A Highly Emissive Surface Layer in Mixed-Halide Multication Perovskites.

Area of Science:

• Materials Science
• Photovoltaics
• Optoelectronics

Background:

• Mixed-halide lead perovskites are crucial for photovoltaics and optoelectronics due to tunable bandgaps.
• Understanding their behavior under illumination is key to improving device performance.

Purpose of the Study:

• To investigate the effects of solar-equivalent illumination on the photoluminescence and photoconductance of triple-cation mixed-halide perovskite films.
• To elucidate the mechanisms behind enhanced luminescence and potential limitations.

Main Methods:

• Solution-processed triple-cation mixed-halide (Cs$_{0.06}$ MA$_{0.15}$ FA$_{0.79}$ )Pb(Br$_{0.4}$ I$_{0.6}$ )₃ perovskite films were studied.
• Time- and spectrally resolved photoluminescence measurements were employed under solar-equivalent illumination.

Main Results:

• Illumination induced phase segregation, forming iodide-rich surface sites passivated with PbI$_{2}$.
• Photoexcited charges efficiently transferred to these surface sites, significantly increasing local carrier densities.
• Photoluminescence quantum efficiency rose from 3% to over 45% under illumination.
• Nonradiative Auger recombination became dominant at higher excitation densities due to high surface charge concentrations.

Conclusions:

• Illumination drives beneficial phase segregation in mixed-halide perovskites, enhancing radiative efficiency.
• Controlling charge density and transfer on these surface sites offers a route to highly luminescent films.
• Insights into phase segregation and carrier dynamics are crucial for designing advanced perovskite optoelectronic devices.