The recent sky-rocketing performance of perovskite solar cells has triggered a strong interest in further upgrading the fabrication techniques to meet the scalability requirements of the photovoltaic industry. The integration of vapor-deposition into the solution process in a sequential fashion can boost the uniformity and reproducibility of the perovskite solar cells.Besides, mixed-halide perovskites have exhibited outstanding crystallinity as well as higher stability compared with iodide-only perovskite. An extensive study was carried out to identify a reproducible process leading to highly crystalline perovskite films that when integrated into solar cells exhibited high power conversion efficiency (max. 19.8%). This was achieved by optimizing the deposition rate of the PbI2 layer as well as by inserting small amounts of methylammonium (MA) bromide and chloride salts to the primary MAI salt in the solution-based conversion step. 3The optimum MABr/MAI molar ratio leading to the most efficient and stable solar cells was found to be 0.4. Stabilities were in excess of 90 hours for p-i-n type solar cells. This reproducible approach towards the fabrication of triple halide perovskites using a hybrid vapor-solution method is a promising method towards scalable production techniques.Recently, Rafizadeh et. al. used a hybrid vapor-solution method to fabricate planar MAPI-based devices with 18.9% efficiency in the n-i-p structure 26 . In that work, TiO2 was used as the Supporting Information.XRD, AFM, and, SEM of the PbI2 layer deposited at different rates, device statistical data depending on PbI2 deposition rate, XRD of MAPI-BrCl depending on MACl concentration, the effect of MABr/MAI ratio on the absorbance edge and on the Shockley-Queisser limit and average values of J-V parameters, stability analysis of the devices.
Vacuum processing of multicomponent perovskites is not straightforward, because the number of precursors is in principle limited by the number of available thermal sources. Herein, we present a process which allows increasing the complexity of the formulation of vacuum-deposited lead halide perovskite films by multisource deposition and premixing both inorganic and organic components. We apply it to the preparation of wide-bandgap CsMAFA triple-cation perovskite solar cells, which are found to be efficient but not thermally stable. With the aim of stabilizing the perovskite phase, we add guanidinium (GA + ) to the material formulation and obtained CsMAFAGA quadruple-cation perovskite films with enhanced thermal stability, as observed by X-ray diffraction and rationalized by microstructural analysis. The corresponding solar cells showed similar performance with improved thermal stability. This work paves the way toward the vacuum processing of complex perovskite formulations, with important implications not only for photovoltaics but also for other fields of application.
A series of copper(I) complexes of the type [Cu(HN‐xantphos)(N^N)][PF6] and [Cu(BnN‐xantphos)(N^N)][PF6], in which N^N = bpy, Mebpy, and Me2bpy, HN‐xantphos = 4,6‐bis(diphenylphosphanyl)‐10H‐phenoxazine and BnN‐xantphos = 10‐benzyl‐4,6‐bis(diphenylphosphanyl)‐10H‐phenoxazine is described. The single crystal structures of [Cu(HN‐xantphos)(Mebpy)][PF6] and [Cu(BnN‐xantphos)(Me2bpy)][PF6] confirm the presence of N^N and P^P chelating ligands with the copper(I) atoms in distorted coordination environments. Solution electrochemical and photophysical properties of the BnN‐xantphos‐containing compounds (for which the highest‐occupied molecular orbital is located on the phenoxazine moiety) are reported. The first oxidation of [Cu(BnN‐xantphos)(N^N)][PF6] occurs on the BnN‐xantphos ligand. Time‐dependent density functional theory (TD‐DFT) calculations have been used to analyze the solution absorption spectra of the [Cu(BnN‐xantphos)(N^N)][PF6] compounds. In the solid‐state, the compounds show photoluminescence in the range 518–555 nm for [Cu(HN‐xantphos)(N^N)][PF6] and 520–575 nm for [Cu(BnN‐xantphos)(N^N)][PF6] with a blue‐shift on going from bpy to Mebpy to Me2bpy. [Cu(BnN‐xantphos)(Me2bpy)][PF6] exhibits a solid‐state photoluminescence quantum yield of 55% with an excited state lifetime of 17.4 µs. Bright light‐emitting electrochemical cells are obtained using this complex, and it is shown that the electroluminescence quantum yield can be enhanced by using less conducting hole injection layers.
Narrowband photodetectors (PDs) are sought after for many applications requiring selective spectral response. The most common systems combine optical bandpass filters with broadband photodiodes. This work reports a method to obtain a narrowband response in a perovskite PD by the monolithic integration of a perovskite photoconductor and a perovskite photodiode. The spectral response of the tandem PD is determined by the bandgap energy difference of the two perovskites, and exhibits a full width at half maximum below 85 nm, an external quantum efficiency up to 68% and a high specific detectivity of ≈1012 Jones in reverse bias, enabling the device to detect weak light signals. The absorption profile of the narrowband PD can be tuned by changing the thickness and bandgap of the wide bandgap perovskite absorber.
A general protocol is presented to prepare hybrid magneto-plasmonic Au-PBA nanostructures formed by PBA decorated by different Au nanoparticles.
The development of vacuum‐deposited perovskite materials and devices is partially slowed down by the minor research effort in this direction, due to the high cost of the required research tools. But there is also another factor, thermal co‐deposition in high vacuum involves the simultaneous sublimation of several precursors with an overall deposition rate in the range of few Å s−1. This leads to a deposition time of hours with only a single set of process parameters per batch, hence to a long timeframe to optimize even a single perovskite composition. Here we report the combinatorial vacuum deposition of wide bandgap perovskites using 4 sources and a non‐rotating sample holder. By using small pixel substrates, more than 100 solar cells can be produced with different perovskite absorbers in a single deposition run. The materials are characterized by spatially resolved methods, including optical, morphological, and structural techniques. By fine‐tuning of the deposition rates, the gradient can be altered and the best‐performing formulations in standard depositions with rotation can be reproduced. This is viewed as an approach that can serve as a basis to prototype other compositions, overcoming the current limitations of vacuum deposition as a research tool for perovskite films.
Thin polymeric and small‐molecular‐weight organic semiconductors are widely employed as hole transport layers (HTLs) in perovskite solar cells. To ensure ohmic contact with the electrodes, the use of doping or additional high work function (WF) interlayer is common. In some cases, however, intrinsic organic semiconductors can be used without any additive or buffer layers, although their thickness must be tuned to ensure selective and ohmic hole transport. Herein, the characteristics of thin HTLs in vacuum‐deposited perovskite solar cells are studied, and it is found that only very thin (<5 nm) HTLs readily result in high‐performing devices, as the HTL acts as a WF enhancer while still ensuring selective hole transfer, as suggested by ultraviolet photoemission spectroscopy and Kelvin probe measurements. For thicker films (≥5 nm), a dynamic behavior for consecutive electrical measurements is observed, a phenomenon which is also common to other widely used HTLs. Finally, it is found that despite their glass transition temperature, small‐molecule HTLs lead to thermally unstable solar cells, as opposed to polymeric materials. The origin of the degradation is still not clear, but might be related to chemical reactions/diffusion at the HTL/perovskite interface, in detriment of the device stability.
Wide bandgap perovskites are being widely studied in view of their potential applications in tandem devices and other semitransparent photovoltaics. Vacuum deposition of perovskite thin films is advantageous as it allows the fabrication of multilayer devices, fine control over thickness and purity, and it can be upscaled to meet production needs. However, the vacuum processing of multicomponent perovskites (typically used to achieve wide bandgaps) is not straightforward, because one needs to simultaneously control several thermal sources during the deposition. Here a simplified dual-source vacuum deposition method to obtain wide bandgap perovskite films is shown. The solar cells obtained with these materials have similar or even larger efficiency as those including multiple A-cations, but are much more thermally stable, up to 3500 h at 85 °C for a perovskite with a bandgap of 1.64 eV. With optimized thickness, record efficiency of >19% and semitransparent devices with stabilized power output in excess of 17% are achieved.
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