Study of the Influence of Graphene Contacts on the Efficiency of Photovoltaic Conversion in a Multi-junction Solar Cell with Vertical p–n Junctions

Purpose. The research is aimed at improving the design of a multi-junction solar cell with vertically arranged p–n junctions. The purpose of the study is to increase the efficiency of photovoltaic conversion under oblique incidence of sunlight. Methodology. To achieve the goal of the research, it is proposed to use transparent graphene layers as contacts between the series-connected elementary p–i–n cells of a multi-junction solar cell instead of metallizing the side surfaces of the cells with aluminum. A model of the studied solar cell was built using the Silvaco TCAD software package, and a series of computer experiments were conducted to obtain the main electrical characteristics and analyze their dependence on the parameters of the solar cell. The mathematical model used in Silvaco TCAD for modeling semiconductor devices involves solving the fundamental Poisson equations, continuity, and transport equations based on the diffusion-drift transport model. Findings. Based on the computer modeling, the authors proved that the use of graphene contacts between the elementary p–i–n cells of a multi-junction solar cell instead of traditional aluminum metallization allows to significantly increase the solar cell efficiency under oblique incidence of sunlight. Thus, replacing metal contacts with graphene ones allows to increase the efficiency coefficient of the solar cell by 15% at an angle of 45° of solar radiation incidence. Originality. The authors first proposed the design and conducted computer simulation of a multi-junction solar cell with vertically arranged p-n junctions in which the usual metal contacts between the series-connected elementary solar cells are replaced by transparent layers of graphene. Practical value. The simulation results confirm the possibility of using the proposed solar cell design in conditions of oblique incidence of sunlight. Such properties of the solar cell allow its use on vertical, inclined or moving surfaces, including vehicles and transport infrastructure, where it is practically impossible to ensure the optimal angle of incidence of solar radiation.