Planar and textured heterojunction organic photovoltaics based on chloroindium phthalocyanine (ClInPc) versus titanyl phthalocyanine (TiOPc) donor layers

Planar and textured heterojunction solar cells (OPVs) are reported for vacuum deposited chloroindium phthalocyanine (ClInPc)/C₆₀ heterojunctions, and their response compared to previously explored OPVs based on titanyl phthalocyanine (TiOPc)/C₆₀ heterojunctions. As for TiOPc/C₆₀ OPVs, the photoelectrical activity of ClInPc/C₆₀ OPVs extends well into the near infrared, with good activity out to ca. 900 nm. As-deposited ClInPc films (Phase I) produce open-circuit photopotentials, V_OC as high as ca. 0.8 V (Phase I form of ClInPc), ca. 0.15 V larger than previously observed for Phase I TiOPc/C₆₀ OPVs. The offsets in frontier orbital energies (EHOMOPc-ELUMOC60) revealed by UV-photoemission studies (UPS) are slightly smaller for ClInPc/C₆₀ versus TiOPc/C ₆₀ heterojunctions, and the interface dipole contribution (shift in local vacuum level) to these offsets is in the opposite direction for ClInPc/C₆₀ versus TiOPc/C₆₀ heterojunctions, or missing altogether, suggesting differences in molecular interaction at the Pc/C ₆₀ interface. Higher V_OC values are correlated with lower reverse saturation currents, J_o, for ClInPc/C₆₀, versus other Pc or pentacene/C₆₀ heterojunctions, suggesting weak intermolecular interactions at the ClInPc/C₆₀ interface and large barriers to dark charge injection. Solvent annealing of the ClInPc films enhances the near-IR response, and textures the Pc film, enhancing the Pc/C ₆₀ interfacial contact area and the short-circuit photocurrent, J_SC. J_SC under AM 1.5 illumination conditions was estimated by integration of the incident photon current efficiency (IPCE) response, to compare relative power conversion efficiencies for the two different device types. The estimated efficiency of Phase I ClInPc/C ₆₀ OPVs is ca. 2.6%. The estimated AM 1.5 efficiency of ClInPc/C ₆₀ OPVs with solvent annealed Pc layers is estimated to be ca. 3.3%, arising from the extensive texturing achieved of the Pc layer, which nearly doubles J_SC for the Phase II versus Phase I Pc films.