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

摘要

Efficient exciton diffusion and charge transport play a vital role in advancingthe power conversion efficiency (PCE) of organic solar cells (OSCs). Here, afacile strategy is presented to simultaneously enhance exciton/charge transportof the widely studied PM6:Y6-based OSCs by employing highly emissivetrans-bis(dimesitylboron)stilbene (BBS) as a solid additive. BBS transformsthe emissive sites from a more H-type aggregate into a more J-type aggregate,which benefits the resonance energy transfer for PM6 exciton diffusion andenergy transfer from PM6 to Y6. Transient gated photoluminescence spectroscopymeasurements indicate that addition of BBS improves the excitondiffusion coefficient of PM6 and the dissociation of PM6 excitons in thePM6:Y6:BBS film. Transient absorption spectroscopy measurements confirmfaster charge generation in PM6:Y6:BBS. Moreover, BBS helps improve Y6crystallization, and current-sensing atomic force microscopy characterizationreveals an improved charge-carrier diffusion length in PM6:Y6:BBS. Owing tothe enhanced exciton diffusion, exciton dissociation, charge generation, andcharge transport, as well as reduced charge recombination and energy loss,a higher PCE of 17.6 with simultaneously improved open-circuit voltage,short-circuit current density, and fill factor is achieved for the PM6:Y6:BBSdevices compared to the devices without BBS (16.2).