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

Abstract

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.

Simultaneously Enhancing Exciton/Charge Transport in Organic Solar Cells by an Organoboron Additive

“…[ 13 ] Delayed fluorescence materials, which have small energy gap and strong spin‐orbit coupling between singlet and triplet state, were used to improve exciton diffusion length as a third component in efficient FREA‐based OSCs. [ 14–16 ] Based on Förster energy transfer theory, exciton diffusion length and photoluminescence quantum yield (PLQY) have positive correlation, [ 17 ] accordingly exciton diffusion length can be increased through increasing PLQY. [ 18 ] For example, introduction of 9‐fluorenone‐1‐carboxylic acid into the FREAs results in higher PLQY and longer lifetime of singlet excitons.…”

Simultaneously Decreasing the Bandgap and Voc Loss in Efficient Ternary Organic Solar Cells

“…[45] In the PM6:Y6-based OSC, with the addition of non-fullerene and PCBM-based third acceptor materials, more than 17% power conversion efficiency has been obtained. [46][47][48][49] The addition of a third polymer donor component with lower HOMO energy levels has also been investigated, where a gradually increasing V oc is obtained as the third donor ratio increases. [50][51][52] The ternary OSCs composed of two donors have rarely been observed as there are fewer choices for the third donor materials with HOMO levels lower than the PM6 molecule.…”