Double Perovskite Tandem Solar Cells: Design and Performance Investigation of the Use of CABB and CCSC as Top and Bottom Cell Absorber Materials

Double-junction tandem solar cells (TSCs), featuring a wide-bandgap top cell (TC) and narrow-bandgap bottom cell (BC), outperform single-junction photovoltaics, demanding meticulous subcell selection and optimization. Lead-free double perovskites offer sustainable photovoltaic solutions and are less toxic with enhanced stability, versatile compositions, and favorable optoelectronic characteristics. This study investigates the design and performance of a lead-free all-double-perovskite tandem solar cell (DPTSC), utilizing \({{\text{Cs}}}_{2}{{\text{AgBiBr}}}_{6}\) (CABB) with a bandgap of 2.05 eV and \({{\text{Cs}}}_{4}{{\text{CuSb}}}_{2}{{\text{Cl}}}_{12}\) (CCSC) with a bandgap 1.6 eV as absorbers in the TC and BC, respectively. The TC and BC were individually simulated and calibrated against experimental data, forming the basis for tandem device design and optimization. Series and shunt resistance, along with temperature effects on their performance, were examined. Meticulous adjustment of absorber thicknesses achieved optimal current matching between subcells. This fine-tuning closely matches TC current under AM 1.5G spectrum with BC current under a filtered spectrum. At optimal current matching (absorber thickness: 0.365 µm for the TC and 1.4 µm for BC), the DPTSC exhibits impressive power conversion efficiency (PCE) of 28.08% (with \({V}_{{\text{oc}}}=2.47\) V, \({J}_{{\text{sc}}}=12.78\) \({{\text{mA}}/{\text{cm}}}^{2}\), FF = 88.95%). The external quantum efficiency (EQE), Mott–Schottky and carrier generation/recombination profiles under current matching conditions have also been acquired to provide comprehensive device design insights. The designed TSC shows improved stability against temperature variations. These findings highlight the potential for lead-free and stable double perovskites to serve as subcell absorbers, enabling highly efficient, commercially viable, nontoxic, and eco-friendly tandem photovoltaic technologies. This work contributes valuable insights for advancing TSC technology, supported by comparisons with existing simulated and experimental data.