Research

Halide perovskite crystal structure.

Halide Perovskites

Perovskite is the scientific name of a class of minerals which share the same crystal structure and chemical stoichiometry, AMX3 (see the figure at the right). Recent developments in halide perovsite semiconductors (where X = chlorine, bromine, or iodine) have led to new possibilities for solar energy harvesting with photovoltaics (solar cells), light emitting diodes (LEDs), photodetectors, and other applications. The three key benefits of halide perovskites for all of these applications is that they are:

  1. earth abundant
  2. defect tolerant
  3. solution-processable

Together, these three things mean that (1) we do not have to worry too much about supply issues for large-scale deployment of the technology (for example, for solar energy harvesting), (2) we do not need halide perovskites to be as pure/high quality as other materials to reach the same performance, which allows us to (3) explore new methods of making the materials at scale by “solution-processing” (think technologies like printing and coating).

In the Christians’ research group, we explore different aspects of halide perovskites for energy applications because we believe that energy is one of the most important (perhaps THE most important) global issue we face. As scientists and engineers, we seek to use our expertise to contribute to the societal search for better energy alternatives. our group, we are working to take

Halide Perovskite Solar Cells and Degradation

All solar cell technologies need efficiency (how efficiently sunlight is converted to electricity), cost, and durability. Halide perovskite solar cells can compete with the efficiency of commercial technology and offer likely lower-cost production methods. That leaves durability or stability as their major technological hurdle. Silicon solar cells, the present market leader, typically last for many decades and often come with warranties on their performance of 25 years. Developing a printable material which can last for that long in direct sunlight and widely variable climates is extremely challenging. Much of the work in the Christians’ lab focuses on understanding and mitigating degradation mechanisms in perovskite solar cells.

Color-Changing Solar Windows

Imagine something which can be a high-efficiency solar cell one moment and a window the next, similar to how eyeglasses can transition between “clear” and “sunglasses.” This could lead to unique opportunities like an electric car with a sunroof that can be highly transparent while driving, but an efficient solar cell while parked.

The unique properties of halide perovskites make new applications like this possible. Already we can change the color of the solar cell absorber from “dark” to “clear” (as seen at the left), but we quickly lose solar cell performance. In our group, we are working to take some of the lessons from rechargeable batteries to improve the reproducibility of this color-cycling.