Factors that influence the open circuit voltage and stability of polymer : fullerene bulk heterojunction solar cells
Abstract/Contents
- Abstract
- Solution processed organic photovoltaics offer the potential of providing solar energy at a significantly lower cost than conventional solar cells due to scalable manufacturing by roll-to-roll printing, low materials costs and facile installation of light-weight modules. Recently, power conversion efficiencies of over 10% have been achieved in small area multijunction devices, and stability lifetimes of several years have been demonstrated, though these are not yet sufficient for commercialization. The development of new materials that can produce high open circuit voltage devices is critically important for improving the efficiency of multijunction organic solar cells. Polymer:fullerene solar cells with power conversion efficiencies of over 7% are demonstrated with blends of the polymer PBDTTPD and the fullerene PCBM. These devices achieve an open circuit voltage of 0.94V and internal quantum efficiencies of 88% and thus are an ideal candidate for the large bandgap junction of tandem organic solar cells. The open circuit voltage is increased above 1V when the polymer is blended with multi-adduct fullerenes, but the current and fill factor are greatly reduced. Photoluminescence, electroluminescence and photocurrent measurements indicate that excitons undergo energy transfer to the fullerene rather than dissociate to form charges at the heterojunction interface due to the small difference in energy between the fullerene bandgap and charge transfer states. Consequently new non-fullerene electron acceptor materials with larger bandgaps may be required for devices to achieve both near unity internal quantum efficiencies and open circuit voltages exceeding 1.0V. The photodegradation of polymer:fullerene blend films exposed to ambient conditions for a variety of polymer and fullerene derivative combinations is also presented. The rate of irreversible polymer photobleaching in blend films was found to consistently and dramatically increase with decreasing electron affinity of the fullerene derivative. Furthermore, blends containing fullerenes with the smallest electron affinities photobleached at a faster rate than films of the pure polymer. These observations can be explained by a mechanism where both the polymer and fullerene donate photogenerated electrons to diatomic oxygen to form the superoxide radical anion which degrades the polymer.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2012 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Hoke, Eric Tong |
|---|---|
| Associated with | Stanford University, Department of Applied Physics |
| Primary advisor | Harris, J. S. (James Stewart), 1942- |
| Primary advisor | McGehee, Michael |
| Thesis advisor | Harris, J. S. (James Stewart), 1942- |
| Thesis advisor | McGehee, Michael |
| Thesis advisor | Salleo, Alberto |
| Advisor | Salleo, Alberto |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Eric Tong Hoke. |
|---|---|
| Note | Submitted to the Department of Applied Physics. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2012. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2012 by Eric Tong Hoke
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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