The distribution of the inner electric field in organic solar cells studied by electroabsorption spectroscopy

研究了以下三种类型的有机太阳能电池的内电场与光电流之间的关系，以寻找光电流产生的机理：1.锌酞菁（ZnPc）肖特基势垒太阳能电池2.锌酞菁（ZnPc）/苝衍生物（PTCBI）异质结太阳能电池3.锌酞菁（ZnPc）/<60>C_2异质结太阳能电池。或者载流子的产生是由内部电场引起的。特别是在异质结中，尽管许多研究者认为电荷的产生是由于异质结中两种有机半导体的电子亲合势的不同而引起的，但内部电场是电荷产生的最重要的驱动力。研究还发现，在Au/ZnPc界面处存在着一种称为能带滑移的反常现象，这种反常现象影响了内电场的分布和光伏特性，对于ZnPc肖特基势垒太阳电池，在反向偏压条件下，内电场服从通常的耗尽层理论，而在正向偏压条件下，内电场服从通常的耗尽层理论。ZnPc和电极之间的能带滑移使内电场猝灭。在ZnPc/PTCBI异质结的情况下，PTCBI层的内电场与偏置电压无关，并且与光电流无关。这种内电场不是PTCBI薄膜中的体电场，而是PTCBI与In电极界面处的异常电场。在ZnPc/C_2异质结的情况下<60>，在C_2层中检测到体电场<60>。对于ZnPc和C_2<60>层，观察到内电场和光电流之间有很好的相关性，表明载流子是由内电场产生的。

The correlation between the inner electric field and the photocurrent was studied for the following three types of organic solar cells, in order to find the mechanism of the photocurrent generation.1.Zn-phthalocyanine(ZnPc) Schottky-barrier solar cells2.Zn-phthalocyanine(ZnPc)/Perylene derivative(PTCBI) heterojunction solar cells3.Zn-phthalocyanine(ZnPc)/C_<60> heterojunction solar cellsAn obtained result is that the dissociation of the excitons, or the carrier generation is caused by the inner electric field. Especially, in the cases of the heterojunctions, the inner electric field is the most important driving force for the charge generation, although many researchers believe that the charge generation is caused by the difference in the electron affinities of the two organic semiconductors in a heterojunction. It has also be found that an anomaly, which we call band slipping, occurs at Au/ZnPc interface, which affects the distribution of the inner electric field and the photovoltaic properties.In the case of the ZnPc Schottky-barrier solar cells, the inner electric field obeys the usual theory of depletion layer for the reverse bias condition, but for the forward bias, the inner electric field is quenched by the band slipping between ZnPc and the electrode. In the case of the ZnPc/PTCBI heterojunctions, the inner electric field of the PTCBI layer is independent of the bias voltage and has no correlation with the photocurrent. This inner electric field is not the bulk field in the PTCBI film but is an anomalous field at the interface between PTCBI and In electrode. In the case of ZnPc/C_<60> heterojunctions, the bulk electric field in the C_<60> layer was detected. Both for the ZnPc and C_<60> layers, very good correlation was observed between the inner electric field and the photocurrent, indicating that the carriers are generated by the inner electric filed.