Switchable Photocurrent Generation in an Ultrathin Resonant Cavity Solar Cell

Fabry-Perot-type resonant nanocavities allow for broadband enhancement of light absorption in ultrathin absorber layers. By introducing a switchable mirror, these thin film structures can be used as unique optical devices enabling interesting applications with switchable absorption. We use a thin film photovoltaic layer stack based on an amorphous germanium absorber layer and combine it with a thin Mg/Pd mirror to create a switchable solar cell. In this work we demonstrate how we can switch the light absorption and, hence, the photocurrent generation of the thin film solar cell by changing the refractive index of Mg due to hydrogen absorption. Our results show how optical resonances in the absorber can be switched “on/off” by the change of optical properties of the magnesium reflector. The multilayer system can be switched from a light absorbing and photocurrent generating state to a transparent window state with excellent color neutrality. We emphasize our study as an important step toward the realization of switchable photovoltaic windows, which paves the way for larger scale building integrated photovoltaic applications.