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首页> 外文期刊>Physical review >Phonovoltaic. Ⅲ. Electron-phonon coupling and figure of merit of graphene: BN
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Phonovoltaic. Ⅲ. Electron-phonon coupling and figure of merit of graphene: BN

机译：声母。 Ⅲ。电子-声子耦合和石墨烯的品质因数：BN

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The phonovoltaic cell harvests optical phonons like a photovoltaic harvests photons, that is, a nonequilibrium (hot) population of optical phonons (at temperature T_(p,O)) more energetic than the band gap produces electron-hole pairs in a p-n junction, which separates these pairs to produce power. A phonovoltaic material requires an optical phonon mode more energetic than its band gap and much more energetic than the thermal energy (E_(p,O) > ΔE_(e,g) » k_BT), which relaxes by generating electrons and power (at rate γ_(e-p)) rather than acoustic phonons and heat (at rate γ_(p-p)). Graphene (h-C) is the most promising material candidate: when its band gap is tuned to its optical phonon energy without greatly reducing the electron-phonon (e-p) coupling, it reaches a substantial figure of merit [Z_(pv) = ΔE_(e,g)γ_(e-p)/E_(p,O)(γ_(e-p) + γ_(p-p)) ≈ 0.8]. A simple tight-binding (TB) model presented here predicts that lifting the sublattice symmetry of graphene in order to open a band gap proscribes the e-p interaction at the band edge, such that γ_(e-p) → 0 as ΔE_(e,g) → E_(p,O). However, ab initio (DFT-LDA) simulations of layered h-C/BN and substitutional h-C:BN show that the e-p coupling remains substantial in these asymmetric crystals. Indeed, h-C:BN achieves a high figure of merit (Z_(pv) ≈ 0.6). At 300 K and for a Carnot limit of 0.5 (T_(p,O) = 600 K), a h-C:BN phonovoltaic can reach an efficiency of η_(pv) ≈ 0.2, double the thermoelectric efficiency (ZT ≈1) under similar conditions.
机译：声伏电池像光电池一样收集光子，也就是说，非能带（热）光子（在温度T_（p，O）处）比带隙更能产生能量，从而在pn结中产生电子-空穴对，分离这些对以产生能量。声波材料需要一种比其带隙高能且比热能（E_（p，O）>ΔE_（e，g）»k_BT）高能的光子声子模式，后者通过产生电子和功率来放松（速率为γ_（ep））而不是声子和热量（以γ_（pp）的速率）。石墨烯（hC）是最有前途的材料候选者：当将其带隙调整至其光学声子能量而又不大大降低电子-声子（ep）耦合时，它的品质因数[Z_（pv）=ΔE_（e ，g）γ_（ep）/ E_（p，O）（γ_（ep）+γ_（pp））≈0.8]。此处介绍的一个简单的紧密结合（TB）模型预测，为了打开带隙而解除石墨烯的亚晶格对称性会限制带边缘处的ep相互作用，使得γ_（ep）→0为ΔE_（e，g） →E_（p，O）。但是，分层h-C / BN和取代h-C：BN的从头算（DFT-LDA）模拟表明，在这些不对称晶体中e-p耦合仍然很重要。实际上，h-C：BN实现了很高的品质因数（Z_（pv）≈0.6）。在300 K且卡诺极限为0.5（T_（p，O）= 600 K）时，hC：BN声伏能的效率可达η_（pv）≈0.2，是类似条件下热电效率（ZT≈1）的两倍条件。

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  • 来源
    《Physical review》 |2016年第24期|245412.1-245412.14|共14页
  • 作者

    Corey Melnick; Massoud Kaviany;

  • 作者单位

    Department of Mechanical Engineering and Ann Arbor, University of Michigan, Michigan 48105-2125, USA;

    Department of Mechanical Engineering and Ann Arbor, University of Michigan, Michigan 48105-2125, USA;

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