Document Type

Dissertation - Open Access

Award Date

2016

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical Engineering and Computer Science

First Advisor

Qiquan Qiao

Abstract

Organic-inorganic perovskite solar cells have become a promising alternative to fossil fuel based energy sources due to their unique properties such as tunable low bandgap, long charge diffusion length, low exciton binding energy and balanced charge transport. The semiconducting perovskite films are typically prepared from low temperature solution processing and the corresponding solar cells have exhibited power conversion efficiency (PCE) of more than 20%. However, perovskite solar cells suffer from poor stability in presence of moisture and use of toxic element (Pb). Understanding the crystallization process and the effects of moisture and water is important to obtain high quality perovskite films and highly efficient device performance. Room temperature ambient air crystallization of perovskite is important for making the overall processing simple and cost effective. The goal of this dissertation was to study the room temperature processing of perovskite films in ambient air at 40% relative humidity and to understand the effects of water as co-precursor solvent in improving the perovskite film quality. Role of moisture was studied by keeping the films in ambient air at room temperature and the perovskite crystallization was studied by monitoring the conversion of intermediate phase to pure perovskite phase. Crystallization process was correlated with morphological changes in perovskite films and fabrication conditions were optimized to achieve large grain size for higher device efficiency. Slowing down the crystallization of perovskite films was also studied with an aim to further improve film quality and device performance. Finally, the effects of water as co-solvent in improving film morphology was studied and correlated with device performance. Room temperature crystallized perovskite devices gave the highest efficiency of 16.83%. Slow grown perovskite films led to an improvement in fill factor, open circuit voltage and reduced hysteresis in the devices. Use of water as cosolvent improved the film morphology, but adding up to 25 vol. % water in the precursor solution does not significantly affect the power conversion efficiency. Future work on understanding the crystallization process under varying humidity levels and the role of water may open new insights on the crystallization process of perovskite films.

Library of Congress Subject Headings

Perovskite.
Solar cells.
Crystallization.
Moisture.

Description

Includes bibliographical references (pages 93-108)

Format

application/pdf

Number of Pages

123

Publisher

South Dakota State University

Rights

Copyright © 2016 Ashish Dubey

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