LAUSR

Generating desired efficiency enhancements in organic solar cells (OSC) by charge transfer doping requires to obtain modified opto-electronic properties with remaining the favorable nanomorphology. We report a thermally-assisted dop-ing based on Lewis acid tris(pentafluorophenyl)-borane (BCF) as a p-dopant for two groups of OSC comprising of the PBDB-TF and PBDB-T donors and a non-fullerene acceptor IT-4F. We found that the face-on molecular packing in the PBDB-TF:IT-4F blend or neat PBDB-TF donor films is favorably modified with the formation of frustrated Lewis pairs (FLPs) in the donor, which contrasts to the hampered π-π stacking in the doped PBDB-T film. The different impacts of BCF dopants on the morphology lead to contrasting photovoltaic behaviors where the PBDB-TF based devices receive enhanced PCEs in the presence of BCF while reduction of efficiencies is observed in the PBDB-T device. In the best doping conditions with the proposed hot-film deposition, we achieve a boosted PCE of 14.1% in PBDB-TF:IT-4F solar cells at low BCF concentrations. Based on the same fluorinated donor, the described BCF doping also applies to NF-solar cells based on a NF-acceptor Y6, leading to increasing the PCE to 16.0%. Our results suggest that controlling the degree of FLPs formation in the donor component with addition of BCF is a key to obtaining desired improvements on nanomorphology and relevant photophysical properties in OSCs.