Researchers from the University of Regensburg, the University of Basel, and the Ioffe Institute have delved into the spin dynamics of excitons and charge carriers in mixed-cation perovskite semiconductors. Their work, published in the journal Physical Review Materials, offers insights that could help optimize these materials for use in solar cells and other optoelectronic devices.
Perovskite semiconductors have gained significant attention in the energy sector due to their potential to improve the efficiency of solar cells. Mixed-cation perovskites, specifically those with a mix of methylammonium (MA) and formamidinium (FA) cations, have shown promise in enhancing the stability and performance of these devices. However, the impact of these mixed cations on the spin dynamics of excitons and charge carriers has not been fully understood.
The researchers studied the spin dynamics of mixed-cation MA$_{x}$FA$_{1-x}$PbI$_{3}$ perovskite single crystals with varying compositions (x = 0.1, 0.4, and 0.8) at cryogenic temperatures. They used time-resolved photoluminescence to measure the optical spin orientation under nonresonant excitation. They found that the degree of exciton optical orientation was highest (75-80%) for crystals with x = 0.1 and 0.8, but decreased to about 60% for x = 0.4. A similar trend was observed for the carrier spin optical orientation. This reduction in optical orientation is attributed to enhanced scattering of free excitons and carriers due to increased compositional and structural disorder in the alloys.
The researchers also measured the Larmor spin precession in an external magnetic field applied in the Voigt geometry. From this, they evaluated the electron and hole g-factors, which describe the response of the spin to an external magnetic field. They found that the dependence of these g-factors on the band gap energy in MA$_{x}$FA$_{1-x}$PbI$_{3}$ crystals follows a universal trend previously established for lead halide perovskites.
The practical applications of this research for the energy sector are significant. Understanding the spin dynamics of excitons and charge carriers in mixed-cation perovskites can help in the design and optimization of perovskite solar cells. By tailoring the composition of these materials, it may be possible to minimize disorder and enhance the performance of these devices. This work contributes to the ongoing efforts to improve the efficiency and stability of perovskite-based solar cells, bringing us closer to a future of more efficient and sustainable energy solutions.
This article is based on research available at arXiv.