From pv magazine Germany
Perovskite solar cells can theoretically achieve a power conversion efficiency of around 30.5%. In order to approach these efficiency levels, however, the optoelectronic quality of perovskite semiconductors must increase.
In principle, materials suitable for photovoltaics should not only absorb light but also emit it again efficiently — a process known as photoluminescence. The associated measurement parameter, called photoluminescence quantum yield, is ideally suited to determine the quality of the perovskite semiconductor.
A group of researchers at Germany's Karlsruhe Institute of Technology (KIT), the University of Heidelberg and the Technical University of Dresden developed a new model with which the photoluminescence quantum yield of perovskite layers can be reliably and precisely determined for the first time.
In the paper Revealing the internal luminescence quantum efficiency of perovskite films via accurate quantification of photon recycling, published in Matter, the research team shows how the novel method they developed is able to determine the photoluminescence quantum yield under solar irradiation conditions more precisely than previously assumed.
“It depends on the photon recycling, that is, the proportion of the photons emitted by the perovskite that is reabsorbed within the thin layers and re-emitted again, KIT scientist Paul Fassl explained.
The researchers applied their model to methylammonium lead triiodide (CH3NH3PbI3), one of the perovskites with the highest photoluminescence quantum yield. This was previously estimated at around 90%, but the model calculations made by the German academics found this value to actually be around 78%.
According to the scientists, the previous estimates had not adequately taken into account the effect of light scattering, which means that these estimates underestimated the probability that photons — the quanta of light energy — escape from the layer before they are reabsorbed.
“Our results show that the potential for optimizing these materials is significantly higher than previously assumed,” said Ulrich W. Paetzold, head of the Advanced Optics and Materials for Next Generation Photovoltaics group at KIT's Institute of Microstructure Technology (IMT).
The research team provides an open-source application with which the photoluminescence quantum yield of various perovskite materials can be calculated using their model.
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