a) PL of a neat film under illumination, b) quasi-Fermi level splitting in a perovskite film for different light intensities and c) the resulting intensity dependent PL emission. d) Using these measurements, we can measure the implied efficiency of perovskite films on glass without making complete devices allowing to understand different loss processes.
Emission and absorption are both fundamental to solar cells and inherently linked via the principals of detail balance and the black body radiation. It also means, a good solar cell must be a good LED! While the quality of a light emitting diode is measured by applying a voltage to the cell and detecting the number of emitted photons (i.e. the electroluminescence), the photoluminescence (PL) is measured by applying light to the cell. The advantage of photoluminescence is that it can be measured on incomplete or partial cells. For example, the neat material, or the neat material in combination with any of the transport layers or the electrodes. PL measurements therefore enable insights into the electro-optical quality of certain parts of the cells that are otherwise not accessible in measurements of complete cells. In principal, this allows to quantify how much non-radiative recombination is caused by each layer of the device. Perovskites are particularly suited for PL characterizations due to their sharp absorption onsets and low exciton binding energies.
The Perovskite group at the University of Potsdam is using these principals to assess the quality of single and multi-junction perovskite cells and has recently demonstrated novel PL characterization techniques. This includes, quasi-Fermi level splitting (or internal voltage) measurements, intensity and voltage dependent PL and the quantification of the efficiency potential of neat perovskite films and partial stacks. Contact us for more information!
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