Enhancement of tetracene photovoltaic devices with heat treatment

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Abstract
An efficient photovoltaic heterojunction of tetracene and fullerene has been investigated, and high performance organic solar cells have been demonstrated by thermal deposition and successive heat treatment. After the heat treatment, the open circuit voltage of the devices was enhanced greatly and at the same time the photocurrent remained almost unchanged. The series resistance of the devices was reduced and the fill factor was slightly enhanced. Consequently, the power conversion efficiency was improved from 1.7% to 2.2%. The preliminary conclusion for this enhancement is due to the part crystallization of the tetracene layer and consequent morphological change, which were supported by atomic force microscopy images, absorption spectra, and x-ray diffraction analysis. The part crystallization results in increase in hole mobility as evidenced by hole mobility measurements.