Abstract
The correct determination of the exciton diffusion length (LD) in novel organic photovoltaics (OPV) materials is an important, albeit challenging, task required to understand these systems. Herein, a high‐throughput approach to probe LD in nonfullerene acceptors (NFAs) is reported, that builds upon the conventional photoluminescence (PL) surface quenching method using NFA layers with a graded thickness variation in combination with spectroscopic PL mapping. The method is explored for two archetypal NFAs, namely, ITIC and IT‐4F, using PEDOT:PSS and the donor polymer PM6 as two distinct and practically relevant quencher materials. Interestingly, conventional analysis of quenching efficiency as a function of acceptor layer thickness results in a threefold difference in LD values depending on the specific quencher. This discrepancy can be reconciled by accounting for the differences in light in‐ and outcoupling efficiency for different multilayer architectures. In particular, it is shown that the analysis of glass/acceptor/PM6 structures results in a major overestimation of LD, whereas glass/acceptor/PEDOT:PSS structures give no significant contribution to outcoupling, yielding LD values of 6−12 and 8−18 nm for ITIC and IT‐4F, respectively. Hence, practical guidelines for quencher choice, sample geometries, and analysis approach for the accurate assessment of LD are provided.
Highlights
The field of solution-processed organic photovoltaics (OPV) has been experiencing renewed interest since the introduction of high-performance small-molecular nonfullerene acceptors (NFAs).[1,2,3,4] Solar cell efficiencies approaching 18% have, method is explored for two archetypal NFAs, namely, ITIC and IT-4F, using PEDOT:PSS and the donor polymer PM6 as two distinct and practically relevant quencher materials
We present a combined experimental and computational study on the effect of light outcoupling on the determination of the exciton LD in archetypal NFA materials, ITIC and IT-4F
Two typical OPV materials with very different optical properties were applied as exciton quenchers, PEDOT:PSS and PM6
Summary
The field of solution-processed organic photovoltaics (OPV) has been experiencing renewed interest since the introduction of high-performance small-molecular nonfullerene acceptors (NFAs).[1,2,3,4] Solar cell efficiencies approaching 18% have, method is explored for two archetypal NFAs, namely, ITIC and IT-4F, using PEDOT:PSS and the donor polymer PM6 as two distinct and practically relevant quencher materials. Conventional analysis of quenching efficiency as a function of acceptor layer thickness results in a threefold difference in LD values depending on the specific quencher. This discrepancy can be reconciled by accounting for the differences in light in- and outcoupling efficiency for different been reported when using these materials in single-junction devices.[4,5] To understand what makes the NFA family so special, a significant interest in their photophysical properties has been sparked.[6,7,8,9] One key material characteristic that has been claimed to play an allmultilayer architectures. Practical guidelines for quencher choice, sample geometries, and analysis important role is the large exciton diffusion length, LD, reported for these systems compared with fullerene-based acceptors.[6,8,10] LD, representing an average distance that an exciton can travel within its lifetime τ, describes the exciton migration in material approach for the accurate assessment of LD are provided
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