The central role of ligands in electron transfer from perovskite nanocrystals
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The central role of ligands in electron transfer from perovskite nanocrystals Alberto Privitera1, Marcello Righetto1, Renato Bozio1, Lorenzo Franco1 1 Department of Chemical Science and U.R. INSTM, University of Padova, Via Marzolo 1, I35131 Padova, Italy ABSTRACT The nanoscale miniaturization of hybrid organic-inorganic perovskite has given rise to new functionalities, but the full understanding of the multifaceted properties of perovskite nanostructures is still incomplete. Using a combination of optical and magnetic resonance (EPR) spectroscopies, we focused our investigation on the photoinduced electron transfer process taking place in perovskite nanocrystals blended with the fullerene derivative PCBM. In particular we analyzed the different effect of two types of nanocrystal ligands, namely octylamine and oleylamine, on the photoinduced processes. The electron transfer process resulted in efficient fluorescence quenching in a mixed solution and in the formation of charges (PCBM anions) detected by EPR in the blends. Both the optical and EPR techniques revealed a stronger effect when the shorter ligand is present. Finally, pulsed EPR demonstrated the stabilization of the photogenerated charges in proximity of perovskite nanocrystals. INTRODUCTION Hybrid organic/inorganic perovskites have recently attracted immense scientific interest due to the outstanding upsurge in their photovoltaic performances in a remarkably short time frame.[1, 2] The key to this success is the combination of the advantages coming from the organic (flexibility, easy solution processability, low-cost) and inorganic (excellent charge carrier mobility, small exciton binding energy, large absorption coefficient) constituents.[3] In order to enhance their coupling with electromagnetic radiation, exploiting quantum size effect, their miniaturization down to nanoscale was pursued.[4-7] The synthesis of colloidally stable perovskite nanocrystals disclosed a wide variety of new physical properties. In particular, the high photoluminescence quantum yield (90%) and the strong quantum confinement effect demonstrated that perovskite NCs are excellent materials for light emitting devices.[8-10] In order to unravel new functionalities and new applications, it is important not only to focus the attention on the synthesis and the technological development of these materials, but also on the interfacial energy and charge dynamics. In the past, the knowledge of interfacial charge transfer (CT) processes within the context of semiconducting Quantum Dots (QDs) allowed to create and optimize a multitude of opto-electronic devices, so it is reasonable to predict that analogous results can be reached for perovskites NCs.[11] In addition, despite the fact that research efforts concerning interfacial CT in these materials are limited so far, highly promising results have been already reported. In particular, Ahmed et al. investigated the effect of the shape of hybrid perovskite NCs on interfacial CT in presence of tetracyanoethylene (molecular acceptor) and a dram
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