Off-campus South Dakota State University users: To download campus access theses, please use the following link to log into our proxy server with your South Dakota State University ID and password.

Non-South Dakota State University users: Please talk to your librarian about requesting this thesis through interlibrary loan.

Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)


Electrical Engineering and Computer Science

First Advisor

Qiquan Qiao


Photovoltaics is a very promising renewable energy technology that can fulfill a singnificant part of the global energy demand. Silicon based solar cells have dominated the photovoltaic industry but production cost is of major concern. An alternative to silicon solar cells is organic solar cells which are cheaper, lighter, flexible and more applicable to real life situations like low light and high temperature conditions. However, a major draw back of organic solar cell is its instability in ambient conditions. An inverted structure polymer solar cell was developed to improve the lifetime of the solar cell using an air stable top electrode. The highest efficiency was achieved by treating electron transport layer consisting of ZnO-PVP with UV-ozone. The effect of UV-ozone treatment on ZnO was also studied but in a P3HT:ZnO hybrid solar cell system, where the role of ZnO was as an acceptor rather than an electron transport layer. There are no reports of the effect of UV-ozone treatment of ZnO sol gel as an electron transport layer. The objective of this thesis was to study the effect of UV-ozone treatment on sol-gel processed ZnO thin films and to optimize the functional layers of inverted BHJ solar cell to achieve high efficiency. UV-ozone is an effective means to convert carbon related impurities into volatile fragments which can evaporate into the atmosphere to make the surface free of impurities. Morphological, optical and electrical characterization of UV-ozone treated ZnO surface indicated diffusion of oxygen species inside the film, improvement in crystallinity of the film and introduction of oxygen interstitials inside the ZnO film. An inverted solar cell, based on PBDTTT-C-T:PC70BM as the active layer, using UV ozone treated ZnO as an electron transport layer for different times were fabricated. 29.1 % improvement in cell efficiency was observed for 5 min UV-ozone treated ZnO cell (8.34%) vs 6.46% for untreated ZnO. This was attributed to improved charge transport. An inverted device using a PDPP3T:PCBM system had a higher cell efficiency (4.45 %) than the normal device structure (4.02%) due to additional interfacial area provided by ZnO for exciton dissociation. Future work should address increasing the charge carrier concentration of the ZnO film by dopants, and improving active layer morphology by using additives such as DIO.

Library of Congress Subject Headings

Solar cells
Zinc oxide thin films
Electron transport
Ultraviolet radiation


Includes bibliographical references (pages 85-90)



Number of Pages



South Dakota State University


In Copyright - Educational Use Permitted