Creating Side Transport Pathways in Organic Solar Cells by Introducing Delayed Fluorescence Molecules

Organic molecules that exhibit delayed fluorescence (DF) have been widely used in organic light-emitting diodes. In this work, we have introduced DF molecules to fullerene-free organic solar cells. A significant increase (up to 20%) in power conversion efficiencies in multiple organic photovoltaic systems is found with a ternary blending strategy, even though the DF molecules contribute little to light harvest. Transient absorption spectroscopic results indicate a significantly lengthened lifetime of excited states in optimal ternary blend films, which can be attributed to the assistance of the DF property of the third component. Meanwhile, the electron mobilities of ternary solar cells are dramatically enhanced, which could come from the extra electron transport pathways created by DF molecules in the acceptor-rich matrix. The function of creating two types of side transport pathways by introducing DF molecules is a newly found and useful strategy to enhance the performance of organic solar cells.