Enhancing Two-Dimensional Electronic Spectroscopy for Layered Halide Perovskites

The photophysics of layered halide perovskites reveals a rich disposition of exciton behavior. Two-dimensional electronic spectroscopy (2DES) is a powerful technique for investigating such excitonic interactions and dynamics. However, the wide spectral range of layered perovskites presents a challenge in studies utilizing conventional 2DES setups to simultaneously probe their interacting excitonic states. Herein, we put forward a versatile 2DES setup employing a hollow-core fiber compressor (HCFC) to generate stable and optimized broadband laser pulses (6 fs) covering a spectral range of 500–950 nm. 2D spectra with high temporal and spectral resolution are possible even with a pulse-shaper-based commercial 2DES setup. Application to a representative two-phase Ruddlesden–Popper perovskite thin film reveals well-defined signals at the diagonal and off-diagonal positions, indicative of exciton delocalization between the two transitions. Our straightforward modification of a commercial 2DES setup extends its capabilities to investigate the large family of layered perovskites currently under intense scrutiny in the development of perovskite optoelectronics

High-Performance Semi-Transparent Perovskite Solar Cells with over 22% Visible Transparency: Pushing the Limit through MXene Interface Engineering

Semi-transparent perovskite solar cells (ST-PSCs) have attracted enormous attention recently due to their potential in building-integrated photovoltaic. To obtain adequate average visible transmittance (AVT), a thin perovskite is commonly employed in ST-PSCs. While the thinner perovskite layer has higher transparency, its light absorption efficiency is reduced, and the device shows lower power conversion efficiency (PCE). In this work, a combination of high-quality transparent conducting layers and surface engineering using 2D-MXene results in a superior PCE. In situ high-temperature X-ray diffraction provides direct evidence that the MXene interlayer retards the perovskite crystallization process and leads to larger perovskite grains with fewer grain boundaries, which are favorable for carrier transport. The interfacial carrier recombination is decreased due to fewer defects in the perovskite. Consequently, the current density of the devices with MXene increased significantly. Also, optimized indium tin oxide provides appreciable transparency and conductivity as the top electrode. The semi-transparent device with a PCE of 14.78% and AVT of over 26.7% (400–800 nm) was successfully obtained, outperforming most reported ST-PSCs. The unencapsulated device maintained 85.58% of its original efficiency after over 1000 h under ambient conditions. This work provides a new strategy to prepare high-efficiency ST-PSCs with remarkable AVT and extended stability