Enhanced photovoltaic properties of polymer–fullerene bulk heterojunction solar cells by thermal annealing

The effect of a thermal annealing treatment on the performance of bulk heterojunction photovoltaic cells based on poly[2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV) and fullerene (C60) composites is investigated. Upon thermal annealing at 120 ∘C, short-circuit current ( I sc ) and power conversion efficiency ( η ) are more than tripled, while a sharp rise by eight times in I sc and η is found for the device annealed at 200 ∘C. It is concluded that the improved phase separation between MEH-PPV and C60 leads to the enhancement of I sc and η at 120 ∘C, while thermodynamic molecule arrangement at the higher temperature of ∼200 ∘C induces a significant increase in all photovoltaic parameters of composite devices except the open-circuit voltage ( V oc ) .