| Budget Amount *help |
¥1,500,000 (Direct Cost: ¥1,500,000)
Fiscal Year 2004: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 2003: ¥1,000,000 (Direct Cost: ¥1,000,000)
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| Research Abstract |
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 cells
2.Zn-phthalocyanine(ZnPc)/Perylene derivative(PTCBI) heterojunction solar cells
3.Zn-phthalocyanine(ZnPc)/C_<60> heterojunction solar cells
An 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.
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