**3.1 Expérimental details**

*Solar Cells - Theory, Materials and Recent Advances*

intensity of PL as a function of the inverse of the temperature. Taking into account these two transfer processes, we fitted the experimental curve using the twoenergy model, this empirical model is presented in Eq. (1) below [37]:

> + − + ×

1 a exp 1 exp kT a kT

where e1: first thermal activation energy; e2: second thermal activation energy;

From the results, it can be seen that the thermal activation energy of one energy level is different from that of another level. This phenomenon can be explained by the increase in the Tunnel process with the increase in temperature [35]. We can

Spectroscopic ellipsometry is a very sensitive optical surface analysis method that allows the physical and morphological properties of a flat sample to be probed at different scales and at different energies. It has experienced significant growth over the past 100 years [38] and particularly over the past 20 years with modern computing. The

1 2

e 1 e

 

(1)

2

( ) ( )

**3. Ellipsometric spectroscopy measurement**

1

A, a1 and a2: the fixing parameters; and IPL: the intensity PL. The different values found are presented in **Table 4**.

= × +

*Variation of the integrated intensity of PL as a function of the inverse of the temperature.*

**e1** 36.6044\*8.33E-5 = 3.05 meV

**e2** 1205.8422\*8.33E-5 = 100.44 meV

**IPL** 0.0232 **a1** 0.4046

**A** 1.7293

**a2** 1.1545E13

*The values obtained from the parameters of the equation.*

also know the thermal activation energy of phonons in porous silicon.

I 0 <sup>A</sup> I T <sup>1</sup>

PL PL 2

**116**

**Figure 9.**

**Table 4.**

Ellipsometric measurements were performed on the porous silicon substrate for an angle of incidence of 78° in the spectral range 250–2000 nm using the GES5 Sopra made rotating polarizer spectroscopic ellipsometer was used for the (SE) spectroscopic ellipsometry measurement, controlled by the WinElli-II software.

To extract the thickness of the PS layer from measuring of SE, an optical model must be assumed, as well as the calculated data have to follow experimental spectra. In applying EMA software, we utilized a model of a multi-layer model, whereas the first mixture of the layer (void/SiO2), while the second layer is (Sic/void), As indicated in **Figure 10**, a high improvement in the fit quality was observed [31].
