Ultrasmooth, Large‐Area, High‐Uniformity, Conductive Transparent Single‐Walled‐Carbon‐Nanotube Films for Photovoltaics Produced by Ultrasonic Spraying

Abstract

Transparent conducting (TC) films of single-walled carbon nanotubes (SWNTs) have the potential to replace conventional TC oxides in a wide variety of optoelectronic devices. [1][2][3][4][5] TC-SWNT films are particularly attractive for photovoltaics (PV) due to their high transparency over much of the solar spectrum, excellent electrical conductivity, and the potential for inexpensive roll-to-roll processing. SWNT films have been used, by us and others, in cadmium telluride, [6] copper indium gallium diselenide, [7] and organic PV (OPV) devices. [8][9][10] In several reports, SWNTelectrodes for OPV have been prepared by filtering a sodium dodecyl sulfate (SDS)-stabilized dispersion of SWNTs to form a thin film. [9,10] The film can be released by dissolution of the filter, and then transferred to a transparent substrate.[11] This so-called ''transfer method'' produces highly transparent films with excellent conductivity, but the films possess irregular morphologies and significant roughness, which can lead to short-circuits and overall poor reproducibility during device fabrication.[12] Moreover, the process is not scalable. TC-SWNT films have also been produced for optical and electrical studies by air-brush spraying using surfactant-stabilized SWNT inks. Such films are inhomogeneous because SWNTs sprayed from surfactant solutions agglomerate on heated substrates. To move TC-SWNT electrodes beyond the proof-of-concept stage for PV and other optoelectronic applications, methods are required for producing large-area, transparent, conducting SWNT films that are smooth and homogeneous over large areas.Here, we report methods to prepare SWNT films with high transparency, electrical conductivity, and uniformity, with exceptionally low surface roughness, on arbitrarily large (6 inch  6 inch) substrates by ultrasonic spraying. A side-by-side comparison of OPV devices fabricated on SWNT and indiumdoped tin oxide (ITO) electrodes showed very good performance with energy-conversion efficiencies of $3.1 and 3.6%, respectively, under AM 1.5 illumination. Several factors are critical to the success of the approach. First, we prepared aqueous SWNT dispersions using a high-molecular-weight (MW $90 000) polymeric derivative of cellulose (sodium carboxymethyl cellulose (CMC)). CMC has been previously reported as an excellent agent for dispersing SWNTs in water, [13] and transparent films have been drop-cast, [14] but this is the first report of CMC-based dispersions for spraying SWNT films. A second advance is the use of ultrasonic spraying, which, when combined with the CMC-based dispersions, permits precise amounts of SWNTs to be reproducibly and uniformly dispensed over arbitrarily large areas. In fact, by measuring the weight and optical properties of films as a function of the number of deposited layers, the SWNT absorption coefficient could be accurately determined. Finally, we used SWNTs produced by laser vaporization (LV), which have lower defect densities [15,16] than tubes produced by chemical vapor deposition (CVD). Th...

Carbon nanotubes for organic/inorganic hybrid solar cells

“…But all these methods create groups at CNT walls, which can act as recombination. Alternativelly, CNTs are suspended in aqueous media by non-covalent interactions using surfactants [7,20,[63][64][65].…”

“…Therefore, developing the strategies to seperate metallic and semiconducting SWNTs is an actual target with great importance for solar cell applications of CNTs. Absorbance [20] and Raman [21] measurements are the characterization tools, which allows to distinguish whether the SWNT is a metallic or semiconducting. If the SWNTs are in the mixed state state consisting of metallic and the semiconducting types, the samples possess the black color [22], because the absorption bands caused by the metallic and the semiconducting nanotubes cover almost the entire range of the visible region.…”

High Stable, Transparent and Conductive ZnO/Ag/ZnO Nanofilm Electrodes on Rigid/Flexible Substrates

“…Nowadays, several alternative transparent electrodes have been reported, such as carbon nanotubes [5,6], grapheme [7,8], doped ZnO conducting films [9,10], conducting polymes [11,12], metal materials [13,14], etc. Currently, Ag nanomaterial is regarded as one of the most appealing transparent electrodes due to its excellent conductivity.…”

Highly conductive and transparent carbon nanotube composite thin films deposited on polyethylene terephthalate solution dipping

“…The preliminary results are close to those of the commercial available ITO thin films deposited on PET, such as the ones from Sigma-Aldrich (35 Ω/□, N86% transmission at 550 nm). With the optimization of the composition of the SWCNT composite, plus other techniques reported in the literature [11][12][13][14][15], SWCNT/conducting polymer composite thin films might potentially offer better or comparable performances as the conductive oxides.…”

“…T h em a i nc h a l l e n g eh e r ei st oa d d r e s st h et r a d e -o f fb e t w e e n transparency and conductivity. Many factors have been studied in order to improve the conductivity of the CNT thin films without sacrificing their transparency [4,[11][12][13][14][15]. For example: processing techniques and parameters [4,11]; length of the CNT [12]; doping [13,14]; and metallic amount of the CNT in the mixture [14].…”