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

Abstract

A ∼70% improvement in power conversion efficiency (PCE, η) 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) [η ≈ 2.43%, for an optimized weight ratio (0.5 : 1)] as compared to the pristine ZnO NR device (η ≈ 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⁻/S_n²⁻) 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.