Optimizing conduction and valence bands for lead-free vacancy-ordered Cs2PtI6 based perovskite solar cells with zinc and kesterite charge transport layers

• Cs 2 PtI 6 enhances cell performance; PCE 26.25%. • SCAPS-1D deepens performance insights. • Zinc, kesterite boost UV stability, mobility. • Positive CBO, robust VBO reduce recombination. • Top cell: Jsc 28.5 mA/cm 2 , Voc 1.11 V, FF 82.86 %. This study introduces numerical models for Cs 2 PtI 6 -based perovskite solar cells (PSCs) using SCAPS-1D to optimize the conduction band offset (CBO) and valence band offset (VBO) at the interfaces between the charge transport layers (CTL) and Cs 2 PtI 6 . The structure investigated includes FTO as the glass substrate, zinc-based materials as electron transport layers (ETLs), and kesterites as hole transport layers (HTLs) and Au as the back contact. We focused on interfaces where the configuration induced significant impacts on device efficiency by adjusting band alignments. At the IGZO/Cs 2 PtI 6 interface, a favorable CBO facilitated spike formation, enhancing built-in potential and reducing recombination, a pattern also observed with ZnO and ZnSe interfaces. CZTS-based structures demonstrated the best performance with a J sc of 28.5 mA/cm 2 , a V oc of 1.11 V, an FF of 82.86 %, and a PCE of 26.25 %. These insights suggest that careful interface engineering in Cs 2 PtI 6 devices can significantly reduce common losses, guiding future performance improvements.