The electronic behavior of poly(3-octylthiophene) electrochemically synthesized onto Au substrate

Abstract

We investigate the electronic characteristics and the absorption spectra of poly(3-octylthiophene), POT, films grown by electrochemical methods onto Au substrates. We discuss the results considering the morphological factor. POT films thickness can be controlled by current density in the electropolymerization process. The film roughness depends on the thickness, being about 12% of film thickness. The samples for electrical measurements were made in sandwich structure, Au/POT/metal (metal: Ni, Al). Analyzing current-voltage data we were able to estimate the positive charge carrier mobility (5×10 −4 cm 2 V −1 s −1 ) and the potential barrier height in the metal/polymer interfaces (0.1 eV for Au/POT and Ni/POT and 0.85 eV for Al/POT). I IntroductionConjugated polymers have been object of intense research in the last years. These organic semiconductors present good mechanical features, facility of production and offer the possibility of construction of devices with larger active areas than their inorganic counterparts. Among these polymers, polythiophene and its derivatives have received special considerations. Polythiophenes have a good chemical stability upon environmental conditions and produce stable interfaces with electrode metals commonly used in electronics, like aluminum and gold [1,2]. Another important feature of polythiophene films is a large absorption coefficient in the visible range of the electromagnetic spectrum [3,4,5]. These characteristics make polythiophene and its derivatives interesting materials for solar cell applications [6]. One of the major problems in polymer devices is the small charge carrier mobility. The morphology of the polymer film takes important place in this situation. In amorphous materials the transport occurs via hopping between localized states and disorder contributes to a further reduction of mobility. Many methods have been used to improve the order degree or the crystallinity in polymer films [7,8]. The use of polymers with large side chain segments is one of the methods employed with this intent. The increase in the side chain length improves the order and the planarity of the polymer chains [9]. So, the order is expected to be higher in poly(3-octylthiophene), POT, than in other polythiophene derivatives, like poly(3-metylthiophene) and consequently, also the charge carrier mobility.When a potential barrier energy ϕ for the charge carriers injection at the interface between the electrode and the polymer is so that ϕ >> kT (k is the constant of Boltzmann and T is the absolute temperature) the transport is better described by Simmons current density expression, derived for thermionic injection into low mobility materials [10].

Application of Conducting Polymers in Solar Water-Splitting Catalysis

“…PTh's useful features include (1) high charge carrier mobility, (2) environmental stability, and (3) higher wavelength absorption compared to other conductive polymers. The incorporation of substituents on PTh may improve its physical properties [71,72] and make it easier to polymerize. These features allow PTh to be used in many applications or potential applications, including the use in transistors, solar cells, sensors, electrochromic devices, supercapacitors, and light-emitting diodes.…”

Single-Wall Carbon Nanotubes Chemically Modified with Cysteamine and Their Application in Polymer Solar Cells: Influence of the Chemical Modification on Device Performance

“…Our J SC values similar to those observed by other groups, 20-28 however they are too low in comparison to bulk heterojunctions devices constructed using fullerenes. The cause of the might be ascribed to the low charge carrier mobility of the P3HT matrix, 71 the high recombination rate due to the low dispersion of the nanotubes, electrical shorting as the nanotubes penetrate the photoactive layer compromising the diode, and to the presence of impurities. [15][16][17][18][19] Much work still needs to be done in order to obtain practical J SC and V OC values, especially if that SWCNT are to be competitive with fullerenes.…”

Simple and Fast Organic Device Encapsulation Using Polyisobutene

“…Organic devices made with poly(3-octylthiophene) (POT) electrochemically deposited onto an Au contact were used to perform the experiment. [10] Fourteen Al contacts were vacuum evaporated onto a 200 nm thick POT film forming fourteen independent devices, each one with 1 mm 2 active area. The PIB encapsulation was made under N 2 atmosphere and the glass substrate was heated to 40 8C.…”