Synergistic Plasmonic Effects of Metal Nanoparticle–Decorated PEGylated Graphene Oxides in Polymer Solar Cells

Metal nanostructures that trigger plasmonic near-field effects are often incorporated in organic photovoltaic devices (OPVs) to improve their light-harvesting ability. These nanostructures usually can be positioned in two different locations in a device: (i) within the photon absorption layers and (ii) at the interfaces between the active layer and the metal electrodes. In this study, we developed amphiphilic gold nanoparticles (Au NPs) for use in dual plasmonic nanostructures within OPVs. We employed graphene oxide as the template to anchor the Au NPs, thereby avoiding their aggregation. Furthermore, we added poly­(ethylene glycol) (PEG) bis­(amine) to the synthesis medium to improve the solubility of the nanocomposites, such that they could be dispersed well in water and in several organic solvents. Accordingly, we could incorporate the PEGylated Au NP/graphene oxides readily into both the buffer layer and photoactive layer of OPVs, which, as a result, exhibited obvious enhancements in their photocurrents and overall device efficiencies. Moreover, we observed different spectral enhancement regions when we positioned the nanocomposites at different locations, reflecting the different dielectric environments surrounding the NPs; this unexpected behavior should assist in enhancing the broadband absorption of solar irradiation

Cross-Linkable Hole-Transport Materials Improve the Device Performance of Perovskite Light-Emitting Diodes

Hybrid organic/inorganic perovskites are promising candidate materials for use in photovoltaic applications. More recently, they have also become highly attractive as active materials for other optoelectronic devices, including lasers, light-emitting diodes, and photodetectors. Nevertheless, difficulties in forming continuous and uniform films and the existence of a charge-injection barrier between the perovskite layer and the electrodes have hindered the development of high-performance perovskite light-emitting diodes (PeLEDs). In this study, a cross-linked hole-transport layer (HTL) is introduced to improve the hole-injection efficiency of PeLEDs. Furthermore, this layer simultaneously facilitates the formation of smooth perovskite layers, presumably because of the different surface energies. More interestingly, the HTL also exhibits strong solvent effects on the device performance. When the processing solvent for fabricating the HTLs is changed from chlorobenzene to <i>N</i>,<i>N</i>-dimethylformamide (DMF), the perovskite layer becomes more uniform and continuous, leading to better surface coverage and higher device efficiency, presumably because DMF has strong affinity toward the perovskite precursors. The approach presented herein could become a general method for decreasing the hole-injection barrier of PeLEDs and, eventually, lead to higher device performance

Self-Assembled Poly(ethylene glycol) Buffer Layers in Polymer Solar Cells: Toward Superior Stability and Efficiency

In this study, we have systematically investigated the mechanism behind the formation of nanoscale self-assembled polymer buffer layers at the cathode interfaces of polymer solar cells. Poly(ethylene glycol) (PEG) molecules in a polymer blend, comprising poly(3-hexylthiophene) and [6,6]-phenyl-C₆₁-butyric acid methyl ester, spontaneously migrated to the surface where they reacted with the Al cathode to form ohmic contacts. In terms of thermodynamics, the surface energy of the substrates played an important role in triggering the vertical-type morphology. From a kinetics point of view, PEG polymers having lower molecular weights readily underwent vertical phase separation prior to solidification of the polymer films, due to their higher mobilities, whereas PEG polymers of higher molecular weights tended to become trapped in the active layer. Employing this knowledge, we prepared organic photovoltaic cells exhibiting both high efficiency and appreciable improvement in stability

Solution-Processed Nanocomposites Containing Molybdenum Oxide and Gold Nanoparticles as Anode Buffer Layers in Plasmonic-Enhanced Organic Photovoltaic Devices

Solution-processed nanocomposites containing molybdenum oxide (MoO₃) and gold nanoparticles (Au NPs) have been used as anode buffer layers in organic photovoltaic devices (OPVs). The resulting devices exhibit a remarkable enhancement in power conversion efficiency after Au NPs were incorporated into the device. Such enhancements can be attributed to the localized surface plasmon resonance induced by the metallic nanostructures. We have also found that the rate of exciton generation and the probability of exciton dissociation were increased. Furthermore, the devices made of the MoO₃ buffer layer containing Au NPs exhibited superior stability. This work opens up the possibility of fabricating OPVs with both high efficiency and a prolonged lifetime

Organic Photovoltaics and Bioelectrodes Providing Electrical Stimulation for PC12 Cell Differentiation and Neurite Outgrowth

Current bioelectronic medicines for neurological therapies generally involve treatment with a bioelectronic system comprising a power supply unit and a bioelectrode device. Further integration of wireless and self-powered units is of practical importance for implantable bioelectronics. In this study, we developed biocompatible organic photovoltaics (OPVs) for serving as wireless electrical power supply units that can be operated under illumination with near-infrared (NIR) light, and organic bioelectronic interface (OBEI) electrode devices as neural stimulation electrodes. The OPV/OBEI integrated system is capable to provide electrical stimulation (ES) as a means of enhancing neuron-like PC12 cell differentiation and neurite outgrowth. For the OPV design, we prepared devices incorporating two photoactive material systemsβ-carotene/<i>N</i>,<i>N</i>′-dioctyl-3,4,9,10-perylenedicarboximide (β-carotene/PTCDI-C8) and poly­(3-hexylthiophene)/phenyl-C₆₁-butyric acid methyl ester (P3HT/PCBM)that exhibited open circuit voltages of 0.11 and 0.49 V, respectively, under NIR light LED (NLED) illumination. Then, we connected OBEI devices with different electrode gaps, incorporating biocompatible poly­(hydroxymethylated-3,4-ethylenedioxythiophene), to OPVs to precisely tailor the direct current electric field conditions during the culturing of PC12 cells. This NIR light-driven OPV/OBEI system could be engineered to provide tunable control over the electric field (from 220 to 980 mV mm^–1) to promote 64% enhancement in the neurite length, direct the neurite orientation on chips, or both. The OPV/OBEI integrated systems under NIR illumination appear to function as effective power delivery platforms that should meet the requirements for wirelessly offering medical ES to a portion of the nervous system; they might also be a key technology for the development of next-generation implantable bioelectronics

Improving the Light Trapping Efficiency of Plasmonic Polymer Solar Cells through Photon Management

In this study, we have explored how light trapping efficiency can be enhanced by using gold nanoparticles (Au NPs) of various sizes and shapes on the front of polymer solar cells (PSCs) with the active layerblends of poly­(3-hexyl thiophene) and [6,6]-phenyl-C₆₁-butyric acid methyl ester. The light-concentrating behavior was enhanced after we had incorporated gold nanospheres or nanorods into the anodic buffer layer [based on poly­(3,4-ethylenedioxythiophene):polystyrenesulfonate] to trigger various localized surface plasmon resonance (LSPR) bands. Comparison of the optical characteristics and the performance of the PSCs prepared with and without Au NPs, and we found that the UV–vis and wavelength-dependent photoluminescent spectral data corroborated with the device performance due to the photon management by considering the light scattering and LSPR effects at the active layer. The presence of Au NPs increased the power conversion efficiency to approximately 4.3% (an enhancement of 24%)

Mn-Doped Organic–Inorganic Perovskite Nanocrystals for a Flexible Luminescent Solar Concentrator

We report a robust method of hot addition (HAM) to prepare methylammonium lead trichloride (MAPbCl3) and Mn-doped MAPbCl3 (Mn:MAPbCl3) perovskite nanocrystals (PeNCs) for application in luminescent solar concentrators (LSCs). The HAM, which is free of solvent and operates at high temperatures, is applicable to the synthesis of highly crystalline and stable organic–inorganic PeNCs with tunable optical properties. The Mn:MAPbCl3 PeNCs showed a remarkable energy-transfer shift from 400 to 600 nm that enhanced the optical efficiency when these PeNCs were incorporated in an LSC with a silicon solar-cell module. An optical efficiency (OE) greater than 8% was achieved on incorporation of only 0.094 mass % Mn:MAPbCl3 PeNCs in the LSC. A Monte-Carlo ray-tracing simulation was developed to improve the understanding of the experimental results and estimate the ultimate device performance for future application in building-integrated photovoltaic devices

Chemically Doped and Cross-linked Hole-Transporting Materials as an Efficient Anode Buffer Layer for Polymer Solar Cells

A series of cross-linkable hole-transporting materials (X-HTMs) consisting of indacenodithiophene, bithiophene, and thiophene units bookended by two triarylamine groups have been designed and synthesized to investigate their suitability as new anode buffer layer for bulk heterojunction polymer solar cells (PSCs). These X-HTMs can be thermally cross-linked at temperature between 150 and 180 °C to form robust, solvent-resistant films for subsequent spin-coating of another upper layer. Energy levels of these cross-linked materials were measured by cyclic voltammetry, and the data suggest that these X-HTMs have desirable hole-collecting and electron-blocking abilities to function as an anode buffer layer for PSCs. In addition, by incorporating thiophene or fused ring units into the X-HTM backbone, it effectively improved the hole-carrier motilities. To further improve the conductivity and optical transparency for PSCs, the X-HTM films were p-doped with nitrosonium hexafluoroantimonate (NOSbF₆). The doped X-HTM layers showed remarkably enhanced hole-current densities compared to neutral X-HTM under the same electric field bias. The properties of the doped X-HTM film as anode buffer layer has been investigated in PSCs. The resulting devices showed similar performance compared to those made using conducting polymer, poly­(3,4-ethylene- dioxylenethiophene):poly­(styrenesulfonate) (PEDOT:PSS), as the anode buffer layer. Moreover, a novel bilayer HTM structure consisting of a doped and a neutral layer was employed to exploit the feasibility of combining high conductivity from the doped X-HTM and good electron-blocking ability from the neutral X-HTM together. Interestingly, PSC devices based on this bilayer structure showed enhanced <i>V</i>_oc, <i>J</i>_sc, and FF compared to the devices with only a single-layer doped X-HTM. These results indicate that such X-HTMs are promising alternative materials to PEDOT:PSS as an anode buffer layer for polymer solar cells