On the Use of Graphene to Improve the Performance of Concentrator III-V Multijunction Solar Cells

Graphene has been intensively studied in photovoltaics focusing on emerging solar cells based on thin films, dye-sensitized, quantum dots, nanowires, etc. However, the typical efficiency of these solar cells incorporating graphene are below 16%. Therefore, the photovoltaic potential of graphene has not been already shown. In this work the use of graphene for concentration applications on III-V multijunction solar cells, which indeed are the solar cells with the highest efficiency, is demonstrated. Firstly, a wide optoelectronic characterization of graphene layers is carried out. Then, the graphene layer is incorporated onto triple-junction solar cells, which decreases their series resistance by 35% (relative), leading to an increase in Fill Factor of 4% (absolute) at concentrations of 1,000 suns. Simultaneously, the optical absorption of graphene produces a relative short circuit current density decrease in the range of 0-1.8%. As a result, an absolute efficiency improvement close to 1% at concentrations of 1,000 suns was achieved with respect to triple junction solar cells without graphene. The impact of incorporating one and two graphene monolayers is also evaluated.