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

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.