No dominant changes were observed in the optical transmittance spectra after doping, except for the appearance of a slight adsorption around 500 nm by TCNQ molecules [27]. The sheet resistance, R s , as a function of Dasatinib cell line transmittance at 550 nm

is summarized in Figure 7. Due to carrier doping via the CT interaction from TCNQ, the sheet resistance of the RGO + TCNQ complex films drastically decreased by two orders of magnitude without significant degradation of the optical transparency as a result of increasing the sheet carrier density from 1.02 × 1010 cm-2 to 1.17 × 1012 cm-2 estimated from Hall measurement. Doping stability with time evolution at room temperature under ambient atmosphere was monitored. R s increased Staurosporine by less than 10% after 1 year, whereas it increased by up to 40 % after 20 days in the case of AuCl3 which showed one of the highest doping effect [19]. Thermal stability of our doped films was examined by stepwise annealing from 100°C to 250°C under vacuum. The doping effect was preserved after annealing even at 250°C without any remarkable

degradation. This result indicates higher thermal stability than F4-TCNQ [34]. Those stabilities are quite critical issue of doping technique in any application fields. Finally, our chemical doping method was tried by dipping chemical vapor deposition (CVD) graphene purchased from Graphene Platform, Inc. (Houston, TX, USA) in radicalized TCNQ in order to show that our method can be adapted also for CVD graphene. The sheet resistance of the

doped CVD graphene decreased to 400 Ω from 1.2 kΩ at 97% of optical transparency. Our doping method exhibits the compatibility with the CVD graphene-based transparent conductive films. Figure 7 Sheet resistance of different films as a function of optical transmittance at 550 nm. Pristine RGO films (black squares), doped RGO films by surface adsorption (blue triangles), and RGO + TCNQ complex films (red circles). The sheet resistance of the RGO + TCNQ complex films decreased drastically by two orders of magnitude, acetylcholine without degradation of optical transparency, which was a more drastic change than the case of doping by surface adsorption. Conclusions We developed a novel method for the carrier doping of graphene using radical-assisted conjugated organic molecules in the liquid phase. The absorbance data and the Raman spectra results indicated strong charge transfer interactions between RGO and TCNQ. The high doping efficiency of our method was demonstrated as an improvement in sheet resistance by two orders of magnitude, without degradation of the optical transparency. First-principles calculation predicted the model of our doping mechanism and the origin of high doping efficiency. Furthermore, the doping effect was quite chemically stable.