Efficiency limit and example of a photonic solar cell
Abstract
Restricting the angular emission characteristics of a solar cell results in a reduction of entropy generation and allows for higher solar cell efficiencies. In this paper, we present the concept of a photonic solar cell which exhibits the combination of a solar cell and a photonic crystal. The basic idea is to structure a solar cell in such a way that the applied structure is a photonic crystal consisting of the solar cell material. The aim of having a solar cell in the form of a photonic crystal is to restrict the emission of the solar cell into certain angles This reduction reduces the radiative losses and results in a higher VOC and, consequently, a higher efficiency of the cell. To calculate the efficiency of a photonic solar cell we introduce an adaptation of the detailed balance approach. This adaptation takes into account the reduced radiative losses due to the presence of a photonic band structure. In the second part of the paper we use this approach to calculat e the efficiency for an exemplary system. The exemplary system is an idealized edge filter, similar to a Bragg stack. The idealization concerns the reflection characteristic of this filter and its dependence on the polarization. For this idealized system we calculate an efficiency that exceeds that of a conventional solar cell by up to 2.5% absolute.
