Proceedings of Perovskite Thin Film Photovoltaics (ABXPV17)
Publication date: 18th December 2016
For thin-film solar cells, interfaces play an important role in understanding mechanisms of charge separation and loss. Photoemission spectroscopy, including XPS and UPS, is used to reveal the nature of interfaces. Significant measure of interfaces are band bending, offsets in the conduction band for electrons and offsets for the holes in valence band or chemical reactions. Photoemission spectroscopy conveys the intricate electronic structure of the device, further contributing to device performance improvements. For these studies, it is necessary to grow the cell in ultra-thin layers and measure photoemission after each step. Therefore, it is mandatory to prepare the different layers inside of a UHV system to avoid any influence of the atmosphere. The preparation chambers are therefore directly connected to the measurement device, which allows in situ photoemission characterization. The growth of ultra-thin layers allows tracking of the electronic structure throughout the whole device. Our study focused on the two absorber materials CH3NH3PbI3 and CH3NH3SnI3 with different selective contacts. The interfaces to some of the most common hole transport materials, such as spiro-MeOTAD, CuSCN, and CuI, as contacts to TiO2 and Au, were analyzed. A better understanding of the interface helps to advance the functionality of photodiodes. Further optimization of the cell requires more effective interfaces to minimize voltage losses and reduce recombination at the interfaces.