Characterising new perovskite inks using X-ray Scattering

Posted on 16 Nov 11:44

The development of new perovskite inks is a key priority for Ossila. Perovskites are a class of semiconductor material that are easy to process using ultra-cheap solution-based techniques, and combine efficient optical absorption with very high charge carrier mobility. For this reason, many researchers are excited by the prospect that perovskite thin-films could be used in a range of optoelectronic devices including light-emitting diodes, lasers and photovoltaic devices. Currently, the best efficiency for a perovskite photovoltaic device stands at a little over 20% -  a value not far behind that of crystalline silicon but to reach these high figures the perovskite devices required a relatively complex architecture with difficult processing conditions. The current best-selling off-the-shelf perovskite precursor ink offered by Ossila (I101) has a champion device efficiency of 13.1% (as measured in Ossila's labs) and is easy to use. However, we are working hard to increase this efficiency, and are exploring various process additives that control organisation during film deposition, drying and annealing.

Recently Ossila researchers, together with scientists from the University of Sheffield and the University of Cambridge have measured the structure of a range of perovskite thin films using small and large-angle grazing incidence x-ray scattering (GIWAXS) at the Diamond Light Source (http://www.diamond.ac.uk/).  In this technique, a high-intensity, focussed beam of X-rays is shone onto a sample, and optical scattering as a result of diffraction from the atoms in the sample can reveal critical information about characteristic length-scales, crystallisation, film morphology and organisation. We found that the addition of a small quality of a particular process  additive results in a significant increase in perovskite film crystallisation. Most promisingly, such perovskite films also perform even better in PV devices.  We are currently helping to write the work up for publication, and will release full details of the experiments as soon as we can. Analysis of the results and follow up work to identify mechanisms is in progress. The new precursor ink is undergoing further trials and optimisation in our laboratories, and we hope to release this as a new product in 2016.

The photos show the I07 beam-line at Diamond where the GIWAXS experiments were done. The samples are placed in the small box in front of the Pilatus X-ray detector.

 

The Io7 beamline at the Diamond Light Source used to characterise the I101 perovskite inks.
The Io7 beamline at the Diamond Light Source used to characterise the I101 perovskite inks. The Pilatus detector is the grey box visible in the centre.

 

 

The outside of the Diamond Light Source building
The outside of the Diamond Light Source building

 

 

A typical scattering profile of the I101 perovskite thin films as recorded by the Pilatus X-ray detector
A typical scattering profile (plotted on a logarithmic scale) of the I101 perovskite thin films as recorded by the Pilatus X-ray detector