Performance degradation of P3HT:PCBM Polymer/fullerene photovoltaic cells under gamma irradiation

Open Access
- Author:
- Todd, Aaron M
- Graduate Program:
- Engineering Science
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- August 20, 2009
- Committee Members:
- Jian Xu, Thesis Advisor/Co-Advisor
Jian Xu, Thesis Advisor/Co-Advisor
Osama O Awadelkarim, Thesis Advisor/Co-Advisor
S Ashok, Thesis Advisor/Co-Advisor - Keywords:
- solar cells
gamma irradiation
CELIV
radiation damage - Abstract:
- The gamma radiation damage effect on polymer-based hybrid photovoltaic cells consisting of a blend of poly-3-hexylthiophene (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) is investigated. The device is a bulk heterojunction photovoltaic cell with aluminum and ITO electrical contacts. Each glass substrate contains 6-to-9 usable devices. The samples were exposed to a cesium-137 gamma ray source (661 KeV) with radiation doses ranging from 1 krad to 5 krad. Electronic characterization by current-voltage (I-V) measurements were carried out before and after exposure. Decreases in the short-circuit photocurrent and the filling factor (FF) are observed with increasing radiation doses. Charge transport characterization was completed by the use of the integral-mode time-of-flight (I-TOF) technique and the current extraction by a linearly increasing voltage (CELIV) technique. Decreases in the charge carrier mobility are observed for both techniques with the increasing radiation dose. The CELIV results also show a decrease in the extraction current maximum and the post-extraction displacement current ramp. Optical characterization by the measurement of absorption and photoluminescence spectra were carried out. The results show that radiation exposure in the presence of oxygen strongly degrades the P3HT material. Damage in this material is in the form of polymer chain scission and conformational changes (twisting) which detrimentally affect the charge transport process inside the active layer.