Title: Device Physics of PTB7-based Bulk Heterojunction Solar Cells
Speaker: Mehran Samiee Esfahani, ECpE Graduate Student
Abstract: PTB7 is an important material in organic photovoltaics. We report on basic electronic and optical properties and effect of thermal annealing on device characteristics of PTB7:PCBM70 bulk heterojunction solar cells. Density of defects and interfacial bandgap of the blend are assessed through capacitance spectroscopy and subgap quantum efficiency, respectively. Our numerical calculations based on the blend properties coupled with our results from photovoltage vs. light intensity and dark I-V vs. temperature measurements strongly suggest that trap-assisted recombination is the major source of loss in the device, and that tail state recombination is the main limiting factor for open circuit voltage.