Structuring of perovskite-silicon tandem solar cells for reduced reflectance and thermalization losses.

Perovskite-silicon tandem solar cells have made rapid progress in the last decade. Still, they suffer from multiple loss channels, one of them being optical losses including reflection and thermalization. In this study, the effect of structures at the air-perovskite and perovskite-silicon interface of the tandem solar cell stack on these two loss channels are evaluated. Regarding reflectance, every structure evaluated led to a reduction relative to the optimized planar stack. The best combination of structures evaluated reduced the reflection loss from 3.1 mA/cm2 (planar reference) to 1.0 mA/cm2 equivalent current. Additionally, nanostructured interfaces can lead to a reduction in thermalization losses by enhancing the absorptance in the perovskite sub-cell close to the bandgap. This means that more current can be generated at a higher voltage under the assumption that current-matching is maintained and the perovskite bandgap is increased accordingly, pathing the way towards higher efficiencies. Here, the largest benefit was obtained using a structure at the upper interface. The best result yielded an increase of 4.9%rel in efficiency. A comparison to a tandem solar cell using a fully textured approach with random pyramids on silicon shows potential benefits for the suggested nanostructured approach regarding thermalization losses, while reflectance is reduced at a similar level. In addition, the applicability of the concept in the module context is shown.

Modeling of thin-film interference filters on structured substrates: microfacet-based BSDF versus ray tracing.

We compare two model approaches for the ray optical description of PV modules with coloring based on an interference layer system on the inside of the cover glass. The light scattering is described by a microfacet-based bidirectional scattering distribution function (BSDF) model on the one hand and ray tracing on the other hand. We show that the microfacet-based BSDF model is largely sufficient for the structures used in the context of the MorphoColor application. A structure inversion shows a significant influence only for extreme angles and very steep structures showing correlated heights and surface normal orientations. Regarding an angle-independent color appearance, the model-based comparison of possible module configurations shows a clear advantage of a structured layer system compared to planar interference layers in combination with a scattering structure on the front side of the glass.

Nanopatterning of Perovskite Thin Films for Enhanced and Directional Light Emission.

Lead-halide perovskites offer excellent properties for lighting and display applications. Nanopatterning perovskite films could enable perovskite-based devices with designer properties, increasing their performance and adding novel functionalities. We demonstrate the potential of nanopatterning for achieving light emission of a perovskite film into a specific angular range by introducing periodic sol-gel structures between the injection and emissive layer by using substrate conformal imprint lithography (SCIL). Structural and optical characterization reveals that the emission is funnelled into a well-defined angular range by optical resonances, while the emission wavelength and the structural properties of the perovskite film are preserved. The results demonstrate a flexible and scalable approach to the patterning of perovskite layers, paving the way toward perovskite LEDs with designer angular emission patterns.

Modeling the optical properties of Morpho-inspired thin-film interference filters on structured surfaces.

We present a method for modeling the optical properties of interference layer systems on structured surfaces as used in the MorphoColor technology for coloring integrated photovoltaic modules. By combining a microfacet-based bidirectional scattering distribution function model with a transfer matrix formalism, we can simulate the spectrally resolved reflection and transmission properties of the system in good agreement with measurement data. To consider the MorphoColor technology in an overall optical system and compare the application on the front side of the module glass with the application in the composite, the model is additionally combined with a formalism called Optical Properties of Textured Optical Sheets. For a representative illumination and viewing geometry, the composite configuration causes a significantly improved homogeneity of the color appearance.