Temperature-dependent morphology evolution of P3HT:PCBM blend solar cells during annealing processes

In this paper, the morphology evolution of [6,6]-phenyl-C-61(or 71)-butyric acid methyl ester (PC₆₁BM or PC₇₁BM) in poly(3-hexylthiophene) (P3HT) annealed at different temperatures was investigated. One result which was observed is that PCBM clusters aggregate more readily at higher annealing temperatures. The aggregation of PCBM could be avoided after coating the Al layer on the active layer, which is due to the hindering effect of the Al layer for the formation of PCBM clusters. SEM images show that the active layer with Al coating is smoother than that without Al layer. The performance of so-fabricated devices was analyzed with different annealing temperatures. Open-circuit voltage, fill factor and power conversion efficiency (PCE) of the devices were improved subsequently with increased annealing temperatures, while the absorption intensity of the devices was also improved. The P3HT:PC₆₁BM and P3HT:PC₇₁BM blend devices had highest PCEs of 4.55% and 4.84%, respectively. Crystallinity of the active layer is raised with higher annealing temperatures, which may result in the increased performance of devices.     

Accelerated lifetime measurements of P3HT:PCBM solar cells

We describe in this article the quick optimization of bulk heterojunction organic solar cells based on poly-3-hexylthiophene and [6,6]-phenyl C₆₁ butyric acid methylester blend. Best cells are found to be based on 1:1 in weight ratio and yield 3.6% power conversion efficiency under air-mass 1.5, 100 mW/cm² illumination. On the optimized cells, ageing measurements have been realized to collect the absolute values of photovoltaic parameters along the time. On this study, accelerated lifetime has been calculated using the Arrhenius model for a first-order kinetic of degradation. According to the model, we can predict a long lifetime keeping more than 80% of the initial short-circuit current density after 1000 h of working.     

Effect of monodisperse Cu2S nanodisks on photovoltaic performance of P3HT/PCBM polymer solar cells

Hybrid solar cells using monodisperse Cu₂S nanodisks compositing with the mixture of poly (3-hexylthiophene):1-(3-methoxycarbonyl) propyl-1-pheny [6,6] C61 (P3HT:PC₆₀BM) as the active layer have been fabricated and characterized. The hybrid solar cells exhibit the highest efficiency of 1.35% when the weight ratio of P3HT:PC₆₀BM:Cu₂S is 1:0.8:0.224. The power conversion efficiency (PCE) of nanocomposite device is increased 22.7% comparing with that of the device based on pure P3HT/PC₆₀BM. It is due to that the effect of high-quality Cu₂S nanodisks with good dispersity contributes the increased electronic transportation in the active layer and results in the enhancement in photovoltaic performance. We also investigated the morphology of photoactive layer by microscope; it is found that the dispersity of nanomaterial in active layer is very important for device performance and improvement of carrier mobility.     

Investigation of annealing effects on microstructure of hybrid nanocrystal–polymer solar cells by impedance spectroscopy

We have fabricated hybrid bulk heterojunction solar cells with blends of MEH-PPV (poly[2-methoxy,5-(2-ethylhexoxy)-1,4-phenylene vinylene]) and nano-CdS as electron donor and electron acceptor, respectively. The effect of thermal annealing was investigated with impedance spectroscopy (IS) and capacitance–voltage (C–V) characteristic measurements on devices. The IS and C–V characteristic manifested very different before and after thermal annealing. We performed equivalent circuit to explain the effect of thermal annealing. The thermal treatment of nanocrystal–polymer films is seen to aid in the formation of a continuous network for electron transport between nanorods, and hence improves devices performance. The method based on the IS is available to probe the microstructure of hybrid bulk heterojunction solar cells before and after thermal annealing, and therefore detect the mechanism for the annealing improvements.     

Enhance of TiO_2 dopants incorporated reduced graphene oxide via RF magnetron sputtering for efficient dye-sensitised solar cells

In particular, the dye-sensitised solar cells(DSSCs) have a high potential in the rational energy conversion efficiency to secure our sustainable energy source.In the present study, advanced radio frequency(RF) magnetron sputtering technique was applied to incorporate titanium dioxide(TiO_2) dopants into reduced graphene oxide(rGO) nanosheet for improving the power conversion efficiency(PCE) of DSSCs device. An optimum TiO_2 content incorporated onto rGO nanosheet plays an important role in improving the PCE of DSSCs by minimising the recombination losses of photo-induced charge carriers.Based on the results obtained, 40-s sputtering duration for incorporating TiO_2 dopants onto rGO nanosheet exhibits a maximum PCE of 8.78% than that of pure rGO film(0.68%). In fact, the presence of optimum content of TiO_2 dopants within rGO nanosheet could act as mediators for efficient separation photo-induced charge carriers. However, the excessive of sputtering duration(e.g. 60 s) of TiO_2 dopants onto rGO nanosheet results higher charge recombination and lowers the PCE of DSSCs(5.39%).     

Behavior of mixed multi-walled carbon nanotube/P3HT monolayer at the air/water interface

The sidewall structure of multi-walled carbon nanotubes (MWNTs) was successfully functionalized with poly(3-hexylthiophene) (P3HT) by a non-covalent bond method. P3HT plays an important role in dispersing MWNTs, and assists them to have a stable existence at the air/water interface. The behavior of mixed MWNT/P3HT monolayer at the air/water interface was investigated after obtaining a homogeneously dispersed solution. The effect of MWNT concentration on the mixed MWNT/P3HT monolayer was investigated using the pressure–area (π–A) isotherm, relaxation curve and transmission electron microscopy (TEM). The mixed MWNT/P3HT monolayer was transferred onto a solid substrate using the Langmuir–Blodgett (LB) technique with horizontal or vertical deposition. The multilayer film was delicately fabricated by repeated deposition of the ultra-thin film. Scanning electron microscopy (SEM) images revealed non-uniformity in morphology of the ultra-thin MWNT/P3HT films. The absorption intensity at 250 nm by UV/vis spectroscopy illustrates that a uniform formation of mixed MWNT/P3HT monolayer into multilayer film was successfully obtained by horizontal deposition. The current–voltage characteristic of the ultra-thin MWNT/P3HT film shows that the current increases linearly with the increasing voltage, which indicates that MWNT/P3HT film forms an ohmic contact with gold. And, the electric current was estimated to be mainly contributed by MWNTs.     

Impact of selective thermal annealing on rubrene–C60 heterojunction solar cells

The influence of thermal annealing at different fabrication stages on rubrene–C₆₀ heterojunction organic solar cells is presented. Devices grown at room temperature showed s-shaped current density–voltage (J–V) characteristic. A pre- or post-fabrication thermal treatment step is found effective in elimination of s-shaped J–V. An exclusive gain in open-circuit voltage was measured when rubrene–C₆₀ layer was fabricated at elevated substrate temperature of 80 °C. The results indicate that introduction of temperature at various stage of device fabrication allows selective control over organic layer growth and hence organic–organic interface formation. The 133 mV increase in open-circuit voltage in solar cells fabricated at substrate temperature is due to temperature induced molecular conformation change at the light in-coupling ITO/PEDOT interface.     

Organic/inorganic hybrid solar cells based on SnS/SnO nanocrystals and MDMO-PPV

SnS/SnO heterojunction structured nanocrystals with zigzag rod-like connected morphology were prepared by using a simple two-step method. Bulk heterojunction solar cells were fabricated using the SnS/SnO nanocrystals blended with poly(2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylene vinylene) (MDMO-PPV) as the active layer. Compared with solar cells using SnS nanoparticles hybridized with MDMO-PPV as the active layer, the SnS/SnO devices showed better performance, with a power conversion efficiency higher by about one order in magnitude.     

Fabrication and characterization of cuprous oxide: fullerene solar cells

Cuprous oxide (Cu₂O)-based solar cells with fullerene (C₆₀) were fabricated on indium tin oxide (ITO) by a spin-coating method. The microstructure and cell performance of the solar cells with the Cu₂O:C₆₀ structure was investigated. A photovoltaic device based on an ITO/Cu₂O:C₆₀ bulk heterojunction structure fabricated by the spin-coating method provided short-circuit current density of 0.11 mA cm^?2 and open-circuit voltage of 0.17 V under an Air Mass 1.5 illumination. The microstructures of the Cu₂O active layer were examined by using X-ray diffraction and transmission electron microscopy. The energy levels of the present solar cells are also discussed.     

Enhanced performance of P3HT/PCBM bulk heterojunction photovoltaic devices by adding spin ½ radicals

We have studied bulk heterojunction organic photovoltaic devices (solar cells) based on polymer/fullerene blends using both electrical and magneto-optical methods. We show that adding spin ½ galvinoxyl radicals to the device active layer, consisting of a regio-regular polythiophene/fullerene derivative [P3HT/PCBM] blend, significantly improves the device performance. Compared to pristine photovoltaic devices, the radical-rich devices show improved short-circuit current density, fill factor, and power conversion efficiency. The enhanced device performance is attributed to a reduced geminate recombination rate and improved carrier transport, both of which result from spin–spin interactions between the radical impurities and the photogenerated carriers. Optically detected magnetic resonance, a technique that is sensitive to spin-lattice relaxation rates, is used to verify the proposed mechanism.     

Water/oil repellency and work of adhesion of liquid droplets on graphene oxide and graphene surfaces

The study examines the water/ethylene glycol (EG) repellency of graphene and graphene oxide sheets prepared by the chemical exfoliation of natural graphite powders. The graphene nanosheets were produced by reducing graphene oxide with EG under microwave irradiation. The graphene sheets were assembled into a thin paper, and a facile fluorination was used to coat a thin fluorine layer over the graphene paper. The graphene oxide paper is generally hydrophilic, whereas without aid of any fluorination, the resulting graphene paper displays superhydrophobicity (contact angle: 150.1 ± 2.3°) and low fraction in contact with solid (12.2%). Such low solid fraction may be attributed to the air pocket trapped in (i) the interspaces between graphene powders and (ii) the flake-like voids between graphene sheets, referred to as the Cassie state. The EG repellency of graphene paper can be significantly improved by surface fluorination. Taking into account Young-Duprè's equation incorporated with the Cassie parameter, the W_ad values of the graphene papers for water repellency were found to fall in the region of 9.62-12.5 mJ/m². The low W_ad value between the droplets and the graphene surface can be ascribed to the fact that porous graphene sheets offer an air cushion to repel the drop penetration, inducing the low work required for the movement of droplets on graphene paper. On the basis of the results, this study offers fundamentals on the water and EG repellency of graphene and graphene oxide surfaces.     

Surfactant-enhanced electrochemical detection of bisphenol A based on Au on ZnO/reduced graphene oxide sensor

Bisphenol A(BPA),one of the most commonly used plastic organic monomers,is widely used in manufacturing food packaging and containers.However,the gradual emissions of BPA from manufacturing plastic products bring great potential in human health threats,which urgently need to develop a simple and rapid method for detecting BPA.Cetyltrimethylammonium bromide(CTAB),a typical surfactant,is used to enhance the electrochemical detection of trace endocrine disruptors due to the fact that it can effecti...     

Effects of annealing conditions on the properties of TiO2/ITO-based photoanode and the photovoltaic performance of dye-sensitized solar cells

Photovoltaic performance of dye-sensitized solar cell (DSSC) is enhanced by a two-step annealing process of the photoanode. The 1st-step of annealing is performed in oxygen at 450 °C for 30 min which effectively removes the residual organics originated from the TiO₂ precursor pastes. This enhances the dye adsorption on the TiO₂ nanoparticles and raises the short-circuit current density (J_SC). The 2nd-step of annealing is performed in nitrogen at 450 °C for 10 min which removes extra oxygen atoms resulted from the incorporation of oxygen atoms into the tin-doped indium oxide (ITO) film during the 1st-step of annealing. This reduces the sheet resistance of ITO and thereby enhances the fill factor (FF). With the enhanced J_SC of 15.9mAcm⁻² and FF of 0.65, the AM1.5 solar to electric conversion efficiency (η) of DSSC reaches 6.7% which is better than that based on the conventional one-step air annealing (η = 5.53%, J_SC = 14.08 mA cm⁻², FF = 0.6).     

Precipitant-free solvothermal construction of spindle-like CoCO3/reduced graphene oxide hybrid anode toward high-performance lithium-ion batteries

Recently,CoCO₃ has attracted enormous attention as anodes for lithium-ion batteries(LIBs),benefiting from its high theoretical capacity and simple synthesis.However,the modest electronic conductivity and structural instability over cycling hinder its wider applications.To well address the intrinsic issues,we explored a precipitantfree hydrothermal methodology for mass production of spindle-like CoCO₃/reduced graphene oxide(S-CoCO₃/rGO) toward advanced LIBs as a h...     

Magnetic annealing effects on multiferroic BiFeO3/CoFe2O4 bilayered films

In situ magnetic annealing effects on c-axis-preferred multiferroic BiFeO₃/CoFe₂O₄ bilayered by chemical solution deposition route are investigated. It is observed that magnetic annealing can enhance the crystallization quality, texture and densification as well as dielectric properties. In addition, the magnetolosses decrease with increasing the magnetic fields. Moreover, both increase of the polarization and decrease of the leakage current due to magnetic annealing are beneficial for potential applications of BiFeO₃ films.     

Performance and stability of La0.8Sr0.2MnO3 cathode promoted with palladium based catalysts in solid oxide fuel cells

The effect of catalyst loading, operation temperature and co-infiltration of the palladium-based catalysts on the performance and stability of La_0.8Sr_0.2MnO₃ (LSM) cathode of solid oxide fuel cells (SOFCs) is investigated. The result shows that adding a small amount of Pd catalyst (0.08 mg cm⁻²) has a remarkable effect on the reduction of overpotential of LSM cathodes and high palladium loading is detrimental to the electrochemical activity of LSM cathodes. The performance and stability of the Pd-impregnated LSM cathodes can be enhanced significantly by co-infiltration of palladium with either 20 mol% of silver or 5 mol% of cobalt. Increased stability of the co-infiltrated catalyst materials is probably related to the enhanced resistance of the co-impregnated Pd_0.95Co_0.05 and Pd_0.8Ag_0.2 nanoparticles against agglomeration and sintering at SOFC operation temperatures. The results indicate the co-impregnation is effective not only to enhance the electrochemical activity but also to improve the stability of LSM cathodes for the O₂ reduction reaction of SOFCs.     

Al2O3/WB2 composite ceramic tool material reinforced with graphene oxide self-assembly coated silicon nitride

Graphene oxide coated silicon nitride coated powder was prepared by electrostatic self-assembly technique. Microstructure analysis shows that GO is uniformly coated on the surface of silicon nitride and evenly dispersed in the matrix material. The microstructure analysis and performance tests were carried out on ceramic tools with different volume contents of Si₃N₄@GO coated powder. The results show that when the content of Si₃N₄@GO is 7. 94 vol%, the comprehensive mechanical properties of Al₂O₃/WB₂/(Si₃N₄@GO) ceramic tool materials are the best, with the Vickers hardness, flexural strength and fracture toughness 18.7GPa, 740 MPa and 8 .2MPa·m^1/2, respectively. Compared with the Al₂O₃/WB₂ ceramic tool material, the ceramic tool with Si₃N₄@GO coated powder increased the flexural strength and fracture toughness by 30.3% and 36.7%.     

Unique structural features and electrical properties of electrospun conjugated polymer poly(3-hexylthiophene) (P3HT) fibers

This study examines and compares the internal structure conjugated polymeric fibers fabricated by electrospinning with cast films. Despite rigidity of polymer chain and the inability of its molecular chains to entangle to form viscoelastic jets, regioregular poly(hexyl-3-thiophene) (P3HT) exhibited the remarkable capability to be electrospun when the solution was subjected to gelation. In order to investigate the influence of additional mechanical stretching on the fibers, P3HT was electrospun with the aid of a rotating disc collector. Structure of electrospun fibers was probed via characterization techniques such as differential scanning calorimetry (DSC), Fourier transform infrared and photoluminescence (PL) spectroscopies. The findings indicated internal structural modifications developed within P3HT fibers, as a consequence of additional mechanical stretching induced by the rotating collector. Polarized FTIR and PL spectroscopies suggested that the molecular chains were aligned along the fiber axis. Electrical conductivity of iodine doped P3HT electrospun fibers was between 3 × 10³ S/m and 6 × 10³ S/m.     

Nitrogen redistribution in /γ-iron nitride compound layers upon annealing

An /γ^′-iron nitride compound layer grown on α-Fe at 823 K by gas nitriding shows a nitrogen redistribution upon annealing at 630 K: an until now not observed “backwards growth” of the γ^′-sublayer occurs, accompanied by a nitrogen enrichment of the remaining -sublayer. The observed thickness changes can be explained theoretically.     

高迁移率的钛掺杂氧化铟薄膜在晶硅/非晶硅异质结电池上的应用研究

采用钛掺杂氧化铟旋转靶制备透明导电薄膜应用在晶硅/非晶硅异质结电池上。在不同氧含量下,研究钛掺杂氧化铟薄膜(T100薄膜)的光电性能,同时对比分析ITO薄膜。在电镜下T100薄膜呈现出柱状结构,并且展示出优异的光学性能。T100薄膜最大载流子迁移率可以达到75.6 cm~2·(V·s)^-1。相比于ITO薄膜,T100薄膜具有优异的电学传导和透光率,因此在异质结电池量产线上电池转换效率可以实现0.26%的提升。