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.     

Improved mobility and lifetime of carrier for highly efficient ternary polymer solar cells based on TIPS-pentacene in PTB7: PC71BM

Highly efficient ternary polymer solar cells (T-PSCs) realized by the improved mobility and lifetime of carrier in PTB7: PC₇₁BM: TIPS-pentacene blends were fabricated. By adjusting the weight ratios of third component TIPS-pentacene in the binary PTB7: PC₇₁BM blends, we found that the short circuit current and fill factor (FF) were simultaneously enhanced, resulting in a maximum power conversion efficiency (PCE) of 8.09% with 21.3% improvement. The improved photovoltaic performance of T-PSC was mainly due to the enhanced light absorption, energy level cascading, optimized blend morphology, and increased hole mobility. It was also found that the incorporation of TIPS-pentacene increased the average hole lifetime, ensuring efficient hole transport and collection with suppressed bimolecular recombination, contributing to the photocurrent. Additionally, the low thickness dependent row-off of FF indicates TIPS-pentacene is a promising third component for the realization of thick film T-PSC. The improved PCEs were obtained as well for other ternary donor: acceptor: TIPS-pentacene systems, demonstrating that the incorporation of TIPS-pentacene is a wide practicable methodology for the development of highly efficient T-PSCs.     

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.     

Charge carrier mobility,bimolecular recombination and trapping in polycarbazole copolymer:fullerene (PCDTBT:PCBM) bulk heterojunction solar cells

Organic photovoltaic devices based on the donor:acceptor blend of poly[N-9″-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) and [6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM) have received considerable attention in recent years due to their high power conversion efficiencies and the ability to achieve close to 100% internal quantum efficiency. However, the highest efficiencies were all attained using active layers of less than 100 nm, which is not ideal for either maximised potential performance or commercial viability. Furthermore, more recent reports have documented significant charge carrier trapping in these devices. In this paper two charge extraction techniques (photo-CELIV and time-of-flight) have been used to investigate the mobility and recombination behaviour in a series of PCDTBT:PCBM devices. The results not only confirm significant charge carrier trapping in this system, but also reveal close to Langevin-type bimolecular recombination. The Langevin recombination causes a short charge carrier lifetime that results in a short drift length. The combination of these two characteristics (trapping and fast bimolecular recombination) has a detrimental effect on the charge extraction efficiency when active layers greater than ∼100 nm are used. This accounts for the pronounced decrease in fill factor with increasing active layer thickness that is typically observed in PCDTBT:PCBM devices.     

金纳米颗粒增强富硅氮化硅发光特性的研究

采用时域有限差分(FDTD)方法,对Au纳米颗粒的尺寸和形貌对于其光学特性的影响进行了系统的理论研究。通过采用等离子体增强化学气相沉积(PECVD)、晶化处理、电子束蒸发和高温退火等工艺,制备基于局域表面等离子共振(LSPR)效应的富硅氮化硅发光芯片。利用拉曼光谱仪、扫描电子显微镜(SEM)、奥林巴斯显微镜等对不同结构Au纳米颗粒富硅氮化硅发光器件的特性进行了表征。研究表明,通过对Au纳米颗粒的大小、形状和分布合理优化,富硅氮化硅芯片的发光强度在570nm波长附近提升了7倍,增强峰的位置红移了10nm。     

Conjugated dendritic oligothiophenes for solution-processed bulk heterojunction solar cells

This mini-review summarizes the recent achievements of developing conjugated dendritic oligothiophenes (DOT) for use in solution-processed bulk heterojunction (BHJ) solar cells. These DOTs are structurally defined molecules with relatively high molecular weight. Therefore, this novel class of thiophene based material possesses not only some advantages of oligomers,such as defined and monodispersed molecular structure,high chemical purity, but also some characteristics of polymers, for example, good solution-processability.In addition, the step-by-step approach of its synthesis allows precise fimctionalization of dendritic backbones with desired moieties, which is helpful to finely tune the optical and electronic properties of materials. Power conversion efficiencies (PCE) of BHJ solar cells were achieved up to 2.5% when functionalized thiophene dendrimers were used as electron donor and electron acceptor was a fullerene derivative. These results indicated that dendritic oligothiophenes are a novel class of the materials of electron donor for solution-processed organic solar cells.     

纳米Au增强掺Er3＋铋酸盐玻璃近红外发光特性

研究了掺Er³⁺含Au纳米颗粒铋酸盐玻璃在波 长为980nm的LD抽运下1.53μm波长处的发光 特性。测试得到表征 Au纳米颗粒存在的表面等离子体共振(SPR)峰位于565～586nm波长 之间,透射电镜(TEM)图像中观察到密集分布形状各 异的Au纳米颗粒,尺寸约为5～16nm。研究表明,随着AuCl含量增加 ,1.53μm波长处荧光强度呈现先增强后减弱 的趋势,在AuCl掺杂浓度为0.2wt%时取得最大值,为未掺杂时的4.3倍;荧光增强原因归结于Au纳米颗粒SPR引起的局域场增强以及Au 0→Er³⁺的能量转移,荧光淬灭原因归结于Er³⁺→Au⁰的能量反向转移。     

Hierarchically Ordered Arrays of Noncircular Silicon Nanowires Featured by Holographic Lithography Toward a High‐Fidelity Sensing Platform

A novel, highly uniform and tunable hybrid plasmonic array is created via ion‐milling, catalytic wet‐etching and electron‐beam evaporation, using a holographically featured structure as a milling mask. A simple and low‐cost prism holographic lithography (HL) technique is applied to create an unprecedentedly coordinated array of elliptic gold (Au) holes, which act as the silicon (Si) etching catalyst in the reaction solution used to fabricate an elliptic silicon nanowire (SiNW) array; here, the SiNWs are arrayed hierarchically in such a way that three SiNWs are triangularly coordinated, and the triangles are arranged hexagonally. After removing the polymeric mask and metal thin film, the highly anisotropic thick Au film is deposited on the SiNW arrays. This hybrid substrate shows tunable optical properties in the near‐infrared (NIR) region from 875 nm to 1030 nm and surface‐enhanced Raman scattering (SERS) activities; these characteristics depend on the catalytic wet etching time, which changes the size of the vertical gap between the Au thick films deposited separately on the SiNWs. In addition, lateral interparticle coupling induces highly intensified SERS signals with good homogeneity. Finally, the Au‐capped elliptical SiNW arrays can be hierarchically patterned by combining prism HL and conventional photolithography, and the highly enhanced fluorescence intensity associated with both the structural effects and the plasmon resonances is investigated.     

Investigation of the s-shape caused by the hole selective layer in bulk heterojunction solar cells

A common failure mechanism of organic solar cells is the development of an s-shaped current voltage curve. Herein, we investigated the origin of this degradation mechanism by replacing the commonly used hole selective layer poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) with a co-evaporated layer of N,N′-bis(3-methylphenyl)-N,N′-bis(phenyl)benzidine (TPD) and Dipyrazino[2,3-f:2′,3′-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile (HATCN). By varying the ratio of TPD to HATCN we are able to tune both the mobility and work function of the hole selective layer. Using a combination of field effect mobility measurements, Kelvin-Probe work function measurements, and numerical modeling we demonstrate that a degraded mobility of the hole selective layer leads to a buildup of charge within the device and reduction of fill factor.     

Ag、Au纳米颗粒的激光表面修饰

通过用Nd：YAG激光（λ=1064nm）对氧化还原法制备的Ag、Au纳米颗粒的修饰,使Ag、Au纳米颗粒的尺寸均匀性得到更好的改善。用透射电子显微镜（TEM）和紫外-可见表面等离于体吸收（SPA）光谱对激光修饰后的Ag、Au纳米颗粒进行了测量和表征,结果表明,这些被修饰过的Ag、Au纳米颗粒由于自身体系发生了改变,可以作为更高效表面增强拉曼光谱（SERS）的增强基底。     

Performance enhancement in inverted polymer solar cells incorporating ultrathin Au and LiF modified ZnO electron transporting interlayer

The performance enhancement of inverted polymer solar cells (PSCs), based on the blend system of regioregular poly(3-hexylthiophene) and [6,6]-phenyl C₆₁-butyric acid methylester, due to incorporating ultrathin Au and LiF interlayer between the front transparent indium tin oxide and a ZnO electron transporting layer was analyzed. The results reveal that a 40% increase in PCE, e.g., from 2.62% to 3.67%, was observed for PSCs made with an optimal Au/LiF interlayer as compared to the one having a bare ZnO electron transporting layer. The presence of Au/LiF-modified ZnO interlayer between ITO and the organic layer helps to improve the charge collection. The absorption enhancement arising from the plasmon resonance of Au nanostructures also contributed to the improvement in PCE. It is shown that PSCs with LiF incorporated ZnO electron transporting layer allow improving cell lifetime, demonstrating <50% decrease in PCE compared to that of the ones with a bare ZnO interlayer after 240 day aging test for cells without encapsulation in air.     

纳米等离子体及其在生物传感器中的应用

近年来,基于表面等离子体的材料和器件在基础科学和应用科学研究领域受到了极大关注。首先介绍了纳米等离子体与激发光的作用机理及其展现的独特效应;然后分别介绍了纳米等离子体作为传感手段在DNA分子尺、单纳米粒子检测、表面增强型喇曼光谱等研究方向的最新进展,以及作为纳米操控手段在基因表达和抑制方面的研究进展;最后对表面等离子体在纳米技术领域的应用进行了讨论,并对其广阔的发展前景进行了展望。     

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.     

Formation of charge transfer complexes significantly improves the electron transfer process of polymer solar cells

A fluorescent inhibitor, 1-Bromo-4-Nitrobenzene (1-Br-4-NB, C₆H₄BrNO₂), is introduced to poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) active layer of polymer solar cells (PSCs). When the amount of 1-Br-4-NB added is 25 wt%, the device performance of PSCs is optimal. To investigate the means by which the power conversion efficiency (PCE) is improved, external quantum efficiency (EQE), fluorescence spectrum, transient absorption spectroscopy and dynamics photoresponse, X-ray diffraction (XRD) patterns are measured and density functional theory (DFT) calculations are carried out. The results indicate that excitonic recombination to the ground state is reduced and excitonic dissociation at the donor–acceptor interface is enhanced, which explains the inhibitory effect on the generation of fluorescence. Moreover, the electron transfer complexes (P3HT–C₆H₄BrNO₂) is demonstrated to be formed after the addition of 1-Br-4-NB. The PCE of PSCs achieves an improvement of more than 57% compared to the reference solar cell without 1-Br-4-NB.     

The impact of MOCVD growth ambient on carrier transport,defects, and performance of CdTe/CdS heterojunction solar cells

CdTe solar cells were fabricated by depositing CdTe films on CdS/SnO₂/glass substrates in various metalorganic chemical vapor deposition growth ambient with varying Te/Cd mole ratio in the range of 0.02 to 15. The short-circuit current density (J_sc) showed a minimum at a Te/Cd ratio of 0.1 and increased on both sides of this minimum. The open-circuit voltage (V_oc) was found to be the highest for the Te-rich growth ambient (Te/Cd∼6)and was appreciably lower (600 mV as opposed to 720 mV) for the stoichiometric and the Cd-rich growth conditions. This pattern resulted in highest cell efficiency (12%) on Te-rich CdTe films. Auger electron spectroscopy revealed a high degree of atomic interdiffusion at the CdS/CdTe interface when the CdTe films were grown in the Te-rich conditions. It was found that the current transport in the cells grown in the Cd-rich ambient was controlled by the tunneling/interface recombination mechanism, but the depletion region recombination became dominant in the Te-rich cells. These observations suggest that the enhanced interdiffusion reduces interface states due to stress reduction or to the gradual transition from CdS to CdTe. The hypothesis of reduced defect density in the CdTe cells grown in the Te-rich conditions is further supported by the high effective lifetime, measured by time-resolved photoluminescence, and the reduced sensitivity of quantum efficiency to forward/light bias.     

Near‐Infrared Plasmonic 2D Semimetals for Applications in Communication and Biology

Localized surface plasmon resonance (LSPR) has many applications which require meeting specific wavelength windows. The most prominent examples are photothermal therapy in biology, matched to the biological window (650–1350 nm), and communication relying on photodetection in optoelectronics, matched to the communication window (1260–1675 nm). However, for the classic noble metals (Au, Ag), tuning LSPRs from visible region to these two windows is still a demanding task due to their intrinsic limitations on charge density and dielectric function. Here, the discovery of near‐infrared biological and communication window‐matched plasmonic properties of semimetal TiS₂ nanosheets (NSs) is reported for the first time. Developed synthesis procedures allow fine‐tuning width and thickness of single‐crystal TiS₂ NSs. During characterization a new and intensive absorption peak in the 1000–1400 nm range is observed from both TiS₂ NS colloid solutions and films. This peak is attributed to LSPR due to its dependence on particle shape and on the refractive index of solvents. The superiority of such LSPRs is demonstrated in both, biological and optical applications: excitation at 808 and 980 nm generates a ≈50 °C photothermal temperature rise, while excitation at 1310 nm results in two‐times enhanced photocurrents of PbS photodetectors compared to untreated devices.     

Influence of molar mass ratio,annealing temperature and cathode buffer layer on power conversion efficiency of P3HT:PC71BM based organic bulk heterojunction solar cell

In bulk heterojunction (BHJ) solar cells, the molar mass ratio of donor-acceptor polymers, the annealing temperature (T_an) and the cathode buffer layer plays very consequential role in improving the power conversion efficiency (PCE) by tuning the film morphology and enhancing the charge carrier dynamics. A comprehensive understanding of each of these factors is essential in order to optimize the performance of organic solar cells (OSCs). Albeit there are several fundamental reports regarding these factors, an altogether meticulous correlation of these physical processes with experimental evidence of the photo active layer are required. In this work, we systematically analyzed the influence of different molar mass ratio, the annealing temperature (T_an) and the cathode buffer layer of rrP3HT:PC₇₁BM based BHJ solar cells and their corresponding photovoltaic performances were correlated carefully with their thin film growth structure and energy level diagram. The device having 1:0.8 molar mass ratio of rrP3HT:PC₇₁BM and T_an = 150 °C annealing temperature with Bathocuproine (BCP) as the cathode buffer layer having ITO/PEDOT:PSS/rrP3HT:PC₇₁BM (molar mass ratio = 1:0.8; (T_an = 150 °C)/BCP/Al) configuration showed the best device performance with PCE, ɳ = 4.79%, Jsc = 14.21 mA/cm², V_oc = 0.58 V and FF = 57.8%. This drastic variation in PCE of the device having BCP/Al as the cathode contact compared to the other device configurations is due to the coalesced effects of better hole-blocking capacity of BCP along with Al and better phase separation of the active blend layer at 150 °C annealing temperature. These results explicate the cumulate role of all these physical parameters and their combined contribution to the PCE amendment and overall device performance with rrP3HT:PC₇₁BM based organic BHJ solar cell.     

Investigation on surface plasmon polaritons and localized surface plasmon production mechanism in micro-nano structures

The simulation mechanism of surface plasmon polaritons (SPPs) and localized surface plasmon (LSP) in different structures was studied, including the Au reflection grating (Au grating), Au substrate with dielectric ribbons grating (Au substrate grating), and pure electric conductor (PEC) substrate with Au ribbons grating (Au ribbons grating). And the characteristics of the Smith-Purcell radiation in these structures were presented. Simulation results show that SPPs are excited on the bottom surface of Au substrate grating grooves and LSP is stimulated on the upper surface both of Au ribbons grating grooves and Au grating grooves. Owing to the irreconcilable contradiction between optimizing the grating diffraction radiation efficiency and optimizing the SPPs excitation efficiency in the Au substrate grating, only 40-times enhancement of the radiation intensity was obtained by excited SPPs. However, the LSP enhanced structure overcomes the above problem and gains much better radiation enhancement ability, with about 200-times enhancement obtained in the Au ribbons grating and more than 500-times enhancement obtained in the Au grating. The results presented here provide a way of developing miniature, integratable, tunable, high-power-density radiation sources from visible light to ultraviolet rays at room temperature.     

Improvement of photovoltaic performance of inverted hybrid solar cells by adding single-wall carbon nanotubes in poly(3-hexylthiophene)

Solution prepared hybrid solar cells show promising low cost technology for electricity generation from sun light, although their power conversion efficiency has to be improved. One of the approaches is to increase the absorbance or charge carrier mobility of organic semiconductors. In this work, pristine single walled carbon nanotubes (SWCNT) were added into poly(3-hexylthiophene) (P3HT) solution to form P3HT:SWCNT composite films with different weight percent (wt%) of SWCNT. It is observed that optical absorbance spectra as well as the morphology of the composite films were modified by the addition of SWCNTs. This phenomenon could be explained by the π-π interaction between the conjugated polymer and carbon nanotubes. Most importantly, the electrical conductivities of the composite films increased with the SWCNT wt%. When these films were used as hole conductor layers in inverted planar hybrid solar cell, with CdS thin films as electron acceptor layers, the fill factor (FF) and open-circuit voltage (Voc) of the corresponding cells were decreased with the increase of the wt% of SWCNT. However, the short-circuit current density (Jsc) and the power conversion efficiency (PCE) showed a maximum value at about 0.4 wt% of SWCNT in P3HT. The transient photovoltage measurements (TPV) revealed that the presence of SWNCT promoted the charge recombination process at P3HT/CdS interface, and as a result, reduced the Voc. The photovoltaic performance of the hybrid solar cells could be optimized by choosing an adequate weight percentage of SWCNT in P3HT to balance the charge carrier transport and charge recombination processes at the donor-acceptor interface.