EXPLORING THE STRUCTURAL FORMATION OF COPPER PHTHALOCYANINE (CuPc) USING IN SITU SPECTROSCOPY

Abstract

Organic semiconducting materials are promising candidates for solar cell materials and hold many benefits over traditional semiconducting materials including ease of manufacturing, low production cost, and substrate flexibility. A current obstacle that is holding back organic photovoltaics (OPV) is their low efficiency when compared to their traditional silicon-based counterparts. The efficiency of an OPV is dependent on many factors, including the structural formation of the electron donor and electron acceptor layers within the OPV along with the electronic dynamics of the donor/acceptor systems. Further understanding these parameters in potential active layer materials is crucial in optimizing the efficiency of OPVs and revolutionizing the photovoltaic industry. We worked with a potential electron donor candidate, copper phthalocyanine (CuPc). CuPc has been shown to form a pyramidal like structure when cast as an organic thin film which could lead to a desirable crystal formation within the active layer of an OPV. Work has been done characterizing both the structure and electronic dynamics of CuPc in the dried film state, but we are interested in what is happening during the deposition process. To probe this interest, we use in situ spectroscopic techniques that include UV-Vis spectroscopy and the novel technique, single shot transient absorption (SSTA) spectroscopy that was developed by the Wong Lab. SSTA allows us to obtain dynamical information of the CuPc in situ which can lead to a stronger understanding of how charges (electrons) transfer throughout the system, which is vital when considering the efficiency of an OPV. Through our use of in situ spectroscopy, we unveiled an intermediate phase within the CuPc deposition that led to unexpected spectral characteristics. During the intermediate phase there was a single featured spectrum that had never been reported before. When probed with SSTA, we saw a large spike in the negative signal during the intermediate phase. The UV-Vis spectra of the intermediate phase was blue-shifted, indicating that it may be due to the sole formation of H-aggregated (molecules stacking face to face with one another) CuPc molecules. To explore this, we attempted the isolation of the intermediate phase through a supersaturated solution of CuPc. Although we weren’t able to isolate the intermediate phase, this supersaturated solution of CuPc exhibited different film phase characteristics, both structurally and electronically, than the normal CuPc solution. Through our work we were able to identify a CuPc material that could be altered through the preparation method which could lead to beneficial application to OPVs.