals (LUMO), charge carrier mobility, the morphologies of blend films, and their photovoltaic properties as electron donor material in the photoactive layer are investigated. By incorporating multiple fluorine substituents of benzothiadiazole and inserting two thiophene spacers, the fill factor (FF), open-circuit voltage, and short-circuit current density are dramatically improved in comparison with fluorinated-free materials. With the solvent vapor annealing treatment, further enhancement in charge carrier mobility and power conversion efficiency (PCE) are achieved. Finally, a high PCE of 8.1% with very-high FF of 0.76 for BIT-4F-T/PC₇₁BM is achieved without additional additive, which is among one of the highest reported for small-molecules-based solar cells with PCE over 8%. The results reported here clearly indicate that high PCE in solar cells based small molecules can be significantly increased through careful engineering of the molecular structure and optimization on the morphology of blend films by solvent vapor annealing.

Small molecules (BIT-4F-T) based on indacenodithiophene (IDT) and difluorobenzothiadiazole are synthesized for bulk-heterojunction organic solar cells (BHJ-OSCs). Best power conversion efficiency (PCE) of 8.1% and very-high FF of 0.76 are achieved, positioning them among the best small-molecule donor materials in simple single-junction organic solar cells. These exciting results verify the significant importance of multiple fluorine substituents of benzothiadiazole and two thiophene moieties for high PCE.

Fluorinated n-type conjugated polymers are used as efficient electron acceptor to demonstrate high-performance all-polymer solar cells. The exciton generation, dissociation, and charge-transporting properties of blend films are improved by using these fluorinated n-type polymers to result in enhanced photocurrent and suppressed charge recombination.

Arylene linkers in a series of new tetraaza­benzodifluoranthene diimide dimers enable tuning of the 3D molecular structure of nonfullerene electron acceptors, facilitating observation of dramatic variation of the power conversion efficiency from 2.6% to 6.4% as the twist angle between the monomeric building blocks in the dimer is varied.