Hybrid lead halide perovskites are promising materials for future photovoltaics applications.Their spectral response can be readily tuned by controlling the halide composition, while their stability is strongly dependent on the film morphology and on the type of organic cation used.Mixed cation and mixed halide systems have led to the most efficient and stable perovskite solar cells reported, so far prepared exclusively by solution-processing. This might be due to the technical difficulties associated with the vacuum deposition from multiple thermal sources, requiring a high level of control over the deposition rate of each precursor during the film formation. In this report, we use multiple sources (3 and 4) thermal vacuum deposition to prepare for the first time multi-cations/anions perovskite compounds. These thin-film absorbers were implemented into fully vacuum deposited solar cells using doped organic semiconductors.A maximum power conversion efficiency (PCE) of 16 % was obtained, with promising device stability. We highlight the importance of the control over the film morphology, which differs substantially when these compounds are vacuum processed. Avenues to improve the
Herein, [Cu(P^P)(N^N)][PF6] complexes (P^P=bis[2‐(diphenylphosphino)phenyl]ether (POP) or 4,5‐bis(diphenylphosphino)‐9,9‐dimethylxanthene (xantphos); N^N=CF3‐substituted 2,2′‐bipyridines (6,6′‐(CF3)2bpy, 6‐CF3bpy, 5,5′‐(CF3)2bpy, 4,4′‐(CF3)2bpy, 6,6′‐Me2‐4,4′‐(CF3)2bpy)) are reported. The effects of CF3 substitution on their structure as well as their electrochemical and photophysical properties are also presented. The HOMO–LUMO gap was tuned by the N^N ligand; the largest redshift in the metal‐to‐ligand charge transfer (MLCT) band was for [Cu(P^P){5,5′‐(CF3)2bpy}][PF6]. In solution, the compounds are weak yellow to red emitters. The emission properties depend on the substitution pattern, but this cannot be explained by simple electronic arguments. Among powders, [Cu(xantphos){4,4′‐(CF3)2bpy}][PF6] has the highest photoluminescence quantum yield (PLQY; 50.3 %) with an emission lifetime of 12 μs. Compared to 298 K solution behavior, excited‐state lifetimes became longer in frozen Me‐THF (77 K; THF=tetrahydrofuran), thus indicating thermally activated delayed fluorescence (TADF). Time‐dependent (TD)‐DFT calculations show that the energy gap between the lowest‐energy singlet and triplet excited states (0.12–0.20 eV) permits TADF. Light‐emitting electrochemical cells (LECs) with [Cu(POP)+(6‐CF3bpy)][PF6], [Cu(xantphos)(6‐CF3bpy)][PF6], or [Cu(xantphos){6,6′‐Me2‐4,4′‐(CF3)2bpy}][PF6] emit yellow electroluminescence. The LEC with [Cu(xantphos){6,6′‐Me2‐4,4′‐(CF3)2bpy}][PF6] had the fastest turn‐on time (8 min), and the LEC with the longest lifetime (t1/2=31 h) contained [Cu(xantphos)(6‐CF3bpy)][PF6]; these LECs reached maximum luminances of 131 and 109 cd m−2, respectively.
Low-dimensional (quasi-) 2D perovskites are being extensively studied in order to enhance the stability and the open-circuit voltage of perovskite solar cells. Up to no, thin 2D perovskite layers on the surface and/or at the grain boundaries of 3D perovskite have been deposited solely by solution processing, leading to unavoidable intermixing between the two phases. In this work, we report the fabrication of 2D/3D/2D perovskite heterostructures by dual source vacuum deposition, with the aim of studying the interaction between the 3D and 2D phases as well as the charge transport properties of 2D perovskites in neat 2D/3D interfaces. Unlike what normally observed in solution-processed 3D/2D systems, we found a reduced charge transport with no direct evidence of surface passivation. This is likely due to a non-favorable orientation of the 2D perovskite with respect to the MAPI and to the formation of 2D phases with very low dimensionality (virtually pure 2D).
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