Presenter(s): Nicole Wales—Chemistry and Physics
Faculty Mentor(s): Mark Lonergan, Zack Crawford
Session 5: The Bonds that Make Us
In order to improve perovskite solar cell efficiency, it is necessary to minimize defects within the perovskite absorber layer, which may include crystallographic point defects . By understanding how these defects form and contribute to the material’s electronic structure, we will gain insight into routes of Shockley-Read-Hall recombination and associated efficiency loss . Theoretical studies have credited some point defects with the production of energy trap states within the bandgap. As such, we aim to measure and describe the nature and formation of traps in real materials. External quantum efficiency measurements are used to describe a gaussian distribution of traps . Additionally, capacitance techniques are applied with the added advantage of increased sensitivity to the absorber layer . However, capacitance techniques are complicated by the hysteretic perovskite system, which is discussed . The samples used in this study include methylenediammonium dichloride- stabilized alpha-formamidinium lead triiodide, a perovskite with interstitially incorporated chloride . External quantum efficiency measurements showed lower defect densities compared to devices of different compositions, however, one sample did show a small signal with a defect transition energy of 1 .08 ± 0 .01 eV . Findings may point to material suppression of sub-gap defects associated with methylenediammonium dichloride-stabilization compared to alternative compositions . It will be interesting to determine if methylenediammonium dichloride is the source of defect suppression in these samples . To understand how the composition might affect defect states, it will also be necessary to take measurements of other stabilizing agents with different compositions .