2018/02/28 by Wenchao Yang, Yang, Wenchao
Engineering · Materials Science · #Conducting polymers and applications #FOS: Physical sciences #Materials Science (cond-mat.mtrl-sci) #Molecular Junctions and Nanostructures #Organic Electronics and Photovoltaics
paper · pdf · doi:10.48550/arxiv.1802.10390
openalex publication_date 2018/02/28 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
In organic bulk heterojunction solar cells, the donor/acceptor interfacial energy offset (ΔE) is found to provide the driving force for efficient charge separation which gives rise to high short circuit current density (Jsc), but a high ΔE inevitably undermines the open circuit voltage (Voc). In this paper, employing the device model method we calculated the steady state current density-voltage (J-V) and the Jsc-ΔE curves under two different charge separation mechanisms to investigate the optimum driving force required for achieving sizable Voc and Jsc simultaneously. Under the Marcus charge transfer mechanism, with the increased ΔE the Jsc increases rapidly for ΔE≤ 0.2 eV, and then maintains a nearly constant value before decreasing at the Marcus inverted region, which is due to the accumulation of undissociated excitons within their lifetime and is beneficial for obtaining a sizable Jsc under a ΔE much smaller than the reorganization energy λ. For the coherent charge transfer mechanism in which the driving force act as the energy window of accessible charge separated states, with two typical types of density of states for the charge transfer excitons, it is shown that the highest Jsc can also be achieved under a small ΔE of 0.2 eV if the high-lying delocalized states are harvested in high proportion. This work demonstrates the existence of the optimum driving force of 0.2 eV and provides some guidelines for engineering the interfacial energetics to achieve the high balanced Jsc and Voc.