Regulating Crystallinity Mismatch Between Donor and Acceptor to Improve Exciton/Charge Transport in Efficient Organic Solar Cells

Abstract

Achieving a more balanced charge transport by morphological control is crucial in reducing bimolecular and trap‐assisted recombination and enhancing the critical parameters for efficient organic solar cells (OSCs). Hence, a facile strategy is proposed to reduce the crystallinity difference between donor and acceptor by incorporating a novel multifunctional liquid crystal small molecule (LCSM) BDTPF4‐C6 into the binary blend. BDTTPF4‐C6 is the first LCSM based on a tetrafluorobenzene unit and features a low liquid crystal phase transition temperature and strong self‐assembly ability, conducive to regulating the active layer morphology. When BDTPF4‐C6 is introduced as a guest molecule into the PM6:Y6 binary, it exhibits better compatibility with the donor PM6 and primarily resides within the PM6 phase because of the similarity‐intermiscibility principle. Moreover, systematic studies revealed that BDTPF4‐C6 could be used as a seeding agent for PM6 to enhance its crystallinity, thereby forming a more balanced and favourable charge transport with suppressed charge recombination. Intriguingly, dual Förster resonance energy transfer was observed between the guest molecule and the host donor and acceptor, resulting in an improved current density. This study demonstrates a facile approach to balance the charge mobilities and offers new insights into boosting the efficiency of single‐junction OSCs beyond 20%.

High-Performance PM6:Y6-Based Ternary Solar Cells with Enhanced Open Circuit Voltage and Balanced Mobilities via Doping a Wide-Band-Gap Amorphous Acceptor

“…Lately, by adding an original multifunctional liquid crystal small molecule BDTPF4-C6 into the PM6:Y6 binary blend, Chen et al significantly improved the crystallinity of PM6 and reduced the π–π stacking distances, further enhancing μ h (from 1.41 to 2.95 × 10 –4 cm 2 V –1 s –1 ) and resulting in a more balanced charge transport (μ e /μ h from 1.54 to 1.2). Finally, ternary device PM6: Y6: BDTPF4-C6 achieves an excellent FF of 79.16% and a PCE of 17.93% …”

“…Finally, ternary device PM6: Y6: BDTPF4-C6 achieves an excellent FF of 79.16% and a PCE of 17.93%. 45 On the other hand, the incorporation of a suitable third component into Y-series-based binary OSCs to prevent the overaggregation of Y-type acceptors to slightly decrease the μ e for balanced charge transport has proven to be an alternative approach to further promote the FF and efficiency of Y6-based devices. Kan et al applied 1-fluoronaphthalene (FN) instead of 1-chloronaphthalene (CN) as the additive into PM6:Y6, which induced the miscibility and optimized the morphology, leading to a μ h of 5.24 × 10 −4 cm 2 V −1 s −1 and a μ e of 5.28 × 10 −4 cm 2 V −1 s −1 , lower than those of the CN-based device (7.34 and 5.55 × 10 −4 cm 2 V −1 s −1 ), and the FF was enhanced from 71.9 to 77.8%, with PCE being increased from 15.7 to 17.5%.…”