Graphitic carbon nitride as a photovoltaic booster in quantum dot sensitized solar cells: a synergistic approach for enhanced charge separation and injection

A similar to 70% improvement in power conversion efficiency (PCE, eta) is observed for the devices fabricated with a binary hybrid composite of graphitic carbon nitride and zinc oxide nanorods, i.e., (g-C3N4-ZnO NR) [eta approximate to 2.43%, for an optimized weight ratio (0.5 : 1)] as compared to the pristine ZnO NR device (eta approximate to 0.65%). Systematic investigations reveal that g-C3N4 boosts the light harvesting ability of the photovoltaic devices primarily by impeding photo-induced electron interception to the redox couple and injecting electrons into the conduction band of the semiconductor. Electrochemical impedance spectroscopy (EIS) analysis shows a reduced tunneling of photo-induced electrons to the sulfide-polysulfide (S2-/Sn2-) redox shuttle in the case of (g-C3N4-ZnO NR) composite devices. Higher recombination resistance (R-k) indicates that the g-C3N4 sheet acts as a barrier for photo-induced electron interception at the working electrode/electrolyte interface. Preliminary investigation using steady state and dynamic photoluminescence analyses suggest a similar fact about the photo-induced electron injection from g-C3N4 sheets to ZnO, contributing to the enhanced light harvesting ability of (g-C3N4-ZnO NR) composite devices.