Different Photoresponses for Positive and Negative Biases of CuPc/C60 Heterojunction Nanostructures

Photoresponse characteristic from efficient exciton dissociated heterojunction based on copper phthalocyanine (CuPc) and fullerene (C60) layers was observed the different spectrum responses under positive and negative biases. The nanostructures of CuPc and C60 thin films were fabricated between transparent indium tin oxide (ITO) and aluminum (Al) electrodes. The 100 nm thick of CuPc and C60 layers were deposited on patterned ITO glass substrates by thermal evaporation with quartz thickness monitor. Photoresponses of the fabricated devices were investigated by current measuring as a function of wavelength in range of 400 to 700 nm. Measured current in Al/C60/CuPc/ITO structure when applied negative voltage to ITO electrode is higher than that of positive voltage case. Under monochromatic light, the photoresponse characteristic of Al/C60/CuPc/ITO structure under negative bias shows dominate response current peak at around 450 nm and double peaks in range of 500-700 nm originated from C60 and CuPc layers, respectively. These two response characteristics can be described by the combination of responses from Al/C60/ITO and Al/CuPc/ITO structures. The response current characteristics of Al/C60/ITO and Al/CuPc/ITO structures also agree with the optical absorptions of C60 and CuPc layers, respectively. By applying positive bias to Al/C60/CuPc/ITO structure, the photoresponse characteristic has only one peak at about 450 nm that is similar to the response in Al/C60/ITO structure only. This indicates that under positive bias, the photocurrent only from C60 layer can be observed.