Publication date: 17th February 2025
Photoluminescence quantum yield (PLQY) is one of the most significant parameters to determine the optoelectronic quality of semiconducting materials, especially those with applications in solar cells. It is the ratio of emitted photons to absorbed photons and is a direct measure of the efficiency of a material in converting absorbed light into radiative recombination. In perovskites, high PLQY is typically associated with low nonradiative recombination rates, which imply fewer defects and better crystalline quality. This makes PLQY an essential metric for assessing the effectiveness of passivation techniques, tracking material degradation, and optimizing synthesis conditions.
Continuous measurement of PLQY could provide interesting insight into the effect of certain parameters on the perovskite material as well as shed some light on the crystallization process.
The setup for continuous PLQY measurement consists of an integrating sphere—essential for collecting light from all angles and creating a uniform measurement environment through internal diffusion—a light source, and two separate photodiodes for concurrently measuring absorbed and emitted light.
So far, we have investigated perovskite samples with different cation compositions (MA, FA, and MAFA-Cs) and observed a similar light-induced effect on their PLQY when using light intensities comparable to one-sun illumination. During the measurement, PL—and consequently PLQY—initially decreases, most likely due to light-induced heating, as suggested by shifts and broadening in the PL spectrum. However, when measured after a period of rest, the PLQY increases. By repeating this cycle of illumination and cooling, we observed that the final PLQY reached values up to three times higher than the initial measurement. This increase is often accompanied by a narrowing of the PL peak and a redshift (shift to longer wavelengths), further indicating relaxation of non-radiative pathways or trap state passivation.
Although these results are positive—showing an increase in PLQY—they also raise important questions. How long was the sample exposed to light? Was it previously measured? And are the results from different measurements truly comparable?
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