The photonic solar cell. System design and efficiency estimations
The possibility to increase the efficiency of solar cells by a restriction of the maximal angle of emission has been proposed for several times. Typically, this is achieved by applying a directionally selective filter on top of the solar cell. This filter leads to a reflection of emitted light under certain angles back into the cell, where it then can be reabsorbed. A system where the emission process itself is inhibited for certain angles (photonic solar cell) is in principle a better system, because then optical losses in the system can be suppressed as the emission in fact does not take place. In this contribution, we focus on a photonic solar cell, where the cell and the filter are combined in one single optoelectronic device. This means that the solar cell itself has a photonic structure or is implemented into a photonic crystal. The interesting question is how such a device could look like and how it performs. Here, design concepts for photonic solar cells are shown and simulated optically. An interesting system could be an integration of a solar cell as defect layer into a thin film stack. To get an idea of the potential of such systems, the emission out of a photonic solar cell has to be compared to the emission out of a standard solar cell. To this end, a scattering-matrix-formalism is used. First estimations of the possible system efficiencies are given as indication of the system quality.