Superficial fluoropolymer layers for efficient light-emitting diodes
Superficial fluoropolymer layers for efficient light-emitting diodes
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DOI：
10.1016/j.orgel.2012.02.019
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发表时间：
2012-06
影响因子：
3.2
通讯作者：
G. Latini;L. Tan;F. Cacialli;S. Silva
中科院分区：
文献类型：
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作者：
G. Latini;L. Tan;F. Cacialli;S. Silva
含氟聚合物的特点是化学惰性高，在固态时，由于C-F键的作用，电荷密度会发生强烈的位移，从而产生表面偶极。这里利用这两个特性来精细控制有机发光器件中的电荷平衡，并防止异质层之间的电化学相互作用。在聚(乙烯二氧基噻吩基)：聚苯磺酸(PEDOT：PSS)和电致发光聚合物之间的界面上插入一层薄薄的聚四氟乙烯(PTFE)，可以提高器件效率和寿命。表面偶极子的存在增加了阳极的有效功函数，并改善了电荷平衡，从而使器件的外部量子效率EQE提高了高达两倍，而对亮度水平没有显著影响。PTFE层的插入降低了PEDOT：PSS/聚合物界面的光致发光猝灭，但我们发现EQE的增强主要是由于少数载流子电子在有源层中得到了更好的限制。随着聚四氟乙烯层的插入，器件寿命显著提高。这些改进归因于电致发光聚合物与PEDOT：PSS之间的电化学相互作用减少，这是由于PTFE的化学惰性。聚四氟乙烯作为两种不同介质的化学拉链，增加了控制电荷平衡的功能。
Fluoropolymers are characterized by high chemical inertness and, when in solid state, by superficial dipoles due to the C–F bond where the charge density is strongly displaced. These two characteristics are exploited here for fine control of charge balance in organic light-emitting devices and for preventing electrochemical interaction between heterogeneous layers. The insertion of a thin layer of polytetrafluoroethylene, PTFE, at the interface between poly(ethylene dioxythiophene):poly(styrene sulfonic acid), PEDOT:PSS, and an electroluminescent polymer leads to improved device efficiency and longevity. The presence of the superficial dipole increases the effective work function of the anode and improves the charge balance which enhances the external quantum efficiency, EQE, of the devices by up to a factor of two without significant effects on the luminance levels. The insertion of the PTFE layer reduces the photoluminescence quenching at the PEDOT:PSS/polymer interface, however we show that the EQE enhancement is mainly due to a better confinement of minority carrier electrons in the active layer. The lifetime of the devices shows a remarkable increase correlated with the insertion of the PTFE layer. Such improvements are ascribed to the reduced electrochemical interaction between the electroluminescent polymer and PEDOT:PSS due to the chemically inert nature of PTFE. The PTFE acts as a chemical zipper of two heterogeneous media with the added functionality of control over the charge balance.