The doctoral thesis encompasses a combined research effort presented by compiling eight papers published in distinguished scientific journals. It entails a detailed analysis of the mentioned scientific investigations and findings related to the development of the novel photovoltaic thermal (PVT) collector design, meticulously documented and presented in a coherent and systematic manner. Analysis of the state of the art in PVT collector design revealed a research gap regarding the technical solutions of conventional hybrid solar collectors, i.e., PVT collectors, leading to investigating ways to improve performances by implementing phase change materials (PCM). Phase change materials have limited thermophysical properties, so an approach to enhance properties using nanotechnology was considered. Suitable nano-enhanced phase change materials (NEPCM) for energy technologies were analyzed, based on which the research of novel NEPCMs was carried out. Thus, novel NEPCMs were subjected to thermal characteristics testing using the Transient Plane Source (TPS) method. Due to the potential toxicity of NEPCMs and high unit cost, novel hybrid phase change materials of animalistic origin were designed and subjected to thermal properties testing using the TPS method. Furthermore, the existing PVT systems with incorporated phase change materials were analyzed to determine the possible PCM implementation modalities in the novel PVT collector system. Based on this analysis, a new PVT design was conceptualized and subsequently successfully subjected to experimental field testing in Mediterranean climate circumstances. Finally, a multi-parameter numerical model of the novel PVT-PCM collector was developed and verified.