Zhang Yubo, Wang Youwei, Xi Lili, Qiu Ruihao, Shi Xun, Zhang Peihong, Zhang Wenqing
State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China.
Department of Physics, University at Buffalo, SUNY, Buffalo, New York 14260, USA.
J Chem Phys. 2014 Feb 21;140(7):074702. doi: 10.1063/1.4865257.
The traditional photon absorbers Cu2-xX (X = S, Se, and Te) have regained significant research attention in the search of earth-abundant photovoltaic materials. These moderate- and narrow-gap materials have also been shown to exhibit excellent thermoelectric properties recently. However, semimetallic band structures with inverted band orderings are predicted for antifluorite structure Cu2X using density functional theory with the local density approximation or the generalized gradient approximation. We find that semiconducting band structures and normal band orderings can be obtained using the modified Becke-Johnson potential plus an on-site Coulomb U (the mBJ+U approach), which is consistent with our earlier finding for diamond-like Cu-based multinary semiconductors [Y. Zhang, J. Zhang, W. Gao, T. A. Abtew, Y. Wang, P. Zhang, and W. Zhang, J. Chem. Phys. 139, 184706 (2013)]. The trend of the chemical bonding of Cu2X is analyzed, which shows that the positions of the valence band maximum and conduction band minimum are strongly affected by the inter-site pd and intra-site sp hybridizations, respectively. The calculated gaps of Cu2S and Cu2Se still seem to be underestimated compared with experimental results. We also discuss the effects of different structural phases and Cu disordering and deficiency on the bandgaps of these materials.
在寻找储量丰富的地球光伏材料的过程中，传统的光子吸收剂Cu2-xX（X = S、Se和Te）重新受到了广泛的研究关注。最近研究表明，这些中能隙和窄能隙材料还具有优异的热电性能。然而，采用局域密度近似或广义梯度近似的密度泛函理论预测，反萤石结构的Cu2X具有半金属能带结构且能带顺序反转。我们发现，使用修正的Becke-Johnson势加上在位库仑U（mBJ+U方法）可以得到半导体能带结构和正常的能带顺序，这与我们之前对类金刚石铜基多元半导体的研究结果一致[Y. Zhang, J. Zhang, W. Gao, T. A. Abtew, Y. Wang, P. Zhang, and W. Zhang, J. Chem. Phys. 139, 184706 (2013)]。分析了Cu2X的化学键合趋势，结果表明价带最大值和导带最小值的位置分别受位间pd杂化和位内sp杂化的强烈影响。与实验结果相比，计算得到的Cu2S和Cu2Se的能隙似乎仍然被低估。我们还讨论了不同结构相以及Cu无序和缺陷对这些材料能隙的影响。
