ON-DEVICE SIMULATION, THICKNESS AND DEFECT OPTIMIZATION, AND ETL/HTL ENGINEERING OF RB₂NAALI₆-BASED LEAD-FREE DOUBLE PEROVSKITE SOLAR CELLS USING SCAPS-1D

Abstract

Lead-free double perovskites have emerged as promising candidates for environmentally responsible photovoltaic technologies because of their compositional flexibility, structural stability and potential for tunable optoelectronic properties. However, the transition from favorable absorber properties to efficient photovoltaic devices remains constrained by carrier recombination, defect states, absorber-thickness limitations and unfavorable energy-level alignment at charge-transport interfaces. This study presents a device-level computational framework for investigating Rb₂NaAlI₆-based lead-free double perovskite solar cells using the Solar Cell Capacitance Simulator in One Dimension (SCAPS-1D). The proposed analysis systematically examines absorber thickness, bulk defect density, interface defect density and electron-transport-layer (ETL)/hole-transport-layer (HTL) engineering under standard AM1.5G illumination. Candidate transport layers are evaluated according to band alignment, carrier selectivity, transport properties and interfacial recombination characteristics. The analysis establishes that absorber thickness must be optimized by balancing photon absorption against bulk recombination and carrier-transport losses. Similarly, reduction of bulk and interface defect densities is expected to enhance carrier lifetime, open-circuit voltage and fill factor. ETL/HTL engineering is particularly important because appropriate conduction- and valence-band offsets can facilitate selective carrier extraction while suppressing interfacial recombination. The study develops a reproducible SCAPS-1D workflow for translating the theoretically promising characteristics of Rb₂NaAlI₆ into an optimized device architecture. The findings provide a foundation for subsequent numerical validation and experimental fabrication of Rb₂NaAlI₆-based lead-free double perovskite solar cells.