Highly-efficient heterojunction solar cells based on 2D Janus transition-metal nitride halide (TNH) monolayers with ultrahigh carrier mobility

• Published in: Nanoscale 2023-11, Vol.15 (45), p.18328-18336
• Main Authors: Xie, Wanying, Pang, Jiafei, Yang, Jinni, Kuang, Xiaoyu, Mao, Aijie
• Format: Article
• Language: English
• Subjects: Absorptivity; Broken symmetry; Carrier mobility; Dynamic stability; Electric fields; Electric properties; Electromagnetic absorption; Electrons; Energy conversion efficiency; Halides; Heterojunctions; Heterostructures; Iron; Metal nitrides; Monolayers; Optical properties; Palladium; Photoelectricity; Photovoltaic cells; Solar cells; Symmetry; Transition metals; Transport properties; Zirconium
• ISSN: 2040-3364; 2040-3372
• DOI: 10.1039/d3nr03417h

Symmetry breaking has a crucial effect on electronic band structure and subsequently affects the light-absorption coefficient of monolayers. We systematically report a family of two-dimensional (2D) Janus transition-metal nitride halides (TNHs, T = Ti, Zr, Hf, Fe, Pd, Pt, Os, and Re; H = Cl and F) with breaking of both in-plane and out-of-plane structural symmetry. The dynamical, thermal and mechanical stabilities are calculated to check the stability of the Janus TNHs. The electric properties of ten TNHs are studied via the HSE06+SOC method and the band gaps range from 0.93 eV (PdNCl) to 4.74 eV (HfNCl). Desirable light adsorption coefficients of up to 10 5 cm −1 are obtained for the Janus TNHs with no central symmetry. The Janus OsNCl monolayer shows excellent electrical transport properties and ultrahigh carrier mobility (10 4 cm 2 V −1 s −1 ). Heterojunctions formed by stacking two Janus TNH monolayers are further investigated for solar cell applications. Eight of the heterojunctions have type-II band alignments. Surprisingly, the OsNCl/FeNCl heterojunction has a power conversion efficiency (PCE) of 23.45%, which is a larger value compared to the PCE of GeSe/SnSe heterostructures (21.47%). The optical properties and the built-in electric field of the OsNCl/FeNCl heterojunction are investigated. These results indicate that the stable Janus TNH monolayers have potential applications in photoelectric devices, and the vertical heterojunctions can be used in solar cells. We systematically report a family of two-dimensional (2D) Janus transition-metal nitride halides (TNHs, T = Ti, Zr, Hf, Fe, Pd, Pt, Os, and Re; H = Cl and F) with breaking of both in-plane and out-of-plane structural symmetry.