Material Design & Device Physics

Charge mobility in the metal oxide material, preventing the rapid extraction of electrons to the electrode, is an inherent limitation in hybrid and dye sensitized solar cells. Using materials with extremely high charge mobilities, such as the lead perovskite CH3NH3PbI3, has recently resulted in a dramatic and impressive increase in the performance, up to 20 %, in these hybrid like devices.

Commonly, groups have focused on improving dye absorption or polymer mobilities for hybrid solar cells due to the versatility of the organic groups. However, the metal oxide structure, typically TiO2 or ZnO, has been generally limited to morphological studies. Recently, it has been proposed that using a core-shell structure can be advantageous, with careful design considerations, to confine the electrons within the core thereby reducing recombination with higher mobility materials.  Previous research has used two distinct materials for this core-shell structure, typically a high mobility metal oxide such as ZnO or SnO2 in the core with a stable TiO2 layer as the shell, leading to additional solid interfaces.

Our group is currently focusing on removing these solid interfaces while still producing high mobility materials. By doping the TiO2 nanostructures with various transition metals, such as Sn, Ta, Nb, W, etc., we are able to control the charge dynamics within the metal oxides limiting the formation of both grain boundaries and solid interfaces. Important to this study is understanding the role of the dopant on the electronic, physical, optical and chemical properties and the effect these have on solar cell performance. Specifically, we probed how the dopant and core-shell morphology changes the band structure and Fermi level alignment, the local binding environment, and crystal quality in order to elucidate the charge dynamics.