Renewable flower-based dye-sensitized solar cells using natural dye and natural carbon counter electrode†

To advance the application of renewable biowaste in the renewable energy field, biowaste-derived natural dyes (BND) and biowaste-derived carbon materials (BCM) were individually prepared from five common flowers as raw materials and then facilely integrated into dye-sensitized solar cells (DSSCs). The five extracted BNDs contained anthocyanins with subtly different molecular structures, which were employed as photosensitizers to assemble mono-biowaste based devices with a Pt counter electrode, each of which showed a significantly different conversion efficiency (η), varying from 0.17% to 0.43%. The five pyrolyzed BCMs with an amorphous structure were used as counter electrodes to configure mono-biowaste based devices with the photosensitizer N719, and their η values ranged between 1.08% and 2.13%. The high efficiency of the BCM-based devices was mainly derived from their unique microstructure and the N,S-codoped oxygen-group-containing carbon skeleton of the BCM, which provided more catalytic active sites for reduction of the electrolyte. A dual-biowaste device based on crape myrtle violet flower with an η of 0.181% was finally fabricated by using the corresponding BND and BCM. Moreover, a combination strategy was carried out by introducing the BND extracted from willow leaf into the cell with the pyrolyzed crape myrtle violet flower BCM, resulting in an enhanced η of 0.32%.