INFLUENCE OF MORPHOLOGY AND SOLID-STATE STRUCTURE ON NON-FULLERENE ORGANIC SOLAR CELL PERFORMANCE
Date
2022-05-02
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0001-7283-3704
Type
Thesis
Degree Level
Doctoral
Abstract
The current trend of rising global energy demand and global temperatures requires action. Photovoltaic (solar cell) technologies offer relief on both accords - renewable energy production and no greenhouse gas emission during operation. Organic solar cells also offer numerous benefits such as flexible form-factors, lightweight modules, tunable colors (for differing applications and aesthetics), short energy-payback times, low-cost production, and excellent low-light efficiency.
While organic solar cells have historically lagged behind other solar technology in terms of efficiency, they have recently become competitive with other established solar technologies. This rapid development was mostly the product of a better understanding of the morphology of the light absorbing (active) layer and the solid-state structure of its constituent parts: donor and acceptor semiconducting materials. This better understanding of the active layer has helped to shape both material development and processing methods, leading to better solar cells.
This thesis describes ways in which the solid-state structure and film morphology of the active layer in an organic solar cell can be influenced to afford better devices. These methods involve making structural changes to the light absorbing molecules and post-deposition processing of the active layer. This thesis shows that molecular shape, specifically whether the chromophore is linear or x-shaped, can greatly influence the molecular interactions within the active layer. Linear chromophores are better able to closely pack together and produce a better morphology through improved cross and self interactions of the donor and acceptor. This thesis also demonstrates how controlled swelling and solvation of the active layer (solvent vapor annealing) can have remarkable changes to the solid-state structure and active layer morphology, drastically changing the efficiency of the devices. In particular, solvent vapor exposure below the saturation vapor pressure can control the level of acceptor crystallization and phase-separation, contributing to better devices. Lastly, this thesis describes how the conformational freedom of the chromophore backbone strongly influences both the self- and cross-interactions of the donor and acceptor. The use of a heteroatom, specifically bromine, to reduce conformational disorder can have multiple beneficial effects on the morphology of the active layer, leading to better devices in both indoor and outdoor applications. The broader implication of these findings will be discussed.
Description
Keywords
Solar, Organic Solar Cells, Photovoltaics
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Chemistry
Program
Chemistry