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Bifacial perovskite solar cells (Bi-PSCs) require thick perovskite layers to sufficiently absorb higher wavelength light. Also, it is critical to know which electrode (top or bottom) can more efficiently harvest the direct incident solar irradiance. Here, fully vacuum-deposited Bi-PSCs are reported with perovskite layer thicknesses ranging from ∼720 nm to 1.3 μm. With an optimized ITO top-electrode, the Bi-PSCs generated higher current density under top-illumination by >1 mA/cm 2 , attaining the highest value of 24.98 mA/cm 2 . The best Bi-PSC exhibited an efficiency of 19.6% under top-illumination and 18.71% under bottom-illumination, resulting in a high bifaciality factor of ∼0.95. Furthermore, even after employing cover glass encapsulation on the top-electrode, the Bi-PSCs still produced higher current density from top-illumination. Upon bifacial illumination using simulated 1-Sun light as the main illumination and a white LED light albedo of ∼0.21, the champion Bi-PSC demonstrated a current density value of ∼30.00 mA/cm 2 ., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

The CsPbI 3 perovskite has a suitable bandgap (≈1.7 eV) for application in tandem solar cells. One challenge for this compound is that the semiconducting perovskite phase is not stable at room temperature, when it tends to form a yellow nonperovskite phase with a bandgap of approximately 2.8 eV. Therefore, many reports have been focused on the stabilization of the CsPbI 3 black perovskite phase through the use of additives during solution processing. Vacuum deposited CsPbI 3 has been seldom reported, as in this case, the insertion of stabilizing agents is more challenging. In this work, we demonstrate the vacuum processing of CsPbI 3 perovskite films at room temperature, obtained by incorporating dimethylammonium iodide by cosublimation with CsI and PbI 2 . As-prepared films were applied in planar solar cells, leading to an average power conversion efficiency (PCE) exceeding 12%. In order to improve the device performance, we introduced a third A-site cation (methylammonium) in a four-source deposition process. This pure iodide formulation can be used in wide bandgap solar cells with a PCE up to 14.8%., Competing Interests: The authors declare no competing financial interest., (© 2023 American Chemical Society.)

Coevaporation of perovskite films allows for a fine control over the material stoichiometry and thickness but is typically slow, leading to several-hour processes to obtain thick films required for photovoltaic applications. In this work, we demonstrate the coevaporation of perovskite layers using faster deposition rates, obtaining 1 μm thick films in approximately 50 min. We observed distinct structural properties and obtained devices with efficiency exceeding 19%, demonstrating the relevance of this deposition process from a material perspective and also in view of potential industrialization., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Electron transport layers (ETL) based on tin(IV) oxide (SnO 2 ) are recurrently employed in perovskite solar cells (PSCs) by many deposition techniques. Pulsed laser deposition (PLD) offers a few advantages for the fabrication of such layers, such as being compatible with large scale, patternable, and allowing deposition at fast rates. However, a precise understanding of how the deposition parameters can affect the SnO 2 film, and as a consequence the solar cell performance, is needed. Herein, we use a PLD tool equipped with a droplet trap to minimize the number of excess particles (originated from debris) reaching the substrate, and we show how to control the PLD chamber pressure to obtain surfaces with very low roughness and how the concentration of oxygen in the background gas can affect the number of oxygen vacancies in the film. Using optimized deposition conditions, we obtained solar cells in the n-i-p configuration employing methylammonium lead iodide perovskite as the absorber layer with power conversion efficiencies exceeding 18% and identical performance to devices having the more typical atomic layer deposited SnO 2 ETL.

Perovskite/perovskite tandem solar cells have recently exceeded the record power conversion efficiency (PCE) of single-junction perovskite solar cells. They are typically built in the superstrate configuration, in which the device is illuminated from the substrate side. This limits the fabrication of the solar cell to transparent substrates, typically glass coated with a transparent conductive oxide (TCO), and adds constraints because the first subcell that is deposited on the substrate must contain the wide-bandgap perovskite. However, devices in the substrate configuration could potentially be fabricated on a large variety of opaque and inexpensive substrates, such as plastic and metal foils. Importantly, in the substrate configuration the narrow-bandgap subcell is deposited first, which allows for more freedom in the device design. In this work, we report perovskite/perovskite tandem solar cells fabricated in the substrate configuration. As the substrate we use TCO-coated glass on which a solution-processed narrow-bandgap perovskite solar cell is deposited. All of the other layers are then processed using vacuum sublimation, starting with the charge recombination layers, then the wide-bandgap perovskite subcell, and finishing with the transparent top TCO electrode. Proof-of-concept tandem solar cells show a maximum PCE of 20%, which is still moderate compared to those of best-in-class devices realized in the superstrate configuration yet higher than those of the corresponding single-junction devices in the substrate configuration. As both the top and bottom electrodes are semitransparent, these devices also have the potential to be used as bifacial tandem solar cells., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

Organically modified mesoporous silica nanoparticles (MSNs) containing Ir complexes (Ir1, Ir2 and Ir3) were successfully synthesized. These Ir-entrapped MCM41-COOH nanoparticles have shown relevant photophysical characteristics including high efficiency in the photoproduction and delivery of singlet oxygen ( 1 O 2 ), which is particularly promising for photodynamic therapy (PDT) applications. In vitro tests have evidenced that complex@MCM41-COOH are able to reduce cell proliferation after 10 min of blue-light irradiation in Hep-G2 liver cancer cells., Competing Interests: Declaration of Competing Interest There are no conflicts of interest to declare., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Hole transport layers (HTLs) are of fundamental importance in perovskite solar cells (PSCs), as they must ensure an efficient and selective hole extraction, and ohmic charge transfer to the corresponding electrodes. In p-i-n solar cells, the ITO/HTL is usually not ohmic, and an additional interlayer such as MoO 3 is usually placed in between the two materials by vacuum sublimation. In this work, we evaluated the properties of the MoO 3 /TaTm (TaTm is the HTL N4,N4,N4″,N4″-tetra([1,1'-biphenyl]-4-yl)-[1,1':4',1″-terphenyl]-4,4″-diamine) hole extraction interface by selectively annealing either MoO 3 (prior to the deposition of TaTm) or the bilayer MoO 3 /TaTm (without pre-treatment on the MoO 3 ), at temperature ranging from 60 to 200°C. We then used these p-contacts for the fabrication of a large batch of fully vacuum deposited PSCs, using methylammonium lead iodide as the active layer. We show that annealing the MoO 3 /TaTm bilayers at high temperature is crucial to obtain high rectification with low non-radiative recombination, due to an increase of the electrode work function and the formation of an ohmic interface with TaTm., (Copyright © 2020 Babaei, Zanoni, Gil-Escrig, Pérez-del-Rey, Boix, Sessolo and Bolink.)

A variety of experiments on vacuum-deposited methylammonium lead iodide perovskite solar cells are presented, including JV curves with different scan rates, light intensity-dependent open-circuit voltage, impedance spectra, intensity-modulated photocurrent spectra, transient photocurrents, and transient voltage step responses. All these experimental data sets are successfully reproduced by a charge drift-diffusion simulation model incorporating mobile ions and charge traps using a single set of parameters. While previous modeling studies focused on a single experimental technique, we combine steady-state, transient, and frequency-domain simulations and measurements. Our study is an important step toward quantitative simulation of perovskite solar cells, leading to a deeper understanding of the physical effects in these materials. The analysis of the transient current upon voltage turn-on in the dark reveals that the charge injection properties of the interfaces are triggered by the accumulation of mobile ionic defects. We show that the current rise of voltage step experiments allow for conclusions about the recombination at the interface. Whether one or two mobile ionic species are used in the model has only a minor influence on the observed effects. A delayed current rise observed upon reversing the bias from +3 to -3 V in the dark cannot be reproduced yet by our drift-diffusion model. We speculate that a reversible chemical reaction of mobile ions with the contact material may be the cause of this effect, thus requiring a future model extension. A parameter variation is performed in order to understand the performance-limiting factors of the device under investigation.

In the search for understanding and improving the luminescence of optical materials based on Ir(III) complexes, three [Ir(C ∧ N) 2 (dnbp)] + (dnbp = 4,4'-dinonyl-2,2'-bipyridine) emitters were immobilized in MCM-41 mesoporous nanoparticles. By taking advantage of the amphiphilic nature of [Ir(C ∧ N) 2 (dnbp)] + , the complexes were mixed with an appropriate surfactant and the resulting micelles served as templates for the synthesis of mesoporous silica host materials in a one-step sol-gel route. The MCM-encapsulated [Ir(C ∧ N) 2 (dnbp)] + complexes present intense emissions with prominent rigidochromic spectral changes that are substantially less affected by O 2 as compared to methanolic solutions, with a thousand-fold decrease in quenching rate constants. These photophysical results points to a possible suitability of Ir(III)-complex-MCM-41 host-guest systems for possible future optoelectronic devices, rigidity optical sensors, or biological markers in different colors.

Sol-gel chemistry has been extensively employed to produce several classes of materials (e.g. nanoparticles, thin films, fibers, gels, glasses and ceramic powders) with desired easily-controllable morphological, crystallographic and mechanical properties. In particular, the methodology can be explored for the development of optical supramolecular materials with interesting properties for light-emitting devices, chemical and biological sensing, biomarking and targeting, among many others. To this end, the strategies usually adopted consist of embedding a luminescent guest species into normally non-emissive sol-gel host materials, resulting in optical systems that preserve both the guest's photophysical characteristics and the host's mechanical and morphological properties. This concise review provides insights into the development of promising new host-guest optical materials based on versatile sol-gel hosts (i.e. mesoporous MCM-41 nanoparticles, mesoporous sodium-aluminosilicate glasses and other mesoporous matrices for sensors) and highly luminescent guests (i.e. organic dyes, d 6 complexes and lanthanide complexes), mostly focusing on the findings from our group and similar findings in the literature of the past decade.

Cyclometalated Ir III complexes are promising candidates for biomedical applications but high cytotoxicity limits their use as imaging and sensing agents. We herein introduce the use of Laponite as carrier for triplet-emitting cyclometalated Ir III complexes. Laponite is a versatile nanoplatform because of its biocompatibility, dispersion stability and large surface area that readily adsorbs functional nonpolar and cationic molecules. These inorganic-organic hybrid nanomaterials mask cytotoxicity, show efficient cell uptake and increase luminescent properties and photostability. By camouflaging intrinsic cytotoxicity, this simple method potentially extends the palette of available imaging and sensing dyes to any metal-organic complexes, especially those that are usually cytotoxic.

In this work, efficient trans ⇌ cis photoswitchings of 4-(4-cyano)styrylpyridine (stpyCN) coordinated to organometallic bipyridyl tricarbonyl rhenium(I) complexes, fac-[Re(CO) 3 (NN)( trans-stpyCN)] + , where NN = 2,2'-bipyridine (bpy) or 4,4'-dimethyl-2,2'-bipyridine (dmb), are described. For both complexes, the true trans-to- cis quantum yields determined by 1 H NMR spectroscopy are similar at 313, 334, and 365 nm irradiations (Φ trans→ cis true(313-365 nm) ∼ 0.45), with a small decrease at 404 nm (Φ trans→ cis true(404 nm) ∼ 0.37). The investigated complexes also exhibit significant quantum yields for the reversible cis-to- trans photoreactions (Φ cis→ trans (255 nm) = 0.22). The luminescent properties of these complexes were also analyzed in different media to elucidate a key role of the 3 IL stpyCN state in photophysical and photochemical processes, giving new insights on their intriguing photobehavior.

A versatile Ru(II) complex bearing an anthracene moiety was synthesized in our search for suitable compounds towards efficient molecular devices. The new engineered dye, cis‑[Ru(dcbH 2 )(NCS) 2 (mbpy‑anth)] (dcbH 2 =2,2'‑bipyridyl‑4,4'‑dicarboxylic acid, mbpy‑anth=4‑[N‑(2‑anthryl)carbamoyl]‑4'‑methyl‑2,2'‑bipyridine), exhibits a blueish emission in a vibronically structured spectrum ascribed to the fluorescence of a 1 LC Anth (ligand centered) excited state in the anthracene and has a potential to be exploited in the fields of smart lighting and displays. This complex was also employed in dye-sensitized solar cells with fairly efficient solar energy conversion with the use of self-assembled TiO 2 compact layers beneath the TiO 2 mesoporous film to prevent meso‑TiO 2 /dye back reactions. Further photoelectrochemical investigations through incident photon-to-current efficiency and electrochemical impedance spectra showed that the all-nano-TiO 2 compact layer acts as contact layers that increase the electron harvesting in the external circuit, enhancing efficiencies up to 50%., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The photophysical dynamics of three complexes in the highly-emissive [Ir(pqi) 2 (NN)] + series were investigated aiming at unique photophysical features and applications in light-emitting and singlet oxygen sensitizing research fields. Rational elucidation and Franck-Condon analyses of the observed emission spectra in nitrile solutions at 298 and 77 K reveal the true emissive nature of the lowest-lying triplet excited state (T 1 ), consisting of a hybrid 3 MLCT/LC Ir(pqi)→pqi state. Emissive deactivations from T 1 occur mainly by very intense, yellow-orange phosphorescence with high quantum yields and radiative rates. The emission nature experimentally verified is corroborated by theoretical calculations (TD-DFT), with T 1 arising from a mixing of several transitions induced by the spin-orbit coupling, majorly ascribed to 3 MLCT/LC Ir(pqi)→pqi and increasing contributions of 3 MLCT/LLCT Ir(pqi)→NN . The microsecond-lived emission of T 1 is rapidly quenched by molecular oxygen, with an efficient generation of singlet oxygen. Our findings show that the photophysics of [Ir(pqi) 2 (NN)][PF 6 ] complexes is suitable for many applications, from the active layer of electroluminescent devices to photosensitizers for photodynamic therapy and theranostics.

In our search for light powered molecular devices, a novel fac-[Re(CO) 3 (ph 2 phen)(trans-stpyCN)] + complex was synthesized to show switchable trans-cis configurations of the coordinated stpyCN ligand through efficient and reversible photoassisted isomerizations. Controlled photolyses of acetonitrile solutions led to spectral changes ascribed to reversible trans⇌cis photoisomerization processes. A remarkable quantum yield for the back cis-to-trans isomerization was obtained, with the same magnitude of the trans-to-cis photoprocess, and curiously, both trans- and cis-isomers are emissive at room temperature. Photochemical and photophysical characterization studies for fac-[Re(CO) 3 (ph 2 phen)(stpyCN)] + provided insights into the isomerization and emissive light-driven pathways that are resulted from the interactions between the close-lying intraligand and charge transfer states. The reversible cis-trans photoisomerization has potential to be exploited as light-powered molecular motors and geometry regulators in molecular machines.

An innovative all-nano-TiO2 thin film capable of enhancing dye-sensitized solar cell (DSC) photoefficiencies was prepared by a layer-by-layer method beneath the meso-TiO2 film, employing acid and basic nano-TiO2 sols as cations and anions, respectively. TiO2 syntheses were performed under absolute control to lead to appropriate morphological and optical properties to yield high-quality compact films using profilometry, tuning, and scanning electron microscopy. A detailed study by photoelectrochemical parameters, incident photon-to-current efficiency, electron lifetime, and electrochemical impedance spectroscopy demonstrates that the physical contact between FTO and the electrolyte is prevented and the role of the compact film has been elucidated. DSCs with TiO2 bilayers on top of FTO improved the conversion efficiency up to 62%, mainly because of the prevention of FTO/I3(-) charge recombination and an improved contact between FTO and TiO2.

Synthesis and photophysical properties of the highly emissive complex [Ir(Fppy)2(dmb)](+) are reported along with those of additional heteroleptic cyclometalated Ir(III) complexes, [Ir(ppy)2(NN)](PF6): FppyH = 2-(2,4-difluorophenyl)pyridine; ppyH = 2-phenylpyridine; NN = 4,4'-dimethyl-2,2'-bipyridine (dmb), 1,10-phenanthroline (phen), or 4,7-diphenyl-1,10-phenanthroline (Ph2phen). TD-DFT calculations and Franck-Condon emission spectral band shape analyses show that the broad and structureless emission from [Ir(Fppy)2(dmb)](+) in acetonitrile at 298 K mainly arises from a triplet metal-to-ligand charge-transfer excited state, (3)MLCTIr(ppy)→NN. The emission maximum varies systematically with variations in electron-donating or -withdrawing substituents on both the NN and the Xppy ligands, and emission efficiencies are high, with an impressive ϕ ≈ 1 for [Ir(Fppy)2(dmb)](+). At 77 K in propionitrile/butyronitrile (4/5, v/v), emission from [Ir(Fppy)2(dmb)](+) is narrow and highly structured consistent with a triplet ligand-centered transition ((3)LCNN) and an inversion in excited-state ordering between the (3)MLCTIr(ppy)→NN and (3)LCNN states. In a semirigid film of the poly(ethyleneglycol)dimethacrylate with nine ethylene glycol spacers, PEG-DMA550, emission from [Ir(Fppy)2(dmb)](+) is MLCT-based. The thermal sensitivity of the photophysical properties of this excited state points to a possible application as a temperature sensor in addition to its more known use in light-emitting devices.