How defects affect to PLQY?

28 February 2024 1 2K Report

Is there a difference in PLQY between direct transition type semiconductors and indirect transition type semiconductors? I am curious about how defects affect PLQY.

Also, what is the difference between Br defect concentration and Cl defect concentration for PLQY?

Len Leonid Mizrah

Dear Jun Park ,

Let’s delve into the semiconductor properties and their impact on photoluminescence quantum yield (PLQY).

Direct vs. Indirect Band Gap Semiconductors: The band gap represents the minimum energy difference between the top of the valence band and the bottom of the conduction band in a semiconductor. In a direct band gap semiconductor, the top of the valence band and the bottom of the conduction band occur at the same value of momentum. This means that an electron can directly emit a photon when transitioning from the conduction band to the valence band. In an indirect band gap semiconductor, the maximum energy of the valence band occurs at a different value of momentum compared to the minimum energy in the conduction band. Here, an electron must interact with a lattice vibration (a phonon) to either gain or lose momentum during the transition. The difference between direct and indirect band gap semiconductors is most important in optical devices. In direct band gap semiconductors, photons can easily produce electron-hole pairs, while in indirect band gap semiconductors, the process is slower due to the additional momentum change required 1.

Defects and PLQY: Defects play a crucial role in determining the PLQY of semiconductors. Non-radiative recombination losses due to defects can limit the efficiency of light-emitting devices. At low temperatures, defects are frozen out, reducing non-radiative recombination. However, at elevated temperatures, fluctuating defect concentrations can lead to reversible PL intensity loss 2. Defects can act as efficient quenchers, affecting the PLQY. Even a small concentration of such quenchers can substantially reduce the PLQY 3.

Br Defect Concentration vs. Cl Defect Concentration: In perovskite light-emitting diodes (PeLEDs), halide perovskites (such as CsPbBrCl) are promising materials. Chloride vacancies (VCl) in mixed halide compositions (CsPbBrxCl3−x) can lead to lower PLQYs (10-25%) compared to pure CsPbBr or CsPbI nanocrystals (PLQYs over 90%)

The presence of Br defects (bromine-related) or I defects (iodine-related) can significantly impact the PLQY in these materials.

In summary, defects influence PLQY, and understanding their behavior is essential for optimizing semiconductor devices. Researchers continue to explore ways to suppress non-radiative recombination and enhance efficiency in light-emitting devices.

You

Is there a difference in PLQY between direct transition type semiconductors and indirect transition type semiconductors? I am curious about how defects affect PLQY. Also, what is the difference between Br defect concentration and Cl defect concentration for PLQY?

Let’s explore the fascinating world of semiconductor properties and their impact on photoluminescence quantum yield (PLQY).

Defects and PLQY: Defects play a crucial role in determining the PLQY of semiconductors. Non-radiative recombination losses due to defects can limit the efficiency of light-emitting devices. At low temperatures, defects are frozen out, reducing non-radiative recombination. However, at elevated temperatures, fluctuating defect concentrations can lead to reversible PL intensity loss 1. Defects can act as efficient quenchers, affecting the PLQY. Even a small concentration of such quenchers can substantially reduce the PLQY 2.

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