## 1 Introduction
The diffusion rate of Cu ions in CuO oxide was shown to be much lower than in Cu\({}_{2}\)O; therefore, at lower temperatures, e.g., 300 \({}^{\circ}\)C, the diffusion is too slow for a thick CuO layer to form in the Cu\({}_{2}\)O layer formed from Cu oxidation. The process of oxide transformation is related to the movement of Cu ions toward the upper edge of the Cu\({}_{2}\)O layer through cation vacancies. [PERSON] et al. [15] also studied the course of copper oxidation processes but at relatively low temperatures of below 300 \({}^{\circ}\)C. This work confirmed that during oxidation, a Cu\({}_{2}\)O layer first appears, and on its outer surface, even at low temperatures, a thin CuO layer forms. The authors also proposed a passivation process by heating a sample for 3 min in a N\({}_{2}\) atmosphere at 600 \({}^{\circ}\)C, which slowed the oxidation process by an order of magnitude. Cuprous oxide (Cu\({}_{2}\)O) and cupric oxide (CuO) can be produced in many ways, including low-temperature processes. Article [16] describes the process of obtaining Cu\({}_{2}\)O by converting the CuI layer in a NaOH solution, and the further oxidation of the compound obtained at 250 \({}^{\circ}\)C led to the formation of the CuO layer. These layers were used as hole-transporting materials in perovskite-based solar cells, leading to high efficiencies. Another technique for obtaining copper oxide can be pyrolysis. This method also allows doping the CuO oxide with metals; for example, manganese [17]. Such doping leadsto a change in the properties of the oxide, including the control of the energy gap width, which may make this material advantageous from the point of view of optoelectronic applications. An interesting solution that increases the efficiency of photovoltaic cells is a cogeneration system that combines the generation of electricity with the simultaneous production of hydrogen and an additional mechanism for obtaining thermal energy, which is generated during the operation of photovoltaic panels. This combination ensures a better use of solar energy. Techniques to optimize the parameters that affect the operating conditions of the hybrid device are presented in [18]. [PERSON] et al. [19], who provided a fairly extensive review of research in this field, presented the analysis of such systems both on the model and on the experimental side. Interestingly, the elements used to optimize the operating parameters of the systems were determined using artificial intelligence. A detailed discussion on the formation of copper oxide layers and the role of copper and oxygen diffusion in them can be found in the paper by [PERSON] et al. [20]. The authors also described the rate of oxidation processes at different temperatures (in the range from 400 to 700 \({}^{\circ}\)C). However, by performing tests using scanning and transmission electron microscopes, the authors also described the morphology of the cross-section of the layers. These microstructural studies revealed that randomly oriented, columnar Cu\({}_{2}\)O grains first appear during annealing, followed by CuO grains oriented in preferred directions. At the Cu/Cu\({}_{2}\)O boundary, the grains were smaller than at a greater distance from this boundary and have an equiaxed character. In turn, on the upper side of the Cu\({}_{2}\)O layer, small CuO grains with strong texturization were observed. Surfaces that separate individual layers have a temperature-dependent morphology. At low temperatures, the surface between the oxide layers did not show visible losses or cracks, while annealing at high temperature caused cracks and holes at the Cu/Cu\({}_{2}\)O interface. This caused the diffusion of copper ions towards the oxides to cease. In the process of the deposition of thin-film heterostructures, the surface diffusion process, which is the main process, makes it possible to control the uniformity of the film in the horizontal (lateral) and normal directions.