Photocurrent Generation in Fullerene Based Organic Solar Cells

Fullerene-based organic solar cells (OSCs) with only a minute amount of donor show a substantial photocurrent while maintaining a large open-circuit voltage. The performance of this type of devices is not limited by the trade-off between short-circuit current density (Jsc) and open-circuit voltage (Voc), unlike bulk heterojunction (BHJ) OSCs. At low concentrations the donor is fully dispersed within the fullerene and no percolation pathways of holes towards the anode exist; this morphology is in contrast to BHJ donor:acceptor blends where percolation pathways for both electrons and holes are present within their respective transport phases. Therefore, the question arises as to how photogenerated holes and electrons can reach respective electrodes without being trapped. In this talk I will discuss our understanding of photogenerated carrier transport mechanism based on kinetic Monte Carlo simulations,[1] quantitative evaluation of various generation and recombination pathways that lead to an optimized donor concentration of 5-10 wt% P3HT in PC₇₁BM-based solar cells,[2] and recent experimental results to test the proposed mechanism.