Flair for solar performance

A peak in global emissions from energy generation is predicted for 2020¹, so the search for cost-effective and efficient means of generating energy via renewable sources is on. Between 2012 and 2013, there was a 20% increase in electricity generation from solar power in the European Union², signifying a substantial growth in the investigation and application solar technology.

What was done?

The high efficiency of the perovskite cells can be attributed to their highly crystalline framework which has a very precise and symmetrical structure. However, despite many advances being made in the electrical performance of the cells, the interplay between their efficiency and crystal structure was unknown. This link was explored through the application of the synchrotron.

Scientists from the University of Cambridge, the University of Oxford, and the Adolphe Merkle Institute in Switzerland investigated the influence of different atmospheres (air versus nitrogen) on the annealing of perovskite films deposited from a mixed halide precursor. The samples consisted of powder obtained from spin-coated films, and the WAXS on I22 was performed while annealing at 100 °C for 2.5 hours. A wide q-range was employed to map out the structural features that appeared during annealing. Dr Alessandro Sepe, group leader of the synchrotron studies at the University of Cambridge, who led the synchrotron study team explained: “the WAXS technique allowed us to see the crystal properties of the photovoltaic cell in real-time at a very high resolution. We knew what we wanted to observe, but we were unsure what we could expect to see, so we had to adapt the parameters of the experiment as we gathered the results.”

Fig.1: 2D in situ WAXS maps showing the kinetics of the crystal structure of bulk perovskite monitored in real-time while annealing the material at 100 °C for 2.5 h in air (a) and nitrogen (d). The 2D reconstructions illustrates defined reflections that confirms retaining of the perovskite crystallinity upon annealing, which explains the increasing in performance of the final devices. Pathak et al. (2015).

What was discovered?

Fig. 2: 3D in situ WAXS map showing the kinetics of the crystal structure of bulk perovskite monitored in real-time while annealing the material at 100 °C for 2.5 h in air. The 3D reconstruction illustrates defined reflections that confirms retaining of the perovskite crystallinity upon annealing, which explains the increasing in performance of the final devices.