European researchers used a nanosecond pulsed ultraviolet laser to reduce surface defects in perovskite films in solar cells. The result is a significant increase in cell efficiency and stability. The new technology may be particularly suitable for roll-to-roll (R2R) production lines.
“Our work is a proof of concept, and we are consistently working towards advanced results,” said lead co-author Monika Rai. pv magazinepoint out that the proposed approach is solvent-free and industrially scalable.
They used an industrial nanosecond pulsed ultraviolet (UV) laser at two different energy intensities, 160 nJ and 650 nJ, respectively.
They then use scanning electron microscopy (SEM) and X-ray diffraction (XRD) measurements to evaluate the effect of the laser pulse on the film morphology, and found that both intensities lead to a uniform grain size distribution and clear grain boundaries, although the higher intensity also showed some dispersed perovskite grains.
In contrast, the lower intensity laser pulse did not damage the perovskite surface or affect the bulk properties of the perovskite thin film. “There is no detectable difference in binding energy or spectral broadening at low laser energy, suggesting negligible change in the chemical properties of the perovskite surface,” the researchers said. “At high laser energy, the total absorption decreases due to the apparent destruction of the film, as supported by XRD and SEM measurements.”
The team applied the treatment to a solar cell based on triple cesium methylammonium formamidinium (CsMAFA) and found that its efficiency increased from 18.0% to 19.3%, and the stability ability was also improved. “The energy-optimized laser-polished devices show improved open-circuit voltage (VoC) and duty factor due to reduced interfacial recombination losses, releasing the potential of high Voc from similar bandgap perovskites,” they said, adding that the cell achieved a remarkable Voc of 1.21 V -value.
The cell was able to retain approximately 90% of its original efficiency for 1,000 hours, compared to 75% for the reference device that did not use laser treatment.
“This technology may be particularly suitable for roll-to-roll (R2R) production lines,” said co-author Micahel Saliba. pv magazinee.
Details of the approach, laser power fine-tuning and measurement methods are documented in “Light does the right thing: Laser polishing for surface modification of perovskite solar cells”, published ACS Energy Letters. The research team includes researchers from the University of Stuttgart and the Brandenburg University of Technology Cottbus–Senftenberg in Germany, the University of Luxembourg and the University of Valencia in Spain.