Tin oxides are the most promising electron transport layers in perovskite solar cells. An ambipolar carrier transport property has been recently demonstrated which enables a simple interconnection structure for all-perovskite tandem solar cells. However, the underlying mechanism for its ambipolar behavior is unclear, which cannot be explained by the intrinsic defects in SnO_2−x. Here, by using density functional theory calculations, we unveil the origin of the ambipolar carrier transport of non-stoichiometry SnO_2−x with a structure of SnO embedded in the SnO₂ matrix. The hybridization of O 2p and Sn 5s orbitals of SnO introduces mid-gap states in the bandgap of SnO₂, enabling hole transport property for SnO_2−x when x is > 0.2. Increasing the percentage of SnO in SnO_2−x significantly enhances the hole transport capability of SnO_2−x due to the enlarged Sn–O–Sn angles that increase orbital overlapping between O and Sn atoms, thus providing strategies for the further tuning of the carrier transport properties of SnO_2−x by compositional and structural designs.

中文翻译：

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揭示用于钙钛矿太阳能电池多功能中间层的 SnO2-X 的双极性载流子传输特性

氧化锡是钙钛矿太阳能电池中最有前途的电子传输层。最近已经证明了双极载流子传输特性，这使得全钙钛矿串联太阳能电池具有简单的互连结构。然而，其双极性行为的潜在机制尚不清楚，这无法用 SnO _{2-x 中}的固有缺陷来解释。在这里，通过使用密度泛函理论计算，我们揭示了具有嵌入 SnO ₂基质中的 SnO 结构的非化学计量 SnO _2-x的双极载流子传输的起源。SnO 的 O 2p 和 Sn 5s 轨道的杂化在 SnO ₂的带隙中引入了中带隙态，从而实现了 SnO _{2-x 的}空穴传输特性当 x > 0.2 时。增加SnO的百分比以SnO _2-X显著增强SnO的空穴传输能力_2-X由于扩大的SnO-Sn系角O和Sn的原子之间的增加轨道重叠，从而为的所述另一调谐提供策略SnO _2-x的载流子传输特性通过成分和结构设计。