Assessing the Potential Roles of Silicon and Germanium Phthalocyanines in Planar Heterojunction Organic Photovoltaic Devices and How Pentafluoro Phenoxylation Can Enhance pi-pi Interactions and Device Performance

摘要

In this study, we have assessed the potential application of dichloro silicon phthalocyanine (Cl-2-SiPc) and dichloro germanium phthalocyanine (Cl-2-GePc) in modern planar heterojunction organic photovoltaic (PHJ OPV) devices. We have determined that Cl-2-SiPc can act as an electron donating material when paired with C60 and that Cl-2-SiPc or Cl-2-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 Cl-2-SiPc with no evidence of photocurrent contribution from Cl-2-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 (F-10-SiPc) and bis(pentafluoro phenoxy) germanium phthalocyanine (F-10-GePc) were synthesized and characterized. During thermal processing, it was discovered that F-10-SiPc and F-10-GePc underwent a reaction forming small amounts of difluoro SiPc (F-2-SiPc) and difluoro GePc (F-2-GePc). This undesirable reaction could be circumvented for F-10-SiPc but not for F-10-GePc. Using single crystal X-ray diffraction, it was determined that F-10-SiPc has significantly enhanced p-p interactions compared with that of Cl-2-SiPc, which had little to none. Unoptimized PHJ OPV devices based on F-10-SiPc were fabricated and directly compared to those constructed from Cl-2-SiPc, and in all cases, PHJ OPV devices based on F-10-SiPc had significantly improved device characteristics compared to Cl-2-SiPc.