The Problem: Ion transport in hybrid organic-inorganic  trihalide perovskites (HOIPs) has been implicated as the cause of many important properties associated with these compounds, such as instability to light and heat, hysteresis in current-voltage curves, switchable photovoltaic effects, and thermoelectricity. Yet, the chemical identity of the migrating ion and its mechanism of transport remain unclear. The lack of understanding of ion transport in these systems hinders our ability to design new OTPs with desired and improved properties for solar energy harvesting.  Thus, there is an urgent need to establish a clear understanding of the chemical identity of the mobile ion(s) and the mechanisms of ion transport.

Our Approach:Our long-term goal is to design new perovskites with improved stability and superior device performance for energy harvesting and electronic applications. The overall objective of our current study is to elucidate the mechanism for ion transport in metal halide perovskites containing organic cations.  We evaluate kinetics of ion transport in operando in a set of specifically-designed compounds in functional devices, and pristine thin films and single crystals using imepdance spectroscopy. We also use x-ray diffraction, Kelvin probe microscopy and other techniques to probe ion transport in these solids. 

Impact of our Work: We anticipate that our work will lead to the unequivocal resolution of the long-standing issue of the chemical identity of the mobile ion and the mechanism of ion transport in lead halide perovskites—will change the status quo and lead to a coherent explanation for many of the observed properties in existing materials. Moreover, we expect these outcomes to enable designs for new metal halide perovskites containing organic counterions with improved stability and desired properties.

Status: Current and Ongoing

Our papers in this area are provided here.

Using impedance spectroscopy and computation, we show that incorporation of multi-walled carbon nanotubes (MWCNTs) in the bulk of the active layer of perovskite-based solar cells reduces charge recombination and increases the open circuit voltage. An…

Perovskite-containing tandem solar cells are attracting attention for their potential to achieve high efficiencies. We demonstrate a series connection of a similar to 90 nm thick perovskite front subcell and similar to 100 nm thick polymer:fullerene…