Boosting light harvesting of quaternary polymer solar cells through co-donor and co-acceptor with amine-functionalized graphene quantum dots and a ruthenium-based sensitizer

Currently, the quaternary polymer solar cells (PSCs) stand out as one of the most promising strategies for sustainable energy harvesting. However, it is challenging to successfully achieve efficient PSCs with a broad light absorption window and effective charge transport via introducing third and fourth components into the binary systems, while minimizing morphological heterogeneity, charge recombination, and cost of active materials. In this work, the amine-functionalized graphene quantum dots (NGQDs) with outstanding properties such as quantum confinement and doping ability are synthesized and characterized as the ternary component in PSCs. We report that the immobilization of tetrabutylammonium cis-bis(isothiocyanate)bis(2,2′-bipyridyl-4,4′-dicaboxylato) ruthenium (II) (N719) dye onto the surface of NGQDs and incorporation of them into the poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C71-butyric acid methyl ester (PCBM) (P3HT:PCBM) system can promote the charge generation and Förster resonance energy transfer (FRET) between the photoactive materials. The photovoltaic results show more than 40 % improvement in power conversion efficiency (PCE) and a short circuit current (JSC) of 11.62 mA.cm−2 with only 0.25 wt% of co-sensitizers for the P3HT:PCBM:NGQD:N719 photovoltaic devices. The AFM results indicate that the quaternary modulation can improve the surface nanomorphology of bulk heterojunction towards reduced charge carrier recombination. The outcomes demonstrate a significant improvement in light harvesting and photovoltaic performance of the bulk heterojunction PSCs. These advancements contribute to the development of high-efficiency single-junction polymer solar cells. [Display omitted]