Advancing Perovskite Solar Cell Development and Stability Using In-Line Electrochemical Methodologies

Understanding the chemical factors that dictate long term stability in metal halide perovskite thin films is critical in the optimization of fully commercialized printable energy conversion, display and optoelectronic platforms, X-ray detectors, and photodetectors. The origin of these instabilities has been associated with defects within the perovskite crystal lattice many of which are mobile and redox active. This talk will discuss established (spectro)electrochemistry-based measurement science approaches to quantify the distribution and energetics of donor and acceptor defects in prototypical perovskite solar cell materials and at buried charge selective interlayers (i.e., hole transport layers). Connections to device performance, benchmarked with time-resolved photoluminescence measurements, will be shown. Results demonstrating the connection between defect quantification and durability will also be discussed in the context of activated corrosion of metal halide perovskites, as probed by dynamic near-ambient pressure X-ray photoelectron spectroscopy.

We utilize a solid-state electrolyte top contact that equilibrates with the perovskite film to create “half-cells” of device-relevant material stacks and study them under solar cell-relevant electric fields. This allows us to spectroscopically assess onsets in valence and conduction bands under operando conditions, as well as quantify near-band edge defects using redox-active hole or electron capturing molecular probes. The combination of spectroscopy and electrochemistry characterizes the energetic distribution of donor defect states at an energy resolution of <10 meV in “stoichiometric” triple cation, mixed halide perovskite thin films (Cs0.05FA0.79 MA0.16)Pb(I0.87Br0.13)3) or CsFAMA under device-relevant electric fields (i.e. electrochemical biasing). Limits of detection are at the 10¹⁴ defects/cm³. Such detection limits are better than spectroscopic, electronic and photoemission protocols, with speciation (anion versus cation defects) not available in those other approaches.

The technique is exquisitely sensitive, allowing for detection of clear differences in buried perovskite/metal oxide interfaces to better understand photovoltaic performance. Ongoing efforts to characterize defects and distributions include both nickel oxide nanoparticles and sputtered nickel oxide hole-transport contacts, modified with molecular species. Advancements towards development of defect quantification to elucidate active corrosion mechanisms, as probed by dynamic near-ambient pressure X-ray photoelectron spectroscopy, will be shown.