Modeling and optimization of high-efficiency ZnO /RbGeBr₃ Perovskite solar cells using organic hole-transport layers

Perovskite solar cells (PSCs) have attracted increasing attention due to their promising optoelectronic properties and potential for efficient photovoltaic applications. In this work, numerical modeling is employed to investigate the influence of organic hole-transport layers (HTLs) on the performance of all-inorganic RbGeBr₃-based perovskite solar cells using ZnO as the electron transport layer (ETL). Three commonly used organic HTLs, PEDOT: PSS, P3HT, and Spiro-OMeTAD, are examined to assess their impact on charge transport and overall device characteristics. The study systematically analyzes the effects of absorber thickness, transport layer thicknesses, defect density, metal contact selection, and operating temperature on device performance, with particular attention to HTL-dependent trends. The integration of Cr as an alternative back metal contact is also considered to evaluate its influence on photovoltaic parameters. The results reveal noticeable differences in current density, open-circuit voltage, and fill factor depending on the selected HTL and device configuration. Among the investigated structures, the FTO/ZnO/RbGeBr₃/Spiro-OMeTAD/Au configuration exhibits the highest efficiency, achieving a power conversion efficiency of 25.22%, a short-circuit current density of 27.61 mA cm⁻², an open-circuit voltage of 1.08 V, and a fill factor of 85.3%. Overall, the findings suggest that appropriate selection of organic hole-transport layers, together with careful optimization of contacts and operating conditions, can contribute to performance enhancement in ZnO/RbGeBr₃ perovskite solar cells. The results provide useful insights for the modeling and design of efficient perovskite photovoltaic devices. • Optimized FTO/ZnO/RbGeBr₃/Spiro-MeOTAD/Au architecture achieved a remarkable PCE of over 25%. • Thickness engineering revealed ZnO (~50 nm) and absorber (~200–300 nm) as the most effective design windows. • Device efficiency is highly sensitive to defect density; reducing N t enables a theoretical PCE close to 29%. • Thermal stability analysis showed J sc remains stable, while V oc and FF degrade with temperature rise, proving real-world reliability limits. • Devices with PEDOT:PSS as HTL exhibit superior thermal resilience compared to Spiro-MeOTAD, suggesting material choice is critical for stability. • Replacing Au with Cr lowers efficiency but offers a cost-effective and mechanically robust back contact, vital for commercialization.