DFT‐Guided Device Engineering of Cs 2 LiTlCl 6 Double‐Perovskite Solar Cells for High‐Efficiency Photovoltaics

This work investigates the photovoltaic (PV) potential of the emerging double‐perovskite Cs 2 LiTlCl 6 (cesium lithium thallium hexachloride) as an absorber in hybrid perovskite solar cells (PSCs). Several hole‐transport layers (HTLs), such as BiI 3 , CuI,WSe 2 ,CNTS, and SnS, along with wide‐bandgap chalcogenide electron transport layers (ETLs) like In 2 S 3 , CdS, TiO 2 , ZnS, and ZnSe, were initially screened to identify suitable charge‐selective contacts. ZnSe and CNTS were found to provide the most favorable band alignment and transport characteristics and were therefore subjected to full device‐level optimization using the SCAPS‐1D simulator. Three device configurations were explored: an HTL‐free structure (FTO/ZnSe/Cs 2 LiTlCl 6 /Ni), a SnS‐based HTL device (FTO/ZnSe/Cs 2 LiTlCl 6 /SnS/Ni), and a CNTS–HTL device (FTO/ZnSe/Cs 2 LiTlCl 6 /CNTS/Ni). The influence of absorber and transport‐layer thickness, doping concentration, bulk and interface defect densities, operating temperature, and carrier recombination dynamics was systematically examined. The optimized architecture, (FTO/ZnSe/Cs 2 LiTlCl 6 /CNTS/Ni) delivered the highest performance, reaching a power conversion efficiency (PCE) of 28.58%, with open‐circuit voltage ( V OC ) = 1.277 V, short‐circuit current density ( J SC ) = 25.106 mA.cm −2 , and FF = 89.12%. In comparison, the SnS–HTL device achieved 25.36%, while the HTL‐free structure yielded 20.27%. Analysis of series and shunt resistances, quantum efficiency (QE), carrier concentrations, and generation–recombination profiles further confirmed the superior charge extraction and reduced recombination losses in the CNTS‐based system. These results position CNTS–HTL coupled with ZnSe–ETL as a promising configuration for high‐efficiency Cs 2 LiTlCl 6 ‐based hybrid perovskite PV and provide one of the first comprehensive device‐level assessments of this underexplored absorber.