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Significant work has been directed at measuring the exciton diffusion length (L_D) in organic semiconductors due to its significance in determining the performance of photovoltaic cells. Several techniques have been developed to measureL_D, often probing photoluminescence or charge carrier generation. Interestingly, in this study it is shown that when different techniques are compared, both the diffusive behavior of the exciton and active carrier recombination loss pathways can be decoupled. Here, a planar heterojunction device based on the donor–acceptor pairing of boron subphthalocyanine chloride‐C₆₀is examined using photoluminescence quenching, photovoltage‐, and photocurrent‐basedL_Dmeasurement techniques. Photovoltage yields the device relevantL_Dof both active materials as a function of forward bias subject to geminate recombination losses. These values are used to accurately predict the photocurrent as a function of voltage, suggesting geminate recombination is the dominant mechanism responsible for photocurrent loss. By combining these measurements with photocurrent and photoluminescence quenching, the intrinsicL_D, as well as the voltage‐dependent charge transfer state dissociation and charge collection efficiencies are quantitatively determined. The results of this work provide a method to decouple all relevant loss pathways during photoconversion, and establish the factors that can limit the performance of excitonic photovoltaic cells.

 

The electronic communication between two ferrocene groups in the electron-deficient expanded aza-BODIPY analogue of zinc manitoba-dipyrromethene (MB-DIPY) was probed by spectroscopic, electrochemical, spectroelectrochemical, and theoretical methods. The excited-state dynamics involved sub- ps formation of the charge-separated state in the organometallic zinc MB-DIPYs, followed by recovery of the ground state via charge recombination in 12 ps. The excited-state behavior was contrasted with that observed in the parent complex that lacked the ferrocene electron donors and has a much longer excited-state lifetime (670 ps for the singlet state). Much longer decay times observed for the parent complex without ferrocene confirm that the main quenching mechanism in the ferrocene-containing 4 is reflective of the ultrafast ferrocene-to-MB-DIPY core charge transfer (CT 

We demonstrate the impact of subtle changes in molecular structure on the singlet and triplet exciton diffusion lengths ( L D ) for derivatives of the archetypical electron-transport material 4,7-diphenyl-1,10-phenanthroline (BPhen). Specifically, this work offers a systematic characterization of singlet and triplet exciton transport in identically prepared thin films, highlighting the differing dependence on molecular photophysics and intermolecular spacing. For luminescent singlet excitons, photoluminescence quenching measurements yield an L D from <1 nm for BPhen, increasing to (5.4 ± 1.2) nm for 2,9-dichloro-4,7-diphenyl-1,10-phenanthroline (BPhen-Cl 2 ) and (3.9 ± 1.1) nm for 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP). The diffusion of dark triplet excitons is probed using a phosphorescent sensitizer-based method where triplets are selectively injected into the material of interest, with those migrating through the material detected via energy transfer to an adjacent, phosphorescent sensitizer. Interestingly, the triplet exciton L D decreases from (15.4 ± 0.4) nm for BPhen to (8.0 ± 0.7) nm for BPhen-Cl 2 and (4.0 ± 0.5) nm for BCP. The stark difference in behavior observed for singlets and triplets with functionalization is explicitly understood using long-range Förster and short-range Dexter energy transfer mechanisms, respectively.