Considerable efforts are being invested into developing new, improved materials for solar cells that are more sustainable and cost-effective than silicon. Metal halide perovskites are the frontrunning materials for the next generation of photovoltaics. These cells, which have a distinctive crystal structure, have attained an efficiency of 25.5 percent – close to conventional silicon cells.
Perovskite cells have a theoretical efficiency of 30.5 percent, but to get closer to this sweet spot, the optoelectronic properties of the materials must be improved. In other words, the semiconductors must not only be able to absorb light, but to emit it highly efficiently as well – a characteristic known as photoluminescence. In order to test a solar cell’s performance, scientists must therefore be able to measure the “photoluminescence quantum efficiency” or (PLQE) of the semiconductors.
A first-of-its-kind model for determining this elusive PLQE has now been developed by researchers at the Institute of Microstructure Technology (IMT) and Light Technology Institute (LTI) at the Karlsruhe Institute of Technology (KIT), with input from the Centre for Advanced Materials (CAM) at the Heidelberg University and the TU Dresden.
“With the help of our model, photoluminescence quantum efficiency under solar irradiation can be determined far more precisely,” says Dr Paul Fassl from IMT in a . “Photon recycling is of high importance. This is the share of photons emitted by the perovskite, which is re-absorbed and re-emitted in the thin films.”
When the model was applied to a perovskite material called methylammonium lead triiodide, for example, it revealed that the PLQ efficiency was actually 12 percent less than previously thought. Through the new process, efficiency losses can now be pinpointed and reduced in the perovskite cells of the future.