Charge Generation and Recombination in High Fullerene Content Organic Bulk Heterojunction Solar Cells

Organic bulk heterojunction solar cells with a high fullerene content (larger than 70%) have been studied in this work. The device performances of this kind of solar cell could be tuned by adjusting the blend ratio in the active layer. An appropriate amount of p-type semiconductor in the high fullerene content active blend layer is beneficial for light absorbance and exciton dissociation. The proper energy alignment between the highest occupied molecular orbital of a p-type material and an n-type fullerene derivative has a strong influence on the exciton dissociation efficiency. In addition, the mechanism of photogenerated charge recombination in the solar cells has been identified through intensity-dependent current density-voltage (J-V) measurements and results show that the mechanisms governing the recombination are crucial for solar cell performance.