Ultrafast Charge Separation and Nongeminate Electron-Hole Recombination in Organic Photovoltaics

Abstract

The mechanism of electron-hole separation in organic solar cells is currently hotly debated. Recent experimental work suggests that these charges can separate on extremely short timescales (<100 fs). This can be understood in terms of delocalised transport within fullerene aggregates, which is thought to emerge on short timescales before vibronic relaxation induces polaron formation. However, in the optimal heterojunction morphology, electrons and holes will often re-encounter each other before reaching the electrodes. If such charges trap and cannot separate, then device efficiency will suffer. Here we extend the theory of ultrafast charge separation to incorporate polaron formation, and find that the same delocalised transport used to explain ultrafast charge separation can account for the suppression of nongeminate recombination in the best devices.

Accepted for publication in PCCP

Cited by in corpus (4)

• Even a little delocalization produces large kinetic enhancements of charge-separation efficiency in organic photovoltaics
• Delocalisation enables efficient charge generation in organic photovoltaics, even with little to no energetic offset
• Origin of space-separated charges in photoexcited organic heterojunctions on ultrafast time scales
• Identification of Ultrafast Photophysical Pathways in Photoexcited Organic Heterojunctions