npj: 新碳相电子传输材料—支撑高效钙钛矿太阳能电池

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近年来，有机-无机杂化钙钛矿体系是太阳能电池家族极为高效的一员。在短短9年时间内，钙钛矿太阳能电池（PSC）功率转换效率就已从3.8%的认证值提高到了22.7％，逐渐成为下一代太阳能光伏技术的领导者，并拥有巨大的商业潜力。然而，PSC的快速发展仍面临一个不小的挑战：目前的半导体很难作为有效的电子传输材料，因其既不具有高的电子迁移率，也很难具有与钙钛矿相匹配的能级。

来自新加坡南洋理工大学的周昆教授领导的团队，通过第一性原理方法和变形势理论研究了一种新兴的碳同素异形体（T-碳）的电子性质和载流子迁移率。他们的结果表明，T-碳是一种直接带隙为2.273 eV的本征半导体。其导带底的能级位置比钙钛矿低0.5 eV，电子注入力较大，且在紫外光区的光吸收不会与紫外-可见光区的钙钛矿光捕获能力相竞争。更重要的是，T-碳具有2.36×10³cm²s^-1V^–1的高电子迁移率，优于传统的电子传输材料（ETM），如TiO₂、ZnO、SnO₂，甚至MAPbI₃钙钛矿，这将促进更高效的电子分离和更迅速地电子扩散，即快速离开钙钛矿吸收料的生成位点。这些特征预示着T-碳有望成为一种卓越的高性能PSC的电子传输材料。从拉伸和压缩应变对应的不同能带结构显示，施加应变是调节其电输运性能的有效手段之一。基于其特殊结构和很大的应用潜力，对其开展实验研究以实现这些预测的各种实际应用将会非常有趣。

该文近期发表于npj Computational Materials 5: 9 (2019)，英文标题与摘要如下，点击左下角“阅读原文”可以自由获取论文PDF。

A new carbon phase with direct bandgap and high carrier mobility as electron transport material for perovskite solar cells 

Ping-Ping Sun, Lichun Bai, Devesh R. Kripalani & Kun Zhou 

Abstract Rapid development of perovskite solar cells is challenged by the fact that current semiconductors hardly act as efficient electron transport materials that can feature both high electron mobility and a well-matched energy level to that of the perovskite. Here we show that T-carbon, a newly emerging carbon allotrope, could be an ideal candidate to meet this challenge. By using first-principles calculations and deformation potential theory, it is found that T-carbon is a semiconductor with a direct bandgap of 2.273 eV, and the energy level in the conduction band is lower than that of perovskite by 0.5 eV, showing a larger force of electron injection. Moreover, the calculated electron mobility can reach up to  2.36 × 10³ cm² s^–1 V^–1, superior to conventional electron transport materials such as TiO₂, ZnO and SnO₂, which will facilitate more efficient electron separation and more rapid diffusion away from their locus of generation with in the perovskite absorbers. Furthermore, the bandgap of T-carbon is highly sensitive to strain, thus providing a convenient method to tune the carrier transport capability. Overall, T-carbon satisfies the requirements for a potential efficient electron transport material and could therefore be capable of accelerating the development of perovskite solar cells.

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