Transparent conductors

Lewis, J. Grego, S. Chalamala, B. Vick, E. Temple, D. 2004. Electromechanics of a highly flexible transparent conductor for display applications. Society of Vacuum Coaters 47th Annual Techn. Conf. Dig. 47 129-132. 

K.L. Chopra, S. Major, and D.K. Pandya, Transparent conductors — a status review, Thin Solid Films, 102 1-46, 1983. 

Y. Park, V. Choong, Y. Gao, B.R. Hsieh, and C.W. Tang, Work function of indium tin oxide transparent conductor measured by photoelectron spectroscopy, Appl. Phys. I ett., 68 2699-2701,1996. 

N-n Heterojunction Another heterojunction that could favor charge separation is the contact between a transparent conductor, in the form of a degenerated semi-... 

The combination of low optical absorbance and high electrical conductivity has attracted a lot of interest for transparent conductor applications. When coupled with its flexibility, it is widely seen as a possible replacement for indium-doped tin oxide (ITO), which has a sheet resistance of 100 Q/cm at 90 % transparency. By growing graphene on copper foils, sheet resistances of 125 Q/cm at 97.4% transparency have been achieved [19]. This has been improved by combining four layers with doping of the graphene, giving resistance of 30 Q/cm at 90% transparency, all done on 30-inch roll-to-roll production scale. 

H.A. Becerril, J. Mao, Z. Liu, R.M. Stoitenberg, Z. Bao, Y. Chen, Evaluation of solution-processed reduced graphene oxide films as transparent conductors, ACS Nano, 2 (2008)... 

In addition to their potential use as structural composites, these macroscopic assemblies of nanocarbons have shown promise as mechanical sensors [83], artificial muscles [84], capacitors [85], electrical wires [59], battery elements [85], dye-sensitized solar cells [86], transparent conductors [87], etc. What stands out is not only the wide range of properties of these type of materials but also the possibility of engineering them to produce such diverse structures, ranging from transparent films to woven fibers. This versatility derives from their hierarchical structure consisting of multiple nano building blocks that are assembled from bottom to top. 

Tung VC, Chen L, Allen MJ et al (2009) Low-temperature solution processing of graphene-carbon nanotube hybrid materials for high-performance transparent conductors. Nano Lett 9 1949-1955... 

Li X, Li C, Zhu H et al (2010) Hybrid thin films of graphene nanowhiskers and amorphous carbon as transparent conductors. Chem Commun 46 3502-3504... 

CD Cu-S(e) films have been proposed for a number of different potential applications. Solar control coatings, where the visible and IR transmission and reflectivity can be varied, is probably the most studied, e.g.. Refs. 44 and 45. The relatively high conductivity and the partial transmittance in the visible spectrum are useful for transparent conductors [46]. Other possible applications are for Cu sensor electrodes and electrical contacts for ceramic devices [46]. 

Electrical conductivity measurements of the as-deposited ln(OH)s showed an expectedly high resistivity of ca. 10 ff-cm. That of the annealed oxide film decreased to 33 O-cm (carrier concentration = 1.85 X 10 cm mobility = 10 cm V sec ). The resistivity is high compared to many other ln20s films (which are often used as transparent conductors), mainly due to the low carrier concentration, implying a high degree of stoichiometry. 

CdO, the first discovered and applied transparent conductor [40], which also exhibits the highest reported conductivity (see compilation of data in [41]), is less used today because of its toxicity and its low optical band gap (EStPhotoelectron spectra indicate, however, that the band gap is 1 eV [43]. Although the (direct) optical gap is increased for degenerate doping due to the Burstein-Moss effect [44], it remains difficult to prepare noncolored CdO films. 

In conclusion, for both AP-CVD and LP-CVD processes, only a narrow range of temperatures can be identified for optimum performance (a range that is typically 40°C-wide). Within this narrow temperature range highly oriented films are obtained that have electrical and optical properties suitable to act as transparent conductors in solar cells. The typical substrate temperature is around 400°C for the AP-CVD process, whereas it is around 160°C for the LP-CVD process. The two processes yield film orientations that are perpendicular to each other. 

As an alternative to numerical simulation, we may also use experimental measurements and evaluate the latter with an appropriate figure of merit (FoM). Such a FoM will allow us to compare the performance of different transparent conductors. 

The geometry we use is shown in Fig. 20a. A semitransparent conductor, a photoconductor, a second semitransparent conductor, and a polymer film are successively deposited on a glass substrate. The semitransparent conductors are about 10-nm-thick layers of Nb deposited by ion-beam sputtering. Although the films have an optical density of—0.25, they are very stable and easy to contact. More transparent conductors, such as indium-tin-oxide, can be used if the subsequent processing temperature remains below 250°C. 

Chopra, K. L., Major, S. and Pandya, D.K. (1983) Transparent conductors - A status review. Thin... 

Cadmium stannate, used as electrodes in photogalvanic cells, is another example of a transparent conductor oxide (TCO) having desirable properties, such as good durability and chemical resistance. It can be produced by the spray pyrolysis CVD method with organic solutions of CdCH and SnCH or [Cd(hfa)2 (TMEDA)] and [Sn(acac)2]. ° It also shows the unexpected effect of improving transparency with increasing Him conductivity higher than tin-doped indium oxide. 

---