Solar Cells Efficiency enhancement using multilevel Selective Energy Contacts (SECs)

Abstract

\n High-energy coming photons can be absorbed and lead to generate hot carriers. In normal solar cells, these carriers are scattered, by electron-electron and electron-lattice mechanisms, and rapidly lose extra energy then approach the conduction band energy edge. This event in addition to other loss mechanisms causes the efficiency reduction in the solar cells to a limited value, theoretically 33%. Accordingly, the efficiency of solar cells can be enhanced considerably, if one makes the possibility for carriers that can be extracted rapidly before scattering and releasing extra energy to the lattice. This type of solar cell is called hot carrier solar cells (HCSCs). To this end, to improve the conversional efficiency, multilevel energy selective contacts (ESCs) as a new concept and new mechanism in solar cells can be utilized. 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.