Organic electronics is a rapidly expanding field that develops and recently around organic materials based on ¿-conjugated molecules. The objective of this work focuses on the design and study of geometric, optoelectronic, and photovoltaic properties of new organic material candidates for applications in the field of organic solar cells (DSSCs and BHJ). In this book, firstly and using the methods of quantum chemistry, a predictive study is performed on carbazole-based materials and other ¿-conjugated heterocyclic derivatives. The goal is to determine geometric properties, optoelectronic, and spectroscopic, especially the emission and absorption spectra. Next, a structure-property correlation is performed and photovoltaic properties are calculated, studied and allowed to provide these materials as future solar cell type BHJ and DSSCs. The molecular architecture of these systems is widely studied especially the design of new Donor-¿-acceptor-type systems.