Design and numerical investigation of perovskite solar cells with stacked bilayer absorber and P3HT/graphene hole transport layer

The performance of perovskite solar cells (PSCs) is strongly governed by device architecture and the optoelectronic properties of constituent materials. In this work, a two-dimensional (2D) finite element method (FEM) simulation is employed to investigate a single-junction PSC incorporating a stacked bilayer perovskite absorber and engineered hole transport layers (HTLs), with the aim of enhancing light harvesting and charge transport.To extend the absorption spectrum, a bilayer absorber composed of MAPbI₃ and MASnI₃ is introduced, leading to an increase in short-circuit current density (J sc ) from 17.5 to 18.34 mA/cm 2 and an improvement in power conversion efficiency (PCE) from 13.31 to 15.01%. The MASnI 3 layer primarily acts as a complementary absorber in the near-infrared region while simultaneously modifying the interfacial band alignment, resulting in reduced non-radiative recombination losses. Furthermore, poly(3-hexylthiophene) (P3HT) and P3HT/graphene (P3HT/Gr) nanocomposites with graphene weight ratios of 1, 3, and 5% are employed as HTLs to improve carrier extraction. The incorporation of graphene enhances charge transport through increased electrical conductivity and percolation-assisted pathways within the HTL. The optimized device with 5% graphene-doped P3HT exhibits an open-circuit voltage (V oc ) of 1.025 V and a maximum PCE of 17.79%. These results demonstrate that the synergistic integration of a bilayer perovskite absorber and graphene-enhanced HTLs provides an effective strategy for improving PSC performance while maintaining a single-junction device architecture.