Tuning the Charge Transfer in Fx‐TCNQ/Rubrene Single‐Crystal Interfaces
Tuning the Charge Transfer in Fx‐TCNQ/Rubrene Single‐Crystal Interfaces
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DOI：
10.1002/adfm.201502082
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发表时间：
2015-12
影响因子：
19
通讯作者：
Y. Krupskaya;I. G. Lezama;A. Morpurgo
中科院分区：
文献类型：
--
作者：
Y. Krupskaya;I. G. Lezama;A. Morpurgo
由两种不同的有机半导体形成的界面通常表现出很大的导电性，这源于组成材料之间的电荷转移。驱动电荷转移和决定其大小的精确机制仍然非常未被探索，也没有从微观上理解。为了开始解决这个问题，我们对基于Rubrene(四苯基萘)和FX-TCNQ(氟化四氰基喹二甲烷)的高重复性单晶界面进行了系统的研究，这两个分子家族的电子亲和力可以通过增加氟含量来调节。输运和扫描开尔文探针测量的联合分析表明，界面载流子密度、电阻率和激活能与FX-TCNQ晶体的电子亲和力有关，亲和力越高，电荷转移越大。虽然输运性质可以用迁移率边模型一致地定量描述，但我们发现用单粒子能带图对电荷转移进行的定量分析揭示了界面能级排列的差异≈为100 meV。我们将这种差异归因于已知的影响有机半导体能级的现象，而这些现象被单粒子描述所忽略--例如由于屏蔽而导致的分子弛豫和带隙重整化。FX-TCNQ/Rubrene界面的系统行为为在受控条件下实验研究这些现象提供了可能。
Interfaces formed by two different organic semiconductors often exhibit a large conductivity, originating from transfer of charge between the constituent materials. The precise mechanisms driving charge transfer and determining its magnitude remain vastly unexplored, and are not understood microscopically. To start addressing this issue, we have performed a systematic study of highly reproducible single‐crystal interfaces based on rubrene (tetraphenylnaphthacene) and Fx‐TCNQ (fluorinated tetracyanoquinodimethane), a family of molecules whose electron affinity can be tuned by increasing the fluorine content. The combined analysis of transport and scanning Kelvin probe measurements reveals that the interfacial charge‐carrier density, resistivity, and activation energy correlate with the electron affinity of Fx‐TCNQ crystals, with a higher affinity resulting in larger charge transfer. Although the transport properties can be described consistently and quantitatively using a mobility‐edge model, we find that a quantitative analysis of charge transfer in terms of single‐particle band diagrams reveals a discrepancy ≈100 meV in the interfacial energy level alignment. We attribute the discrepancy to phenomena known to affect the energetics of organic semiconductors, which are neglected by a single‐particle description—such as molecular relaxation and bandgap renormalization due to screening. The systematic behavior of the Fx‐TCNQ/rubrene interfaces opens the possibility to investigate these phenomena experimentally, under controlled conditions.