Adsorption of porphyrin and carminic acid on TiO2 nanoparticles: A photo-active nano-hybrid material for hybrid bulk heterojunction solar cells

• Carminic acid interacts with porphyrin and TiO2 forming a charge transfer complex.
• Sulphonic acid functionalized free base porphyrin is converted into its metallated form.
• Carminic acid and porphyrin extend the absorption potential of TiO2 to visible region.
• Co-functionalized TiO2 enhanced the current density and overall efficiency of solar cells.
• Charge transfer absorption band contributed to the EQE of fabricated solar cells.

A photo-active nano-hybrid material consisting of titania nanoparticles, carminic acid, and sulphonic acid functionalized porphyrin is reported here. In an attempt to extend the absorption spectrum of titania to visible region by co-adsorbing carminic acid and sulphonic acid functionalized porphyrin on its surface. Interesting changes in the UV–visible and fluorescence spectra were noticed. The adsorption of carminic acid resulted in the formation of charge transfer complex with titania nanoparticles. This was confirmed by the electronic absorption and fluorescence emission spectroscopies. Chemisorption of porphyrin on the carminic acid functionalized titania further boosted the charge transfer effect. This was noticed by the increase in intensity and width of the charge transfer absorption and emission bands. Energy level diagram showed that the interaction among the constituents of the nano-hybrid assembly permitted the flow of electron in a cascade manner from carminic acid to TiO2.This also allowed direct flow of electrons either from carminic acid or porphyrin toward titania. The material was used as an active blend in hybrid bulk heterojunction solar cells. Co-functionalized TiO2-based devices were found 3.5 times more efficient than the reference device but morphology of the device proved a major setback.

Graphical AbstractThe uni directional flow of electrons in the nanohybrid assembly of TiO2, porphyrin and carminic acid. The electrons ultimately reach the conduction band of TiO2, no matter, they follow direct or cascade route.Figure optionsDownload as PowerPoint slide