Transient Infrared Spectroscopy of Charge Transport in Emerging Photovoltaic Materials.
Open Access
- Author:
- Jeong, Kwang Seob
- Graduate Program:
- Chemistry
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- July 03, 2013
- Committee Members:
- John B Asbury, Dissertation Advisor/Co-Advisor
John B Asbury, Committee Chair/Co-Chair
David Lawrence Allara, Committee Member
Mark Maroncelli, Committee Member
Jian Xu, Committee Member - Keywords:
- Transient infrared spectroscopy
PbS CQD
Nanomaterials
Organic photovoltaic materials
Solar cell. - Abstract:
- Colloidal quantum dot (CQD) photovoltaic and organic photovoltaic (OPV) materials are promising alternative light absorbers for solar cells. Both CQD photovoltaics and OPVs can be fabricated on flexible substrates using low-cost solution cast fabrication methods at room temperature. Although intense research has been done for the last two decades in both materials, photophysical events underlying the device performance remain unclear. Here, the origin of the charge transport state in PbS CQD solids was explored and identified. The charge transport state was investigated using various optical and electrical methods: ultrafast transient infrared spectroscopy (UFIR), microsecond transient infrared spectroscopy (TRIR), steady state absorption spectroscopy, steady state photoluminescence emission spectroscopy, temperature dependent TRIR, temperature dependent transient photoconductivity and temperature dependent transient short-circuit current measurements. Furthermore, it was found that the mobility-lifetime product, which is dependent on the surface passivation strategy, significantly influences the device performance in CQD solar cells. Additionally, it was examined how the dielectric permittivity influences the photophysics in organic photovoltaic materials in conjunction with device performance. The experiments revealed that the increase of dielectric permittivity leads to enhancement of the mobility-lifetime product. For efficient conversion of excitons into charge carriers, it was suggested that high surface area between electron donor and acceptor materials is necessary. The findings provide better understanding of the fundamental properties of CQD and OPV materials and suggest pathways to improve the efficiency of solar cell based on these materials.