In this study, we have assessed the potential application of dichloro silicon phthalocyanine (Cl2-SiPc) and dichloro germanium phthalocyanine (Cl2-GePc) in modern planar heterojunction organic photovoltaic (PHJ OPV) devices. We have determined that Cl2-SiPc can act as an electron donating material when paired with C60 and that Cl2-SiPc or Cl2-GePc can also act as an electron acceptor material when paired with pentacene. These two materials enabled the harvesting of triplet energy resulting from the singlet fission process in pentacene. However, contributions to the generation of photocurrent were observed for Cl2-SiPc with no evidence of photocurrent contribution from Cl2-GePc. The result of our initial assessment established the potential for the application of SiPc and GePc in PHJ OPV devices. Thereafter, bis(pentafluoro phenoxy) silicon phthalocyanine (F10-SiPc) and bis(pentafluoro phenoxy) germanium phthalocyanine (F10-GePc) were synthesized and characterized. During thermal processing, it was discovered that F10-SiPc and F10-GePc underwent a reaction forming small amounts of difluoro SiPc (F2-SiPc) and difluoro GePc (F2-GePc). This undesirable reaction could be circumvented for F10-SiPc but not for F10-GePc. Using single crystal X-ray diffraction, it was determined that F10-SiPc has significantly enhanced π-π interactions compared with that of Cl2-SiPc, which had little to none. Unoptimized PHJ OPV devices based on F10-SiPc were fabricated and directly compared to those constructed from Cl2-SiPc, and in all cases, PHJ OPV devices based on F10-SiPc had significantly improved device characteristics compared to Cl2-SiPc.

ARTICLE This journal isFluoro aluminum phthalocyanine (F-AlPc) was synthesized by simply heating a DMSO solution of chloro aluminum phthalocyanine (Cl-AlPc) in the presence of CsF, KF or NaF for less than an hour. The resulting F-AlPc has a significant blue shift in the absorbance of ≈ 8 nm in solution and ≈ 130 nm in a solid film compared to Cl-AlPc. Ultraviolet photoelectron spectroscopy (UPS) identified a change in work function and E HOMO of as much as 1 eV between Cl-AlPc and F-AlPc. Our observed change in UPS data, solid-state absorbance and sublimation temperature for F-AlPc further confirms the stacked fluorine bridge solid-state structure for F-AlPc previously described by Kenney et al. Preliminary planar heterojunction (PHJ) organic photovoltaic (OPV) devices were then fabricated using F-AlPc as an electron donating material paired with C 60 and a ternary device including a Cl-AlPc interlayer. Additionally an all AlPc device where F-AlPc functioned as the electron donor and Cl-AlPc as the electron acceptor was fabricated. The EQE plots of the resulting PHJ OPV devices illustrate that an exciton-rectifying layer is present between the Cl-AlPc and F-AlPc layers in the ternary devices as well as the all AlPc device. These results further exemplify that the seemingly minor change from chloride to fluoride in the AlPc structure has significant implications in optoelectronic properties and functionality of AlPc in PHJ OPV devices.

Phenoxylation of chloro aluminum phthalocyanine (Cl-AlPc) can be easily achieved only when using “acidic phenols”. Once incorporated into unoptimized organic photovoltaics (OPVs) the result is an increase in the VOC.

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