Synergistic concurrent enhancement of charge generation, dissociation, and transport in organic solar cells with plasmonic metal-carbon nanotube hybrids

Simultaneous Guidance of Intraoperative Tumor Resection by Near-Infrared-II Imaging Combined with Complementary Surface-Enhanced Raman Imaging via Janus Au-PbS Nanoparticles

The development of sophisticated nanomaterials with synergistically enhanced functionalities and applications has been greatly promoted via the construction of Janus nanoparticles with controlled compositions. In this work, we described and demonstrated the formation of Janus Au-PbS nanoparticles (NPs) by Au NPs-mediated spontaneous epitaxial nucleation and growth. The mechanism of formation of Janus Au-PbS NPs was investigated in detail. Then, we also found that there was a strong electronic interaction between the Au NPs and PbS quantum dots (QDs) in Janus Au-PbS NPs, where electrons were transferred from the Au NPs domain to the PbS QDs domain. Moreover, the Janus Au-PbS NPs integrated the high-brightness tunable second near-infrared (NIR-II) photoluminescence emission and surface-enhanced Raman scattering (SERS), which achieved good intraoperative tumor resection. This complementary dual-functional imaging had the potential to enable more accurate tumor imaging and resection.

Integrated Omnidirectional Design of Non-Volatile Solid Additive Enables Binary Organic Solar Cells with Efficiency Exceeding 19.5

Solid additives have drawn great attention due to their numerous appealing benefits in enhancing the power conversion efficiencies (PCEs) of organic solar cells (OSCs). To date, various strategies have been reported for the selection or design of non-volatile solid additives. However, the lack of a general design/evaluation principles for developing non-volatile solid additives often results in individual solid additives offering only one or two efficiency-boosting attributes. In this work, we propose an integrated omnidirectional strategy for designing non-volatile solid additives. By validating the method on the 4,5,9,10-pyrene diimide (PyDI) system, a novel non-volatile solid additive named PyMC5 was designed. PyMC5 is capable of enhancing device performance by establishing synergistic dual charge transfer channels, forming appropriate interactions with active layer materials, reducing non-radiative voltage loss and optimizing film morphology. Notably, the binary device (PM6 : L8-BO) treated by PyMC5 achieved a PCE over 19.5 %, ranking among the highest reported to date. In addition, the integration of PyMC5 mitigated the degradation process of the devices under photo- and thermal-stress conditions. This work demonstrates an efficient integrated omnidirectional approach for designing non-volatile solid additives, offering a promising avenue for further advancements in OSC development.

Synergistic Effect of Plasmonic Gold Nanoparticles Decorated Carbon Nanotubes in Quantum Dots/TiO2 for Optoelectronic Devices

Here, a facile approach to enhance the performance of solar-driven photoelectrochemical (PEC) water splitting is described by means of the synergistic effects of a hybrid network of plasmonic Au nanoparticles (NPs) decorated on multiwalled carbon nanotubes (CNTs). The device based on TiO2-Au:CNTs hybrid network sensitized with colloidal CdSe/(CdSe x S1- x )5/(CdS)1 core/alloyed shell quantum dots (QDs) yields a saturated photocurrent density of 16.10 ± 0.10 mA cm-2 [at 1.0 V vs reversible hydrogen electrode (RHE)] under 1 sun illumination (AM 1.5G, 100 mW cm-2), which is ≈26% higher than the control device. The in-depth mechanism behind this significant improvement is revealed through a combined experimental and theoretical analysis for QDs/TiO2-Au:CNTs hybrid network and demonstrates the multifaceted impact of plasmonic Au NPs and CNTs: i) hot-electron injection from Au NPs into CNTs and TiO2; ii) near-field enhancement of the QDs absorption and carrier generation/separation processes by the plasmonic Au NPs; iii) enhanced photoinjected electron transport due to the highly directional pathways offered by CNTs. These results provide fundamental insights on the properties of QDs/TiO2-Au:CNTs hybrid network, and highlights the possibility to improve the performance of other solar technologies.

Abnormal dewetting of Ag layer on three-dimensional ITO branches to form spatial plasmonic nanoparticles for organic solar cells

Three-dimensional (3D) plasmonic structures have attracted great attention because abnormal wetting behavior of plasmonic nanoparticles (NPs) on 3D nanostructure can enhance the localized surface plasmons (LSPs). However, previous 3D plasmonic nanostructures inherently had weak plasmonic light absorption, low electrical conductivity, and optical transmittance. Here, we fabricated a novel 3D plasmonic nanostructure composed of Ag NPs as the metal for strong LSPs and 3D nano-branched indium tin oxide (ITO BRs) as a transparent and conductive framework. The Ag NPs formed on the ITO BRs have a more dewetted behavior than those formed on the ITO films. We experimentally investigated the reasons for the dewetting behavior of Ag NPs concerning the geometry of ITO BRs. The spherical Ag NPs are spatially separated and have high density, thereby resulting in strong LSPs. Finite-domain time-difference simulation evidenced that spatially-separated, high-density and spherical Ag NPs formed on ITO BRs dramatically boost the localized electric field in the active layer of organic solar cells (OSCs). Photocurrent of PTB7:PCBM OSCs with the ITO BRs/Ag NPs increased by 14%.

Recent progress of light manipulation strategies in organic and perovskite solar cells

Organic and perovskite solar cells are suffering from the insufficient utilization of incident light and thus low light harvesting efficiency despite their rapid progress in the past decade. In this regard, light manipulation strategies have attracted numerous attention to solve this inherent limit. Herein, the recent advances in light manipulation techniques in this area are overviewed. The light manipulation mechanisms are illustrated to classify the structures. Various light manipulation structures, fabrication techniques, and corresponding results are given and discussed, addressing the suppression of surface reflection, nano/micro-structure-induced light scattering, and the plasmonic effects with periodic metallic patterns and metallic nanoparticles. A brief perspective on future research is also proposed for pursuing broadband light harvesting.

Broadband and wide-angle light absorption of organic solar cells based on multiple-depths metal grating

A silver grating containing three grooves with different depths in one period was proposed as the back electrode for improving light absorption in organic solar cells. We found that the broadband absorption enhancement of the active layer covering the visible and near-infrared bands can be obtained due to the excitation of surface plasmon resonance and the multiple resonances of cavity mode. The integrated absorption efficiency of the proposed structure under TM polarization between 350 nm to 900 nm is 57.4%, with consideration of the weight of AM 1.5G solar spectrum, and is increased by 13.4% with respect to the equivalent planar device. Besides, the wide-angle absorption in proposed structure can be observed in the range from 0 to 50 degrees. These findings are of great importance for rationally designing composite nanostructures of metal gratings-based absorbers for sensing and photon-detecting applications.

Plasmon-mediated nonradiative energy transfer from a conjugated polymer to a plane of graphene-nanodot-supported silver nanoparticles: an insight into characteristic distance

Hybrid nanostructures comprising conjugated polymers (CPs) and plasmonic metals show excellent performance in light harvesting. However, the energy transfer mechanism of the CP film to nearby metal nanoparticles, especially knowledge of the characteristic distance, is still unclear. Here, quenching of the emission of a CP film in proximity to a monolayer of graphene-nanodot-supported silver nanoparticles (GND-Ag NPs) is investigated. Uniform Ag NPs with D = 3.2 nm were grown on GNDs in situ under mild light irradiation, and a series of bilayer structures of GND-Ag NPs/CPs were constructed by spin-coating blue, green and red light-emitting poly(9,9-dioctylfluorene) (PFO), poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) and poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV),respectively, on top of the GND-Ag NP plane. The spacer distance was controlled by the layers of assembled polyelectrolytes. Both steady and transient photoluminescence (PL) spectra showed emission quenching of the bilayer structures, providing the maximum efficiency of 99% for the F8BT films. The surface density of GND-Ag NPs and the spacer distance-dependent PL quenching data were analyzed within the plasmonic resonant energy transfer model, and the extracted characteristic distances are 6 nm, 3 nm and 10 nm for the PFO, F8BT and MEH-PPV systems, respectively. Current-sensing atomic force microscopy shows that the GND-Ag NPs/F8BT film exhibits enhanced electrical conductivity. These results are believed to be important for the development of plasmonic enhanced polymer photovoltaics and photocatalysis.

Tailoring optical nonlinearities of LiNbO3 crystals by plasmonic silver nanoparticles for broadband saturable absorbers

We report on the synthesis of plasmonic Ag nanoparticles (NPs) embedded in a LiNbO₃ crystal (AgNP:LN) by ion implantation and its application as an efficient broadband saturable absorber (SA) to realize Q-switched pulsed laser generation at both visible and near-infrared wavelength bands. The nonlinear optical response of AgNP:LN is considered as a synergistic effect between Ag NPs and LiNbO₃. We apply the AgNP:LN as visible-near-infrared broadband saturable absorbers (SAs) into Pr:LuLiF₄ bulk and Nd:YVO₄ waveguide laser cavity, achieving efficient passively Q-switched laser at 639 nm and 1064 nm, respectively. This work paves a new way to tailor the nonlinear optical response of LiNbO₃ crystals by using plasmonic Ag NPs, manifesting the significant potential as broadband SAs in the aspect of pulsed lasing.

Improving charge transport by the ultrathin QDs interlayer in polymer solar cells

Lead sulfide (PbS) quantum dots (QDs) have been incorporated into PTB7:PC71BM BHJ active layers to fabricate polymer solar cells (PSCs) and gather on the top surface of active layers to form an ultrathin interlayer. The PbS QDs ultrathin interlayer with an appropriate thickness increases the carrier transport capacity, exciton dissociation and reduces the carrier recombination, which leads to a higher short circuit current (J sc) and fill factor (FF). Finally, the power conversion efficiency (PCE) improves from 7.03% (control devices) to 7.87% with an ultrathin interlayer by doping 5% PbS QDs, while the current density (J sc) and fill factor (FF) enhances from 13.83 mA cm-2 to 14.81 mA cm-2 and from 68.70% to 70.85%, respectively.

Nanocomposite for Solar Energy Application

Organic and inorganic nanocomposites have been successfully used in the preparation of thin film organic solar cells with the view either to enhance the harvesting of solar energy or to assist in the charge transport processes. The optical absorption, conductivity and environmental stability of the nanocomposite are the main criteria that determine the suitability of the material for solar energy application. This chapter discusses the properties of a number of nanocomposite which are widely used in the preparation of various types of thin film solar cells.

A naphthodithieno[3,2-b]thiophene-based copolymer as a novel third component in ternary polymer solar cells with a simultaneously enhanced open circuit voltage, short circuit current and fill factor

Ternary polymer solar cells with simultaneously improved V_OC, J_SC and FF have been achieved by doping PV12 as a third component.

Recent Development in ITO-free Flexible Polymer Solar Cells

Polymer solar cells have shown good prospect for development due to their advantages of low-cost, light-weight, solution processable fabrication, and mechanical flexibility. Their compatibility with the industrial roll-to-roll manufacturing process makes it superior to other kind of solar cells. Normally, indium tin oxide (ITO) is adopted as the transparent electrode in polymer solar cells, which combines good conductivity and transparency. However, some intrinsic weaknesses of ITO restrict its large scale applications in the future, including a high fabrication price using high temperature vacuum deposition method, scarcity of indium, brittleness and scaling up of resistance with the increase of area. Some substitutes to ITO have emerged in recent years, which can be used in flexible polymer solar cells. This article provides the review on recent progress using other transparent electrodes, including carbon nanotubes, graphene, metal nanowires and nanogrids, conductive polymer, and some other electrodes. Device stability is also discussed briefly.

Photo-stimulated triboelectric generation

A new photo-stimulated triboelectric generation occurring between a metal-oxide and polyimide during friction was demonstrated. The output currents of the triboelectric nanogenerator were significantly enhanced, under light illumination, up to approximately 5 times depending on the wavelength of the light, providing a new route for energy harvesting devices as well as self-powered selective photodetectors.

Multi-Chlorine-Substituted Self-Assembled Molecules As Anode Interlayers: Tuning Surface Properties and Humidity Stability for Organic Photovoltaics

Self-assembled small molecules (SASMs) are effective materials to improve the interfacial properties between a metal/metal oxide and the overlying organic layer. In this work, surface modification of indium tin oxide (ITO) electrode by a series of Cl-containing SASMs has been exploited to control the surface properties of ITO and device performance for organic photovoltaics. Depending on the position and degrees of chlorination for SASMs, we could precisely manipulate the work function of the ITO electrode, and chemisorption of SASMs on ITO as well. Consequently, a power conversion efficiency (PCE) of 9.1% was achieved with tetrachlorobenzoic acid (2,3,4,5-CBA) SASM by a simple solution-processed method based on PTB7-Th-PC₇₁BM heterojunction. More intriguingly, we discover that device performance is closely associated with the humidity of ambient conditions. When the humidity increases from 35-55% to 80-95%, device performance with 2,3,4,5-CBA has negligible reduction, in contrast with other SASMs that show a sharp reduction in PCEs. The increased device performance is primarily attributed to a matched work function, stable chemisorption, and beneficial wettability with overlying active layer. These findings suggest an available approach for manufacturing inexpensive, stable, efficient, and environmentally friendly organic photovoltaics by appropriate self-assembled small molecules.

Upconversion-Triggered Charge Separation in Polymer Semiconductors

Upconversion is a unique optical property that is driven by a sequential photon pumping and generation of higher energy photons in a consecutive manner. The efficiency improvement in photovoltaic devices can be achieved when upconverters are integrated since upconverters contribute to the generation of extra photons. Despite numerous experimental studies confirming the relationship, fundamental explanations for a real contribution of upconversion to photovoltaic efficiency are still in demand. In this respect, we suggest a new approach to visualize the upconversion event in terms of surface photovoltage (SPV) by virtue of Kelvin probe force microscopy (KPFM). One of the most conventional polymer semiconductors, poly(3-hexyl thiophene) (P3HT), is employed as a sensitizer to generate charge carriers by upconverted light. KPFM measurements reveal that the light upconversion enabled the formation of charge carriers in P3HT, resulting in large SPV of -54.9 mV. It confirms that the energy transfer from upconverters to P3HT can positively impact the device performance in organic solar cells (OSCs).

Ultrafast Interfacial Self-Assembly of 2D Transition Metal Dichalcogenides Monolayer Films and Their Vertical and In-Plane Heterostructures

Cost effective scalable method for uniform film formation is highly demanded for the emerging applications of 2D transition metal dichalcogenides (TMDs). We demonstrate a reliable and fast interfacial self-assembly of TMD thin films and their heterostructures. Large-area 2D TMD monolayer films are assembled at air-water interface in a few minutes by simple addition of ethyl acetate (EA) onto dilute aqueous dispersions of TMDs. Assembled TMD films can be directly transferred onto arbitrary nonplanar and flexible substrates. Precise thickness controllability of TMD thin films, which is essential for thickness-dependent applications, can be readily obtained by the number of film stacking. Most importantly, complex structures such as laterally assembled 2D heterostructures of TMDs can be assembled from mixture solution dispersions of two or more different TMDs. This unusually fast interfacial self-assembly could open up a novel applications of 2D TMD materials with precise tunability of layer number and film structures.

Nanostructured carbon–metal hybrid aerogels from bacterial cellulose

Nanostructured carbon–metal hybrid aerogels by carbothermal reduction of nickel or iron hydroxide inside bacterial cellulose at remarkably low temperatures.

Plasmonic Solar Cells: From Rational Design to Mechanism Overview

Plasmonic effects have been proposed as a solution to overcome the limited light absorption in thin-film photovoltaic devices, and various types of plasmonic solar cells have been developed. This review provides a comprehensive overview of the state-of-the-art progress on the design and fabrication of plasmonic solar cells and their enhancement mechanism. The working principle is first addressed in terms of the combined effects of plasmon decay, scattering, near-field enhancement, and plasmonic energy transfer, including direct hot electron transfer and resonant energy transfer. Then, we summarize recent developments for various types of plasmonic solar cells based on silicon, dye-sensitized, organic photovoltaic, and other types of solar cells, including quantum dot and perovskite variants. We also address several issues regarding the limitations of plasmonic nanostructures, including their electrical, chemical, and physical stability, charge recombination, narrowband absorption, and high cost. Next, we propose a few potentially useful approaches that can improve the performance of plasmonic cells, such as the inclusion of graphene plasmonics, plasmon-upconversion coupling, and coupling between fluorescence resonance energy transfer and plasmon resonance energy transfer. This review is concluded with remarks on future prospects for plasmonic solar cell use.

Plasmonic Periodic Nanodot Arrays via Laser Interference Lithography for Organic Photovoltaic Cells with >10% Efficiency

In this study, we demonstrate a viable and promising optical engineering technique enabling the development of high-performance plasmonic organic photovoltaic devices. Laser interference lithography was explored to fabricate metal nanodot (MND) arrays with elaborately controlled dot size as well as periodicity, allowing spectral overlap between the absorption range of the active layers and the surface plasmon band of MND arrays. MND arrays with ∼91 nm dot size and ∼202 nm periodicity embedded in a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) hole transport layer remarkably enhanced the average power conversion efficiency (PCE) from 7.52% up to 10.11%, representing one of the highest PCE and degree of enhancement (∼34.4%) levels compared to the pristine device among plasmonic organic photovoltaics reported to date. The plasmonic enhancement mechanism was investigated by both optical and electrical analyses using finite difference time domain simulation and conductive atomic force microscopy studies.

Increasing Polymer Solar Cell Fill Factor by Trap-Filling with F4-TCNQ at Parts Per Thousand Concentration

Intrinsic traps in organic semiconductors can be eliminated by trap-filling with F4-TCNQ. Photovoltaic tests show that devices with F4-TCNQ at parts per thousand concentration outperform control devices due to an improved fill factor. Further studies confirm the trap-filling pathway and demonstrate the general nature of this finding.

Light Manipulation in Organic Photovoltaics

Organic photovoltaics (OPVs) hold great promise for next-generation photovoltaics in renewable energy because of the potential to realize low-cost mass production via large-area roll-to-roll printing technologies on flexible substrates. To achieve high-efficiency OPVs, one key issue is to overcome the insufficient photon absorption in organic photoactive layers, since their low carrier mobility limits the film thickness for minimized charge recombination loss. To solve the inherent trade-off between photon absorption and charge transport in OPVs, the optical manipulation of light with novel micro/nano-structures has become an increasingly popular strategy to boost the light harvesting efficiency. In this Review, we make an attempt to capture the recent advances in this area. A survey of light trapping schemes implemented to various functional components and interfaces in OPVs is given and discussed from the viewpoint of plasmonic and photonic resonances, addressing the external antireflection coatings, substrate geometry-induced trapping, the role of electrode design in optical enhancement, as well as optically modifying charge extraction and photoactive layers.

Highly stable perovskite solar cells with an all-carbon hole transport layer

Nano-carbon materials (carbon nanotubes, graphene, and graphene oxide) have potential application for photovoltaics because of their excellent optical and electronic properties. Here, we demonstrate that a single-walled carbon nanotubes/graphene oxide buffer layer greatly improves the photovoltaic performance of organo-lead iodide perovskite solar cells. The carbon nanotubes/graphene oxide buffer layer works as an efficient hole transport/electron blocking layer. The photovoltaic conversion efficiency of 13.3% was achieved in the organo-lead iodide perovskite solar cell due to the complementary properties of carbon nanotubes and graphene oxide. Furthermore, the great improvement of photovoltaic performance stability in the perovskite solar cells using carbon nanotubes/graphene oxide/polymethyl methacrylate was demonstrated in comparison with that using a typical organic hole transport layer of 2,2',7,7'-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene.

Recent Development of Plasmonic Resonance-Based Photocatalysis and Photovoltaics for Solar Utilization

Increasing utilization of solar energy is an effective strategy to tackle our energy and energy-related environmental issues. Both solar photocatalysis (PC) and solar photovoltaics (PV) have high potential to develop technologies of many practical applications. Substantial research efforts are devoted to enhancing visible light activation of the photoelectrocatalytic reactions by various modifications of nanostructured semiconductors. This review paper emphasizes the recent advancement in material modifications by means of the promising localized surface plasmonic resonance (LSPR) mechanisms. The principles of LSPR and its effects on the photonic efficiency of PV and PC are discussed here. Many research findings reveal the promise of Au and Ag plasmonic nanoparticles (NPs). Continual investigation for increasing the stability of the plasmonic NPs will be fruitful.

Metal nanoparticles reveal the organization of single-walled carbon nanotubes in bundles

Single-walled carbon nanotubes (SWCNTs) were decorated with Ag and Au nanoparticles. The smaller SWCNTs in bundles are preferentially affected by the presence of metal nanoparticles. We postulate that smaller diameter SWCNTs surround larger ones.

Single-Walled Carbon Nanotube Film as Electrode in Indium-Free Planar Heterojunction Perovskite Solar Cells: Investigation of Electron-Blocking Layers and Dopants

In this work, we fabricated indium-free perovskite solar cells (SCs) using direct- and dry-transferred aerosol single-walled carbon nanotubes (SWNTs). We investigated diverse methodologies to solve SWNTs' hydrophobicity and doping issues in SC devices. These include changing wettability of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (

PEDOT

PSS), MoO3 thermal doping, and HNO3(aq) doping with various dilutions from 15 to 70 v/v% to minimize its instability and toxic nature. We discovered that isopropanol (IPA) modified

PEDOT

PSS works better than surfactant modified

PEDOT

PSS as an electron-blocking layer on SWNTs in perovskite SCs due to superior wettability, whereas MoO3 is not compatible owing to energy level mismatching. Diluted HNO3 (35 v/v%)-doped SWNT-based device produced the highest PCE of 6.32% among SWNT-based perovskite SCs, which is 70% of an indium tin oxide (ITO)-based device (9.05%). Its flexible application showed a PCE of 5.38% on polyethylene terephthalate (PET) substrate.