Facile fabrication of quantum dot–sensitized solar cells with multilayer TiO₂ NCs/TiO₂ HSs/CIS/CdS/CdSe(Xmin)/ZnS photoanode and modification of light scattering and co-sensitization for higher efficiencies

In this research, quantum dot–sensitized solar cells (QDSCs) were created by employing a co-sensitization approach on a new photoelectrode comprising multiple layers with a cascaded energy-gap structure. The new multilayer photoelectrode consisted of double-layer scaffolds, and a bottom layer of TiO₂ nanocrystals (NCs) coated with as-synthesized TiO₂ hollow layers (HSs) was utilized in QDSCs. Herein, we offer an eco-friendly, facile, and ultrafast aqueous method to the preparation of CuInS₂ (CIS) quantum dots (QDs) as the sensitizer for QDSCs with TiO₂ NPs/TiO₂ HSs/CIS/CdS/CdSe/ZnS photoelectrode. The production of CIS NCs took place in an aqueous solution through a facile modified chemical precipitation method, followed by their deposition using a drop-casting process. Additionally, the formation of the CdSe layer was achieved employing a chemical bath deposition (CBD) technique. The time of CBD was varied in a short range of 3–10 min for the CdSe QD layer. The outcomes illustrated a considerable efficiency of 5.17% for the QDSC with TiO₂ NCs/CIS/CdS/CdSe/ZnS photoanode while the CdSe QDs were deposited at 5 min of the CBD process. The other improved TiO₂ NCs/TiO₂ HSs/CIS/CdS/CdSe/ZnS photoanode demonstrated a short circuit current density (J_SC) of 24.18 mA/cm², an open circuit voltage (V_OC) of 621 mV, a fill factor (FF) of 0.40, and a power conversion efficiency (PCE) of 5.86%. This PCE was improved about 106% compared to those of the reference cell with TiO₂ NPs/CIS/ZnS photoanode structure.

Schematic of the CuInS₂/CdS/CdSe QD–sensitized solar cell (a) and corresponding flat band energy diagram (b) and J-V characteristics of the reference and co-sensitized devices (c).