The development of multidimensional heterostructure (2D/3D) lead halide perovskites has emerged as an effective approach to enhancing the efficiency and long-term stability of perovskite solar cells (PSCs). However, a fundamental understanding of the working mechanisms, such as carrier extraction, and carrier transfer dynamics in the multidimensional perovskites heterostructures remains elusive. Here, we observe the ultrafast carrier extraction in highly efficient 2D/ 3D bilayer PSCs (power conversion efficiency of 21.12%) via femtosecond time-resolved pump−probe transient absorption spectroscopy (TAS). Notably, the formation of quasi-equilibrium states resulting in a subband absorption feature with an ultrafast lifetime of 440 fs was observed, and this feature is found only in 2D/3D perovskite heterostructure. The short-lived feature gives rise to the local electric-field-induced electroabsorption, resulting in an enhanced power conversion efficiency in 2D/3D PSCs. These findings can help comprehend the advanced working mechanism of highly efficient solar cells and other 2D/3D bilayer perovskite-based optoelectronic devices.

This study presents a comprehensive analysis of the structural and optical properties of an InGaN-based red micro-LED with a high density of V-shaped pits, offering insights for enhancing emission efficiency. The presence of V-shaped pits is considered advantageous in reducing non-radiative recombination. Furthermore, to systematically investigate the properties of localized states, we conducted temperature-dependent photoluminescence (PL). The results of PL measurements indicate that deep localization in the red double quantum wells can limit carrier escape and improve radiation efficiency. Through a detailed analysis of these results, we extensively investigated the direct impact of epitaxial growth on the efficiency of InGaN red micro-LEDs, thereby laying the foundation for improving efficiency in InGaN-based red micro-LEDs.

Titanium nitride is a refractory material with excellent thermal and mechanical stabilities as well as optical and plasmonic properties in the visible and near-infrared (NIR) regions. Alloying different concentrations of aluminum element in TiN can not only change the dielectric properties from metallic to dielectric but also tune the epsilon-near-zero wavelength (λENZ) over a wide spectral range. Understanding the role of Al in the transient optical responses of Ti1–x Al x N under femtosecond excitation is crucial for optoelectronic, photovoltaic, and photothermal applications. Recently, the electron–phonon (e–ph) coupling rate and time of TiN have been a controversial issue, and moreover, little is known about the transient optical properties of Ti1–x Al x N. In this work, the broadband transient reflectance of highly crystalline Ti1–x Al x N epitaxial films with various Al concentrations (0 ≤ x ≤ 0.67) is investigated by an ultrafast pump–probe experiment. With increasing Al concentration, the optical absorption in the visible to near-infrared region is drastically increased in the Ti1–x Al x N films, showing great potential to serve as an efficient absorbing layer for photovoltaic cells. From the carrier dynamics studies, we found that TiN undergoes wavelength-dependent e–ph coupling processes with distinctly different lifetimes: sub-picosecond (≤0.2 ps) in a narrow spectral region near λENZ and a few tens of picoseconds in the metallic region, followed by a very long heat dissipation process on the nanosecond timescale. As for Ti1–x Al x N, the spectral region where the ultrafast e–ph coupling occurs is extended to the whole visible range. While ultrafast and strong e–ph coupling is advantageous in hot carrier engineering applications, prolonged preservation of heat in the lattice for a nanosecond makes TiN and TiAlN emerging photothermal materials with high conversion efficiency.

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