Calculated tandem efficiency with doping in top and bottom cell hole transport layers. Initially, the top cell doping is fixed at 1 × 10¹⁸ cm⁻³, and the bottom cell efficiency is increased upto 1 × 10¹⁸ cm⁻³. Then, the bottom cell HTL doping is fixed at 1 × 10¹⁸ cm⁻³, and the top cell HTL is doping is varied upto 1 × 10¹⁸ cm⁻³. The top and bottom cell bandgaps are chosen to be 1.55 eV and 1.0 eV, respectively. The top and bottom cell thicknesses are fixed at 250 nm and 350 nm, respectively.