HARRICK PLASMA

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, VOC 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 ( EHOMO Pc - ELUMO C60 ) revealed by UV-photoemission studies (UPS) are slightly smaller for ClInPc/C60 versus TiOPc/C60 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/C60 interface. Higher VOC values are correlated with lower reverse saturation currents, Jo, 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/C60 interfacial contact area and the short-circuit photocurrent, JSC. JSC 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/C60 OPVs is ca. 2.6%. The estimated AM 1.5 efficiency of ClInPc/C60 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 JSC for the Phase II versus Phase I Pc films.

Wang, W., D. Placencia, N.R. Armstrong

Organic Electronics

12 (2)

383-393

2012-10-03

2011

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