Erin Ratcliff1
University of Arizona1
Defects are considered to be one of the most prominent contributions to diminished power conversion efficiencies and long-term stability in printable metal halide perovskite materials and optoelectronic devices. Defects can arise from a combination of point defects, grain boundaries, charge transfer with Lewis acid/base sites at the contacts, and/or mobile redox-active halides. Thus every perovskite composition and contact choice can result in differences in defect distributions.<br/><br/>Defect states have most often been characterized using electrical, optical, and magnetic techniques; however, independently assessing donor and acceptor defect quantities and energetics using a direct experimental approach with few empirical assumptions can be challenging. Realization of high-performing and long-term stable devices requires a combination of method advancement for the quantification of defects and mitigation strategies.<br/><br/>This talk will discuss emerging electrochemistry-based measurement science approaches to quantify the distribution and energetics of donor and acceptor defects in a prototypical perovskite solar cell material (FA.<sub>79</sub>MA<sub>.16</sub>Cs<sub>.05</sub>)Pb(I<sub>.87</sub>Br<sub>.13</sub>)<sub>3</sub> (or Cs<sub>.05</sub>FA<sub>.79</sub>MA<sub>.16</sub>), with demonstrations of the methodology to other perovskite active materials. We utilize a solid-state electrolyte top contact to create “half-cells” of device-relevant material stacks under realistic electric fields. This allows us to spectroscopically assess onsets in valence and conduction bands under conditions of <i>operando,</i> as well as quantify near-band defects using redox probes. Connections to device performance, including modifications to the near-surface region of hole-transporting layers (i.e. NiOx), will be provided as well as preliminary results to understand degradation pathways using near-ambient pressure x-ray photoelectron spectroscopy and <i>operando </i>x-ray scattering. Collectively, this developed tool-suite provides a holistic approach to understand defects, device performance and stability in this exciting class of materials.