Fully-Sprayed and Flexible Organic Photodiodes with Transparent Carbon Nanotube Electrodes

Abstract

In this study, we demonstrate the feasibility of TCO-free, fully sprayed organic photodiodes on flexible polyethylene terephthalate (PET) substrates. Transparent conducting films of single-wall carbon nanotubes are spray deposited from aqueous solutions. Low roughness is achieved, and films with sheet resistance values of 160 Ω/sq at 84% in transmittance are fabricated. Process issues related to the wetting of CNTs are then examined and solved, enabling successive spray depositions of a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layer and a blend of regioregular poly(3-hexylthiophene-2,5-diyl) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM). The active layer is then optimized, achieving a process yield above 90% and dark currents as low as 10(-4) mA/cm(2). An external quantum efficiency of 65% and high reproducibility in the performance of the devices are obtained. Finally, the impact of the characteristics of the transparent electrode (transmittance and sheet resistance) on the performances of the device are investigated and validated through a theoretical model and experimental data.

Single-walled carbon nanotube transparent conductive films fabricated by reductive dissolution and spray coating for organic photovoltaics

“…Due to the considerable SWNT length, smaller bundle size, and absence of surfactant, TCFs from the reductive process ink consistently afforded higher performance (average FOM ¼ 15, minimum 12) than that from the aqueous dispersion (average FOM ¼ 26, minimum 24). The performance of the aqueous SWNT film is in good agreement with that previously reported in the literature for spray-deposited aqueous dispersions, 10 while the organic SWNT is competitive with some of the best performing carbon nanotube films. [25][26][27][28][29] AFM, transmittance, and spot-to-spot Raman measurements show good uniformity and consistent results for each film.…”

“…SWNTs are a promising alternative to ITO due to the great abundance of carbon; the potential for cost reduction due to economies of scale; exceptional flexibility and conductivity; and the ability to deposit nanotube networks from solution using additive, low-temperature printing and coating processes. 5,[8][9][10][11][12][13] Carbon nanotube TCFs have been successfully utilized in organic optoelectronic devices, including light-emitting diodes, 9 photodiodes, 10 and photovoltaics. [12][13][14][15][16] However, while SWNTs have the potential to form networks with simultaneously high conductivity and high transparency, experimentally measured conductivity of transparent SWNT networks tends to be much lower than that of ITO.…”

Organic Photodiodes: The Future of Full Color Detection and Image Sensing

“…[ 37,106 ] Macromolecules such as dendrimers and polymers can be processed from solution using techniques such as aerosol-jet printing, [ 107 ] spin-coating, [ 108 ] inkjet-printing, [ 109,110 ] screen printing, [ 111 ] or spray-coating. [112][113][114][115] …”

Building interconnects in carbon nanotube networks with metal halides for transparent electrodes

“…Compared with other potential candidates of transparent electrodes, CNT films not only enable a lower cost process, but also provide a more stretchable and flexible platform with stronger mechanical strength. Thus, CNT films can be a perspective transparent electrode for optoelectronics including photovoltaics, touch panels, light emitting diodes [4][5][6][7].…”