Bipolarons rule the short-range terahertz conductivity in electrochemically doped P3HT

Abstract

Doping of organic semiconductor films enhances their conductivity for applications in organic electronics, thermoelectrics and bioelectronics. However, much remains to be learnt about the properties of the conductive charges in...

Critical dopant concentrations govern integer and fractional charge-transfer phases in doped P3HT

“…On the other hand, our 17% F4TCNQ spectrum also compares to that reported by Tsokkou et al [62] by drop-casting from common solution (but using chlorobenzene as solvent). They used an advanced deconvolution technique in combination with spectra of electrochemically doped P3HT to ascribe a broad peak at 0.92 eV to the formation of bipolarons.…”

“…They used an advanced deconvolution technique in combination with spectra of electrochemically doped P3HT to ascribe a broad peak at 0.92 eV to the formation of bipolarons. We do not observe any such indication of bipolaron formation for F2TCNQ, FTCNQ, or TCNQ, which is not surprising as even F4TCNQ has been long viewed as incapable of producing (measurable) amounts of bipolarons, restricting this phenomenon rather to stronger dopants or electrochemical doping [62][63][64][65]. For our 17% F4TCNQ spectra we find that the UV-vis/NIR data merged with FTIR thin-film absorbance spectra of P3HT doped with FxTCNQ (x = 0, 1, 2, 4) at increasing dopant molar ratios χ as well as those of the corresponding pure compounds.…”

“…absorbance is less attenuated between the polaron peaks, as compared to the lower dopant concentrations (see also supplementary material figure S1), but no new distinct features can be made out. We recall that the CPX peaks are expected at 0.66 & 1.15 eV [14] and could be held for this additional absorbance, but also a possible bipolaron related contribution at 0.92 eV [62] would be situated directly between the polaronic transition energies and explain this absorbance. Another sign of bipolaron formation-rarely observable due to the often limited experimental spectral ranges-would be a peak around 0.35 eV (inferred from electrochemical doping [64] and computational analysis thereof [66]), which again would largely coincide with the broad low-energy polaron peak.…”

A new single shot THz detection strategy with electro-optic sampling

“…In conclusion, we presented a new single shot THz measurement technique that is very simple to realize. The method is particularly sensitive to the phase which is of great interest when measuring on thin samples like the conductive polymers we use in our research [12]- [14]. The reliability of the recovery could be improved with a better knowledge of the pulses, and with more adapted optics and detection system: in fact the FPE used in this work was not design for the purpose presented in this proceeding, and the specifications of the FPE could be better adapted to THz single shot detection.…”

“…Instead of rastering the THz waveform by physically displacing the probe beam, we placed a FPE in the probe beam and detected the probe with a miniature high resolution CCD spectrometer (HR4000, Ocean Optics, 0.05 nm/pixel, resolution 0.2nm). When passing our short 50fs pulse into the FPE, a pulse train of pulses with exponentially decaying intensity is created [10][11][12]. In the limit when the thickness of the FPE is smaller than the pulse extension in space, the train of pulses becomes a continuous pulse with a sharp rise and an exponentially decaying tail which extensions depends on the free spectral range and finesse of the FPE.…”