Effect of Polymer Morphology in Dilute Donor Organic Solar Cells

Dilute donor organic solar cells (OSCs) aim to circumvent the trade-off between open-circuit voltage Voc and short circuit current density jsc by decreasing the donor/acceptor interface. The main challenge of such architecture is to realize hole extraction pathways. Due to the reduced donor content, there are negligible percolation paths towards the contacts for the photogenerated holes. Hole transport towards the contacts can either happen by tunneling between the diluted polymers, hole-back transfer to the acceptor, and rarely by percolation to the contacts along polymers. However, the detailed morphology of the polymer network strongly controls which is the dominant mechanism and its impact on solar cell performance. We present a kinetic Monte Carlo (kMC) study on the role of the morphology on the performance of diluted donor OSCs with a donor fraction of ~ 1 vol%. The photocurrent generation is investigated for different offsets between the acceptor and donor highest occupied molecular orbitals (HOMO) and different morphologies. Due to the low donor concentration used, we only consider hole back transfer and percolation along polymer networks. We analyze three different morphologies: isolated polymer chains (SAW), polymer chain networks touching the contacts (NTC), and polymer networks not touching the contact (NNTC). Our results show that even a minor amount of polymers forming percolation paths to the contact is sufficient to generate a substantial photocurrent and keep a high Voc. Polymer chains with longer chain length provide substantial short-circuit current from the hole back transfer to the acceptor even at a high HOMO offsets of 0.6 eV.     «

Dilute donor organic solar cells (OSCs) aim to circumvent the trade-off between open-circuit voltage Voc and short circuit current density jsc by decreasing the donor/acceptor interface. The main challenge of such architecture is to realize hole extraction pathways. Due to the reduced donor content, there are negligible percolation paths towards the contacts for the photogenerated holes. Hole transport towards the contacts can either happen by tunneling between the diluted polymers, hole-back tr...     »