Impact of selective thermal annealing on rubrene-C-60 heterojunction solar cells

The influence of thermal annealing at different fabrication stages on rubrene-C heterojunction organic solar cells is presented. Devices grown at room temperature showed s-shaped current density-voltage (J-V) characteristic. A pre- or post-fabrication thermal treatment step is found effective in elimination of s-shaped J-V. An exclusive gain in open-circuit voltage was measured when rubrene-C layer was fabricated at elevated substrate temperature of 80 °C. The results indicate that introduction of temperature at various stage of device fabrication allows selective control over organic layer growth and hence organic-organic interface formation. The 133 mV increase in open-circuit voltage in solar cells fabricated at substrate temperature is due to temperature induced molecular conformation change at the light in-coupling ITO/PEDOT interface