Single crystal structure and opto-electronic properties of oxidized Spiro-OMeTAD

Abstract

Single crystals of Spiro(TFSI)2 were grown and structurally determined. The optical and electronic properties were investigated and compared with neutral Spiro-OMeTAD.

Understanding the dopant induced effects on SFX-MeOTAD for perovskite solar cells: a spectroscopic and computational investigation

“…Splitting of the N1s→π* resonance in 10%, 20% and 100% samples may be attributed to the difference in bond length between the N-C molecules as has been previously observed for Spiro-MeOTAD 40 and SFX-MeOTAD in this study. A modest difference in C-N bond length in the case of Spiro(TFSI)2 has been reported 36 and a similar variation in bond length in case of SFX(TFSI)2 has been observed in this study [Table 1]. This trend would corroborate the fact that the presence of the electron-donating methoxy groups affects the charge density of the molecules and plays a crucial role in influencing the charge transfer process.…”

“…40 As shown by Zhang et al, the +2 oxidation state of spiro-MeOTAD can absorb around 2000 nm. 36 This behaviour was also observed in the SFX-MeOTAD 2+ calculations, where a peak was observed at 1937 nm and corresponds to the transitions between the HOMO-1β orbital to the LUMO+1β orbital (see S5 for visualised MO transitions for SFX-MeOTAD 2+ ). This band was not able to be measured experimentally due to the limitations of the equipment.…”

“…39 As mentioned above, a simplistic picture proposed earlier for spiro-MeOTAD was assumed to be true for the SFX-MeOTAD as well, where it is assumed that all the dicationic salt is used to convert SFX-MeOTAD into its monocation. However, conversion of SFX-MeOTAD 2+ to SFX-MeOTAD 4+ , as proposed by Zhang et al 36 , cannot be ruled out. DFT and TD-DFT computational calculations were also carried out for the +4 triplet, and absorbance maxima were found at ca.…”

“…35 Recently, the absorbance spectrum of spiro-(TFSI)2 single crystals dissolved in acetonitrile were studied in a wide wavelength range (300 -2000) and reported to show peaks at 371 nm, 521 nm, 691nm, 908 nm and 1527 nm. 36 To understand the changes induced by the oxidation processes on the electronic structure and absorption spectrum and to optimise the geometries of the possible oxidised species of SFX-MeOTAD, DFT and TD-DFT computational calculations were carried out. The optimised structure of neutral SFX-MeOTAD shows that both the xanthene and fluorene units of the spiro[fluorene-9,9′-xanthene] core are planar, and the appended triarylamine units are not planar, but are in a propeller orientation (see S1 in Supporting Information (SI)).…”

“…A similar phenomenon is observed in case of Spiro(TFSI)2, where intermolecular charge transfer is hindered as well as orbital overlap and π-π interaction due to the anions involved in the molecules. 36 Significant broadening of I1 in the case of 100% dopant implies delocalisation of π* orbitals. The variation in line shape may also suggest the difference in charge transfer in 100% dopant and other doping concentrations.…”