In recent years, demand for solar generators for Low Earth Orbit missions has been growing, and much research has focused on the use of less expensive silicon-based solar cells that can be integrated on flexible Photovoltaic Assemblies (PVAs). One solution would be to use thin silicon cells based on heterojunction (< 90 µm). However, these cells are sensitive to ultraviolet (UV) light. So, these silicon solar cells must be protected from space UV radiations. The solution advocated here involves incorporated UV-absorbing particles into a spatial polymer matrix. These particles are combined with lanthanide ions based inorganic phosphors to achieve the down-conversion process in order to convert some UV photons into visible ones with energy in the absorption range of photovoltaic cells. The study proposes to assess several solutions based on particles absorbing between 200 and 400 nm, some of which can convert the UV spectrum into a better absorption spectral band for the silicon cell (> 500 nm). Particules are embedded into a silicon-based polymer matrix, then deposited on Ga-doped heterojunction silicon cells (30x30 mm²). The first spatial UV analysis revealed a maximum loss of almost 5 % in short-circuit current for PV devices after 1005 esh. Comparing results in open circuit voltage, the bare cell degrades as the dose increases (-2 % at 425 esh and -5 % at 1005 esh). A positive point lies in the addition of TiO2 particles, which protect the cell, their effectiveness depend on the TiO2 concentration. The complex effect of phosphors is evidenced and analyzed. Results will also be given and discussed after 1000 thermal cycles. These initial results point out that it is possible to produce a protective coating to limit the effects of UV degradation. These developments could be also applied to flexible PVA based on III-V solar cells for geostationary missions.