Success story of organometallic perovskite absorber layers

Organometallic perovskite absorber layers are a new material class for solar cells. In a decade of research and testing, their efficiency jumpred from three per cent to over twenty percent. A team headed by Prof. Dr. Dieter Neher at the University of Potsdam and Dr. Thomas Unold at HZB has succeeded in identifying the loss processes in perovskite solar cells that restrict maximum efficiency.

At certain defects in the crystal lattice of the perovskite layer, charge carriers are  released by sunlight can recombine again and be lost. Whether these defects were located within the perovskite layer or at the interface between the perovskite layer and the transport layer was unclear until now. To determine this, the scientists used photoluminescence techniques. Using laser light, they excited the square-centimetre-sized perovskite layer and detected where and when the material emitted light based on the excitation. "This measurement method at our lab is so precise, we can determine the exact number of photons that have been emitted," explains Unold. The energy of the emitted photons was recorded, analyzed, and was on hyperspectral CCD camera. "In this way, 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," reports Unold. This insight can improve perovskite solar cells. For example, by means of intermediate layers that have a positive effect or through modified fabrication methods. The group led by Prof. Dr. Dieter Neher and Dr. Martin Stolterfoht at the University of Potsdam has succeeded in reducing interfacial recombination. This dramatically increases efficiency of 1cm 2sized perovskite solar cells to well over 20 percent. 

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