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 (TiO2) 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 TiO2-based nanowires (TiO2NWs) dispersed in the polycrystalline methylammonium lead triiodide (MAPbI3) matrix. Our approach is based on observation of the light-induced decrease in intensity of the EPR signal of paramagnetic Ti3+ () in non-stoichiometric TiO2NWs. 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 Ti3+ states to EPR-silent Ti2+ states. Overall, we infer that the technique of low-temperature Photo-EPR is an effective strategy to study the transfer mechanisms of photogenerated carriers at the ETL/MHP interface in MAPbI3-based photovoltaic and photoelectronic systems.
Highlights
Organic–inorganic metal halide perovskites (MHPs) have attracted considerable attention in various domains of optoelectronics, including light emission, sensing and photovoltaics, due to their excellent photophysical properties, such as high light absorption coefficient, technologicallytunable bandgap, absence of deep trap states within the bandgap, high charge mobility and long diffusion lengths as well as excellent photoluminescence quantum yield.Such a variety of attractive properties of MHPs accompanied by their low-cost solution processability, sparked the interest to use these materials in a large number of optoelectronic systems [2, 3]
We demonstrate that a combination of the low-temperature Photo-electron paramagnetic resonance (EPR) with light modulation and lock-in detection allows one to gain additional insight into the temporal evolution of the photo-excited carriers at the MHP/electron transport layer (ETL) interface
MAPbI3/blue-TiO2 nanowires (TiO2NWs)-based visible light photodetector To prove the concept of enhanced light-induced charge transfer at the MAPbI3/blue-TiO2NWs interface, we designed a visible light photodetector
Summary
Organic–inorganic metal halide perovskites (MHPs) have attracted considerable attention in various domains of optoelectronics, including light emission, sensing and photovoltaics (see [1] and references therein), due to their excellent photophysical properties, such as high light absorption coefficient, technologicallytunable bandgap, absence of deep trap states within the bandgap, high charge mobility and long diffusion lengths as well as excellent photoluminescence quantum yield Such a variety of attractive properties of MHPs accompanied by their low-cost solution processability, sparked the interest to use these materials in a large number of optoelectronic systems [2, 3]. Due to better engineering of the electron and hole transport layers (hereinafter ETLs and HTLs), the charge extraction from MHPs has been significantly improved
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