German scientists observe perovskite defects, push higher cell efficiencies

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Scientists in Germany developed a technique using high precision photoluminescence to observe a perovskite solar cell; and detect where the material emits light in response to a laser light source. With this technique, the scientists were able to determine which areas and defects caused the biggest efficiency losses in the planar pin-type perovskite cells they worked with.

The results of the study ‘Visualization and suppression of interfacial recombination for high efficiency large-area pin perovskite solar cells’, published in the journal, Nature Energy, show that the interface between the perovskite absorber and the charge transport layers was responsible for a significant percentage of losses.

“This measurement method at our lab is so precise, we can determine the exact number of photons that have been emitted,” explains Thomas Unold, Deputy Head of HZB’s Structure and Dynamics of Energy Materials Department. “We were able to calculate the losses at every point of the cell and thereby determine that the most harmful defects are located at the interfaces between the perovskite absorber layer and the charge transport layers.”

Armed with this new information, the team was able to develop 1 cm² perovskite cells with 19.83% certified efficiency, stabilized power output, a high VOC (1.17 V) and record fill factor (>81%). This was achieved by inserting ultra thin layers between the two, leading to substantial loss reduction at both the p and n contacts.

The researchers also state that this method allowed them to produce cells with efficiencies higher than 20%, and that modified fabrication methods could provide another solution to the problem observed.