Zn 1-x Mg x O(ZMO)(0≤x≤0.25)合金的能 带结构。计算表明: 随着 Mg 组分增加, ZMO 化合物的导带底及费米能级均向真空能级方向移动, 带隙增宽。基于 理论计算得到 ZMO 的能带结构参数, 使用 SCAPS 软件对 ZMO 作窗口层的 CdTe 薄膜太阳电池的性能进行了仿真 模拟, 并将研究结果与 CdS 作窗口层的 CdTe 太阳电池的性能进行了比较。结果表明: Mg 在 ZMO 中的含量 0≤x ≤0.125 时, ZMO/CdTe 太阳电池具有比 CdS/CdTe 太阳电池更高的开路电压和短路电流密度; ZMO 的导带底高出 CdTe 导带底约 0.13 eV 时, CdTe 薄膜太阳电池的转换效率最高, 达到 18.29%。这些结果为高效率碲化镉薄膜太阳 电池的结构设计和器件制备提供了理论指导。 关 键 词: Zn 1-x Mg x O; 能带结构; 薄膜太阳电池; 转换效率 中图分类号: O447 文献标识码: A Abstract: In this paper, the band structure of Zn 1-x Mg x O(ZMO) alloy with different Mg compositions by using first-principles calculations with GGA+U method was studied. The calculation results show that position of conduction band offset and Fermi level of Zn 1-x Mg x O move towards the vacuum level while the band gap becomes wider with the increasing Mg concentration. Based on theoretical calculation results of ZMO, ZMO/CdTe, CdS/CdTe solar cells were modeled using SCAPS software and its device performances were simulated and analyzed in detail. The results indicate that the conversion efficiency of CdTe solar cell with ZMO is higher than that of solar cell with CdS due to the high open circuit voltage and short circuit current density when x in Zn 1-x Mg x O is in the range of 00.125. Efficiency of CdTe solar cells with ZMO reaches 18.29% because the recombination decreases obviously resulting from appropriate conduction band offset about 0.13 eV at ZMO/CdTe interface. These data provide a theoretical guidance for design and fabrication of high efficiency CdTe solar cells. 无 机 材 料 学 报 第 33 卷 ZnO 是典型的宽禁带半导体, 禁带宽度为 3.37 eV, 室温下的激子束缚能高达 60 meV [1] , 在薄膜太阳电 池及光电设备的透明电极等方面取得了广泛的应 用 [2] 。要实现 ZnO 在光电器件上的全面应用重点是 通过掺杂改变 ZnO 的禁带宽度。实验研究 [3] 发现: Mg 掺入 ZnO 形成的固溶体 Zn 1-x Mg x O(ZMO)是一 种带隙较宽、 电子学性质可调控的新型半导体材料。 Kumar 等 [4] 通过研究发现: 当 0≤x≤0.3 时 Zn 1-x Mg x O 合金保持纤锌矿结构不变, 其禁带宽度可达到 4.06 eV。 由 于 Mg 2+ 离 子 半 径 (0.057 nm) 和 Zn 2+ 离 子 半 径 (0.060 nm)较为接近, Mg 掺入 ZnO 后晶格常数的变 化仅在 1%左右 [5] 。目前,第一性原理计算 Mg 掺杂 ZnO 电子结构和光学性质的文献报道很多 [6-8] , 大 多采用密度泛函理论下 GGA 或 LDA 方法, 得到 ZnO 的带隙值在 0.50~1.08 eV [9-10] , 远低于 ZnO 的
We present a detailed study on Cu x S polycrystalline thin films prepared by chemical bath method and utilized as back contact material for CdTe solar cells. The characteristics of the films deposited on Si-substrate are studied by XRD. The results show that as-deposited Cu x S thin film is in an amorphous phase while after annealing, samples are in polycrystalline phases with increasing temperature. The thickness of Cu x S thin films has great impact on the performance of CdS/CdTe solar cells. When the thickness of the film is about 75 nm the performance of CdS/CdTe thin film solar cells is found to be the best. The energy conversion efficiency can be higher than 12.19%, the filling factor is higher than 68.82% and the open-circuit voltage is more than 820 mV.
The structural, optical and electrical properties of CdSxxTe1-x1-x thin films prepared by co_evaporation of powders of CdS and CdTe ha ve been studie d by x_ray diffraction, atomic force microscopy and optical transmittance spectr a measurements. Results show that the as_deposited CdSxxTe1-x1 -x thi n films are homogeneous, adherent and compact on the glass slides substrates wit hout pinhole and that their conductivity is n_type for x≥05 and p_type fo r xxTe1-x1-x thin f ilms are pol ycrystalline and show highly preferential orientation. The predominant direct op tical transitions were observed and the variation of the optical energy gap E gg is nonlinear with x. Given the values of lattice parameter and opt ical energy gap, the exact composition of the phase change at x=025 has been determined. The films are of a cubic phase for x025. After annealing there is no change in the structure of the films with a slight decrease in optical energy gap. Finally, a new structure of CdS/CdTe/Z nTe/ZnTe:Cu/Au solar cells with a CdSxxTe1-x1-x buffer l ayer has been proposed.
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