The implementation of textured interfaces in solar cells has been proven as an outstanding strategy to reduce optical losses and optimize the performance of solar cells. In perovskite-based solar cells, the application of solution processing deposition methods on textures - particularly on textures with micrometer dimensions - has been considered challenging for a long time due to the difficulties in growing a conformal perovskite layer on the textures. Recently, perovskite-based tandem solar cells with micro-textured interfaces were fabricated using standard solution processing methods [1-3] and showed a lot of potential.

This contribution will show the results on the implementation of periodic inverted micro-pyramidal texture on silicon heterojunction (SHJ) solar cells and single junction perovskite solar cells. Periodic inverted pyramidal textures have been discussed to have the potential to reach or even surpass Lambertian limit of light trapping. [4, 5] We show that the implementation of inverted pyramidal texture on SHJ solar cells, obtained by etching of silicon with potassium hydroxide (KOH) solution, reduces reflection losses by up to 4 mA/cm² in short circuit current density (J_SC) compared to its planar counterparts. Moreover, solution processing of perovskite single junction solar cells on this texture resulted in a fully textured solar cell interfaces, shown by atomic force microscopy (AFM) and scanning electron microscopy (SEM) images. The fully textured perovskite solar cell interfaces also reduce reflection losses of up to 1.2 mA/cm² in J_SC. [6] This contribution also aims at exploring complementary characterization methods for the textured perovskite absorber to understand differences in material properties of the film and on sub-micrometer scale, such as perovskite composition, crystallization, and electronic properties. The characterizations include X-ray diffraction (XRD) in Bragg-Brentano configuration, photoluminescence (PL) microscopy, SEM with energy-dispersive X-ray spectroscopy (EDX), and kelvin probe force microscopy (KPFM) of the top and buried interfaces of the perovskite. PL microscopy with bandpass filters revealed an indication that the perovskite grown on the texture’s valleys are rich in iodine, while the perovskite grown on the texture’s hills are rich in bromine. To prove this, spatially resolved elemental analysis with SEM-EDX was done on the perovskite absorber. SEM-EDX measurement on multiple sites confirmed that at the valleys of the pyramids, there are brighter perovskite domains with higher iodine signal and lower bromine signal compared to the surrounding darker domains. These measurements revealed that fully textured perovskite absorber deposited on periodic inverted micro-pyramids might have slightly different composition, morphology, crystallographic properties, and electronic properties depending on the spatial position within the texture, creating inhomogeneity within the perovskite absorber which might affect the resulting solar cells negatively. Furthermore, from the studies conducted on SHJ and single junction perovskite solar cells based on periodic inverted pyramidal texture, fully textured solution processed perovskite-silicon tandem solar cells based on this texture with improved optical performance was demonstrated.

This study explores how periodic inverted micro-pyramidal textures can be utilized for silicon and perovskite based solar cells to improve their optical performances. It was also revealed that while this texture allows solution processing of perovskite absorber to result in a fully textured interface, the resulting perovskite might differ in its composition and electronic properties depending on the spatial position within the texture. The results of this study lay the foundation for the development of optically and electronically optimized perovskite-silicon tandem solar cells.