Solar cells efficiency enhancement using multilevel selective energy contacts (SECs)

Abstract

High-energy incoming photons can be absorbed and concluded to generate Hot Carriers. In normal solar cells, these carriers are scattered by electron–electron and electron-lattice mechanisms and rapidly lose extra energy and approach to conduction band energy edge. This event plus other loss mechanisms cause that the efficiency of the solar cells to be limited to 33% theoretically. If one makes the possibility for carriers that can be extracted rapidly, before scattering and releasing extra energy to the lattice, the efficiency of solar cells is enhanced considerably. This type of solar cell is named hot carrier solar cells (HCSCs). To this end and improvement the conversion efficiency, multilevel energy selective contacts (ESCs) as a new concept and new mechanism in solar cells are used. In the other words, several appropriate energy levels as carrier extraction contacts in the conduction band are introduced. Here, we use multilevel ESCs, and based on our simulation it is shown that the maximum efficiency of 75% is achievable for low bandgap materials. For a typical material such as Si, the maximum efficiency is increased to 60% using ten ESCs.