Simultaneously Enhancing Exciton/Charge Transport in Organic Solar Cells by an Organoboron Additive.

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• Efficient exciton diffusion and charge transport are crucial for high power conversion efficiency (PCE) in organic solar cells (OSCs).
• The PM6:Y6 system is a widely studied benchmark for OSCs, but further optimization of charge dynamics is needed.
• Understanding and controlling molecular aggregation and energy transfer pathways are key to improving device performance.

Purpose of the Study:

• To investigate the effect of a highly emissive solid additive, trans-bis(dimesitylboron)stilbene (BBS), on exciton/charge transport in PM6:Y6-based OSCs.
• To elucidate the mechanisms by which BBS enhances exciton diffusion, dissociation, and charge transport.
• To achieve improved power conversion efficiency (PCE) in PM6:Y6:BBS devices.

Main Methods:

• Employing trans-bis(dimesitylboron)stilbene (BBS) as a solid additive in PM6:Y6 blend films.
• Utilizing transient gated photoluminescence spectroscopy to study exciton diffusion and dissociation.
• Employing transient absorption spectroscopy to analyze charge generation dynamics.
• Characterizing film morphology and charge-carrier diffusion length using current-sensing atomic force microscopy.

Main Results:

• BBS transforms emissive sites from H-type to J-type aggregates, facilitating resonance energy transfer and exciton diffusion.
• Addition of BBS improves exciton diffusion coefficient and dissociation of PM6 excitons.
• Faster charge generation and improved charge-carrier diffusion length were observed in PM6:Y6:BBS films.
• BBS addition enhances Y6 crystallization.

Conclusions:

• The addition of BBS effectively enhances exciton diffusion, exciton dissociation, charge generation, and charge transport in PM6:Y6 OSCs.
• BBS leads to reduced charge recombination and energy loss, contributing to higher device performance.
• PM6:Y6:BBS devices achieved a significantly improved PCE of 17.6% compared to 16.2% for devices without BBS, with simultaneous improvements in open-circuit voltage, short-circuit current density, and fill factor.