Effects of resonances and surface texturing on light emission in emerging thin-film devices

Abstract

Recent developments in thin-film fabrication and processing open up interesting possibilities for both established and emerging optics technologies. There, one of the key questions requiring more complete understanding is by how much one can improve the performance of thin-film devices by utilizing resonance effects and surface texturation. In this work, we report on our recent theoretical investigations around two aspects of this question: (1) how much the overall (=angle and energy-integrated) emission of extremely thin ($\sim10$ nm) layers can be enhanced through cavity effects, and (2) how much resonances affect the emission of moderately thin ($>100$ nm) layers in a typical device interacting with free space (in this case an ultra-thin solar cell). Beginning with topic (1), we find that the total emission of active layers with thicknesses $<50$ nm in particular can be boosted through resonant effects by placing them in a cavity. For topic (2), the results indicate that a radiative transfer approach (i.e., one not accounting for resonant effects) can give even quantitatively accurate predictions of the total emission of moderately thin layers in a thin-film device, as long as the reflectances of the device's outer boundaries are known, and the emitting layer is not very close to optical elements supporting direct evanescent coupling (such as metal mirrors). Finally, we demonstrate that extending the self-consistent radiative transfer--drift-diffusion approach for diffusive scattering presents an interesting tool to optimize thin-film devices even with textured surfaces.