Multimodal Microscopy of Metal Halide Perovskite Thin Films and Devices

Metal-halide perovskites are an ever-growing class of materials that have shown remarkable success in optoelectronic applications such as solar cells, light emitting diodes and photodetectors. Contrary to established solar cell technologies such as silicon, perovskite devices are typically thin film and polycrystalline. Perovskite thin films, and devices comprised thereof, exhibit remarkable levels of microscopic disorder in their structure, chemistry and morphology¹. This disorder has profound impacts on the properties², performance and long term stability of these materials. Understanding the disorder of perovskite thin-films and their interfaces with contact layers is critical to the rational improvement of these devices.

In this talk, I will discuss the development and application of a multimodal microscopy toolkit designed to probe the interplay between structural, chemical and optoelectronic properties^3,4. We utilise wide-field, hyperspectral, optical microscopy to probe voltage and reflection losses within perovskite films. Spatially correlating these optoelectronic observations with nanoprobe hard X-ray diffraction and fluorescence, we relate nanoscale variations in chemistry and structure to changes in optoelectronic performance. In perovskite films, we find that stochastic, nanoscale chemical variation in composition, baked in upon film formation, creates energetic gradients that charge carriers move upon³. Charge carriers funnel onto high quality, low bandgap regions away from trap states that would otherwise cause power losses. These results help explain how these materials can tolerate such high levels of disorder.

We extend this toolkit to full devices by employing voltage dependent luminescence imaging – a technique that allows us to recreate full current-voltage curves at each spatial point –giving us access to both voltage and current losses at the interfaces with the contacts⁵. We find that full devices can tolerate large chemical disorder, but variations in current extraction efficiency are much more harmful. Minimising current extraction disorder at the interfaces is shown to be a strong predictor of both higher performance and more stable devices.

1.               Tennyson, E. M., Doherty, T. A. S. & Stranks, S. D. Nat. Rev. Mater. 4, 573–587 (2019).

2.               Doherty, T. A. S. et al. Nature 580, 360–366 (2020).

3.               Frohna, K. et al. Nat. Nanotechnol. 17, 190–196 (2022).

4.               Tennyson, E. M. et al. ACS Energy Lett. 6, 2293–2304 (2021).

5.               Frohna, K. et al. Nat. Energy (2024) doi:10.1038/s41560-024-01660-1.