All thermal-evaporated surface plasmon enhanced organic solar cells by Au nanoparticles

Au nanoparticles (NPs) are fabricated on indium-tin-oxide substrates by a thermal evaporation method and incorporated to an efficient small molecule organic solar cell (OSC). This renders an all thermal evaporated surface plasmon enhanced OSC. The optimized device shows a power conversion efficiency of 3.40%, which is 14% higher than that of the reference device without Au 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 NPs and the increased conductivity of the device.     

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.     

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%.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

A new dithienosilole-based oligothiophene with methyldicyanovinyl groups for high performance solution-processed organic solar cells

A new linear dithienosilole-based oligothiophene end-capped with methyl and electron-withdrawing dicyanovinyl groups, DTS(Oct)₂-(2T-DCV-Me)₂, was prepared in good yield. This oligomer exhibited broad absorption spectra in bulk down to the near-IR region with the optical edge at 900 nm, resulting in an initially high power conversion efficiency of 5.44% in solution-processed organic solar cells using PC₇₁BM as an acceptor.     

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.     

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.     

Decahedral-shaped Au nanoparticles as plasmonic centers for high performance polymer solar cells

The photon harvesting of the photoactive layer within a multilayered polymer solar cells (PSCs) greatly affects the output electric power of the devices. For PSCs, the device performance is very sensitive to the photoactive layer thickness. Therefore, how to enhance the light absorption of the photoactive film with fixed thickness is still a big challenge. Plasmonic enhancement induced by noble metal nanoparticles has been proved to be an effective way to enhance light trapping inside the photoactive film without increasing the thickness of film. By incorporating Au decahedra into the poly(3,4-ethylenedioxythiophene): poly(4-styrenesulfonate) (PEDOT:PSS) anode buffer layer, high performance plasmonic PSCs based on P3HT:PC₆₀BM and PBDT-TS1:PC₇₀BM were fabricated and the light response of the PSCs are greatly improved in a broadband wavelength, resulting in a remarkable enhancement in short-circuit current density. The calculation results of finite difference time domain (FDTD) confirm that the plasmonic effects induce enhancement in device performance. Upon optimization, the best power conversion efficiency (PCE) of the device based on P3HT:PC₆₀BM and PBDT-TS1:PC₇₀BM reaches 4.14% and 10.29%, respectively, among the best values reported in literature. These results can provide valuable guidelines for the design of metal nanostructures for organic photovoltaic applications.     

Enhanced carrier mobility and photon-harvesting property by introducing Au nano-particles in bulk heterojunction photovoltaic cells

In this study, polymer solar cells (PSCs) doped with Au nanoparticles (Au NPs) were successfully fabricated to maximize the photon-harvesting properties on the photoactive layer. In addition, a conductivity-enhanced hybrid buffer layer was introduced to improve the photon absorption properties and effectively separate the generated charges by adding Au NPs and dimethylsulfoxide (DMSO) to the PH 500 as a buffer layer. The PSC performance was optimized with a 88% improvement over the conventional PSCs (photoactive area: 225 mm², power conversion efficiency (PCE): 3.2%) by the introduction to the buffer layer of Au NPs and DMSO at 10 wt% and 1.0 wt%, respectively, and with 15 wt% Au NP doping in the photoactive layer. The internal resistance was decreased due to the increased photocurrent caused by the localized surface plasmon resonance (LSPR) effect of the Au NPs in the photoactive layer and by the improvement of carrier mobility induced by the DMSO doping of the buffer layer. As a result, the series resistance (R_S) deceased from 42.3 to 19.7 Ω cm² while the shunt resistance (R_SH) increased from 339 to 487 Ω cm².     

Stability of diketopyrrolopyrrole small-molecule inverted organic solar cells

Small-molecule DPP(TBFu)₂-based inverted organic solar cells were fabricated and their stability investigated. The effects of thermal annealing and solvent annealing on device performance and stability were compared. To increase the stability, mix-PCBM (PC₆₁BM and its C₇₀ analogue), which is reported to give higher device stability, was also included. Solvent-annealed devices showed the highest power conversion efficiency (PCE) of 4.62%, whereas thermally annealed devices showed a PCE of 3.94%. After the aging process, which involved thermal stress and exposure to air, thermally annealed and mix-PCBM devices retained a PCE of 3%, whereas solvent-annealed devices had a much lower PCE of 1.7%. Therefore, our results show that in the long-term stability perspective, thermal annealing is better than solvent annealing, and mix-PCBM is better than PC₆₁BM in the case of DPP(TBFu)₂. We fabricated small-molecule inverted organic solar cells that retain their performance in air for 3 weeks without encapsulation.     

An effective bilayer cathode buffer for highly efficient small molecule organic solar cells

Novel organic/ultrathin low work function metal bilayer cathode buffers for small molecule organic solar cells are proposed. Ultrathin low work function metal layers possess a high built-in electric field for effective carrier extraction and a high cathode reflectivity for maximum absorption in the photoactive layers. This leads to a significant increase of short circuit current density and fill factor of cells. By integrating this bilayer cathode buffer with DTDCTB:C₆₀ small molecular heterojunction, the device exhibits a high power conversion efficiency of up to 5.28%, which is an improvement of 22% compared to a device with a traditional single organic layer buffer.     

基于级联金属光栅结构的有机太阳能电池宽谱吸收增强

为拓宽活性材料对太阳光谱的吸收范围,实现器 件的宽谱吸收增强,本文提出一种基 于光栅结构的新型有机太阳能电池器件,该器件在一个周期内引入不同占空比的光栅来构成 级联光栅。本文采用时域有限差分法从理论上研究了级联光栅结构对器件吸收性能的影响, 结果表明该结构可激发多个表面等离激元谐振,这些不同波长下的谐振模式可以在吸收光谱 中同时存在,从而实现宽谱吸收增强。考虑太阳光谱的影响,在TM和TM/TE混合偏振模式 下,活性材料的整体吸收效率从等效平板结构的23.9%分别提高到54.2%和36.4%,分别增 强126.8%和52.3%,且基于该级联光栅结构的 太阳能电池器件可实现在0到65度入射角范 围内的广角吸收。此外,在TM偏振模式下,该器件的吸收性能对光栅参数微小误差变化的 敏感性较低,适用于实际纳米器件 的制备。这项工作的理论结果有助于纳米金属光栅在有机 太阳能电池中的应用提供新的理论指导。