## 1 Introduction  
Transparent electrodes are viable materials for the further development of optoelectronics, such as semitransparent light-emitting diodes, solar cells, or electrochromic devices [1, 2, 3, 4]. Different materials can be used as transparent electrodes, such as polymers, for example, PEDOT: PSS, carbon-based nanomaterials, ultra-thin metal films, or conductive oxides [5, 6, 7]. Among transparent conductive oxides, two have been well known for years--fluorine-doped tin oxide (FTO) and indium-doped tin oxide (ITO)--while recent research and applications use aluminium-doped zinc oxide (AZO) as an alternative [8, 9, 10, 11].  
Optoelectronic devices can be found in the aerospace field, in space missions, satellites, or future establishments for manned missions [12, 13]. Photovoltaics in particular are already being used in space applications and will remain a reliable source of electrical energy. Moreover, ITO is used as part of thermal control coatings in space missions [14]. The use of a transparent electrode could broaden the range of possible materials to be used in photovoltaics or include electrochromic systems in space applications [15; 16].  
Any material used in the space environment will be exposed to cosmic radiation. The space environment is different depending on the location of a satellite. In the widely used low-Earth orbit, the most significant is proton irradiation, where protons are trapped by the Earth's magnetosphere in the van Allen belts [17]. All charged particles exist in a wide spectrum of energy, from low energy to hundreds of MeV. The protons energies range from 30 keV to 400 MeV at 500 km above the Earth's surface.  
In this study, we investigate how a high-energy proton beam of 226.5 MeV affects the properties of thin films of ITO and AZO transparent conductive oxides. Researchers have previously studied ITO but usually with very low energy. [PERSON] et al. [18] treated ITO thin films with a 100 keV proton beam of different doses, with the highest of 2 \(\times\) 10\({}^{16}\) cm\({}^{-2}\), which is equal to 7 years in the geomagnetic equator region. The irradiation reduced both the conductivity and the transmittance of ITO, while the sheet resistance increased twice. [PERSON] and [PERSON] [19] studied how 20 keV proton irradiation influences K208 glass coated with ITO. They found that degradation of the ITO film caused larger changes in the material reflectivity than in the case of a glass without a coating. [PERSON] et al. [20] studied another transparent conductive oxide, namely FTO. They used a proton beam of 7 MeV and different fluences. With increasing dose of ions, the transmittance of films decreased, and the sheet resistance decreased for lower doses, but at 1 \(\times\) 10\({}^{16}\) cm\({}^{-2}\), it abruptly rose. They found small changes in the crystal structure of the oxide; crystallinity improved after irradiation, and the peaks shifted to lower angle values.  
In this work, we study the influence of high-energy protons on thin films of AZO and ITO. A preliminary simulation using Stopping and Range of Ions in Matter (SRIM-2008) [21] software showed that the influence of this radiation should be low on ITO and AZO thin films. The simulated trajectories of ions showed that the particles would pass through the material in a straight line. SRIM software gives information about energy passed by incident particles into the target material--the results showed that no energy would be transferred into the samples. The structural properties of the films were evaluated with X-ray diffraction (XRD), and the chemical states of the surface were evaluated with X-ray photoelectron spectroscopy (XPS). Optical properties were studied with spectrophotometry, and an optical method of spectroscopic ellipsometry (SE) was used to estimate the homogeneity of thin films. Observations with scanning electron microscopy (SEM) were also made.