ABSTRACT
Introduction: Ferroelectric substances, characterized by inherent spontaneous polarization, can boost photocatalytic efficiency by facilitating the separation of photogenerated carriers. However, conventional photocatalysts with perovskite-class ferroelectricity are generally constrained by their 3D arrangement, leading to less accessible active sites for catalysis and a smaller specific surface area compared to a 2D layout. Methods: In my research, I developed a 2D ferroelectric heterostructure consisting of C2N/α-In2Se3. I performed first-principle calculations on the 2D C2N/α-In2Se3 heterostructure, specifically varying the out-of-plane ferroelectric polarization directions. I primarily focused on C2N/α-In2Se3 (I) and C2N/α-In2Se3 (II) heterostructures. Results: My findings revealed that reversing the ferroelectric polarization of the 2D α-In2Se3 layer in the heterostructures led to a transition from the conventional type-II [C2N/α-In2Se3 (I)] to an S-scheme [C2N/α-In2Se3 (II)]. The S-scheme heterostructure [C2N/α-In2Se3 (II)] demonstrated a high optical absorption rate of 17% in visible light, marking it as a promising photocatalytic material. Discussion: This research underscores the significance of ferroelectric polarization in facilitating charge transfer within heterogeneous structures. It provides a theoretical perspective for developing enhanced S-scheme photocatalysts, highlighting the potential of 2D ferroelectric heterostructures in photocatalytic applications.
ABSTRACT
Electrides are a class of materials in which electrons are not bound to atoms but are similar to anions in crystals. To date, there are more than 300 electrides that have been discovered by first-principles. Alkaline-earth metal nitrides (AE2N, AE = Be, Mg, Ca, Sr, and Ba) are an important component of electride materials. Ca2N, Sr2N, and Ba2N structures have been identified and synthesized in previous research studies. Furthermore, the structures of Be2N (R3Ìm symmetry) and Mg2N (R3m symmetry) were recently identified. For Mg2N, it has zero-dimension (0D) interstitial localized electrons and band structure with semiconductor properties, which is significantly different from the other AE2N structures (two-dimension electrides and metal properties). Consequently, Mg2N was systematically studied in this work. We found that the pristine Mg2N was an indirect band gap semiconductor with a band gap of 0.243 eV. It transitioned to a metal when 2% stretch stress was applied to the c-axis. Moreover, at 5% stretch stress, the structure exhibited 2D interstitial localized electrons with the superconducting transition temperature (Tc) of 0.3 K. These studies thus provide a deeper understanding of the physicochemical properties of Mg2N as an electride.
ABSTRACT
2D transition metal dichalcogenides (TMDs) are promising candidates for realizing ultrathin and high-performance photovoltaic devices. However, the external quantum efficiency (EQE) and power conversion efficiency (PCE) of most 2D photovoltaic devices face great challenges in exceeding 50% and 3%, respectively, due to the low efficiency of photocarrier separation and collection. Here, this study demonstrates photovoltaic devices with defect-free interface and recombination-free channel based on 2D WS2 , showing high EQE of 92% approaching the theoretical limit and high PCE of 5.0%. The high performances are attributed to the van der Waals metal contact without interface defects and Fermi-level pinning, and the fully depleted channel without photocarrier recombination, leading to intrinsic photocarrier separation and collection with high efficiency. Furthermore, this study demonstrates that the strategy can be extended to other TMDs such as MoSe2 and WSe2 with EQE of 92% and 94%, respectively. This work proposes a universal strategy for building high-performance 2D photovoltaic devices. The nearly ideal EQE provides great potential for PCE approaching the Shockley-Queisser limit.