First-principles calculations of monolayered Al ₂ Te ₅ : a promising 2D donor semiconductor with ultrahigh visible light harvesting

Atomically thin two-dimensional (2D) crystals have piqued the curiosity of researchers due to their unique features and potential applications, such as catalysis and ion batteries. One essential and desirable aspect of 2D materials is that they have a large photoreactive contact surface for optical absorption. Here, a 2D crystal is proposed that possesses a moderate adjustable indirect band gap of 1.95 eV (HSE06) and exhibits ultrahigh visible light harvesting with a absorption coefficient of up to 10⁸ cm^-1 in the ∼380 to 800 nm range of the visible light spectrum. Besides that, the indirect band gap can be converted to a direct one under biaxial strain. By means of density functional theory, the 2D Al₂Te₅ monolayer displays great stability and promise of experimental fabrication. These advantages will provide considerable application potential for future photovoltaics (PV) devices.