Next-Generation Tandem Photovoltaics: Role of Multinary Compound Semiconductors in Efficiency Enhancement

Abstract

Tandem cells offer a direct path around the spectral utilisation limit of the single-junction PV devices, by using two absorbers with complementary bandgaps to capture high- and low-energy photons. This study critically explores the numerical dataset of a SCAPS-1D perovskite model in order to investigate the potential for the multinary,“lead-free perovskite absorbers for enhancing the performance of two terminal monolithic tandem perovskite solar cells. The top absorber of two double perovskite designs was either a narrow-bandgap crystalline-silicon heterojunction bottom cell with a 1.3-eV bandgap (CsSnI₃) or a wide-bandgap quaternary-substituted double perovskite with a bandgap of ~1.8 eV. The model is solved for one dimensional Poisson, carrier-continuity and drift-diffusion equations, in AM1.5G illumination at 300K. SCAPS-1D is not capable of solving a full multijunction device, so the sub-cells were calibrated separately, the spectrum transmitted through the top stack was calculated and the absorber thicknesses were swept so that the two sub-cells were close to a common short-circuit current. The perovskite/silicon design has been optimized to achieve JSC = 0.181068 mA cm⁻2 @ 550 nm (top-absorber) and VOC = 0.1812 V @ 230 µm (bottom-absorber), resulting in a FF of 0.7918 and a PCE of 0.2595. The all-perovskite design reached its optimum at 700 nm and 65 nm, respectively, with JSC = 16.91 mA cm⁻², VOC = 1.73 V, FF = 83.72% and PCE = 24.47%.”The tandem configuration achieved a 19.81% and 50.12% improvement in PCE compared to the best stand-alone bottom-cell efficiencies analyzed, for the Si-based and all-perovskite systems, respectively. The results demonstrate the usefulness of multinary composition control for the elimination of lead and bandgap allocation, voltage addition and/or spectral complementarity. Principal unresolved issues include losses due to optical reflection, recombination-junction modelling, migration of ions, long term stability and experimental manufacturability.