Charge Transfer and Retention in 2D Passivated Perovskite-C Systems.

2D perovskites and organic ligands are often implemented as passivating interlayers in perovskite solar cells. Herein, five such passivates are evaluated by using time-resolved spectroscopy to study the carrier dynamics at the perovskite-C interface. The impact of passivation on factors such as charge transfer rate, charge retention in the acceptor layers, surface recombination, and uniformity are mapped onto the solar cell performance.

Contactless analysis of surface passivation and charge transfer at the TiO-Si interface.

Transition metal oxides are pivotal in enhancing surface passivation and facilitating charge transfer (CT) in silicon based photonic devices, improving their efficacy and affordability through interfacial engineering. This study investigates TiO/Si heterojunctions prepared by atomic layer deposition (ALD) with different pre-ALD chemical and post-ALD thermal treatments, exploring their influence on the surface passivation and the correlation with the CT at the TiO-Si interface. Surface passivation quality is evaluated by the photoconductance decay method to study the effective carrier lifetime, while CT from Si to TiO is examined by transient reflectance spectroscopy.

Transient Absorption Spectroscopy of Films: Impact of Refractive Index.

Transient absorption spectroscopy is a powerful technique to study the photoinduced phenomena in a wide range of states from solutions to solid film samples. It was designed and developed based on photoinduced absorption changes or that photoexcitation triggers a chain of reactions with intermediate states or reaction steps with presumably different absorption spectra. However, according to general electromagnetic theory, any change in the absorption properties of a medium is accompanied by a change in the refractive properties.

Effect of Single-Crystal TiO/Perovskite Band Alignment on the Kinetics of Electron Extraction.

The kinetics of electron extraction at the electron transfer layer/perovskite interface strongly affects the efficiency of a perovskite solar cell. By combining transient absorption and time-resolved photoluminescence spectroscopy, the electron extraction process between FACsPb(IBr) and TiO single crystals with different orientations of (100), (110), and (111) were probed from subpicosecond to several hundred nanoseconds. It was revealed that the band alignment between the constituents influenced the relative electron extraction process.

Enhancing the Microstructure of Perovskite-Inspired Cu-Ag-Bi-I Absorber for Efficient Indoor Photovoltaics.

Lead-free perovskite-inspired materials (PIMs) are gaining attention in optoelectronics due to their low toxicity and inherent air stability. Their wide bandgaps (≈2 eV) make them ideal for indoor light harvesting. However, the investigation of PIMs for indoor photovoltaics (IPVs) is still in its infancy.

There is plenty of room at the top: generation of hot charge carriers and their applications in perovskite and other semiconductor-based optoelectronic devices.

Hot charge carriers (HC) are photoexcited electrons and holes that exist in nonequilibrium high-energy states of photoactive materials. Prolonged cooling time and rapid extraction are the current challenges for the development of future innovative HC-based optoelectronic devices, such as HC solar cells (HCSCs), hot energy transistors (HETs), HC photocatalytic reactors, and lasing devices. Based on a thorough analysis of the basic mechanisms of HC generation, thermalization, and cooling dynamics, this review outlines the various possible strategies to delay the HC cooling as well as to speed up their extraction.

B-Site Co-Alloying with Germanium Improves the Efficiency and Stability of All-Inorganic Tin-Based Perovskite Nanocrystal Solar Cells.

Colloidal lead-free perovskite nanocrystals have recently received extensive attention because of their facile synthesis, the outstanding size-tunable optoelectronic properties, and less or no toxicity in their commercial applications. Tin (Sn) has so far led to the most efficient lead-free solar cells, yet showing highly unstable characteristics in ambient conditions. Here, we propose the synthesis of all-inorganic mixture Sn-Ge perovskite nanocrystals, demonstrating the role of Ge in stabilizing Sn cation while enhancing the optical and photophysical properties.

Monitoring Charge Carrier Diffusion across a Perovskite Film with Transient Absorption Spectroscopy.

We have developed a new noninvasive optical method for monitoring charge carrier diffusion and mobility in semiconductor thin films in the direction perpendicular to the surface which is most relevant for devices. The method is based on standard transient absorption measurements carried out in reflectance and transmittance modes at wavelengths below the band gap where the transient response is mainly determined by the change in refractive index, which in turn depends on the distribution of photogenerated carriers across the film. This distribution is initially inhomogeneous because of absorption at the excitation wavelength and becomes uniform over time via diffusion.

Refractive index change dominates the transient absorption response of metal halide perovskite thin films in the near infrared.

Perovskites have lately attracted a lot of attention as promising materials for the next-generation of efficient, low-cost, and solution processable optoelectronics. Their complex transient photophysics, in time scales ranging from femtoseconds to seconds, have been widely investigated. However, in most of the reported works the spectral window of ultrafast transient absorption (TA) spectroscopy of perovskite films is limited to the visible region, hence missing crucial information coming from the near-infrared (NIR).