Perovskite solar cells (PSCs) are viable sources of efficient and affordable energy that has attracted much interest since their onset in 2009 due to rapidly increasing device power conversion efficiencies (PCEs, currently above 25.6% already). [1] Highquality (poly-)crystalline perovskite films have a combination of desirable properties, mainly high absorption coefficient, high ambipolar charge mobility, and long charge carrier diffusion length. [2] These properties are directly related to the film morphology, stoichiometry, and density of defects in the bulk or at the surface. Hence, to ensure reproducible preparation of PSCs, it is crucial that the perovskite growth during deposition is controllable in a repeatable way independent of batchto-batch purity variations of the precursor salts used. A stable reproducible baseline cell performance is crucial to advance the technology and further optimize the efficiency and stability. Numerous deposition processes are investigated, from solvent-based techniques such as spin coating, blade coating, and solvent engineering to vacuum-based methods, such as thermal vacuum deposition or close space sublimation or even hybrid sequential depositions. [2][3][4][5][6][7][8][9][10][11] Physical vapor deposition (PVD) is a very versatile technique that can be used to grow films of many classes of materials, such as metallic, semiconducting, and insulating films for use in photovoltaics and light-emitting devices, as well as resistors, transparent conductive oxides, corrosion resistant coatings, magnetic films, among many others. This technique is widely used in the optoelectronic/semiconductor industry for being compatible with large area and high throughput, granting high purity and uniformity to the deposited films. [9,[12][13][14][15][16][17] It also allows for the in situ monitoring of the deposition rate using quartz crystal microbalances (QCM), which is important when two precursors are cosublimed and to enable precise thickness control. [12,18] Many research groups have reported on vacuum-deposited perovskites, showing that efficient fully evaporated solar cells are readily achievable. Different perovskite compositions have been prepared ranging from the archetypal MAPbI 3 , requiring the coevaporation of PbI 2 and CH 3 NH 3 I (methylammonium iodide, MAI) in only two sources, [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] to more complex multication multihalide structures that require the coevaporation from three or more precursors. [36][37][38][39][40][41][42][43] There are many examples in the literature of coevaporated MAI-based PSCs with PCEs exceeding 20%. [22,25,[43][44][45][46] However, despite these successful demonstrations, the sublimation control of organic ammonium halides remains a critical factor in achieving reproducibility of the perovskite film in vacuum-processed devices.Many authors have found difficulties in monitoring the MAI sublimation, due to fluctuating deposition rates, [20,22,29,[47][48][49][50][51] or in measuring the thic...
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.
Development of perpendicular magnetic anisotropy (PMA) thin films is a requisite for many applications. In this work, we have illustrated the enhancement of the PMA of Hard (Co)/ Soft (Permalloy, Py) ferromagnetic bilayers by depositing them onto nanoporous anodic alumina membranes with different hole diameters varying in the range between 30 nm and 95 nm. A dramatic change in the hysteresis loops behaviour with hole size, D, and magnetic surface cover ratio parameters has been observed: (1) for samples with small antidot hole diameters, the in-plane (INP) hysteresis loops show single-step magnetic behaviour; (2) for D = 75 nm, the hysteresis loops of Co/Py and Py samples exhibit a multistep magnetic behaviour; (3) a decreasing coercivity in the INP hysteresis loops for antidot arrays samples with D > 75 nm has been detected as a consequence of the reduction of the in-plane magnetic anisotropy and the rising of the out-of-plane component. A crossover of magnetic anisotropy from the in-plane to out-of-plane for bilayer antidot samples has been observed for Co/Py ferromagnetic bilayers, favoured by the interfacial exchange coupling between the two ferromagnetic materials. These findings can be of high interest for the development of novel magnetic sensors and for perpendicular-magnetic recording patterned media based on template-assisted deposition techniques.
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