Effect of Quencher, Geometry, and Light Outcoupling on the Determination of Exciton Diffusion Length in Nonfullerene Acceptors

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.

Identifying and Amplifying the Spontaneously Formed Photo‐Charge Contribution in Opaque and Semitransparent Organic Photovoltaics

“…In accordance with previous reports, the L EX values of all three NFAs are below 20.0 nm via PL measurement. [ 46–48 ] BTP‐eC9 and L8‐BO have similar L EX of 18.0 nm and 15.0 nm, which are larger than that of 9.5 nm in N4. The L EX is positively correlated with the EX delocalization extent of the three NFAs by density funciotnal therory (DFT) calculation (Figure S2, Supporting Information).…”

Gas-assisted blade-coating of organic semiconductors: molecular assembly, device fabrication and complex thin-film structuring

“…We demonstrate the applicability of gas-assisted blade-coating for accelerating the film formation kinetics using a benchmark BHJ blend system comprising the polymer donor poly(3-hexylthiophene) (P3HT) and the prototypical nonfullerene acceptor ITIC. Although known to feature a poor photovoltaic efficiency, 10 this widely studied highly crystalline blend system 10,30,31 allows a number of phenomena to be clearly illustrated. The generality of observations is nevertheless corroborated for devices based on the high-performance blend system comprising PM6 (elsewhere referred to as 'PBDB-T-2F') as the polymer donor 3,30 (see section 2.2.3).…”

“…Although known to feature a poor photovoltaic efficiency, 10 this widely studied highly crystalline blend system 10,30,31 allows a number of phenomena to be clearly illustrated. The generality of observations is nevertheless corroborated for devices based on the high-performance blend system comprising PM6 (elsewhere referred to as 'PBDB-T-2F') as the polymer donor 3,30 (see section 2.2.3).…”

Combinatorial screening of wide band-gap organic solar cell materials with open-circuit voltage between 1.1 and 1.4 V

“…For this purpose, our group has developed a platform based on using thickness gradients, generally achieved by blade-coating with variable speed, for the rapid study of important parameters in organic solar cells such as active layer materials, composition, or thickness. 35,38–42…”