Bulk ion-clustering and surface ion-layering effects on work function of self-compensated charged-doped polymer semiconductors,Materials Horizons

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Bulk ion-clustering and surface ion-layering effects on work function of self-compensated charged-doped polymer semiconductors
Materials Horizons ( IF 12.2 ) Pub Date : 2019-12-12 , DOI: 10.1039/c9mh01749f
Mervin Chun-Yi Ang _{1,

2,

3} , Cindy Guanyu Tang _{2,

3,

4} , Qi-Mian Koh _{1,

2,

3} , Chao Zhao _{2,

3,

4} , Qiu-Jing Seah _{1,

2,

3} , Yu Wang _{1,

2,

3} , Martin Callsen _{2,

3,

4} , Yuan-Ping Feng _{2,

3,

4} , Rui-Qi Png _{2,

3,

4} , Lay-Lay Chua _{1,

2,

2,

3,

4}

Affiliation

Hole- and electron-doped polyelectrolytes are of much current interest because they afford workfunction-tuneable charge injection layers that are immune to ‘dopant’ migration. However the role of the covalently tethered ion beyond providing solubility in these systems have not been well understood. Here using two well-known fluorene-alt-triarylamine model semiconductor cores (TFB and mTFF), we show, using variable-angle X-ray and ultraviolet photoemission spectroscopies, that the larger tethered anions—trifluoromethanesulfonylimidosulfonyl and pentafluoroethanesulfonylimidosulfonyl—give stronger surface ionic layering than sulfonate. This contributes to increasing both the HOMO ionization energy of the undoped polymer, and the vacuum work function (WF) of the hole-doped polymer, by about 0.2 eV, which provides the desired ‘fine tuning’ of these parameters. In addition, molecular dynamic simulations of the ion cluster structure in the bulk show that the larger anions produce a larger average distance to the holes. This raises the electrochemical energy of the holes, advantageously increasing their inherent WF by another 0.1 eV or so. Device electroabsorption spectroscopy shows that the increased WF persists into devices, resulting in better hole injection efficiency into large-ionization-energy organic semiconductor layers, and better hole collection efficiency from organic solar cells. Finally, the larger tethered anions also impart better solubility to the hole-doped form in fluorinated alcohols, acetonitrile and propylene carbonate, overcoming a key bottleneck for the deployment of these materials in practical applications.

中文翻译：

体离子簇和表面离子分层对自补偿带电掺杂聚合物半导体功函数的影响

空穴和电子掺杂的聚电解质备受关注，因为它们提供了可调节功函数的电荷注入层，从而不受“掺杂”迁移的影响。然而，对于在这些系统中提供溶解度以外的共价束缚离子的作用还没有很好地理解。这里使用两个知名芴ALT我们使用可变角度X射线和紫外光发射光谱学表明，在三苯胺模型半导体核（TFB和mTFF）中，较大的束缚阴离子（三氟甲磺酰亚胺基磺酰基和五氟乙磺酰亚胺基磺酰基）比磺酸盐具有更强的表面离子分层能力。这有助于将未掺杂聚合物的HOMO电离能和空穴掺杂聚合物的真空功函数（WF）都提高约0.2 eV，这为这些参数提供了所需的“微调”。此外，整体中离子簇结构的分子动力学模拟表明，较大的阴离子与空穴的平均距离较大。这提高了孔的电化学能，有利地将其固有WF增加了另一个0.1 eV左右。器件电吸收光谱表明，增加的WF持续存在于器件中，从而导致向大电离能有机半导体层中注入空穴的效率更高，并从有机太阳能电池中获得更高的空穴收集效率。最后，较大的束缚阴离子还赋予空穴掺杂形式在氟化醇，乙腈和碳酸亚丙酯中的更好溶解性，克服了在实际应用中部署这些材料的关键瓶颈。

更新日期：2019-12-12

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