Systematic stacking of PbS/CdS/CdSe multi-layered quantum dots for the enhancement of solar cell efficiency by harvesting wide solar spectrum

Highlights: • A three layer q-dot solar cell was fabricated with PbS/CdS/CdSe. • Solar cell performance of three layer system strongly depends on stacking order. • A charge recombination barrier layer plays a significant role in cell performance. Fabrication of multi-layered quantum dot sensitized solar cells, especially q-dot solar cells that contain more than two layers of q-dots as light harvesting materials is a great challenge due to adverse effects exert by the q-dots in the outer-layers on the inner optimized q-dot layer. In this work, multi-bandgap q-dots of PbS (bandgap 1.16 eV), CdS (bandgap 2.01 eV) and CdSe (bandgap1.76 eV) are stacked in different combinations on the mesoporous TiO₂ layer to enhance the light harvesting ability. The problems associated with stacking of multi-layers of q-dots on the mesoporous TiO₂ layer were also investigated. The observed photovoltaic properties of multiband q-dot solar cells with different stacking configurations are then compared with the optical and electrical properties of multi-band gap quantum dots. The optimized three-layer PbS/CdS/CdSe q-dot solar cell showed a solar cell efficiency of 6.2% while two-layer q-dot solar cells fabricated with PbS/CdS and CdS/CdSe showed solar cell efficiencies of 5.8 and 4.2% respectively. The enhanced solar cell performance of three-layer PbS/CdS/CdSe q-dot solar cell is found to be mainly due to proper cascade stacking of three q-dot layers in photoanode that ensuing in enhanced charge transport as well as higher light harvesting.