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 (Eg,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 JSC=17.55 mA/cm2, and
PCE=25.69 % for Eg,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.