Molecular orientation-dependent energetic shifts in solution-processed non-fullerene acceptors and their impact on organic photovoltaic performance

Abstract

The non-fullerene acceptors (NFAs) employed in state-of-art organic photovoltaics (OPVs) often exhibit strong quadrupole moments which can strongly impact on material energetics. Herein, we show that changing the orientation of Y6, a prototypical NFA, from face-on to more edge-on by using different processing solvents causes a significant energetic shift of up to 210 meV. The impact of this energetic shift on OPV performance is investigated in both bilayer and bulk-heterojunction (BHJ) devices with PM6 polymer donor. The device electronic bandgap and the rate of non-geminate recombination are found to depend on the Y6 orientation in both bilayer and BHJ devices, attributed to the quadrupole moment-induced band bending. Analogous energetic shifts are also observed in other common polymer/NFA blends, which correlates well with NFA quadrupole moments. This work demonstrates the key impact of NFA quadruple moments and molecular orientation on material energetics and thereby on the efficiency of high-performance OPVs.

The State‐of‐the‐Art Solution‐Processed Single Component Organic Photodetectors Achieved by Strong Quenching of Intermolecular Emissive State and High Quadrupole Moment in Non‐Fullerene Acceptors

“…This energetic offset originates from electrostatic effects due to the high Q 𝜋 of Y6 (Figure 6d) and its tight packing in differently oriented domains. [36] In addition, we observed a significant increase in the surface photovoltage upon illumination for the film exhibiting a mixed morphology. This is indicative of an increase of free charge generation facilitated by the larger density of grain boundaries and the potential steps occurring there due to quadrupole mediated electrostatic effects.…”

Charge transfer complex formation between organic interlayers drives light-soaking in large area perovskite solar cells

“…S20, ESI†). 54–56 A 30% increase in the tail state area of the PCBM:BCP spectrum is observed upon LS, this is compared to a 9% decrease in the tail state area of the C 60 :BCP spectrum. This may explain the reduced SPV magnitude of the PCBM/BCP partial device sample compared to the C 60 /BCP sample (Fig.…”

Vacuum-Deposited Donors for Low-Voltage-Loss Nonfullerene Organic Solar Cells

“…The performance (PCE < 0.1%) and J sc (0.3 mA/cm 2 ) shown in Figure S3 are much lower than the J sc of the NFA bilayer devices we report here (between 2 and 4 mA/cm 2 ). We note that the bilayer device performance not only depends on the donor–acceptor pairing but will be influenced by the microstructure of the bilayer interface, namely, the roughness of the interface, the degree of order, and the molecular orientation, which can be tuned during fabrication. Indeed, the electronic properties of Y6 have been shown to depend on processing conditions − and careful device optimization may yield better exciton diffusion length in Y6 and an improved interface morphology.…”

“…We note that the bilayer device performance not only depends on the donor–acceptor pairing but will be influenced by the microstructure of the bilayer interface, namely, the roughness of the interface, the degree of order, and the molecular orientation, which can be tuned during fabrication. Indeed, the electronic properties of Y6 have been shown to depend on processing conditions − and careful device optimization may yield better exciton diffusion length in Y6 and an improved interface morphology. A fully solution-processed bilayer of Y6/CuSCN, where an interface with CuSCN facilitates the splitting of excitons, achieved similar performance .…”