Fabrication and Evaluation of Two-Junction Carbon Thin Film Photovoltaic Devices

In this work, we have fabricated the two-junction carbon photovoltaic devices which consisted of Al/fullerene (C60)/amorphous carbon (a-C)/C60/a-C/ITO glass structure. We also investigated their photovoltaic properties with the same bandgap and without involving the tunnel-connect layer. We found that the open-circuit voltage in the two-junction photovoltaic device almost doubled compared to the single-junction type and it confirmed that the tandem structure was successfully formed without any tunnel-junction although short-circuit current in the two-junction tended to decrease greatly in comparison to single-junction. Moreover, we studied the effect of film thickness of each film on the photovoltaic properties of two-junction carbon photovoltaic devices and as a result, there was a dependence of film thickness on the photovoltaic performance in the two-junction type. Thus, it can be concluded that the film thickness is one of the significant influences to enhance the photovoltaic performances and our results might be an important approach for fabricating the higher efficiency of two-junction carbon thin film photovoltaic devices made of different band gap.