MoS2 Nanoflowers Grown on Plasma-Induced W-Anchored Graphene for Efficient and Stable H2 Production Through Seawater Electrolysis.

Herein, it is found that 3D transition metal dichalcogenide (TMD)-MoS2 nanoflowers-grown on 2D tungsten oxide-anchored graphene nanosheets (MoS2 @W-G) functions as a superior catalyst for the hydrogen evolution reaction (HER) under both acidic and alkaline conditions. The optimized weight ratio of MoS2 @W-G (MoS2 :W-G/1.5:1) in 0.5 M H2 SO4 achieves a low overpotential of 78 mV at 10 mA cm-2 , a small Tafel slope of 48 mV dec-1 , and a high exchange current density (0.321 mA cm⁻2 ). Furthermore, the same MoS2 @W-G composite exhibits stable HER performance when using real seawater, with Faradaic efficiencies of 96 and 94% in acidic and alkaline media, respectively. Density functional theory calculations based on the hybrid MoS2 @W-G structure model confirm that suitable hybridization of 3D MoS2 and 2D W-G nanosheets can lower the hydrogen adsorption: Gibbs free energy (∆GH* ) from 1.89 eV for MoS2 to -0.13 eV for the MoS2 @W-G composite. The excellent HER activity of the 3D/2D hybridized MoS2 @W-G composite arises from abundance of active heterostructure interfaces, optimizing the electrical configuration, thereby accelerating the adsorption and dissociation of H2 O. These findings suggest a new approach for the rational development of alternative 3D/2D TMD/graphene electrocatalysts for HER applications using seawater.

High-Performance Organic Photovoltaics Incorporating an Active Layer with a Few Nanometer-Thick Third-Component Layer on a Binary Blend Layer.

In this paper, a universal approach toward constructing a new bilayer device architecture, a few-nanometer-thick third-component layer on a bulk-heterojunction (BHJ) binary blend layer, has been demonstrated in two different state-of-the-art organic photovoltaic (OPV) systems. Through a careful selection of a third component, the power conversion efficiency (PCE) of the device based on PM6/Y6/layered PTQ10 layered third-component structure was 16.8%, being higher than those of corresponding devices incorporating the PM6/Y6/PTQ10 BHJ ternary blend (16.1%) and the PM6/Y6 BHJ binary blend (15.5%). Also, the device featuring PM7/Y1-4F/layered PTQ10 layered third-component structure gave a PCE of 15.2%, which is higher than the PCEs of the devices incorporating the PM7/Y1-4F/PTQ10 BHJ ternary blend and the PM7/Y1-4F BHJ binary blend (14.2 and 14.0%, respectively). These enhancements in PCE based on layered third-component structure can be attributed to improvements in the charge separation and charge collection abilities. This simple concept of the layered third-component structure appears to have great promise for achieving high-performance OPVs.

Surface Reconstruction of Halide Perovskites During Post-treatment.

Postfabrication surface treatment strategies have been instrumental to the stability and performance improvements of halide perovskite photovoltaics in recent years. However, a consensus understanding of the complex reconstruction processes occurring at the surface is still lacking. Here, we combined complementary surface-sensitive and depth-resolved techniques to investigate the mechanistic reconstruction of the perovskite surface at the microscale level. We observed a reconstruction toward a more PbI2-rich top surface induced by the commonly used solvent isopropyl alcohol (IPA). We discuss several implications of this reconstruction on the surface thermodynamics and energetics. Particularly, our observations suggest that IPA assists in the adsorption process of organic ammonium salts to the surface to enhance their defect passivation effects.

Potassium-Presenting Zinc Oxide Surfaces Induce Vertical Phase Separation in Fullerene-Free Organic Photovoltaics.

Bulk heterojunction (BHJ) structure based organic photovoltaics (OPVs) have recently showed great potential for achieving high power conversion efficiencies (PCEs). An ideal BHJ structure would feature large donor/acceptor interfacial areas for efficient exciton dissociation and gradient distributions with high donor and acceptor concentrations near the anode and cathode, respectively, for efficient charge extraction. However, the random mixing of donors and acceptors in the BHJ often suffers the severe charge recombination in the interface, resulting in poor charge extraction. Herein, we propose a new approach-treating the surface of the zinc oxide (ZnO) as an electron transport layer with potassium hydroxide-to induce vertical phase separation of an active layer incorporating the nonfullerene acceptor IT-4F. Density functional theory calculations suggested that the binding energy difference between IT-4F and the PBDB-T-2Cl, to the potassium (K)-presenting ZnO interface, is twice as strong as that for IT-4F and PBDB-T-2Cl to the untreated ZnO surface, such that it would induce more IT-4F moving toward the K-presenting ZnO interface than the untreated ZnO interface thermodynamically. Benefiting from efficient charge extraction, the best PCEs increased to 12.8% from 11.8% for PBDB-T-2Cl:IT-4F-based devices, to 12.6% from 11.6% for PBDB-T-2Cl:Y1-4F-based devices, to 13.5% from 12.2% for PBDB-T-2Cl:Y6-based devices, and to 15.7% from 15.1% for PM6:Y6-based devices.

Transparent Flexible Heteroepitaxy of NiO Coated AZO Nanorods Arrays on Muscovites for Enhanced Energy Storage Application.

Transparent flexible energy storage devices are considered as important chains in the next-generation, which are able to store and supply energy for electronic devices. Here, aluminum-doped zinc oxide (AZO) nanorods (NRs) and nickel oxide (NiO)-coated AZO NRs on muscovites are fabricated by a radio frequency (RF) magnetron sputtering deposition method. Interestingly, AZO NRs and AZO/NiO NRs are excellent electrodes for energy storage application with high optical transparency, high conductivity, large surface area, stability under compressive and tensile strain down to a bending radius of 5 mm with 1000 bending cycles. The obtained symmetric solid-state supercapacitors based on these electrodes exhibit good performance with a large areal specific capacitance of 3.4 mF cm-2 , long cycle life 1000 times, robust mechanical properties, and high chemical stability. Furthermore, an AZO/NiO//Zn battery based on these electrodes is demonstrated, yielding a discharge capacity of 195 mAh g-1 at a current rate of 8 A g-1 and a discharge capacity of over 1000 cycles with coulombic efficiency to 92%. These results deliver a concept of opening a new opportunity for future applications in transparent flexible energy storage.

Synthesis of IrO2 decorated core-shell PS@PPyNH2 microspheres for bio-interface application.

In this paper, an effective approach is demonstrated for the fabrication of IrO2-decorated polystyrene@functionalized polypyrrole (core@shell; PS@PPyNH2) microspheres. The synthesis begins with the preparation of monodispersive PS microspheres with a diameter of 490 nm, by a process of emulsifier-free emulsion polymerization, followed by a copolymerization process involving pyrrole and PyNH2 monomers in a PS microsphere aqueous suspension, to produce uniform PS@PPyNH2 microspheres with a diameter of 536 nm. The loading of 2 nm IrO2 nanoparticles onto the PS@PPyNH2 microspheres can be easily adjusted by tuning the pH value of the IrO2 colloidal solution and the PS@PPyNH2 suspension. At pH 4, we successfully obtain IrO2-decorated PS@PPyNH2 microspheres via electrostatic attraction and hydrogen bonding simultaneously between the negatively-charged IrO2 nanoparticles and the positively-charged PS@PPyNH2 microspheres. These IrO2-decorated PS@PPyNH2 microspheres exhibit a characteristic cyclic voltammetric profile, similar to that of an IrO2 thin film. The charge storage capacity is 5.19 mA cm-2, a value almost five times greater than that of PS@PPyNH2 microspheres. In addition, these IrO2-decorated PS@PPyNH2 microspheres exhibit excellent cell viability and biocompatibility.

Realizing Efficient Charge/Energy Transfer and Charge Extraction in Fullerene-Free Organic Photovoltaics via a Versatile Third Component.

Solution-processed organic photovoltaics (OPVs) based on bulk-heterojunctions have gained significant attention to alleviate the increasing demend of fossil fuel in the past two decades. OPVs combined of a wide bandgap polymer donor and a narrow bandgap nonfullerene acceptor show potential to achieve high performance. However, there are still two reasons to limit the OPVs performance. One, although this combination can expand from the ultraviolet to the near-infrared region, the overall external quantum efficiency of the device suffers low values. The other one is the low open-circuit voltage (VOC) of devices resulting from the relatively downshifted lowest unoccupied molecular orbital (LUMO) of the narrow bandgap. Herein, the approach to select and incorporate a versatile third component into the active layer is reported. A third component with a bandgap larger than that of the acceptor, and absorption spectra and LUMO levels lying within that of the donor and acceptor, is demonstrated to be effective to conquer these issues. As a result, the power conversion efficiencies (PCEs) are enhanced by the elevated short-circuit current and VOC; the champion PCEs are 11.1% and 13.1% for PTB7-Th:IEICO-4F based and PBDB-T:Y1 based solar cells, respectively.

Enhanced Photocarrier Generation with Selectable Wavelengths by M-Decorated-CuInS2 Nanocrystals (M = Au and Pt) Synthesized in a Single Surfactant Process on MoS2 Bilayers.

A facile approach for the synthesis of Au- and Pt-decorated CuInS2 nanocrystals (CIS NCs) as sensitizer materials on the top of MoS2 bilayers is demonstrated. A single surfactant (oleylamine) is used to prepare such heterostructured noble metal decorated CIS NCs from the pristine CIS. Such a feasible way to synthesize heterostructured noble metal decorated CIS NCs from the single surfactant can stimulate the development of the functionalized heterostructured NCs in large scale for practical applications such as solar cells and photodetectors. Photodetectors based on MoS2 bilayers with the synthesized nanocrystals display enhanced photocurrent, almost 20-40 times higher responsivity and the On/Off ratio is enlarged one order of magnitude compared with the pristine MoS2 bilayers-based photodetectors. Remarkably, by using Pt- or Au-decorated CIS NCs, the photocurrent enhancement of MoS2 photodetectors can be tuned between blue (405 nm) to green (532 nm). The strategy described here acts as a perspective to significantly improve the performance of MoS2 -based photodetectors with the controllable absorption wavelengths in the visible light range, showing the feasibility of the possible color detection.

Observation of Switchable Photoresponse of a Monolayer WSe2-MoS2 Lateral Heterostructure via Photocurrent Spectral Atomic Force Microscopic Imaging.

In the pursuit of two-dimensional (2D) materials beyond graphene, enormous advances have been made in exploring the exciting and useful properties of transition metal dichalcogenides (TMDCs), such as a permanent band gap in the visible range and the transition from indirect to direct band gap due to 2D quantum confinement, and their potential for a wide range of device applications. In particular, recent success in the synthesis of seamless monolayer lateral heterostructures of different TMDCs via chemical vapor deposition methods has provided an effective solution to producing an in-plane p-n junction, which is a critical component in electronic and optoelectronic device applications. However, spatial variation of the electronic and optoelectonic properties of the synthesized heterojunction crystals throughout the homogeneous as well as the lateral junction region and the charge carrier transport behavior at their nanoscale junctions with metals remain unaddressed. In this work, we use photocurrent spectral atomic force microscopy to image the current and photocurrent generated between a biased PtIr tip and a monolayer WSe2-MoS2 lateral heterostructure. Current measurements in the dark in both forward and reverse bias reveal an opposite characteristic diode behavior for WSe2 and MoS2, owing to the formation of a Schottky barrier of dissimilar properties. Notably, by changing the polarity and magnitude of the tip voltage applied, pixels that show the photoresponse of the heterostructure are observed to be selectively switched on and off, allowing for the realization of a hyper-resolution array of the switchable photodiode pixels. This experimental approach has significant implications toward the development of novel optoelectronic technologies for regioselective photodetection and imaging at nanoscale resolutions. Comparative 2D Fourier analysis of physical height and current images shows high spatial frequency variations in substrate/MoS2 (or WSe2) contact that exceed the frequencies imposed by the underlying substrates. These results should provide important insights in the design and understanding of electronic and optoelectronic devices based on quantum confined atomically thin 2D lateral heterostructures.

Side-chain-bulk effects on the molecular packing and photovoltaic performance of benzotrithiophene-benzooxadiazole conjugated copolymers.

Two alternating donor-acceptor conjugated polymers, PBTTBO-C13 C11 and PBTTBO-C13 C8 , comprising 5-alkylbenzo[1,2-b:3,4-b':5,6-d'']trithiophene (BTT) as the donor and 4,7-bis(4-dodecylthien-2-yl)benzo[1,2,5]oxadiazole (BO) as the acceptor, with different alkyl side-chain architectures on their BTT units are synthesized, and their bulk heterojunction photovoltaic properties when blended with the fullerene PC71 BM are characterized. Even a slight change in the length of the alkyl chain of the BTT units influences the steric bulk to such a degree that it substantially affects the molecular packing of the polymers and the performance of their photovoltaic devices. The bulkier side chains of the polymer PBTTBO-C13 C11 not only prevent its crystallization, but also suppress its light-absorption coefficient relative to that of PBTTBO-C13 C8 , as evidenced by X-ray diffraction and UV/Vis absorption studies, presumably because of weakened intermolecular interactions. Moreover, the polymer bearing bulkier side chains, PBTTBO-C13 C11 , is less miscible with PC71 BM than PBTTBO-C13 C8 , and this characteristic determines the morphology of their annealed blended films, as shown by TEM studies. The best efficiency is obtained with a device containing an annealed PBTTBO-C13 C8 /PC71 BM (1/2 w/w) active layer that was maintained at 120 °C for 10 min, which shows a power conversion efficiency of 6.2 %, an open-circuit voltage of 0.75 V, a short-circuit current density of 12.6 mA cm(-2) , and a fill factor of 66 %.

Conjugated polymer/nanocrystal nanocomposites for renewable energy applications in photovoltaics and photocatalysis.

Conjugated polymer/nanocrystal composites have attracted much attention for use in renewable energy applications because of their versatile and synergistic optical and electronic properties. Upon absorbing photons, charge separation occurs in the nanocrystals, generating electrons and holes for photocurrent flow or reduction/oxidation (redox) reactions under proper conditions. Incorporating these nanocrystals into conjugated polymers can complement the visible light absorption range of the polymers for photovoltaics applications or allow the polymers to sensitize or immobilize the nanocrystals for photocatalysis. Here, the current developments of conjugated polymer/nanocrystal nanocomposites for bulk heterojunction-type photovoltaics incorporating Cd- and Pb-based nanocrystals or quantum dots are reviewed. The effects of manipulating the organic ligands and the concentration of the nanocrystal precursor, critical factors that affect the shape and aggregation of the nanocrystals, are also discussed. In the conclusion, the mechanisms through which conjugated polymers can sensitize semiconductor nanocrystals (TiO2 , ZnO) to ensure efficient charge separation, as well as how they can support immobilized nanocrystals for use in photocatalysis, are addressed.

Three-dimensional molybdenum sulfide sponges for electrocatalytic water splitting.

Electroactive MoSx catalysts on porous 3D sponges synthezied by a simple and scalable thermolysis process are proposed. Although no conducting materials are used to host the MoSx catalysts, they still serve as efficient electrodes for hydrogen evolution. The high current density of the MoSx-coated sponges are attributed to the large electrochemical surface area and their S-rich chemical structure.

Achieving High Efficiency and Stability in Organic Photovoltaics with a Nanometer-Scale Twin p-i-n Structured Active Layer.

In pursuing high stability and power conversion efficiency for organic photovoltaics (OPVs), a sequential deposition (SD) approach to fabricate active layers with p-i-n structures (where p, i, and n represent the electron donor, mixed donor:acceptor, and electron acceptor regions, respectively, distinctively different from the bulk heterojunction (BHJ) structure) has emerged. Here, we present a novel approach that by incorporating two polymer donors, PBDBT-DTBT and PTQ-2F, and one small-molecule acceptor, BTP-3-EH-4Cl, into the active layer with sequential deposition, we formed a device with nanometer-scale twin p-i-n structured active layer. The twin p-i-n PBDBT-DTBT:PTQ-2F/BTP-3-EH-4Cl device involved first depositing a PBDBT-DTBT:PTQ-2F blend under layer and then a BTP-3-EH-4Cl top layer and exhibited an improved power conversion efficiency (PCE) value of 18.6%, as compared to the 16.4% for the control BHJ PBDBT-DTBT:PTQ-2F:BTP-3-EH-4Cl device or 16.6% for the single p-i-n PBDBT-DTBT/BTP-3-EH-4Cl device. The PCE enhancement resulted mainly from the twin p-i-n active layer's multiple nanoscale charge carrier pathways that contributed to an improved fill factor and faster photocurrent generation based on transient absorption studies. The PBDBT-DTBT:PTQ-2F/BTP-3-EH-4Cl film possessed a vertical twin p-i-n morphology that was revealed through secondary ion mass spectrometry and synchrotron grazing-incidence small-angle X-ray scattering analyses. The thermal stability (T80) at 85 °C of the twin p-i-n PBDBT-DTBT:PTQ-2F/BTP-3-EH-4Cl device surpassed that of the single p-i-n PBDBT-DTBT/BTP-3-EH-4Cl devices (906 vs 196 h). This approach of providing a twin p-i-n structure in the active layer can lead to substantial enhancements in both the PCE and stability of organic photovoltaics, laying a solid foundation for future commercialization of the organic photovoltaics technology.

High-Performance Poly(3-hexyl thiophene)-Based Organic Photovoltaics with Side-Chain Engineering of Core Units of Small Molecule Acceptors.

In this study, we synthesized a series of four large-band gap small molecule acceptors with side-chain engineering of the dithieno-pyrrolo-fused pentacyclic benzotriazole (BZTTP or Y1 core) or the fused-ring dithienothiophene-pyrrolobenzothiadiazole (TPBT or Y6 core) with difluoro-indene-dione (IO2F) or dichloro-indene-dione (IO2Cl) end groups to form Y1-IO2F, Y1-IO2Cl, Y6-IO2F, and Y6-IO2Cl acceptors, respectively, for blending with poly(3-hexyl thiophene) (P3HT) for bulk heterojunction organic photovoltaics. The complementary UV-vis absorption spectra of these small molecules and P3HT along with their offset energy bands allow broad absorption and effective electron transfer. Through synchrotron wide-angle X-ray scattering (WAXS) analyses and contact angle measurements, we found that the blend of the small molecule Y6-IO2F (having a TPBT core) and P3HT achieves an optimum morphology that balances their crystallinity and miscibility, among those of these four blends, leading to a substantial enhancement in the short-circuit current density and thus power conversion efficiency (PCE) in their devices. For example, the P3HT:Y6-IO2F (w/w: 1/1.2) device exhibited a champion PCE of 10.5% with a short current density (Jsc) value of 15.9 mA/cm2 as compared to the P3HT:Y1-IO2F device having a PCE of 2.2% with a Jsc value of 5.7 mA/cm2 because of the higher Y6-IO2F (with TPBT core) molecular packing that facilitated carrier transport in the devices. The enhanced thermal stability exhibited by the devices incorporating Y6-IO2F and Y6-IO2Cl, as compared to that of Y1-IO2F and Y1-IO2Cl devices, is also due to the more planar TPBT core structure, while the photostability of devices incorporating Y6-IO2Cl and Y1-IO2Cl is better than that of devices incorporating Y6-IO2F and Y1-IO2F, owing to more photostable chemical structures. These results present an outstanding performance for P3HT-based organic solar cells. Moreover, these small molecule blends are processed with an environmentally friendly solvent tetrahydrofuran, demonstrating both the sustainability and commercial viability of these types of organic photovoltaics.

Synthesis of main-chain metallo-copolymers containing donor and acceptor bis-terpyridyl ligands for photovoltaic applications.

Two random (Zn(II)-based P1-P2) and two alternating (Ru(II)-based P3-P4) metallo-copolymers containing bis-terpyridyl ligands with various central donor (i.e., fluorene or carbazole) and acceptor (i.e., benzothiadiazole) moieties were synthesized. The effects of electron donor-acceptor interactions with metal (Zn(II) and Ru(II)) ions on their thermal, optical, and electrochemical properties were investigated. Because of the strong ICT transitions between donor and acceptor ligands in both Zn(II)- and Ru(II)-based metallo-coplymers and MLCT transitions in Ru(II)-based metallo-coplymers, the absorption spectra covered a broad range of 260-750 nm with the band gaps of 1.57-1.77 eV. In addition, the introduction of Ru(II)-based metallo-coplymer P4 mixed with PC(60)BM as an active layer of the BHJ solar cell device exhibited the highest PCE value up to 0.90%.

Ion accumulation-induced capacitance elevation in a microporous graphene-based supercapacitor.

High-performance porous 3D graphene-based supercapacitors are one of the most promising and challenging directions for future energy technologies. Microporous graphene has been synthesized by the pyrolysis method. The fabricated lightweight graphene with a few layers (FLG) has an ultra-high surface area of 2266 m2 g-1 along with various-sized micropores. The defect-induced morphology and pore size distribution of the fabricated graphene are examined, and the results show that the micropores vary from 0.85 to 1.9 nm and the 1.02 nm pores contribute 30% of the total surface area. The electrochemical behaviour of the electrode fabricated using this graphene has been studied with various concentrations of the KOH electrolyte. The highest specific capacitance of the graphene electrode of 540 F g-1 (close to the theoretical value, ∼550 F g-1) can be achieved by using the 1 M KOH electrolyte. This high specific capacitance contribution involves the counter ion adsorption, co-ion desorption, and ion permutation mechanisms. The formation of a Helmholtz layer, as well as the diffusion of the electrolyte ions, confirms this phenomenon. The symmetrical solid-state supercapacitor fabricated with the graphene electrodes and PVA-KOH gel as the electrolyte exhibits excellent energy and power densities of 18 W h kg-1 and 10.2 kW kg-1, respectively. This supercapacitor also shows a superior 100% coulombic efficiency after 6000 cycles.

Perylene Diimide-Fused Dithiophenepyrroles with Different End Groups as Acceptors for Organic Photovoltaics.

In this study, we synthesized four new A-DA'D-A acceptors (where A and D represent acceptor and donor chemical units) incorporating perylene diimide units (A') as their core structures and presenting various modes of halogenation and substitution of the functional groups at their end groups (A). In these acceptors, by fusing dithiophenepyrrole (DTP) moieties (D) to the helical perylene diimide dimer (hPDI) to form fused-hPDI (FhPDI) cores, we could increase the D/A' oscillator strength in the cores and, thus, the intensity of intramolecular charge transfer (ICT), thereby enhancing the intensity of the absorption bands. With four different end group units─IC2F, IC2Cl, IO2F, and IO2Cl─tested, each of these acceptor molecules exhibited different optical characteristics. Among all of these systems, the organic photovoltaic device incorporating the polymer PCE10 blended with the acceptor FhPDI-IC2F (1:1.1 wt %) had the highest power conversion efficiency (PCE) of 9.0%; the optimal PCEs of PCE10:FhPDI-IO2F, PCE10:FhPDI-IO2Cl, and PCE10:FhPDI-IC2Cl (1:1.1 wt %) devices were 5.2, 4.7, and 7.7%, respectively. The relatively high PCE of the PCE10:FhPDI-IC2F device resulted primarily from the higher absorption coefficients of the FhPDI-IC2F acceptor, lower energy loss, and more efficient charge transfer; the FhPDI-IC2F system experienced a lower degree of geminate recombination─as a result of improved delocalization of π-electrons along the acceptor unit─relative to that of the other three acceptors systems. Thus, altering the end groups of multichromophoric PDI units can increase the PCEs of devices incorporating PDI-derived materials and might also be a new pathway for the creation of other valuable fused-ring derivatives.

Bubble-Channeling Electrophoresis of Honeycomb-Like Chitosan Composites.

A chitosan composite with a vertical array of pore channels is fabricated via an electrophoretic deposition (EPD) technique. The composite consists of chitosan and polyethylene glycol, as well as nanoparticles of silver oxide and silver. The formation of hydrogen bubbles during EPD renders a localized increase of hydroxyl ions that engenders the precipitation of chitosan. In addition, chemical interactions among the constituents facilitate the establishment of vertical channels occupied by hydrogen bubbles that leads to the unique honeycomb-like microstructure; a composite with a porosity of 84%, channel diameter of 488 µm, and channel length of 2 mm. The chitosan composite demonstrates an impressive water uptake of 2100% and a two-stage slow release of silver. In mass transport analysis, both Disperse Red 13 and ZnO powders show a much enhanced transport rate over that of commercial gauze. Due to its excellent structural integrity and channel independence, the chitosan composite is evaluated in a passive suction mode for an adhesive force of 9.8 N (0.56 N cm-2 ). The chitosan composite is flexible and is able to maintain sufficient adhesive force toward objects with different surface curvatures.

Nanostructured nanorod arrays presenting TiO2 nanorods/poly(3-hexylthiophene) for solar cells application.

We have fabricated inverted heterojunction solar cell devices incorporating titanium dioxide nanorod/poly(3-hexylthiophene) (P3HT) rod arrays using melt-assisted anodic alumina oxide template. Using transmission electron microscopy and conductance atomic force microscopy, we revealed that phase-separated TiO2 rich (n-type) and P3HT rich (p-type) regions presents in these rod arrays. The optimized composite rod array structure had a higher hole mobility than that of the blend film consisting of TiO2 nanorod and P3HT as determined by fitting the dark J-V curves into the space charge-limited current model. The more efficient carrier transport of the device incorporating the nanorod arrays provided it with both a higher short-circuit current density and power conversion efficiency.

High-Performance Organic Solar Cells Featuring Double Bulk Heterojunction Structures with Vertical-Gradient Selenium Heterocyclic Nonfullerene Acceptor Concentrations.

In this study, we prepared organic photovoltaics (OPVs) featuring an active layer comprising double bulk heterojunction (BHJ) structures, featuring binary blends of a polymer donor and concentration gradients of two small-molecule acceptors. After forming the first BHJ structure by spin-coating, the second BHJ layer was transfer-printed onto the first using polydimethylsiloxane stamps. A specially designed selenium heterocyclic small-molecule acceptor (Y6-Se-4Cl) was employed as the second acceptor in the BHJ. X-ray photoelectron spectroscopy revealed that the two acceptors formed a gradient concentration profile across the active layer, thereby facilitating charge transportation. The best power conversion efficiencies (PCEs) for the double-BHJ-structured devices incorporating PM6:Y6-Se-4Cl/PM6:Y6 and PM6:Y6-Se-4Cl/PM6:IT-4Cl were 16.4 and 15.8%, respectively; these values were higher than those of devices having one-BHJ structures based on PM6:Y6-Se-4Cl (15.0%), PM6:Y6 (15.4%), and PM6:IT-4Cl (11.6%), presumably because of the favorable vertical concentration gradient of the selenium-containing small-molecule Y6-Se-4Cl in the active layer as well as some complementary light absorption. Thus, combining two BHJ structures with a concentration gradient of the two small-molecule acceptors can be an effective approach for enhancing the PCEs of OPVs.