- Charge carrier dynamics in photovoltaic materials
- Award date
- 20 February 2014
- Number of pages
- Document type
- PhD thesis
- Faculty of Science (FNWI)
- Van der Waals-Zeeman Institute (WZI)
We employ the experimental technique THz Time Domain spectroscopy (THz-TDS) to study the optoelectronic properties of potential photovoltaic materials. This all-optical method is useful for probing photoconductivities in a range of materials on ultrafast timescales without the application of physical contacts.
Using this technique we study the process of carrier multiplication (CM) - the excitation of multiple charge carriers by a single photon - in indium nitride (InN). InN possesses a number of properties favorable for efficient CM. However, we find that CM in InN is rather inefficient, contributing only to a modest efficiency increase in a potential InN based solar cell. Additionally, we study the dynamics of photoexcited carriers in 2-dimensional graphene with emphasis on the process of multiple hot carrier generation, which is related to carrier multiplication. A very efficient energy transfer from an optically excited charge carrier into multiple hot carriers is shown. We also perform a study of the photoconductivity of two types of 1-dimensional graphene-based semiconductors, flat graphene nanoribbons and carbon nanotubes. Free charge carriers are observed immediately after excitation. The mobility of these carriers is found to vary significantly for the different types of 1-D conductors. The applicability of these graphene based conductors in organic solar cell architectures is briefly discussed. Finally, we explore the carrier transport properties of colloidal TiO2 films commonly used in dye- and quantum dot sensitized solar cells. We find that the photoresponse is dominated by long percolation pathways of connected particles, responsible for the materials long range conductivity.
- Research conducted at: Universiteit van Amsterdam
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