**3.1. Micro-Raman spectroscopy experiments**

Micro-Raman spectroscopy is a great investigation tool for SWCNTs characterization. In **Figure 8**, is a comparison of the typical micro-Raman spectra for SWCNTs obtained in our laboratories (blue) and high-quality commercially one (black), provided by Sigma Aldrich. As can be observed the spectra are quite similar leading to the conclusion that quality of SWCNTs obtained in our laboratory is comparable to commercial one.

The excitation laser was green (532 nm). In the zone of radial breathing mode (RBM) in **Figure 8** left top we found peaks characteristic only to SWCNTs and whose frequencies are strongly SWCNTs diameter dependent. The diameters were calculated in accordance with Eq. (1):

*ω* – frequency for vibrations in the radial direction [cm−1];

*c*1, *c*2 – constants [cm−1]; *c*1 = 215 [cm−1]; *c*2 = 18 [cm−1];

*d* – diameter of the nanotube [nm].

$$d = \frac{c\mathbf{l}}{\alpha - c\mathbf{2}}\tag{1}$$

The diameters of our SWCNTs are in the range of *d* = 1.1–1.6 nm with average *d*A = 1.35 nm.

The G band in the Raman spectra clearly demonstrates, depending on the ratio of *I*G+/*I*G− that semiconducting SWCNTs were obtained, **Figure 8** (top right). However by using red excitation laser we obtain evidence of metallic SWCNTs existence (not shown here). So we conclude that our material is a mixture of semiconducting and metallic nanotubes.

**Figure 8.** Micro-Raman spectra of SWCNTs – blue: our product, black: commercial product.

### **3.2. AFM experiments**

Atomic force microscopy (AFM) was involved for the synthesized SWCNTs characterization as well as for SWCNTs mixed with poly(3-octylthiophene) (P3OT) polymer, for solar cell applications.

In **Figure 9** we present AFM images for a synthesized SWCNTs bundle on Si substrate: (a) 2D and; (b) 3D. In (c) is presented the topography of P3OT polymer on glass and (d) is 12% SWCNTs composite in P3OT polymer on glass and we can observe the SWCNTs bundles. We investigated also the adhesions forces on both surface and they increase with the increase of SWCNTs content into polymer (not shown here).
