## 2 Materials and Methods  
In our study we used low-resistivity \(n\)-InSe single crystals grown by the Bridgman method from a non-stoichiometric melt In\({}_{1.03}\)Se\({}_{0.97}\). From the obtained ingot we mechanically cleaved plane-parallel plates with shape suitable for measurements of Hall effect and conductivity in different crystallographic directions. After the electrical characteristics of the pristine samples were measured, samples were subjected to the insertion (intercalation) of a molecular guest component into the lattice by exposing the InSe samples to a melt of RbNO\({}_{3}\) at a temperature \(T=\) 370 \({}^{\circ}\)C for 10 min. A porcelain crucible with the melt was placed in a hermectical box filled with air dried with phosphorus pentoxide (P\({}_{2}\)O\({}_{5}\)). The repeated intercalation was performed at the same technological conditions. To distinguish a possible effect of associated thermal treatment, other pristine samples were annealed in vacuum at the same time-temperature conditions.  
Measurements of the temperature dependences of the conductivity along the layers \(\sigma_{\perp C}\) and Hall coefficient \(R_{\rm H}\) were carried out for samples shaped as rectangular parallelepipeds with typical dimensions of 10 \(\times\) 2.5 \(\times\) 0.8 mm\({}^{3}\) with d.c. passing through the samples in a constant magnetic field. Note that the electrical characteristics for the pristine and intercalated compound were measured for the same sample, whereas the influence of vacuum annealing was established for other samples cleaved from neighboring parts of the ingot. For the pristine and annealed samples, we used indium as a contact material, and for the intercalated ones we used silver paste.  
The mechanical properties of layered InSe crystals make it possible to cut samples with the prevailing dimension across the layers. That is why we used a four-probe method proposed in [23] to measure the conductivity component \(\sigma_{\parallel C}\). In this case, the typical dimensions of samples were \(\sim\)5 \(\times\) 3 mm\({}^{2}\) (cleaved surface) with \(\sim\)0.6 mm thickness. According to this method, a contact material was deposited onto cleaved surfaces perpendicular to the crystallographic C axis. The current contacts covered almost the whole surface of each cleaved side. Voltage was measured between a pair of small-area probe contacts which were located close to the current contacts. The spacing between the contacts on each cleaved surface did not exceed 0.5 mm. This method is based on the assumptions that the voltage \(U\) between the pair of the probe contacts does not differ significantly from the potential difference between the current ones, and that the current density through the sample is uniform. Later, this assumption was confirmed through a numerical analysis of the conductivity across the layers for samples with different \(\sigma_{\perp C}/\sigma_{\parallel C}\) ratios at different sample dimensions and contacts to them [24]. Thus, this technique to measure \(\sigma_{\parallel C}\) in crystals with high \(\sigma_{\perp C}/\sigma_{\parallel C}\) anisotropy is sufficiently reliable, and was later applied in other studies [25; 26; 27].  
The measurements of \"vertical\" conductivity were carried out for the samples cleaved from neighboring parts of the same ingot as the samples for investigations of electrical parameters along the layers. These measurements were carried out only in the temperature range 80 to 300 K. Higher temperatures were not used in order to avoid the decomposition of planar interlayer aggregates of defects.