A key problem for materials that form lead-based perovskite is the part of organic iodide that is oxidized and forms molecular I2, which negatively affects the efficiency and stability of the solar cell. Herein, we explored adding special compounds, two borohydride salts, potassium borohydride (KBH4) and sodium borohydride (NaBH4), into the perovskite precursor solution. These borohydride salts help prevent the oxidation process by acting as reducing agents, preventing the defects caused by I2 by converting it back to I-. Also, I3- is generated from I2 and I-, which has a strong binding affinity to FA+, leading to deprotonation and decomposition of the perovskite. Borohydride salts can prevent this degradation and help stabilize the precursor solution. Furthermore, borohydride salts have a second role, enhancing film crystallinity and defect passivation and increasing humidity resistance, which improves overall stability and device performance. As a result, a promising efficiency of 20% is achieved, exhibiting long-term stability.

High defect concentrations at the interfaces are the basis of charge extraction losses and instability in perovskite solar cells. Surface engineering with organic cations is a common practice to solve this issue. However, the full implications of the counteranions of these cations for device functioning are often neglected. In this work, we used 4-fluorophenethylammonium cation with varying halide counteranions for the modification of both interfaces in methylammonium-free Pb-based n-i-p devices, observing significant differences among iodide, bromide, and chloride. The cation treatment of the buried and top interfaces resulted in improved surface quality of the perovskite films and largely improved carrier dynamics with reduced nonradiative recombination. Consequently, the optimal interface-modified methylammonium-free perovskite solar cells surpassed 20% efficiency and demonstrated remarkable operational stability. Our findings underscore the potential of comprehensive surface engineering strategies in advancing the perovskite film and device quality, thereby facilitating their broader and more successful applications.

Balancing light transmittance and power conversion efficiency (PCE) remains a major challenge for semi-transparent perovskite solar cells (ST-PSCs), particularly for applications in building integration and agrivoltaics. In this work, dielectric-metal-dielectric (DMD) electrodes based on WO3/Ag/WO3 as a high-performance alternative to conventional semi-transparent gold (Au) contacts were integrated into bromide-rich formamidinium lead halide perovskites, with a systematic study across halide compositions from pure bromide to pure iodide. The DMD electrodes consistently enhanced photovoltaic performance and optical quality, achieving an average visible transmittance (AVT) of 43.63%, light utilization efficiency (LUE) of 3.05%, and a PCE of 7% for FAPbBr3-based cells. An optimal composition with 47% bromide yielded a balanced performance with 24% of average visible transmittance (AVT), 2.12% LUE and similar to 9% PCE. Rather than simply increasing bromide content to widen the bandgap and enhance transparency, this study shows that there is an optimal spectral alignment that maximizes transmittance, photocurrent extraction and color. In addition, replacing Au with WO3/Ag/WO3 significantly reduces the environmental footprint, as confirmed by life cycle assessment. This study highlights a photonic design approach to advancing efficient, sustainable, and visually appealing ST-PSCs for next-generation energy applications.

Mixed cation quasi-2D tin iodide perovskites are promising materials for deep-red to NIR emitting light-emitting diode (LED) applications. However, phase purity remains the major concern to avoid mixed emissions from two or more wavelengths. This work presents the evolution of pure deep red electroluminescence (EL) centred at ≈700 nm corresponding to the emission of pure n = 2 2D crystalline phase. However, structural and optical studies evidenced the formation of mixed-phase heterostructures consisting of n = 1, n = 2, and n = ∞ phase (i.e., FASnI3). It is observed that altering the mixed cation ratio, phase distribution is modified, affecting the EL behavior, causing the observation or absence of the n = 1 2D phase EL emission peak. Selective charge transport and their cascade mechanism illustrates the pure color EL evolution with the support from transient absorption spectroscopic studies. In this regard, a case study is provided along with the supportive rationalities behind the exceptional evolution of pure deep red EL even from the mixed-phase perovskite, reported for the first time in case of quasi-2D tin iodide perovskite.

Perovskite light-emitting diodes (PeLEDs) have emerged as a prominent topic within optoelectronic research. Despite remarkable advancements, this technology still faces challenges that must be addressed for successful commercialization. Typical device architectures employ PEDOT:PSS as hole transporting material (HTM). However, besides its expensive cost, PEDOT:PSS has been reported to cause issues with efficiency and long-term stability. Molecular self-assembled monolayers (SAMs) have arisen as potential HTMs, not just to overcome these drawbacks but to enhance the interface properties and performance of LEDs. This technology has been efficiently applied in PeLEDs, but its use in devices based on perovskite nanocrystals (PNCs) remain underexplored. In this work, two benzoxazole derivatives have been analyzed as SAMs to conform the hole selective contact in CsPbBr3 PNCs-based LEDs. The devices demonstrate improved optoelectronic properties compared to the reference composed of PEDOT:PSS, attributed to a suitable band alignment and an enhanced charge injection. Furthermore, optimizing the deposition technique of SAMs on the conducting substrate by dip- or spin-coating has allowed the preparation of efficient LEDs exhibiting external quantum efficiencies (EQEs) up to 6.8% with 300 s of operational stability. This research aims to provide extensive insights into applying SAMs to design PeLEDs with improved carrier mobility.

Interfaces between photoactive perovskite layer and selective contacts play a key role in the performance of perovskite solar cells (PSCs). The properties of the interface can be modified by the introduction of molecular interlayers between the halide perovskite and the transporting layers. Herein, two novel structurally related molecules, 1,3,5-tris(α-carbolin-6-yl)benzene (TACB) and the hexamethylated derivative of truxenotris(7-azaindole) (TTAI), are reported. Both molecules have the ability to self-assemble through reciprocal hydrogen bond interactions, but they have different degrees of conformational freedom. The benefits of combining these tripodal 2D-self-assembled small molecular materials with well-known hole transporting layers (HTLs), such as PEDOT:PSS and PTAA, in PSCs with inverted configuration are described. The use of these molecules, particularly the more rigid TTAI, enhanced the charge extraction efficiency and reduced the charge recombination. Consequently, an improved photovoltaic performance was achieved in comparison to the devices fabricated with the standard HTLs.

Up-to-date studies propose that strain in halide perovskites is one of the key factors that determine a device's efficiency and stability. Here, we show a systematic approach to characterize the phenomenon in the standard methylammonium lead iodine (MAPbI3) perovskite system by: (i) the substitution of some MA by guanidinium (Gu); (ii) the incorporation of PbS quantum dot (QD) additives and (iii) addition of both Gu and PbS at the same time. We studied the effect of these incorporations on the film strain and crystal cell unit volume, and on the solar cell device efficiency and stability. Gu cations and PbS QDs affect the strain, the former due to the relatively large dimensions of Gu, and the latter due to the lattice matching parameters. With the control of Gu and PbS QD content, higher performance and longer solar cell stability are obtained. We demonstrated that the presence of Gu and PbS QDs alters the structure of perovskite, in terms of modification of the unit cell volume and strain. The greater size of Gu cations produces a MAPbI3 unit cell volume expansion as Gu is incorporated, modifying the strain from compressive to tensile. PbS QDs aid Gu incorporation, producing a unit cell volume expansion. In the case of 15% mol Gu incorporation, the addition of PbS QDs modifies strain from compressive to tensile, limiting the deleterious effect. At the same time the unit cell volume is less affected, increasing the solar cell stability. Our work shows that the control of compressive strain and the unit cell volume expansion lead to a 50% increase in T 80, the time in which the PCE decreases to 80% of its original value, increasing the T 80 value from 120 to 187 days under air conditions. Moreover it highlights the importance of exploiting not only the control of the strain induced by internal component, the cation, but also the strain induced by the external component, the QD, associated instead with critical volume variation of metastable perovskite unit cell volume.

Defects in polycrystalline halide perovskite films can cause a decrease of the solar cell photoconversion efficiency and stability. The perovskite film enhanced during crystal growth by controlling the processing method can alleviate defects and the related recombination sites that affect the performance of cells. Herein, flash infrared annealing is employed to crystallize methylammonium lead iodide perovskite with a single heating pulse, where uniform grain domains are optically observed and mapped. Films are annealed with different temperature ramps up to 48 °C s−1 heating rate. Annealing with higher heating rates presents lower defect densities, decreases the Urbach energy tail, and improves the optoelectrical performance of the films. These improvements are rationalized by Raman spectroscopy of nucleation points and grain surface differences among the process variations. The role of crystal growth and subsequent film quality allows to achieve a champion photovoltaic device growth at 48 °C s−1 with stability around 250 h under 1 sun illumination and 60% relative humidity for 100 h under 3 sun (AM1.5G) illumination. In situ optical imaging is recorded during the process, confirming that rapid annealing, i.e., higher heating rates, contributes to obtain more stable devices with the added advantage of shorter processing time.

All inorganic halide perovskite nanocrystals (NCs) are considered as fascinating materials for a wide range of optoelectronic applications encompassing photovoltaics, lasing, sensing, and photocatalysis due to their outstanding optoelectronic properties. Herein, it is demonstrated that the photoelectrochemical behavior of CsPbBr3 NC films can be tailored through engineering the selective contacts and accepting species in the electrolyte. This concept has been successfully applied to the photoelectrochemical oxidation of benzyl alcohol (BzOH) to benzyl aldehyde (BzCHO) and the reverse photoelectrochemical reduction of BzCHO to BzOH, demonstrating that CsPbBr3 NCs activate both reactions with photocurrents up to 40 μA cm−2 toward BzCHO production and 5 μA cm−2 for the reverse reaction at 0.15 V versus normal hydrogen electrode. The obtained results highlight the huge potential and versatility of halide perovskite NCs for photoelectrocatalytic applications, validating the implementation of these materials for a wide range of solar‐driven complex organic transformations, and emphasizing the urgent need for stabilization strategies to move beyond the proof‐of‐concept stage to relevant technological developments.

Despite the promising properties of tin-based halide perovskites, one clear limitation is the fast Sn+2 oxidation. Consequently, the preparation of long-lasting devices remains challenging. Here, we report a chemical engineering approach, based on adding Dipropylammonium iodide (DipI) together with a well-known reducing agent, sodium borohydride (NaBH4), aimed at preventing the premature degradation of Sn-HPs. This strategy allows for obtaining efficiencies (PCE) above 10% with enhanced stability. The initial PCE remained unchanged upon 5 h in air (60% RH) at maximum-power point (MPP). Remarkably, 96% of the initial PCE was kept after 1,300 h at MPP in N-2. To the best of our knowledge, these are the highest reported values for Sn-based solar cells. Our findings demonstrate a beneficial synergistic effect when additives are incorporated, highlight the important role of iodide in the performance upon light soaking, and, ultimately, unveil the relevance of controlling the halide chemistry for future improvement of Sn-based perovskite devices.

Due to the high industrial interest for perovskite-based photovoltaic devices, there is an urgent need to fabricate them under ambient atmosphere, not limited to low relative humidity (RH) conditions. The formamidinium lead iodide (FAPI) perovskite α-black phase is not stable at room temperature and is challenging to stabilize in an ambient environment. In this work, we show that pure FAPI perovskite solar cells (PSCs) have a dramatic increase of device long-term stability when prepared under ambient air compared to FAPI PSCs made under nitrogen, both fabricated with N-methylpyrrolidone (NMP). The T80 parameter, the time in which the efficiency drops to 80% of the initial value, increases from 21 (in N2) to 112 days (in ambient) to 145 days if PbS quantum dots (QDs) are introduced as additives in air-prepared FAPI PSCs. Furthermore, by adding methylammonium chloride (MACl) the power conversion efficiency (PCE) reaches 19.4% and devices maintain 100% of the original performance for at least 53 days. The presence of Pb–O bonds only in the FAPI films prepared in ambient conditions blocks the propagation of α- to δ-FAPI phase conversion. Thus, these results open the way to a new strategy for the stabilization in ambient air toward perovskite solar cells commercialization.

An outstanding potentiality of layered two-dimensional (2D) organic-inorganic hybrid perovskites (2DHPs) is in the development of solar cells, photodetectors, and light-emitting diodes. In 2DHPs, an exciton is localized in an atomically thin lead(II) halide inorganic layer of sub-nanometer thickness as in a quantum well sandwiched between organic layers as energetic and dielectric barriers. In previous years, versatile optical characterization of 2DHPs has been carried out mainly for thin flakes of single crystals and ultrathin (of the order of 20 nm) polycrystalline films, whereas there is a lack of optical characterization of thick (hundreds of nanometers) polycrystalline films, fundamentals for fabrication of devices. Here, with the use of photoluminescence (PL) and absorption spectroscopies, we studied the exciton behavior in ∼200 nm polycrystalline thin films of 2D perovskite (PEA)2PbI4, where PEA is phenethylammonium. Contrary to the case of ultrathin films, we have found that peak energies and line width of the excitonic bands in our films demonstrate unusual extremely weak sensitivity to temperature in 20-300 K diapason. The excitonic PL band is characterized by a significant (∼30 meV) Stokes shift with respect to the corresponding absorption band as well as by a full absence of the exciton fine structure at cryogenic temperatures. We suggest that the observed effects are due to the large inhomogeneous broadening of the excitonic PL and absorption bands resulting from the (PEA)2PbI4 band gap energy dependence on the number of lead(II) halide layers of individual crystallites. The characteristic time of the exciton energy funneling from higher- to lower-energy crystallites within (PEA)2PbI4 polycrystalline thin films is about 100 ps.

While 2D/3D layered perovskites have been the object of comprehensive research principally focused on increasing the long-term stability observed in 3D perovskites, significant opportunities still exist concerning the application of different kinds of cations outside the sphere of primary amines, which are the cations most usually applied. Our results demonstrate that the materials and the solar cells prepared with dipropylammonium iodide (DipI), a bulky secondary ammonium cation of small size, lead to obtaining materials that are not only efficient and thermodynamically stable but also robust toward heat stress. Time-resolved studies indicate longer carrier lifetime for 2D/3D layered perovskites fabricated with this bulky cation than for systems based on bulky primary ammonium cations, which allowed us to obtain PCE = 12.51% (n = 10), 15.78% (n = 50), and 17.90% (n = 90). We determine that the concentration of perovskite material after 240 min at 100 degrees C is up to 575% greater in the 2D/3D perovskite (n = 10) than that observed in 3D perovskite films. The material stability also improves the thermal stability of the photovoltaic devices, presenting an efficiency drop of just 4% for n = 50 and n = 10 after thermal annealing while the performance drop for reference 3D samples in the same conditions was greater than 80%.

Thermochromism is a color change phenomenon for a compound when it undergoes a heating/cooling process. The observation of this phenomenon mostly relies on the naked eye, rather than an exact optical technique, which retards better new thermochromic material design and is detrimental to the understanding of its fundamental mechanism. In this paper, we present a facile and noninvasive in situ ellipsometric method to monitor the optical properties evolution of CsPbI3 film in its thermochromic process with three notable phase transitions from room temperature to 340 degrees C. We monitored the in situ structure evolution of CsPbI3 film by three techniques, namely, temperature-dependent X-ray diffraction, Raman spectroscopy, and spectroscopic ellipsometry. Four phases of CsPbI3, that is, alpha, beta, gamma, and delta, could be detected in temperature-dependent spectroscopic ellipsometry measurement. Especially, we found the most expected "stable" alpha and gamma phases show temperature-dependent bandgap evolution even in their phase-stable temperature region. The in situ spectroscopic ellipsometry therefore could function as a facile and noninvasive technique for detection of phase and band evolution with potential applications in smart windows, semiconductor, and optical devices.

Inorganic hole-transporting materials (HTMs) for stable and cheap inverted perovskite-based solar cells are highly desired. In this context, NiOx, with low synthesis temperature, has been employed. However, the low conductivity and the large number of defects limit the boost of the efficiency. An approach to improve the conductivity is metal doping. In this work, we have synthesized cobalt-doped NiOx nanoparticles containing 0.75, 1, 1.25, 2.5, and 5 mol% cobalt (Co) ions to be used for the inverted planar perovskite solar cells. The best efficiency of the devices utilizing the low temperature-deposited Co-doped NiOx HTM obtained a champion photoconversion efficiency of 16.42%, with 0.75 mol% of doping. Interestingly, we demonstrated that the improvement is not from an increase of the conductivity of the NiOx film, but due to the improvement of the perovskite layer morphology. We observe that the Co-doping raises the interfacial recombination of the device but more importantly improves the perovskite morphology, enlarging grain size and reducing the density of bulk defects and the bulk recombination. In the case of 0.75 mol% of doping, the beneficial effects do not just compensate for the deleterious one but increase performance further. Therefore, 0.75 mol% Co doping results in a significant improvement in the performance of NiOx-based inverted planar perovskite solar cells, and represents a good compromise to synthesize, and deposit, the inorganic material at low temperature, without losing the performance, due to the strong impact on the structural properties of the perovskite. This work highlights the importance of the interface from two different points of view, electrical and structural, recognizing the role of a low doping Co concentration, as a key to improve the inverted perovskite-based solar cells’ performance.

The development of lanthanide-doped Y3Al5O12(Ln:YAG) garnet nanostructures is a hot topic in the field of inorganic nanophosphors due to the current interest in developing small nanoparticles for solid-state lighting (SSL), displays, lasers and scintillation applications. In this study, we report the preparation of homogeneous Ln:YAG (Ln: Ho/Yb ions) nanospheres through a combined two-steps coprecipitation-solvothermal synthesis at low temperature. The crystal growth takes place in ethylene glycol, which is an inexpensive, non-toxic and easily available solvent. Monodisperse and crystalline spherical YAG particles of 80 nm in diameter were obtained. Furthermore, the protocol can be extended to other compositions (Tb/Yb, Tm/Yb horizontal ellipsis ) to explore different luminescent properties, without affecting the morphology of the material, indicating the robustness and practical utility of the reported methodology. Thermal treatment of the nanogarnets at 1200 degrees C is necessary for making materials optically active upon both UV and NIR excitation. The spherical morphology of annealed samples is preserved, what helps their further dispersion in solvents, barbotines, inks or printing vehicles. The lanthanide-doped nanogarnets exhibited the characteristic blue, green and red emissions from lanthanide upconversion photoluminescence (UCPL) upon NIR excitation. The UCPL mechanism was studied and CIE chromate coordinates were obtained. These nanogarnets were further evaluated as functional ceramic phosphors by incorporating them into commercial glazes. The materials exhibited an exceptional chemical stability in a harsh medium such as a fused glaze. Consequently, the visible emissions of the nanoparticles were transferred to the whole glass matrix, thus providing a functional glaze that emits intense blue and green light upon NIR excitation. These luminescent nanogarnets have promising applications in smart enamels, but can also be useful for lighting displays (white LEDs horizontal ellipsis ), smart paintings or plastics, and anti-counterfeiting systems.

Formamidinium-based perovskite solar cells (PSCs) present the maximum theoretical efficiency of the lead perovskite family. However, formamidinium perovskite exhibits significant degradation in air. The surface chemistry of PbS has been used to improve the formamidinium black phase stability. Here, the use of PbS nanoplatelets with (100) preferential crystal orientation is reported, to potentiate the repercussion on the crystal growth of perovskite grains and to improve the stability of the material and consequently of the solar cells. As a result, a vertical growth of perovskite grains, a stable current density of 23 mA cm(-2), and a stable incident photon to current efficiency in the infrared region of the spectrum for 4 months is obtained, one of the best stability achievements for planar PSCs. Moreover, a better reproducibility than the control device, by optimizing the PbS concentration in the perovskite matrix, is achieved. These outcomes validate the synergistic use of PbS nanoplatelets to improve formamidinium long-term stability and performance reproducibility, and pave the way for using metastable perovskite active phases preserving their light harvesting capability.

Co-adsorbing molecules attain certain control in the surrounding of the dyes leading to enhanced efficiencies mainly by affecting the recombination of the photogenerated electrons and aggregation of dyes. Bile acids such as deoxycholic acid (DOA) and chenodeoxycholic acid (CDOA) yield competitive photovoltaic parameters. We harness the steroid backbone of bile acids to chemically modified it at its R3 position attaching sterically demanding amide groups rather than typically terminal hydroxyl groups (3 beta-position) as in DOA and CDOA. All possible resultant effects on the performance in complete DSSCs were studied by current density-voltage curves (e.g., percentage of efficiency, %eta; open-circuit voltage, V-oc; short-circuit photocurrent, J(sc); and fill factor, FF), incident photon-to-current conversion efficiency (IPCE), and a set of interfacial data by electrochemical impedance spectroscopy (EIS). Our co-adsorbates stand out by enhancing the conversion efficiencies, being in some cases competitive with photovoltaic parameters of DOA and CDOA.