• Stevens, Jeremy
• Sienkiewicz, Andrzej
• Kollar, Marton
• Glushkova, Anastasiia
• Rossi, Lidia
• Andričević, Pavao
• Forró, László
• Náfrádi, Bálint
• Bugnon, Philippe
• Szirmai, Péter
• Mantulnikovs, Konstantins
• Horváth, Endre

Abstract

<jats:title>Abstract</jats:title><jats:p>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<jats:sub>2</jats:sub>) 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 <jats:italic>in situ</jats:italic> illuminations (Photo-EPR). Specifically, we focus on a model nanohybrid material consisting of TiO<jats:sub>2</jats:sub>-based nanowires (TiO<jats:sub>2</jats:sub>NWs) dispersed in the polycrystalline methylammonium lead triiodide (MAPbI<jats:sub>3</jats:sub>) matrix. Our approach is based on observation of the light-induced decrease in intensity of the EPR signal of paramagnetic Ti<jats:sup>3+</jats:sup> (<jats:inline-formula><jats:tex-math> <?CDATA ${{S}}=1/2$?> </jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"><mml:mi mathvariant="bold-italic">S</mml:mi><mml:mo>=</mml:mo><mml:mn>1</mml:mn><mml:mrow><mml:mo stretchy="true">/</mml:mo></mml:mrow><mml:mn>2</mml:mn></mml:math><jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="jpphotonab6276ieqn1.gif" xlink:type="simple" /></jats:inline-formula>) in non-stoichiometric TiO<jats:sub>2</jats:sub>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<jats:sup>3+</jats:sup> states to EPR-silent Ti<jats:sup>2+</jats:sup> 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 MAPbI<jats:sub>3</jats:sub>-based photovoltaic and photoelectronic systems.</jats:p>

Topics

• perovskite
• impedance spectroscopy
• titanium
• electron spin resonance spectroscopy
• band structure