Impact of selective thermal annealing on rubrene-C60 heterojunction solar cells

The influence of thermal annealing at different fabrication stages on rubrene–C60 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–C60 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.