Light-induced charge transfer at the CH₃NH₃PbI₃/TiO₂ interface—a low-temperature photo-electron paramagnetic resonance assay

Abstract

The performance of organic-inorganic metal halide perovskites-based (MHPs) photovoltaic devices critically depends on the design and material properties of the interface between the light-harvesting MHP layer and the electron transport layer (ETL). Therefore, the detailed insight into the transfer mechanisms of photogenerated carriers at the ETL/MHP interface is of utmost importance. Owing to its high charge mobilities and well-matched band structure with MHPs, titanium dioxide (TiO 2 ) has emerged as the most widely used ETL material in MHPs-based photovoltaic devices. Here, we report a contactless method to directly track the photo-carriers at the ETL/MHP interface using the technique of low-temperature electron paramagnetic resonance (EPR) in combination with in situ illuminations (Photo-EPR). Specifically, we focus on a model nanohybrid material consisting of TiO 2 -based nanowires (TiO 2 NWs) dispersed in the polycrystalline methylammonium lead triiodide (MAPbI 3 ) matrix. Our approach is based on observation of the light-induced decrease in intensity of the EPR signal of paramagnetic Ti 3+ ( = S 1 2) in non-stoichiometric TiO 2 NWs. We associate the diminishment of the EPR signal with the photo-excited electrons that cross the ETL/MHP interface and contribute to the conversion of Ti 3+ states to EPR-silent Ti 2+ states. Overall, we infer that the technique of lowtemperature Photo-EPR is an effective strategy to study the transfer mechanisms of photogenerated carriers at the ETL/MHP interface in MAPbI 3 -based photovoltaic and photoelectronic systems.

Photocatalytic Nanowires‐Based Air Filter: Towards Reusable Protective Masks

“…Therefore, the high dielectric constant of TiO 2 —with its concomitant large charge‐storage capacity—contributes to the enhanced electrostatic precipitation of the droplets on the nonwoven network of TiO 2 NWs. Moreover, the presence of numerous Ti 3+ sites on the surface or TiO 2 NWs, previously reported by us, [ 40 ] is highly favorable for water adsorption, leading to super‐hydrophilicity at the macroscale. [ 41 ] Therefore, the super‐hydrophilicty of TiO 2 NWs‐based filtering materials causes water droplets to adhere and spread on the TiO 2 surface, aiding in filtration.…”

Ultralong Charge Carrier Recombination Time in Methylammonium Lead Halide Perovskites

“…The laser beam light was focused on the top edge of the quartz rod, while the sample was attached (glued) at its bottom notch. This method of excitation is similar to the one presented by Mantulnikovs et al 51 We used two different measurement setups, which served for quasi-steady state (QSS)…”

“…The laser beam light was focused on the top edge of the quartz rod, while the sample was attached (glued) at its bottom notch. This method of excitation is similar to the one presented by Mantulnikovs et al 51 We used two different measurement setups, which served for quasi-steady state (QSS) and time-resolved (TR) microwave photoconductivity measurements. In the case of the QSS approach, the beam of the laser light (473 nm, 50 mW) from a CW fiber-coupled laser (Model MBL-III-473, from CNI Lasers Ltd.) was modulated with a mechanical optical chopper (Model SR540 from Stanford Research Systems, Inc.).…”