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Designing high-efficiency bifunctional photocatalysts toward photoinduced overall water splitting is one of the most promising and challenging research directions for clean energy generation. By employing static electronic structure calculation and nonadiabatic molecular dynamics (NAMD) simulation, we herein established a recently synthesized two-dimensional (2D) aza-fused covalent organic framework (aza-COF) as a potential bifunctional photocatalyst toward overall water splitting reactions. Our calculated results reveal that the overpotentials for hydrogen evolution reaction and oxygen evolution reaction are only 0.06 and 0.31 V, respectively, at pH = 4. The dynamics of photoexcited charge carriers studied through NAMD simulation predicts the electron-hole recombination time (25.15 ns), and this confirms that the photogenerated electron and hole carriers migrate to the active sites for the occurrence of reaction before they recombine. Therefore, our results suggest that the 2D aza-COFs exhibit great potential as metal-free and single-material photocatalysts toward overall water splitting under visible light.

In the quest for an efficient solar energy harvester, one should focus on materials that have a large carrier lifetime. Using time-domain density functional theory combined with nonadiabatic molecular dynamics simulations, we herein established that single-atom doping from the pnictogen family can effectively alter the electron-hole recombination time in o-B 2 N 2 monolayer as compared to pristine sheet. Our study reveals that with increasing the mass of the dopant atoms, the carrier lifetime increases. Bismuth having the highest atomic mass among the pnictogen family can extend the carrier lifetime to 4.46 ns as compared to 2.18 ns of the pristine system. This trend of increasing carrier lifetime with the atomic mass of the doping atoms is due to a reduction in the decoherence time. Thus, doping with pnictogen family atoms offers a rational approach to enhance the photovoltaic performance.

Photocatalytic water splitting to spontaneously produce H 2 and O 2 is a long-standing goal in solar energy conversion, presenting a significant challenge without using sacrificial electron donors or external biases. Inspired by natural photosynthesis, the design of artificial Z-scheme photocatalytic systems is at the forefront of this field. These systems achieve higher redox potential by separating photogenerated electrons and holes through a fast interlayer recombination process between valence and conduction band edges. Z-scheme photocatalysis involves using two different semiconductors with distinct bandgap energies. Here, we explore potential systems based on two-dimensional (2D) heterostructures composed of carbon, nitrogen, or similar main group elements. The advantages and disadvantages of these systems are discussed, with a focus on enhancing their efficiency through strategic design. Special emphasis is placed on the dynamics of excited charge carrier transfer and recombination processes, which are crucial for developing efficient photocatalytic systems for overall water splitting.

In search of an efficient solar energy harvester, we herein performed a time domain density functional study coupled with nonadiabatic molecular dynamics (NAMD) simulation to gain atomistic insight into the charge carrier dynamics of a graphitic carbon nitride (g-CN)-tungsten telluride (WTe 2 ) van der Waals heterostructure. Our NAMD study predicted ultrafast electron (589 fs) and hole-transfer (807 fs) dynamics in g-CN/WTe 2 heterostructure and a delayed electron-hole recombination process (2.404 ns) as compared to that of the individual g-CN (3 ps) and WTe 2 (0.55 ps) monolayer. The ultrafast charge transfer is due to strong electron-phonon coupling during the charge-transfer process while comparatively weak electron-phonon coupling, sufficient band gap, comparatively lower nonadiabatic coupling (NAC), and fast decoherence time slow down the electron-hole recombination process. The NAMD results of exciton relaxation dynamics are valuable for insightful understanding of charge carrier dynamics and in designing photovoltaic devices based on organic-inorganic 2D van der Waals heterostructures.