Novel Integration of Nickel Phthalocyanine/Nickel Oxide-Based Photocathodes and Copper-Encapsulated Carbon-Dot-Cosensitized Photoanodes in Tandem for a Highly Efficient Solar Cell

Abstract

A notable strategy to achieve a dramatically high power conversion efficiency (PCE) of 9.76% for a tandem photovoltaic device has been implemented by the use of a nickel phthalocyanine-tetrasulfonic acid tetrasodium salt (NiPcTs) dye-sensitized p-type nickel oxide (NiO) semiconductor-based photocathode supported over carbon (C)-fabric paired with a photoanode scaffold comprising luminescent and conducting core/shell copper@carbon dots (Cu@C-dots) anchored to cadmium sulfide (CdS) quantum dots tethered to n-type titanium oxide (TiO2). The PCE yielded for the n-type quantum dot-sensitized solar cell (n-QDSC) or photoanode-based half-cell (TiO2/CdS/Cu@C-dots-nS2-/Sn2-C-fabric) is 6.82% with a significant contribution from the light-harvesting capability of the plasmonic Cu core encased within the C-dot shell. In spite of the long-wavelength light-harvesting NiPcTs enabling easier reduction of the polysulfide electrolyte because of the additional photoexcited charge transfer, the p-type solar cell (p-SC) or photocathode-based half-cell (NiO/NiPcTs-nS2-/Sn2-C-fabric) delivers a relatively lower PCE of 0.039%, but on coassembling the p- and n-half solar cells in a tandem design (TiO2/CdS/Cu@C-dots-nS2-/Sn2-NiPcTs/NiO/C-fabric) the cell efficiency gets an immense boost under 1 sun illumination in consequence of the maximized range of light absorption afforded by CdS-Cu@C-dots on one side and NiPcTs on the other. This work rationalizes the synergism between the photoanode and photocathode elaborately to obtain a hitherto unmatched solar energy conversion in tandem solar cells.