Cooperative plasmon enhanced organic solar cells with thermal coevaporated Au and Ag nanoparticles

Cooperative plasmon enhanced small molecule organic solar cells are demonstrated based on thermal coevaporated Au and Ag nanoparticles (NPs). The optimized device with an appropriate molar ratio of Au:Ag NPs shows a power conversion efficiency of 3.32%, which is 22.5% higher than that of the reference device without any NPs. The improvement is mainly contributed to the increased short-circuit current which resulted from the enhanced light harvesting due to localized surface plasmon resonance of Au:Ag NPs and the increased conductivity of the device. Besides, factors that determining the performance of the Au:Ag NPs cooperative plasmon enhance organic solar cells are investigated, and it finds that the thickness of MoO₃ buffer layer plays a crucial role. Owing to the different diameter of the thermal evaporated Au and Ag NPs, a suitable MoO₃ buffer layer is required to afford a large electromagnetic enhancement and to avoid significant exciton quenching by the NPs.     

Ag颗粒表面等离子体增强GaAs太阳电池双层减反射膜的设计与模拟

Surface plasmon enhanced antireflection coatings for GaAs solar cells have been designed theoretically.The reflectance of double-layer antireflection coatings（ARCs） with different suspensions of Ag particles is calcu-lated as a function of the wavelength according to the optical interference matrix and the Mie theory.The mean dielectric concept was adopted in the simulations.A significant reduction of reflectance in the spectral region from 300 to 400 nm was found to be beneficial for the design of ARCs.A new SiO2/Ag-ZnS double-layer coating with better antireflection ability can be achieved if the particle volume fraction in ZnS is 1%-2%.     

Ag surface plasmon enhanced double-layer antireflection coatings for GaAs solar cells

Cs. A new SiO2/Ag-ZnS double-layer coating with better antireflection ability can be achieved if the particle volume fraction in ZnS is 1%-2%.     

Enhanced power conversion efficiency of organic solar cells by embedding Ag nanoparticles in exciton blocking layer

We demonstrate the power conversion efficiency of bulk heterojunction organic solar cells can be enhanced by introducing Ag nanoparticles into organic exciton blocking layer. The Ag nanoparticles were incorporated into the exciton blocking layer by thermal evaporation. Compared with the conventional cathode contact materials such as Al, LiF/Al, devices with Ag nanoparticles incorporated in the exciton blocking layer showed lower series resistances and higher fill factors, leading to a 3.2% power conversion efficiency with a 60 nm active layer; whereas, the conventional devices have only 2.0–2.3% power conversion efficiency. Localized surface plasmon resonances by the Ag nanoparticles and their contribution to photocurrent were also discussed by simulating optical absorptions using a FDTD (finite-difference-time-domain) method.     

Vinazene end-capped acceptor-donor-acceptor type small molecule for solution-processed organic solar cells

An acceptor-donor-acceptor (A-D-A) type molecule based on dioctyltertthiophene-benzo[1,2-b:4,5-b′]dithiophene-dioctyltertthiophene central donor and vinazene terminal acceptor was designed and synthesized for solution-processed small molecule bulk-heterojunction (BHJ) solar cells. The thermal and optochemical properties, BHJ morphology and solar cell performance were investigated. The BHJ morphology was systematically optimized by thermal annealing, solvent vapor annealing, and the use of solvent additives. Processed by a combination of thermal annealing and solvent vapor annealing treatments, V-BDT:PC₇₁BM device showed an optimized PCE of 3.73% with a V_OC of 0.89 V, an J_SC of 6.88 mA cm⁻² and a FF of 0.61.     

Realizing improved performance of down-conversion white organic light-emitting diodes by localized surface plasmon resonance effect of Ag nanoparticles

Down-conversion structure white organic light-emitting diodes (WOLEDs), in which white light is generated by a blue emission organic light-emitting diodes (OLEDs) in combination with a color conversion layer (CCL) outside the substrate, has attracted extensive interest due to its significant advantages in low cost and stabilized white-light emissions. However, low color-conversion efficiency of CCL is still a bottleneck for the performance improvement of down-conversion WOLEDs. Here, we demonstrate an approach to enhance the color-conversion efficiency of CCL-WOLEDs by localized surface plasmon resonance (LSPR) effect. In this approach, a blend of Ag nanoparticles and polyvinyl alcohol (PVA) is solution-deposited between the blue organic light emitting diodes and color-conversion layer. Based on the LSPR effect of this modified structure, the color conversion efficiency has improved 32%, from 45.4% to 60%, resulting a 14.4% enhancement of the current efficiency, from 9.73 cd/A to 11.14 cd/A. Our work provides a simple and low-cost way to enhance the performance of down-conversion WOLEDs, which highlights its potential in illumination applications.     

Vacuum deposited ternary mixture organic solar cells

Ternary mixtures of photo-active organic materials are an intuitive approach to achieve enhanced photocurrent in organic solar cells (OSCs). In this work, we study ternary mixtures of vacuum deposited small molecules, complementing the recent surge of interest in solution processed ternary OSCs. The mixed layer composition is systematically varied to study all possible film configurations, and the resulting OSCs are successful in harvesting photocurrent from all three components to grant broad spectral photoresponse. However, the performance of the ternary OSC is generally less than the binary OSC, largely due to reduced fill factors. By examining ternary OSC transient photocurrents and multi-donor planar heterojunction devices, we demonstrate that the ternary OSC is strongly affected by the energy levels of its constituent materials, with small differences in the two donor materials’ highest occupied molecular orbitals degrading hole transport. The results stress the importance of fine molecular engineering for ternary OSCs, and further hint that the enhancements commonly observed in solution processed ternary OSCs may in part be associated with morphological variations that are not present in vacuum deposited OSCs. The research verifies that, by designing small molecules with specific energy levels, ternary OSCs provide an alternative pathway to low cost, high efficiency photovoltaics in lieu of more complicated device architectures.     

The dual localized surface plasmonic effects of gold nanodots and gold nanoparticles enhance the performance of bulk heterojunction polymer solar cells

In this study, we investigated the effects of plasmonic resonances induced by gold nanodots (Au NDs), thermally deposited on the active layer, and octahedral gold nanoparticles (Au NPs), incorporated within the hole transport layer, on the performance of bulk heterojunction polymer solar cells (PSCs) based on poly(3-hexyl thiophene) (P3HT) and [6,6]-phenyl-C₆₁butyric acid methyl ester (PC₆₁BM). Thermal deposition of 5.3-nm Au NDs between the active layer and the cathode in a P3HT:PC₆₁BM device resulted in the power conversion efficiency (PCE) of 4.6%—that is 15% greater than that (4.0%) for the P3HT:PC₆₁BM device without Au NDs. The Au NDs provided near-field enhancement through excitation of the localized surface plasmon resonance (LSPR), thereby enhancing the degree of light absorption.     

Merocyanines for vacuum-deposited small-molecule organic solar cells

We report here synthesis and photovoltaic properties of three merocyanines dyes (DPPT, DTPT, 1-NPPT) which are functionalized with electron withdrawing thiazolidenemalononitrile and electron rich diarylamine functionalities. It is found that structural feature of the diarylamino groups has a profound effect on the physical properties such as the absorption spectrum, oxidation potential, and HOMO/LUMO energy levels. The compound DTPT containing a better electron-donating ditolyl group, exhibits red-shifted absorption with relatively higher molar extinction coefficient, indicating its better light-harvesting ability. Hole mobility of these compounds is found to be strongly dependent on the various intermolecular interactions. Interestingly, single crystal structures reveal that the crystal packing motifs are rather closely related to the observed hole mobility in a trend of DPPT > DTPT > 1-NPPT. Vacuum-processed small-molecule organic solar cells were fabricated using the title merocyanines as p-type materials (donor) in combination with fullerene (C₆₀ or C₇₀) as n-type material (acceptor) with various device configurations. Among them, the DPPT-based devices outperform the devices based on DTPT and 1-NPPT. The power conversion efficiency (PCE) of DPPT-based device was improved from 1.55% of a BHJ device to 2.63% of a PMHJ device and 3.52% of a PMHJ device without the thin donor layer.     

Improved efficiency of solution processed small molecules organic solar cells using thermal annealing

A solution processable A-D-A-D-A structure small molecule DCAEH5TBT using a BT unit as the core has been designed and synthesized for application in BHJ solar cells. The device employing DCAEH5TBT/PC₆₁BM as active layer shows PCE of 2.43% without any post treatment. After thermal annealing (150 °C, 10 min), the PCE of this molecule based device increased to 3.07%, with J_sc of 7.10 mA/cm², V_oc of 0.78 V and FF of 55.4%, which indicates that high performance of solution processed small molecule based solar cells can be achieved using thermal annealing by carefully design molecule structure.     

An on-chip localized surface plasmon resonance-based biosensor for label-free monitoring of antigen–antibody reaction

The unique localized surface plasmon resonance (LSPR) property of gold nanoparticles has been used to design a label-free biosensor in a chip format. In this research, a sensitive and low-cost microfluidic integrated LSPR-based biosensor is developed. The gold nanoparticles were synthesized in solution and immobilized on quartz substrates by a silane layer as molecular glue. The gold nanoparticle-coated substrate was further integrated with a microfluidic chip. An automated sample introduction system was developed to perform a variety of processes including sample loading, chip washing and sample change. A refractive index resolution of 1 × 10⁻⁴ RIU (refractive index unit) was demonstrated by using the on-chip biosensor combined with the automated sampling system. This developed microfluidic integrated system is capable of transporting a specific amount of bio-samples into the sensing chambers to achieve sensitive and specific biosensing with decreased reaction time and less reagent consuming. Proof-of-concept detection of antigen/antibody (biotin/anti-biotin) binding was performed and was quantitatively detected.     

Vacuum-deposited interconnection layers for tandem solar cells

Two different types of vacuum-deposited interconnection layers (ICLs) were investigated for tandem solar cells: (1) a pure metal oxide and (2) an organic matrix doped with conductive dopants. The optical and electrical properties of these ICLs were systematically studied and compared. Taking the characteristics of ICLs into consideration, optical design methodology for balancing the photocurrent of each sub-cell in the tandem cell is presented. According to the design, highly efficient small-molecule tandem solar cells with power conversion efficiencies up to 7.3%–7.4% were experimentally demonstrated in both devices utilizing pure metal oxide and organic matrix ICLs.     

Oligothiophene-based small molecules with 3,3′-difluoro-2,2′-bithiophene central unit for solution-processed organic solar cells

Two new oligothiophene-based small molecules, namely DRCN6T-F and DRCN8T-F, with 3,3′-difluoro-2,2′-bithiophene as the central building block and 2-(1,1-dicyanomethylene)-rhodanine as end groups, were designed and synthesized. Compared to their non-fluorinated counterparts DRCN6T and DRCN8T, DRCN6T-F and DRCN8T-F exhibit enhanced intermolecular interactions and lower HOMO energy levels. However, PCEs of 2.26% and 5.07% were obtained for DRCN6T-F and DRCN8T-F based optimized devices, respectively, lower than those of non-fluorinated molecules DRCN6T and DRCN8T. The relatively poor performance for the DRCN6T-F and DRCN8T-F were mainly caused by their low short-circuit current densities, due to their unfavorable morphologies and low charge carrier mobilities.     

Enhancement of the current efficiency of organic light-emitting devices due to the surface plasmonic resonance effect of dodecanethilol-functionalized Au nanoparticles

The photoluminescence intensity of the dodecanethilol-functionalized Au (DDT-Au) nanoparticle (NP) layer/4,4′-cyclohexylidenebis[N,N-bis(4-methylphenyl)benzenamine] (TAPC)/4,4′-bis(N-carbazolyl)-1,1′-biphenyl:tris(2-phenylpyridine)iridium (III) (CPB:Ir(ppy)₃) film was increased by about 1.15 times compared to that of the TAPC/CPB:Ir(ppy)₃ film due to the effect of coupling between the excitons in the emitting layer and a localized surface plasmonic resonance (LSPR) in the DDT-Au NPs. The current efficiency of the organic light-emitting devices (OLEDs) with the DDT-Au NP layer at 100 cd/m² was 14.9 cd/A larger than that without the DDT-Au NP layer, resulting in an enhancement of the out-coupling efficiency. The increase in the current efficiency of the OLEDs with a DDT-Au NP layer was attributed to the enhanced out-coupling efficiency due to the existence of the LSPR generated by the DDT-Au NPs.     

纳米银颗粒表面增强荧光效应与其覆盖率的关联

实验上获得了纳米银颗粒对光敏剂二氢卟吩f-甲醚(CPD4)的荧光增强效应,基于纳米银颗粒覆盖率对表面增强荧光效应的影响,初步探讨了荧光增强的物理增强机制。不同覆盖率纳米银基底表面吸附的CPD4的增强荧光结果显示,在低颗粒覆盖率时(<30%),激发效率和激发态分子衰减速率不依赖于覆盖率变化;当颗粒覆盖率大于30%接近40%时,激发效率和激发态分子衰减速率都得到提高。实验和理论结果均表明,相比于单个银纳米颗粒,颗粒覆盖率增加提高了颗粒间电磁耦合效应,能够产生更强的表面增强荧光效应。     

Acenaphtho[1,2-b]quinoxaline diimides derivative as a potential small molecule non-fullerene acceptor for organic solar cells

We designed and synthesized a small molecule acenaphtho[1,2-b]quinoxaline diimide derivative AQI-T2 as an electron-accepting material for non-fullerene organic solar cells. This molecule exhibits a relatively broad absorption band from 300 to 650 nm, with a moderately low-lying lowest unoccupied molecular orbital energy level of −3.64 eV. Non-fullerene organic solar cells with conventional structure using PTB7-Th as the electron donor and AQI-T2 as the electron acceptor exhibited moderate photovoltaic performances. The best performance was attained from the pristine device, which showed a power conversion efficiency of 0.77% with a relatively high open-circuit voltage of 0.86 V, a short circuit current of 2.04 mA cm⁻² and a fill factor of 43.98%. These results indicated that this n-type molecule can be a promising electron-accepting material for non-fullerene organic solar cells.     

Nanoparticle‐enhanced light trapping in thin‐film silicon solar cells

A systematic investigation of the nanoparticle‐enhanced light trapping in thin‐film silicon solar cells is reported. The nanoparticles are fabricated by annealing a thin Ag film on the cell surface. An optimisation roadmap for the plasmon‐enhanced light‐trapping scheme for self‐assembled Ag metal nanoparticles is presented, including a comparison of rear‐located and front‐located nanoparticles, an optimisation of the precursor Ag film thickness, an investigation on different conditions of the nanoparticle dielectric environment and a combination of nanoparticles with other supplementary back‐surface reflectors. Significant photocurrent enhancements have been achieved because of high scattering and coupling efficiency of the Ag nanoparticles into the silicon device. For the optimum light‐trapping scheme, a short‐circuit current enhancement of 27% due to Ag nanoparticles is achieved, increasing to 44% for a “nanoparticle/magnesium fluoride/diffuse paint” back‐surface reflector structure. This is 6% higher compared with our previously reported plasmonic short‐circuit current enhancement of 38%. Copyright © 2011 John Wiley & Sons, Ltd.     

Enhanced power conversion efficiency of organic photovoltaic devices due to the surface plasmonic resonance effect generated utilizing Au-WO3 nanocomposites

Au-WO₃ nanocomposites (NCs) were used as a hole transport layer (HTL) to enhance the power conversion efficiency (PCE) of organic photovoltaic (OPV) cells. The photon absorption of the active layer in the OPV cells was increased due to the plasmonic effect caused by the Au-WO₃ NCs, resulting in an enhanced short-circuit current density for the OPV cells with the Au-WO₃ NC HTL. The value of the root-mean-square roughness of the Au-WO₃ NC film was smaller than that of the WO₃ NP film, resulting in a more efficient transport of holes from the active layer. The PCE of the OPV cell with an Au-WO₃ NCs HTL with an Au NP concentration of 10 wt% was improved by 60.37% in comparison with that with WO₃ nanoparticles. The enhancement of the PCE was attributed to both an increase in the efficiency of the hole transport at an Au-WO₃ NCs HTL with an Au NP concentration of 10 wt%/active layer heterointerface and an enhanced photon absorption due to the localized surface plasmon resonance effect of the Au-WO₃ NCs.     

Fabrication of polymer solar cells from organic nanoparticle dispersions by doctor blading or ink-jet printing

Dispersions of surfactant-free organic nanoparticles have proven a viable route to an eco-friendly lab-scale deposition of bulk-heterojunctions for polymer solar cells, matching the performance of solar cells deposited from toxic chlorinated solvents. In this work, we demonstrate the feasibility of doctor blading for the deposition of photo-active layers from organic nanoparticles comprising poly(3-hexylthiophene) and indene C₆₀-bisadduct. The devices yielded power conversion efficiencies of 3.9% on 0.105 cm² photo-active area and 3.4% on 1.1 cm², being close to the performance of their spin cast counterparts. Likewise, the photo-active layers can be ink-jet printed yielding overall power conversion efficiencies of 2.9%, altogether rendering surfactant-free organic nanoparticles in eco-friendly dispersion agents a valuable process route to a sustainable large-area fabrication of organic solar cells.