Energy-Level Alignment of Zn-Phthalocyanine-Physisorbed Graphitic Carbon Nitride: Effects of Corrugation

Abstract

Visible-light-absorbing photosensitizers surface-adsorbed onto two-dimensional (2D) graphitic carbon nitride (g-C3N4) often promote photoinduced interfacial charge transfer (CT) and thereby show huge potential in photovoltaics and photocatalytic applications. Here, an electron-donating Zn-phthalocyanine (ZnPc) photosensitizer physisorbed on a heptazine-based g-C3N4 acceptor is studied for exploring and better understanding the electronic band alignment using dispersion and short-range-corrected density functional theory (DFT) for the extended sheets and also dispersion and long-range corrected DFT for the finite-size composites. The physically relevant corrugated 2D g-C3N4 sheet is found to be energetically more stable (by ∼22.2 kcal mol–1 per heptazine unit) than the corresponding planar analogue. The out-of-plane distortion due to the pseudo-Jahn–Teller effect and repulsive interactions among peripheral N lone pairs cause the corrugation. However, almost similar binding affinity for ZnPc is found for both the planar and corrugated sheets. Importantly, corrugation produces a type-II band alignment for the ZnPc@g-C3N4 blend, independent of the ZnPc adsorption configuration, which is beneficial for efficient charge separation. Further, the presence of low-lying CT electronic states close to the ZnPc Q-band as revealed by time-dependent DFT calculations for finite-size composites offers the possibility of photoinduced CT. These findings shed valuable insights on the energy-level alignment and the interfacial charge separation between the ZnPc donor and the planar/corrugated g-C3N4 acceptor, showing routes to develop high-performance photovoltaic materials and efficient photocatalysts for carbon dioxide reduction and water splitting