Interfacial Engineering of Organic and Inorganic Heterojuction for Solar Cell Application
Date Issued
2015
Date
2015
Author(s)
Lien, Hsiang-Ting
Abstract
This thesis investigates the function of various interfaces in solar cells. These interfaces are of great importance in controlling the key processes in solar cells such as the photocurrent generation, transport and extraction of photo-excited charge carriers. The surface-induced electronic distribution, band alignment and the molecular orientation in different solar cell structures are carefully examined by several techniques. In each study, the standard device fabrication and characterization provide the information to correlate the interface properties with the device performance. These results could be helpful for the understandings of the relationship between interface properties and the device performance of the solar cell. The interfacial engineering approaches presented here could also provide implications for the design of solar cell materials and devices. Firstly, the donor-acceptor interface is investigated by employing metal-phthalocyanine (M-Pc)/Silicon (Si) heterojunction as a model system. The lying-down configuration of PcPs (poly-Pc form) are observed, benefiting the charge transport and better contact in the hybrid based device. The strong metal-metal interaction between Pc molecules and substrate are believed to cause molecular orientation, which can facilitate the lying configuration. At the heterojunction interface also results in a relatively large open circuit voltage in a model solar cell device. Secondly, we investigate the hole transportation properties of an efficient anode interfacial layer of based on copper oxide materials. Significant band alignment and build-in voltage difference between buffer layer and active layer is observed due to the oxidation state difference of CuxO. The conduction band of evaporated- CuxO (e-CuxO) is very close to the highest occupied molecular orbital (HOMO) of donor material in polymer solar cell (eg. Poly(3-hexylthiophene-2,5-diyl), P3HT) facilitate the better charge transportation with minimal energy loss at anode/donor interface. Finally, the chemical-vapor-deposited (CVD) grown graphene modified Cu foil substrate induced orientation of pentacene so that the CVD graphene could be an effective interfacial layer to engineer the ordering of organic materials. The pentacene undergoes an obvious orientation change from a standing configuration on the PEDOT electrode to a less standing configuration on the ITO electrode and Cu foil. The surface free energy also provides a strategic way to control the orientation of organic molecules. Better transporting mobility of the lying-down pentacene on graphene modified electrode facilitate the effective charge transporting in single layer device. This is also affects active in optoelectronic devices.
Subjects
Heterojuction Interface
Solar Cell
X-ray Absorption Spectroscopy
Type
thesis
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