Blending with a phthalocyanine leads to improved P3HT donor layers for OPVs

•Phthalocyanine liquid crystal as efficient additive to P3HT in OPVs.•Charge transport improvement by P3HT:CoPc blends.•Rectangular columnar order of CoPc contributes to the crystallinity of P3HT.•Molecular order and film morphology compete for electric properties of blends. Ternary blended solar cells have been intensively studied in recent years, where the addition of a second donor material in the active layer tends to increase the current density through improved photon absorption along with improving the charge transport properties and the inhibition of charge recombination processes. Here, we investigated a donor layer composed of a liquid crystalline cobalt phthalocyanine (CoPc) and poly(3-hexylthiophene-2,5-diyl) – P3HT. The CoPc presents a complementary absorption spectrum in the near infrared region and compact anisotropic molecular arrangement to promote efficient charge migration. The energy levels of CoPc are properly located between the corresponding levels of P3HT and PCBM, forming an energy cascade alignment. The P3HT/CoPc blend showed improved photophysical and electrical response depending on the CoPc concentration and thermal annealing. We demonstrated that molecular order, morphology and energetic barrier at cluster interfaces are competing effects and need to be taken into account to optimize charge transport.