npj: 室温有机材料中实现体光伏效应—对称性设计策略
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体光伏效应是基本的光电转换效应之一,特指非中心对称材料中自发产生的光电流。与传统的半导体光伏效应不同,体光伏效应不受到Shockley–Queisser 极限的约束,可以实现更高的光电转换效率,因而在过去二十年得到广泛的关注。已有的体光伏效应研究集中于以钙钛矿氧化物为主的无机铁电材料,如BiFeO3、PbTiO3等。相比氧化物,有机材料具有价格低廉、易合成、带隙小且易调控等优势。前期相关研究已经在低温有机固体中发现了光伏效应,然而如何在更高温度,如室温下获得有机光伏响应仍是一个挑战。
该文近期发表于npj Computational Materials 6: 6 (2020),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。
Releasing the hidden shift current in the TTF-CA organic molecular solid via symmetry lowering
Bumseop Kim, Jeongwoo Kim, Dongbin Shin, Min Choi, Junhee Lee and Noejung Park,
Bulk photovoltaic effect, characterized by an excitation-driven unbiased spontaneous photocurrent, has attracted substantial attention mainly due to its potential for harvesting solar energy. Here, we investigate the photovoltaic characteristics of organic molecular solids and focus on the association between the photocurrent and the crystal symmetry in the exemplary case of etrathiafulvalene-p-chloranil. We perform comprehensive first-principles calculations, including direct evaluations of the excitedstate current via real-time propagations of the time-dependent density functional theory. We find that the charge shifting in the low-temperature phase is mainly driven by the intrachain ferroelectricity, which gives rise to a photocurrent not only in the visiblelight range but also near the band-edge infrared region. The shift current that is locked in the symmetry of the high-temperature phase can be released by introducing a potential asymmetry. We suggest that organic molecular solids can be exploited viaappropriate engineering to lower the symmetry, aiming at room-temperature photovoltaics.
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