Design and Simulation of a-Si:H/PbS Colloidal Quantum Dots Monolithic Tandem Solar Cell for 12% Efficiency

Abstract

Tandem solar cells (TSC) is the most promising photovoltaic technology, as it efficiently overcomes the thermalization and nonabsorption losses. In this context, thin-film/colloidal quantum dot (CQD)-based 2-terminal monolithic TSCs are designed using a-Si:H of wide bandgap (1.7 eV) as the top cell and PbS CQD of narrow bandgap (1.2 eV) as the bottom cell. Initially, top and bottom subcells are designed and calibrated to have state-of-the-art power conversion efficiencies (PCE) of 6.86% and 9.38%, respectively. Afterward, the thicknesses of the inverted bottom cell are optimized as 200 nm so as to obtain 8.34% efficiency. The standalone condition reflects current density (JSC)/open-circuit voltage (VOC) of 9.97 mA cm−2 and 0.91 V in the top cell and 21.28 mA cm−2/0.63 V in the bottom cell. Further, both subcells are evaluated for tandem configuration with ITO-based interlayer to provide the current matching conditions. In the proposed tandem design, the thickness of the absorber layers is optimized to achieve the highest JSC, which is indeed limited by the top cell, due to a lower JSC value of 10.61 mA cm−2 in standalone conditions. Optimized tandem design with 200 nm/150 nm-thick absorber layer-based top/bottom subcell results in JSC of 10.52 mA cm−2, VOC of 1.59 V, FF of 71.65%, and PCE of 12.02%.