Structural stability, excitonic effects, and solar photovoltaic energy response in functionalized 2D MOenes

2D MOenes (single-layer dimetal oxides), a recently proposed family of transition-metal oxides with the general formula M n + 1 O n T x , have emerged as oxide analogs of MXenes. However, optoelectronic and photovoltaic properties of these nanosystems remain largely unexplored. Here, using first-principles DFT tool combined with semi-empirical strategies, we systematically investigate the structural, mechanical, electronic, optical, excitonic, and photovoltaic characteristics of functionalized and Janus MOene monolayers. Herein, fifteen candidate MOenes have been examined; phonon dispersion calculations identify twelve dynamically stable structures, while three are unstable. Elastic constant analysis reveals that the stable MOenes and their Janus counterparts are mechanically flexible, isotropic, and possess relatively high Young’s moduli. Electronic structure calculations show that several stable monolayers are indirect-gap semiconductors with band gaps ranging from 0.20 eV to 0.76 eV. Optical response analysis reveals strong, broadband absorption across the infrared, visible, and ultraviolet regions, indicating a favorable light-harvesting capability. In addition, pronounced excitonic effects arising from reduced dimensionality yield binding energies of 48–208 meV, underscoring their critical role in charge-generation processes. These results show that functionalized and Janus MOenes could be applied in photovoltaic devices if efficient methods to enhance their absorbance are developed.