Photonic Structuration of Hybrid Inverse-Opal TiO₂- Perovskite Layers for Enhanced Light Absorption in Solar Cells

Photonic structuration is an efficient way to improve light harvesting in multiple optoelectronic applications. In this study, photonically structured TiO2 is considered as a photoanode layer for perovskite solar cells to enhance light absorption through the excitation of quasi-guided modes within the photoactive perovskite material, while optimizing the charge collection in the photovoltaic assembly and therefore its global efficiency. Practically, polystyrene beads of various diameters are used as hard templating sacrificial agents for the design of inverse-opal TiO2 through spin-coating protocols. The positive impact of the porous photonic structuration in comparison with compact, unstructured photoactive layers is demonstrated. An optimum of light absorption is shown for hybrid TiO2-perovskite structures composed of ∼400 nm diameter TiO2 hollow spheres filled with CH3NH3PbI3, confirming recent numerical predictions. However, electronic-related countereffects are observed in consecutively assembled solar cells when pore dimensions exceed the estimated diffusion length of electrons in the infiltrated perovskite material. Upper conversion efficiency is obtained with solar cells composed of ∼220 nm diameter large TiO2 pores filled with CH3NH3PbI3.