CdTe is the second most-widely deployed photovoltaic (PV) material due to its high efficiency and low manufacturing costs. Currently, polycrystalline CdTe (poly-CdTe) has a record efficiency of ~22%, which is still well below the theoretical limit (~30%). Polycrystalline CdTe films that have incorporated Cl or Se show higher efficiency, possibly due to the segregation of these ions to the grain boundaries (GBs), where they may passivate the dangling bonds. However, the efficiency enhancement mechanisms of passivants in CdTe GBs, and the feasibility of employing alternative passivants, have not been well explored. Here, we present a systematic computational study of CdTe GBs with potential passivants, namely S, P, As, Se, and Sb on Te sites, and Na, Mg, Al, Sc, Cu, and Zn on Cd sites. Density functional theory (DFT) calculations were performed on GB dislocation core structures derived from scanning transmission electron microscopy (STEM) images of a model GB (bicrystal). We computed the segregation thermodynamics, electronic density of states, and charge variations near doped CdTe GBs. We find that segregation of impurities to GBs is thermodynamically favorable. For a Te-terminated core, Se, S, and P on Te sites effectively reduce midgap states. For both Cd- and Te- terminated dislocation cores, Sc and Al reduce midgap states when substituted for Cd atoms. The greatest improvement was achieved with co-doping, i.e. simultaneously substituting Te with Se and substituting Cd with Cu or Al. The elimination of midgap states is predicted to increase the photovoltaic efficiency of CdTe by reducing the recombination at grain boundaries.

由于其高效率和低制造成本，CdTe 是第二大部署最广泛的光伏 (PV) 材料。目前，多晶碲化镉 (poly-CdTe) 的效率创下约 22%，仍远低于理论极限（约 30%）。掺入了 Cl 或 Se 的多晶 CdTe 薄膜显示出更高的效率，这可能是由于这些离子偏析到晶界 (GB)，它们可能会钝化悬空键。然而，CdTe GB 中钝化剂的效率增强机制以及采用替代钝化剂的可行性尚未得到很好的探索。在这里，我们对具有潜在钝化剂的 CdTe GB 进行了系统的计算研究，即 Te 位点上的 S、P、As、Se 和 Sb，以及 Cd 位点上的 Na、Mg、Al、Sc、Cu 和 Zn。对从模型 GB（双晶）的扫描透射电子显微镜 (STEM) 图像得出的 GB 位错核心结构进行了密度泛函理论 (DFT) 计算。我们计算了掺杂 CdTe GB 附近的偏析热力学、电子态密度和电荷变化。我们发现杂质与 GB 的分离在热力学上是有利的。对于 Te 终止的核心，Te 位点上的 Se、S 和 P 有效地减少了中隙态。对于 Cd 和 Te 终止的位错核，Sc 和 Al 在替代 Cd 原子时降低了中能隙状态。共掺杂实现了最大的改进，即同时用 Se 代替 Te 并用 Cu 或 Al 代替 Cd。