Efficient hole transport material formed by atmospheric pressure plasma functionalization of Spiro-OMeTAD

Abstract

A technique to increase the conductivity of Spiro-OMeTAD using an easily scalable, nonthermal atmospheric pressure plasma jet (APPJ) is reported. An investigation of plasma functionalization demonstrated an enhancement in hole conductivity by over an order of magnitude from 9.4 × 10-7 S cm-1 for the pristine film to 1.15 × 10-5 S cm-1 for films after 5 minutes of plasma treatment. The conductivity value after plasma functionalization was comparable to that reported for 10 -25% Li-TFSI-doped Spiro-OMeTAD. The increase in conductivity was correlated with a reduction in phase value observed using electrostatic force microscopy. Kelvin probe force microscopy showed an increase in work function after plasma exposure corresponding to the p-type nature of the doping. X-ray photoelectron spectroscopy revealed surface oxidation of plasma-functionalized films, as well as variation in nitrogen chemistry, with the formation of a higher binding energy quaternary nitrogen tail. Oxidation of Spiro-OMeTAD was also confirmed by the appearance of the 500 nm absorption peak using UV-vis spectroscopy. The synergistic contribution of increase in charge density in Spiro-OMeTAD due to the energetic species in the plasma jet coupled with improvement in π-π stacking of the molecules is thought to underlie the conductivity enhancement. We also attribute the formation of quinoid structures with quaternary nitrogen +N=C to the enhancement in positive charge centres due to loss of methoxy groups during plasma-surface interaction. This work opens up the possibility of using an atmospheric pressure plasma jet as a simple and effective technique for doping and functionalizing Spiro-OMeTAD thin films to circumvent the detrimental issues associated with chemical dopants.

Rubidium Iodide-Doped Spiro-OMeTAD as a Hole-Transporting Material for Efficient Perovskite Photodetectors

“…It is known from the literature that the generation of spiro-OMeTAD + can serve as an indicator that HTMs effectively promote hole mobility at the material interface; the increase in the spiro-OMeTAD + can induce the Fermi energy level to the HOMO level due to increased hole carrier concentration, , which is consistent with the UPS results measured above. And its absorption peak is generally around 400 and 520 nm, but the 400 nm peak is easily mixed with the 395 nm peak of the nonoxidized state spiro-OMeTAD . To be clearly comparable, normalization of the obtained data was achieved, as shown in Figure d, where the inset shows the magnification of the absorption spectra in the range of 450–600 nm, and the highest board absorption band was found in 0.6RbI:spiro around 520 nm, suggesting the formation of oxidized spiro-OMeTAD cation radical.…”

Phenoxy Radical‐Induced Formation of Dual‐Layered Protection Film for High‐Rate and Dendrite‐Free Lithium‐Metal Anodes

“…Theultrahigh Youngsmodulus of organic Spiro-O8-Li film is also verified by the AFM test of Spiro-O8-Li film on conductive glass (Figure S13), which may be attributed to its relatively symmetrical chemical structure,h igh glass transition temperature,molecular rigidity without any alkyl chains, as well as favorable intermolecular interaction in film. [22] After immersed in electrolyte,Spiro-O8-Li@Li still maintains av ery uniform and smooth surface with an average surface roughness of 8.9 nm (Figure S14). Thei ncreased surface roughness is caused by the formation of LiF film upon exposed to the electrolyte.M eanwhile,t he Youngsm odulus mapping values of Spiro-O8-Li@Li are jumped to 6.2 GPa after ar eaction between Spiro-O8-Li and the electrolyte (Figure 4b), which is very close to the Youngsm odulus of electrolyte-derived LiF films in previous works.…”

Influence of Nanostructures in Perovskite Solar Cells

“…The carbon layer plays an important role in water resistance. Moreover, doping and functionalization using atmospheric pressure plasma has been recently exploited to increase the hole conductivity of Spiro-OMeTAD without the necessity of additional chemical dopants (Ghosh et al, 2020).…”