The subject of the thesis is development of novel nanoscale materials for solar energy harvesting. The aim is to theoretically design two types of new luminescent dyes with enhanced efficiency: the first for application in dye-sensitized solar cells (DSSCs) and the second for use in transparent luminescent solar concentrators (TLSCs). More precisely, the objective is to predict photovoltaic and photochemical properties, including energy conversion efficiency and fluorescence quantum yield (QY). The first research direction focuses on novel bio-nano hybrid sensitizers for use in dye-sensitized solar cells, specifically on cyanidin-silver nanocluster hybrids. Furthermore, the influence of odd and even numbers of electrons and the impact of gold or copper doping on the efficiency and stability of these hybrids are investigated. The second research direction emphasises developing the rules for reliable theoretical prediction of fluorescence quantum yield within harmonic approximation. Additionally, it involves the theoretical design of squaraine-based J-aggregates as transparent TLSC luminophores with high QY. The calculations of structural and optical properties are based on density functional theory (DFT) and its time-dependent variant (TDDFT). Overall, the theoretical modeling of photovoltaic and photochemical properties serves to confirm and to stimulate experimental research in the field of new solar technologies.