A review on carbon nanotube/polymer composites for organic solar cells

DOI: 10.1002/er.3194Carbon nanotubes (CNTs) have unique properties, such as their electrical conductivity, that enable them to be combined with conducting polymers to form composites for use in organic solar cells (OSCs). It is envisaged that the improved composite has a higher efficiency of green energy and will reduce the cost of these cells. The use of such alternative energy sources also drastically reduces overuse of fossil fuels and consequently limits environmental degradation. This review compares research and performance between conventional silicon solar cells and OSCs. It also discusses OSC photoexcitation and charge carrier generation with the incorporation of CNTs, physicochemical properties of the composites and other factors that affect the efficiencies of OSCs. In addition, properties of CNTs that favour their dispersion in polymer matrices as acceptors and charge carriers to the electrodes are covered. The effects of CNTs containing dopants, such as nitrogen and boron, on charge transfer are discussed. Also, the fabrication techniques of OSCs that include CNT/polymer composite processing and the methods of film deposition on the substrate are described. Finally, the case studies of OSCs containing polymers with single-walled CNTs, double-walled CNTs or multi-walled CNTs are evaluated

Nitrogen-Doped Carbon Nanotubes Synthesised by Pyrolysis of (4-{[(Pyridine-4-yl)methylidene]amino}phenyl)ferrocene

http://dx.doi.org/10.1155/2013/750318Nitrogen-doped carbon nanotubes (N-CNTs) were synthesized by pyrolysis of (4-{[(pyridine-4-yl)methylidene]amino}phenyl) ferrocene in a solution of either acetonitrile or toluene as carbon source. This was achieved by testing three different growth temperatures (800, 850, and 900∘C), and the 850∘C was found to be the most favourable condition for N-CNT growth. At the lower temperature of 800∘C, amorphous carbon was mainly formed while at the higher temperature of 900∘C, the yield of carbon spheres (CSs) increased. Apart from the variation in temperature, the formation of other shaped carbon nanomaterials (SCNMs) was found to be carbon source dependent. Acetonitrile was found to produce mainly N-CNTs with “bamboo” morphology while toluene formed a mixture of pristine CNTs and N-CNTs in the ratio of 1 : 1. N-CNTs, and other SCNMs synthesized were characterized by means of TEM, SEM, Raman spectroscopy, TGA, and elemental analysis

Effect of boron concentration on physicochemical properties of boron-doped carbon nanotubes

Boron-doped carbon nanotubes (B-CNTs) were synthesized using chemical vapour deposition (CVD) floating catalyst method. Toluene was used as the carbon source, triphenylborane as boron as well as the carbon source while ferrocene was used as the catalyst. The amount of triphenylborane used was varied in a solution of toluene and ferrocene. Ferrocene was kept constant at 2.5 wt.%. while a maximum temperature of 900 °C was used for the synthesis of the shaped carbon nanomaterial (SCNMs). SCNMs obtained were characterized by the use of transmission electron microscope (TEM), scanning electron microscope (SEM), high resolution-electron microscope, electron dispersive X-ay spectroscopy (EDX), Raman spectroscopy, inductively coupled plasma-optical emission spectroscopy (ICP-OES), vibrating sample magnetometer (VSM), nitrogen adsorption at 77 K, and inverse gas chromatography. TEM and SEM analysis confirmed SCNMs obtained were a mixture of B-CNTs and carbon nanofibres (B-CNF). EDX and ICP-OES results showed that boron was successively incorporated into the carbon hexagonal network of CNTs and its concentration was dependent on the amount of triphenylborane used. From the VSM results, the boron doping within the CNTs introduced ferromagnetic properties, and as the percentage of boron increased the magnetic coactivity and squareness changed. In addition, boron doping changed the conductivity and the surface energy among other physicochemical properties of B-CNTs

Organic Solar Cells with Boron- or Nitrogen-Doped Carbon Nanotubes in the P3HT : PCBM Photoactive Layer

Either boron- or nitrogen-doped carbon nanotubes (B- or N-CNTs) were incorporated in bulk heterojunction organic solar cells photoactive layer composed of poly(3-hexylthiophene) (P3HT) : (6,6)-phenyl-C61-butyric acid methyl ester (PCBM). The physical and chemical properties were investigated using different spectroscopic techniques. The cell performance was followed from their current-voltage (J-V) characteristics. Recombination dynamics of the photo-generated free charge carriers were investigated using micro- to milliseconds transient absorption spectroscopy (TAS). Transmission electron microscopy (TEM) images revealed the presence of cone structures and bamboo compartments in B-CNTs and N-CNTs, respectively. X-ray photoelectron spectroscopy (XPS) revealed very little boron was substituted in the carbon network and presence of pyrrolic, pyridinic, and quaternary species of nitrogen in N-CNTs. J-V characteristics were found to be similar for the devices with B- and N-CNTs even though boron- and nitrogen-doped CNTs are known to have different properties, that is, p-type and n-type, respectively. TAS results showed that all devices had long lived free charge carriers but the devices with B- or N-CNTs had low power conservation efficiency and voltage

Charge extracting buffer layers in bulkheterojunction organic solar cell

The effects of boron and nitrogen-doped carbon nanotubes (B- or N-CNTs) have been investigated as photoactive and charge extracting layer in bulk heterojunction organic solar cell composed of poly(3-hexylthiophene) [P3HT] and 1(3-methoxycarbonyl)propyl-1-phenyl-[6,6] C61 (PCBM). Two types of device configurations were employed by casting the doped CNTs close to either the hole or electron collecting electrodes next to a film of P3HT:PCBM blend. The electrical properties of OPV devices measured under standard 1.5 AM illumination suggest that those devices with B-CNTs layer close to the hole collecting electrode improved by 141 % while the devices with N-CNTs layer next to electron collecting electrode improved only by 38 %. The results are attributed to enhanced charge carrier’s transfer to the electrodes by reducing recombination at the interfaces. The doped CNTs layer near the photoactive medium of OPV is found to enhance device performance compared to the incorporation of CNTs in P3HT:PCBM blend

Bulk Heterojunction Solar Cell with Nitrogen-Doped Carbon Nanotubes in the Active Layer: Effect of Nanocomposite Synthesis Technique on Photovoltaic Properties

Nanocomposites of poly(3-hexylthiophene) (P3HT) and nitrogen-doped carbon nanotubes (N-CNTs) have been synthesized by two methods; specifically, direct solution mixing and in situ polymerization. The nanocomposites were characterized by means of transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray dispersive spectroscopy, UV-Vis spectrophotometry, photoluminescence spectrophotometry (PL), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, thermogravimetric analysis, and dispersive surface energy analysis. The nanocomposites were used in the active layer of a bulk heterojunction organic solar cell with the composition ITO/PEDOT:PSS/P3HT:N-CNTS:PCBM/LiF/Al. TEM and SEM analysis showed that the polymer successfully wrapped the N-CNTs. FTIR results indicated good π-π interaction within the nanocomposite synthesized by in situ polymerization as opposed to samples made by direct solution mixing. Dispersive surface energies of the N-CNTs and nanocomposites supported the fact that polymer covered the N-CNTs well. J-V analysis show that good devices were formed from the two nanocomposites, however, the in situ polymerization nanocomposite showed better photovoltaic characteristics

Organic solar cells with boron- or nitrogen-doped carbon nanotubes in the P3HT : PCBM photoactive layer

Either boron- or nitrogen-doped carbon nanotubes (B- or N-CNTs) were incorporated in bulk heterojunction organic solar cells photoactive layer composed of poly(3-hexylthiophene) (P3HT) : (6,6)-phenyl-C61-butyric acid methyl ester (PCBM). The physical and chemical properties were investigated using different spectroscopic techniques. The cell performance was followed from their current-voltage (-) characteristics. Recombination dynamics of the photo-generated free charge carriers were investigated using micro- to milliseconds transient absorption spectroscopy (TAS). Transmission electron microscopy (TEM) images revealed the presence of cone structures and bamboo compartments in B-CNTs and N-CNTs, respectively. X-ray photoelectron spectroscopy (XPS) revealed very little boron was substituted in the carbon network and presence of pyrrolic, pyridinic, and quaternary species of nitrogen in N-CNTs. - characteristics were found to be similar for the devices with B- and N-CNTs even though boron- and nitrogen-doped CNTs are known to have different properties, that is, p-type and n-type, respectively. TAS results showed that all devices had long lived free charge carriers but the devices with B- or N-CNTs had low power conservation efficiency and voltage201