Design and analysis of Perovskite/Sb2Se3 systems: Towards efficient 2-T HTL-free tandem solar cells

This paper investigates the potential of perovskite and Sb2Se3 as front and bottom absorber materials, respectively, for two-terminal tandem solar cells (TSCs), focusing on optimizing design and enhancing performance. The study begins by evaluating the standalone sub-cells, calibrating them against experimental data to establish a reliable baseline. We then examine a fabricated four-terminal perovskite/Sb2Se3 TSC to explore and compare its foundational characteristics. Moving forward, we concentrate on optimizing a 2-T tandem structure, particularly emphasizing the development of a hole-transporting layer (HTL)-free design. This approach aims to address fabrication challenges related to the instability and degradation of organic HTLs typically used in such systems. The 2-T HTL-free tandem device with optimizing thickness of both absorber layers showed a power conversion efficiency (PCE) of 16.96 %. Following the proposed 2-T HTL-free tandem design, the variation of the conduction band offset (CBO) at the electron-transporting layer (ETL)/absorber interfaces and the doping concentration of the ETLs is investigated to evaluate the corresponding effects. A PCE of 23.08 % is obtained upon optimizing the CBO and doping levels of both ETLs. Additionally, we examined the influence of modifying the bandgap of the front perovskite absorber layer (E-g,(Top)), which is vital for achieving balanced spectral absorption and improving overall efficiency. Furthermore, we conducted an in-depth analysis of the influence of different absorber layer thicknesses, aiming to optimize light absorption and realize current matching between both sub-cells. At the designed matching current density, the optimum efficiency is accomplished, giving J(SC)=17.55 mA/cm(2), and PCE=25.69 % for E-g,(Top) = 1.7 eV. Utilizing Silvaco Atlas device simulator package, simulations are performed under standard AM1.5G illumination conditions. Our findings demonstrate the feasibility and potential benefits of a 2-T HTL-free tandem configuration, paving the path for more efficient and stable perovskite/Sb2Se3 TSCs.