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Carbon perovskite solar cells (C-PSCs), using carbon-based counter electrodes (C-CEs), promise to mitigate instability issues while providing solution-processed and low-cost device configurations. In this work, we report the fabrication and characterization of efficient paintable C-PSCs obtained by depositing a low-temperature-processed graphene-based carbon paste atop prototypical mesoscopic and planar n–i–p structures. Small-area (0.09 cm2) mesoscopic C-PSCs reach a power conversion efficiency (PCE) of 15.81% while showing an improved thermal stability under the ISOS-D-2 protocol compared to the reference devices based on Au CEs. The proposed graphene-based C-CEs are applied to large-area (1 cm2) mesoscopic devices and low-temperature-processed planar n–i–p devices, reaching PCEs of 13.85 and 14.06%, respectively. To the best of our knowledge, these PCE values are among the highest reported for large-area C-PSCs in the absence of back-contact metallization or additional stacked conductive components or a thermally evaporated barrier layer between the charge-transporting layer and the C-CE (strategies commonly used for the record-high efficiency C-PSCs). In addition, we report a proof-of-concept of metallized miniwafer-like area C-PSCs (substrate area = 6.76 cm2, aperture area = 4.00 cm2), reaching a PCE on active area of 13.86% and a record-high PCE on aperture area of 12.10%, proving the metallization compatibility with our C-PSCs. Monolithic wafer-like area C-PSCs can be feasible all-solution-processed configurations, more reliable than prototypical perovskite solar (mini)modules based on the serial connection of subcells, since they mitigate hysteresis-induced performance losses and hot-spot-induced irreversible material damage caused by reverse biases.

The halide perovskite photovoltaic technology can be scaled to large area modules and panels using printing processes and laser patterning. Here, we will present the progresses made to scale up from small area solar cells to modules and panels up to a dimension of 0.5 sqm. By working in controlled atmosphere (Glove Box with nitrogen) and apply conventional spin-coating technique it Is possible to easily scale up from 9 to 140 cm2 active area with efficiencies above 20% for the smallest modules and 14.7% for the largest. Specific efforts have been devoted to developing a deposition process out of the glove box (GB) in conventional ambient air. We transfer out of the GB several coating technologies, including blade coating and slot-die. To do this without penalizing efficiency and stability, a specific formulation of perovskite absorber and doping strategies of transporting layer have been formulated together with specific quencing techniques based on air, vacuum and solvents. These optimizations permitted to realized perovskite solar modules with an efficiency of > 17% on an active area of 43 cm2, keeping above 90% of the initial efficiency after 800 h thermal stress at 85 ��C. One of the critical issues scaling the cell to module size is the control of interface properties. We demonstrated that tuning of interface properties can be successfully obtained by applying two-dimensional (2D) materials, such as graphene, functionalized MoS2, MXenes as well as 2D Perovskite. This permitted also to increase the stability of the cell (T80) well beyond 1000h under light soaking and thermal stress tests.https://www.nanoge.org/proceedings/NSM22/61ae458bb25d6d736516cdac

The photoluminescence (PL) intensity is often used as an indicator of the performance of perovskite solar cells and indeed the PL technique is often used for the characterization of these devices and their constituent materials. Herein, a systematic approach is presented to the comparison of the conversion efficiency and the PL intensity of a cell in both open-circuit (OC) and short-circuit (SC) conditions and its application to multiple heterogeneous devices. It is shown that the quenching of the PL observed in SC conditions is a good parameter to assess the device efficiency. The authors explain the dependence of the PL quenching ratio between OC and SC on the cell efficiency with a simple model that is also able to estimate the carrier extraction time of a device.

Nanocluster aggregation sources based on magnetron-sputtering represent precise and versatile means to deposit a controlled quantity of metal nanoparticles at selected interfaces. In this work, we exploit this methodology to produce Ag/MgO nanoparticles (NPs) and deposit them on a glass/FTO/TiO2 substrate, which constitutes the mesoscopic front electrode of a monolithic perovskite-based solar cell (PSC). Herein, the Ag NP growth through magnetron sputtering and gas aggregation, subsequently covered with MgO ultrathin layers, is fully characterized in terms of structural and morphological properties while thermal stability and endurance against air-induced oxidation are demonstrated in accordance with PSC manufacturing processes. Finally, once the NP coverage is optimized, the Ag/MgO engineered PSCs demonstrate an overall increase of 5% in terms of device power conversion efficiencies (up to 17.8%).

Halide Perovskite photovoltaic technology can be scaled to large area modules and panels using printing processes and laser patterning. Here, we will present the progress made to scale up from small area solar cells to modules and panels up to a dimension of 0.5 sqm. Specific efforts have been devoted to developing a deposition process out of the glove box (GB) in conventional ambient air. We transfer out of the GB several coating technologies, including blade coating and slot-die. [1], [2] To do this without penalizing efficiency and stability, a specific formulation of perovskite absorber [2], [3] and doping strategies of transporting layer have been formulated. [4] These optimizations permitted to realized perovskite solar modules with an efficiency of > 17% on an active area of 43 cm2, keeping above 90% of the initial efficiency after 800 h thermal stress at 85 °C. [4] One of the critical issues scaling the cell to module size is the control of interface properties. We demonstrated that tuning of interface properties can be successfully obtained by applying two-dimensional (2D) materials, such as graphene [5], functionalized MoS2 [6], MXenes [7] as well as 2D Perovskite.

In this work, we perform steady-state, continuous wave (cw), photoluminescence (PL) measurements on $\mathrm{MAPb}{\mathrm{I}}_{3}$ thin films in the temperature range of 10--160 K, using excitation densities spanning over almost seven orders of magnitude, in particular investigating very low densities that are rarely used in the published literature. The temperature range used in this study is below or at the edge of the orthorhombic-tetragonal phase transition in $\mathrm{MAPb}{\mathrm{I}}_{3}$. In particular, we show that even in high-quality $\mathrm{MAPb}{\mathrm{I}}_{3}$, capable of providing high photovoltaic efficiency, the defect density is high enough to give rise to an energy level band. Furthermore, we show that the intensity ratio between the two PL components related to the two crystalline phases is a function of temperature and excitation density. At high excitation intensities, we show that amplified spontaneous emission is attainable even in cw conditions. Time-resolved PL is also performed to justify the assignments of the PL features. Finally, our systematic approach, typical for the characterization of semiconductors, suggests that it should also be applied to hybrid halide perovskites and that, under suitable conditions, the PL characteristics of $\mathrm{MAPb}{\mathrm{I}}_{3}$ can be reconciled with those of conventional inorganic semiconductors.

The industrial exploitation of perovskite solar cell technology is still hampered by the lack of repeatable and high-throughput fabrication processes for large-area modules. The joint efforts of the scientific community allowed to demonstrate high-performing small area solar cells; however, retaining such results over large area modules is not trivial. Indeed, the development of deposition methods over large substrates is required together with additional laser processes for the realization of the monolithically integrated cells and their interconnections. In this work, we develop an efficient perovskite solar module based on 2D material engineered structure by optimizing the laser ablation steps (namely P1, P2, P3) required for shaping the module layout in series connected sub-cells. We investigate the impact of the P2 and P3 laser processes, carried out by employing a UV pulsed laser (pulse width = 10 ns; λ = 355 nm), over the final module performance. In particular, a P2 process for removing 2D material-based cell stack from interconnection area among adjacent cells is optimized. Moreover, the impact of the P3 process used to isolate adjacent sub-cells after gold realization over the module performance once laminated in panel configuration is elucidated. The developed fabrication process ensures high-performance repeatability over a large module number by demonstrating the use of laser processing in industrial production.

Ultrafast pump-probe spectroscopies have proved to be an important tool for the investigation of charge carriers dynamics in perovskite materials providing crucial information on the dynamics of the excited carriers, and fundamental in the development of new devices with tailored photovoltaic properties. Fast transient absorbance spectroscopy on mixed-cation hybrid lead halide perovskite samples was used to investigate how the dimensions and the morphology of the perovskite crystals embedded in the capping (large crystals) and mesoporous (small crystals) layers affect the hot-carrier dynamics in the first hundreds of femtoseconds as a function of the excitation energy. The comparative study between samples with perovskite deposited on substrates with and without the mesoporous layer has shown how the small crystals preserve the temperature of the carriers for a longer period after the excitation than the large crystals. This study showed how the high sensitivity of the time-resolved spectroscopies in discriminating the transient response due to the different morphology of the crystals embedded in the layers of the same sample can be applied in the general characterization of materials to be used in solar cell devices and large area modules, providing further and valuable information for the optimization and enhancement of stability and efficiency in the power conversion of new perovskite-based devices.

We present Z-Type Dye Sensitized Solar Modules (DSSMs) with screen printed graphene-based vertical interconnects. This prevents corrosion of interconnects in contact with electrolytic species, unlike conventional Ag interconnects. By enlarging the width of single cells, or by increasing the number of cells, we get an enhancement of the aperture power conversion efficiency ∼+12% with respect to Ag-based modules, with 1000 h stability under 85 °C stress test. This paves the way to original design layouts with decreased dead area and increased generated power per aperture area.

In this study, we report a detailed experimental and theoretical investigation of three glycol derivatives, namely ethane-1,2-diol, 2-methoxyethan-1-ol and 1,2-dimethoxy ethane. For the first time, the X-ray spectra of the latter two liquids was measured at room temperature, and they were compared with the newly measured spectrum of ethane-1,2-diol. The experimental diffraction patterns were interpreted very satisfactorily with molecular dynamics calculations, and suggest that in liquid ethane-1,2-diol most molecules are found in gauche conformation, with intramolecular hydrogen bonds between the two hydroxyl groups. Intramolecular H-bonds are established in the mono-alkylated diol, but the interaction is weaker. The EDXD study also evidences strong intermolecular hydrogen-bond interactions, with short O&middot, &middot, O correlations in both systems, while longer methyl-methyl interactions are found in 1,2-dimethoxy ethane. X-ray studies are complemented by micro Raman investigations at room temperature and at 80 &deg, C, that confirm the conformational analysis predicted by X-ray experiments and simulations.

In this study, we report a detailed experimental and theoretical investigation of three glycols, namely ethane-1,2-diol, 2-methoxyethan-1-ol and 1,2-dimethoxy ethane. For the first time, the X-Ray spectra of the latter two liquids was measured at room temperature, and they were compared with the newly measured spectrum of ethane-1,2-diol. The experimental diffraction patterns were interpreted very satisfactorily with molecular dynamics calculations, and suggest that in liquid ethane-1,2-diol most molecules are found in gauche conformation, with intramolecular hydrogen bond between the two hydroxyl groups. Intramolecular H-bonds are established in the mono-alkylated diol, but the interaction is weaker. The EDXD study also evidences strong intermolecular hydrogen-bond interactions, with short O···O correlations in both systems, while longer methyl-methyl interactions are found in 1,2-dimethoxy ethane. X-Ray studies are complemented by micro Raman investigations at room temperature and at 80°C, that confirm the conformational analysis predicted by X-Ray experiments and simulations.

The application of highly active nano catalysts in advanced oxidation processes (AOPs) improves the production of non-selective hydroxyl radicals and co-oxidants for complete remediation of polluted water. This study focused on the synthesis and characterisation of a highly active visible light C&ndash, N-co-doped TiO2 nano catalyst that we prepared via the sol-gel method and pyrolysed at 350 &deg, C for 105 min in an inert atmosphere to prevent combustion of carbon moieties. Then we prolonged the pyrolysis holding time to 120 and 135 min and studied the effect of these changes on the crystal structure, particle size and morphology, electronic properties and photocatalytic performance. The physico-chemical characterisation proved that alteration of pyrolysis holding time allows control of the amount of carbon in the TiO2 catalyst causing variations in the band gap, particle size and morphology and induced changes in electronic properties. The C&ndash, N&ndash, TiO2 nano composites were active under both visible and UV light. Their improved activity was ascribed to a low electron&ndash, hole pair recombination rate that enhanced the generation of OH. and related oxidants for total deactivation of O.II dye. This study shows that subtle differences in catalyst preparation conditions affect its physico-chemical properties and catalytic efficiency under solar and UV light.

The remarkable high power conversion efficiency (PCE) demonstrated by small area perovskite solar cells (PSCs) are still not accomplished by a clear assessment on long-term stability, while scalability on large modules still penalized a feasible production for the photovoltaic market. In this work, we propose a route to easily produce large area (active area 70 cm2) perovskite solar module with stable performance under real working conditions. The employed graphene interface engineering (GIE) strategy, together with the use of stable polymeric hole transporting layer, allowed to achieve stabilized PCE overcoming 14% with a T 80 life-time (defined by the point at which device efficiency falls to 80% of the initial value) 27 times improved for PTAA cells compared to standard spiro-OMeTAD-based devices.

The [1]benzothieno[3,2-b][1]benzothiophene (BTBT) planar system was used to functionalize the phthalocyanine ring aiming at synthesizing novel electron-rich π-conjugated macrocycles. The resulting ZnPc-BTBT and ZnPc-(BTBT)4 derivatives are the first two examples of a phthalocyanine subclass having potential use as solution-processable p-type organic semiconductors. In particular, the combination of experimental characterizations and theoretical calculations suggests compatible energy level alignments with mixed halide hybrid perovskite-based devices. Furthermore, ZnPc-(BTBT)4 features a high aggregation tendency, a useful tool to design compact molecular films. When tested as hole transport materials in perovskite solar cells under 100 mA cm-2 standard AM 1.5G solar illumination, ZnPc-(BTBT)4 gave power conversion efficiencies as high as 14.13 %, irrespective of the doping process generally required to achieve high photovoltaic performances. This work is a first step toward a new phthalocyanine core engineerization to obtain robust, yet more efficient and cost-effective materials for organic electronics and optoelectronics.

Perovskite/silicon tandem solar cells represent an attractive pathway to upgrade the market-leading crystalline silicon technology beyond its theoretical limit. Two-terminal architectures result in reduced plant costs compared to four-terminal ones. However, it is challenging to monolithically process perovskite solar cells directly onto the micrometer-sized texturing on the front surface of record-high efficiency amorphous/crystalline silicon heterojunction cells, which limits both high-temperature and solution processing of the top cells. To tackle these hurdles, we present a mechanically stacked two-terminal perovskite/silicon tandem solar cell, with the sub-cells independently fabricated, optimized, and subsequently coupled by contacting the back electrode of the mesoscopic perovskite top cell with the texturized and metalized front contact of the silicon bottom cell. By minimizing optical losses, as achieved by engineering the hole selective layer/rear contact structure, and using a graphene-doped mesoporous electron selective layer for the perovskite top cell, the champion tandem device demonstrates a 26.3% efficiency (25.9% stabilized) over an active area of 1.43 cm2. Perovskite/silicon tandem solar cells promise to push the market-leading crystalline silicon technology beyond its theoretical limit while maintaining low fabrication costs. The possibility to fabricate the perovskite top cell by low-cost solution processing may decrease the levelized cost of energy of photovoltaics toward the grid-parity milestone. However, the solution processing of perovskite solar cells directly onto the textured front surface of high-efficiency amorphous/crystalline silicon heterojunction cells is the main bottleneck. Our simple two-terminal mechanical stacking of the sub-cells helps achieve highly performant PV devices. Its crucial advantage is the possibility to fabricate each sub-cell independently before coupling them. Prospectively, performance improvements and upscaling of perovskite solar cells, as well as the background knowledge on electronic component bonding method, make our results relevant to drive economically feasible perovskite/silicon tandem PVs. A novel configuration for high-performant perovskite/silicon tandem solar cells is demonstrated using a facile mechanical stacking of the sub-cells. The resulting champion perovskite/silicon tandem solar cell exhibits a stabilized efficiency of 25.9% over an active area of 1.43 cm2.

Perovskite solar cells (PSCs) represent nowadays a promising starting point to develop a new efficient and low-cost photovoltaic technology due to the demonstrated power conversion efficiency (PCE) exceeding 25% on small area devices. However, best reported devices suffer from stability issue under real working conditions thus slowing down the race for the commercialization. In particular, the hole transporting material commonly employed in mesoscopic n–i–p PSCs (nip-mPSCs), namely spiro-OMeTAD, is strongly corrupted when subjected to temperatures above 70 °C due to intrinsic thermal instability and because of the dopant employed to improve the hole mobility. In this work, the novel use of a copper-based corrole as HTM is proposed to improve the device thermal stability of nip-mPSCs under prolonged 85 °C stress conditions. Corrole-based devices show remarkable PCE above 16% by retaining more than 65% of the initial PCE after 1000 h of thermal stress, while spiro-OMeTAD cells abruptly lose more than 60% after the first 40 h. Once scaled-up to large area modules, the proposed device structure can truly represent a possible way to pass thermal stress tests proposed by IEC-61646 standards and, not less importantly, the high temperature required by the lamination process for panel production.

The stability of perovskite solar cells (PSCs) is a major factor limiting the market breakthrough of this technology. To understand the aging effects in PSCs is mandatory to rationally design implemented architectures and materials combining a viable deposition process, efficiency and stability. Despite of thisevidence, only few experimental works succeeded in the direct quantitative characterization of aging effects in PSCs. In this work, we apply state-of-the-art X-ray photoelectron spectroscopy (XPS) depth profile analysis and time-of-flight secondary ion mass spectrometry (ToF-SIMS) 3D imaging to investigate the light-induced degradation of layers and interfaces in reference (Au/Spiro-OMeTAD/CH3NH3PbI3/m-TiO2/cTiO2/FTO) and interface-engineered mesoscopic PSCs in which graphene flakes are added into the mesoscopic TiO2layer and a solution-processed 2H-MoS2 flakes buffer layer is added at the Spiro-OMeTAD/CH3NH3PbI3 interface. Results show that the graphene addition into the mesoscopic TiO2 layer improves the stability of the PSC by reducing the locally-inhomogeneous light-induced back-conversion of the CH3NH3PbI3 layer into PbIxand PbOx species and the consequent release of iodine species, whichdiffuse across the interfaces and causes the modifications at the gold electrode (Au-I bonding) and themesoscopic TiO2(Ti-I bonding) interfaces. Moreover, where the CH3NH3PbI3 layer is preserved the gold diffusion across the entire device structure is strongly reduced even after the aging. The 2H-MoS2 flakesbuffer layer allows limiting the localized diffusion of gold and the iodine diffusion in as-prepared PSCs while it is rather ineffective in preventing light-induced aging effects. Overall, thanks to the lower average degradation of the layers and interfaces, interface engineered PSCs could retain ~60% of theirinitial PCE after the aging respect to less than ~25% in the reference cells

Interfaces between perovskite solar cell (PSC) layer components play a pivotal role in obtaining high-performance premium cells and large-area modules. Graphene and related two-dimensional materials (GRMs) can be used to "on-demand" tune the interface properties of PSCs. We successfully used GRMs to realize large-area (active area 50.6 cm2) perovskite-based solar modules (PSMs), achieving a record high power conversion efficiency of 12.6%. We on-demand modulated the photoelectrode charge dynamic by doping the mesoporous TiO2 (mTiO2) layer with graphene flakes. Moreover, we exploited lithium-neutralized graphene oxide flakes as interlayer at the mTiO2/perovskite interface to improve charge injection. Notably, prolonged aging tests have shown the long-term stability for both small- and large-area devices using graphene-doped mTiO2. Furthermore, the possibility of producing and processing GRMs in the form of inks opens a promising route for further scale-up and stabilization of the PSM, the gateway for the commercialization of this technology.

Solar cells based on metal halide Perovskites have gained a key role in the field of photovoltaics due to their high efficiencies and low production costs. Still, there is considerable effort invested in tuning the perovskite crystal morphology and interface properties, in order to further improve the device performance. Among the solutions proposed so far, MXenes have recently turned into focus for their possibility of being incorporated within the perovskite and carrier transport layers, resulting in an important improvement of the cell efficiency. In this work, we present device simulations of Perovskite/MXene solar cells, where modeling of the interface energy alignments has been based on measurement data and ab initio calculations.

Ion beam depth profiling is increasingly used to investigate layers and interfaces in complex multilayered devices, including solar cells. This approach is particularly challenging on hybrid perovskite layers and perovskite solar cells because of the presence of organic/inorganic interfaces requiring the fine optimization of the sputtering beam conditions. The ion beam sputtering must ensure a viable sputtering rate on hard inorganic materials while limiting the chemical (fragmentation), compositional (preferential sputtering) or topographical (roughening and intermixing) modifications on soft organic layers. In this work, model (Csx(MA0.17FA0.83)100&minus, xPb(I0.83Br0.17)3/cTiO2/Glass) samples and full mesoscopic perovskite solar cells are profiled using low-energy (500 and 1000 eV) monatomic beams (Ar+ and Cs+) and variable-size argon clusters (Arn+, 75 &lt, n &lt, 4000) with energy up to 20 keV. The ion beam conditions are optimized by systematically comparing the sputtering rates and the surface modifications associated with each sputtering beam. X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, and in-situ scanning probe microscopy are combined to characterize the interfaces and evidence sputtering-related artifacts. Within monatomic beams, 500 eV Cs+ results in the most intense and stable ToF-SIMS molecular profiles, almost material-independent sputtering rates and sharp interfaces. Large argon clusters (n &gt, 500) with insufficient energy (E &lt, 10 keV) result in the preferential sputtering of organic molecules and are highly ineffective to sputter small metal clusters (Pb and Au), which tend to artificially accumulate during the depth profile. This is not the case for the optimized cluster ions having a few hundred argon atoms (300 &lt, 500) and an energy-per-atom value of at least 20 eV. In these conditions, we obtain (i) the low fragmentation of organic molecules, (ii) convenient erosion rates on soft and hard layers (but still different), and (iii) constant molecular profiles in the perovskite layer, i.e., no accumulation of damages.

In this work, we demonstrate the successful application of two-dimensional (2D) materials, i.e., graphene and functionalized MoS2, in perovskite solar cells (PSCs) by interface engineering the standard mesoscopic n-i-p structure. The use of 2D materials has the dual role to improve both the stability and the overall power conversion efficiency (PCE) of the PSCs compared to standard devices. The application of 2D materials is successfully extended to large-area perovskite solar modules (PSMs), achieving PCEs of 13.4% and 15.3% on active areas of 108 cm2 and 82 cm2, respectively. This performance results in record-high active area-indexed aperture PCE (AIAPCE) of 1266.5% cm2. In addition, the 2D materials-based PSMs show a stability under a prolonged (>1000 h) thermal stress test at 65 °C (ISOS-D2), representing a crucial advancement in the exploitation of perovskite photovoltaic technology.

Perovskite/silicon tandem solar cells represent an attractive strategy to push the market-leading crystalline silicon technology beyond its theoretical limit, maintaining low module costs. Record-high efficiency silicon heterojunction cells with a micrometre-sized pyramid textured front-surface hinder high-temperature and low-cost solution processing of the top-cell in a monolithic architecture. We present a mechanically stacked two-terminal perovskite/silicon tandem device, allowing independent fabrication and optimization of the sub-cells, subsequently coupled by contacting the back-electrode of the mesoscopic perovskite top-cell with the texturized and metalized front-contact of the silicon bottom-cell. Our champion device exhibits a stabilized efficiency of 25.9% over a 1.43 cm2 active area, achieved by optically engineering the hole-selective layer/rear-contact structure to minimize the optical losses, and improving the electrical performance with a graphene-doped mesoporous electron-selective layer. This represents a simple path toward fabricating tandem devices overcoming the limit of single junction solar cells and with a competitive levelized cost of energy.

The recent advancements in power conversion efficiency for organic solar cells is still complained by their reliability and stability remaining the main bottlenecks for organic photovoltaics large scale production and commercialization. In this paper, we aim to provide further insights understanding in degradation processes affecting stability in small molecule flat heterojunction (Glass/ITO/MoO 3/ZnPc/C 60/BCP/Ag) solar cells through a systematic aging study coupled with optoelectrical characterizations. In particular, the burn-in phenomenon affecting short-circuit current in thermal-stressed samples has been clearly correlated with the C 60 domain coarsening process and eventually to the decreased exciton lifetime.

To improve the efficiency of perovskite solar cells, careful device design and tailored interface engineering are needed to enhance optoelectronic properties and the charge extraction process at the selective electrodes. Here, we use two-dimensional transition metal carbides (MXene Ti3C2Tx) with various termination groups (Tx) to tune the work function (WF) of the perovskite absorber and the TiO2 electron transport layer (ETL), and to engineer the perovskite/ETL interface. Ultraviolet photoemission spectroscopy measurements and density functional theory calculations show that the addition of Ti3C2Tx to halide perovskite and TiO2 layers permits the tuning of the materials’ WFs without affecting other electronic properties. Moreover, the dipole induced by the Ti3C2Tx at the perovskite/ETL interface can be used to change the band alignment between these layers. The combined action of WF tuning and interface engineering can lead to substantial performance improvements in MXene-modified perovskite solar cells, as shown by the 26% increase of power conversion efficiency and hysteresis reduction with respect to reference cells without MXene. Addition of MXenes in the halide perovskite film, in the electron transport layer and at the interface between these layers is shown to enhance the efficiency of and reduce hysteresis in perovskite solar cells.

Hot-carriers, that is, charge carriers with an effective temperature higher than that of the lattice, may contribute to the high power conversion efficiency (PCE) shown by perovskite-based solar cells (PSCs), which are now competitive with silicon solar cells. Hot-carriers lose their excess energy in very short times, typically in a few picoseconds after excitation. For this reason, the carrier dynamics occurring on this time scale are extremely important in determining the participation of hot-carriers in the photovoltaic process. However, the stability of PSCs over time still remains an issue that calls for a solution. In this work, we demonstrate that the insertion of graphene flakes into the mesoscopic TiO2 scaffold leads to stable values of carrier temperature. In PSCs aged over 1 week, we indeed observe that in the graphene-free perovskite cells the carrier temperature decreases by about 500 K from 1800 to 1300 K, while the graphene-containing cell shows a reduction of less than 200 K after the same aging time delay. The stability of the carrier temperature reflects the stability of the perovskite nanocrystals embedded in the mesoporous graphene-TiO2 layer. Our results, based on femtosecond transient absorption measurements, show that the insertion of graphene can be beneficial for the design of stable PSCs with the aim of exploiting the hot-carrier contribution to the PCE of the PSCs.

Solution-processed hybrid bromide perovskite light-emitting-diodes (PLEDs) represent an attractive alternative technology that would allow overcoming the well-known severe efficiency drop in the green spectrum related to conventional LEDs technologies. In this work, we report on the development and characterization of PLEDs fabricated using, for the first time, a mesostructured layout. Stability of PLEDs is a critical issue; remarkably, mesostructured PLEDs devices tested in ambient conditions and without encapsulation showed a lifetime well-above what previously reported with a planar heterojunction layout. Moreover, mesostructured PLEDs measured under full operative conditions showed a remarkably narrow emission spectrum, even lower than what is typically obtained by nitride- or phosphide-based green LEDs. A dynamic analysis has shown fast rise and fall times, demonstrating the suitability of PLEDs for display applications. Combined electrical and advanced structural analyses (Raman, XPS depth profiling, and ToF-SIMS 3D analysis) have been performed to elucidate the degradation mechanism, the results of which are mainly related to the degradation of the hole-transporting material (HTM) and to the perovskite-HTM interface.

Interface engineering is performed by the addition of graphene and related 2 D materials (GRMs) into perovskite solar cells (PSCs), leading to improvements in the power conversion efficiency (PCE). By doping the mesoporous TiO2 layer with graphene flakes (mTiO2+G), produced by liquid-phase exfoliation of pristine graphite, and by inserting graphene oxide (GO) as an interlayer between the perovskite and hole-transport layers, using a two-step deposition procedure in air, we achieved a PCE of 18.2 %. The obtained PCE value mainly results from improved charge-carrier injection/collection with respect to conventional PSCs. Although the addition of GRMs does not influence the shelf life, it is beneficial for the stability of PSCs under several aging conditions. In particular, mTiO2+G PSCs retain more than 88 % of the initial PCE after 16 h of prolonged 1 sun illumination at the maximum power point. Moreover, when subjected to prolonged heating at 60 °C, the GO-based structures show enhanced stability with respect to mTiO2+G PSCs, as a result of thermally induced modification at the mTiO2+G/perovskite interface. The exploitation of GRMs in the form of dispersions and inks opens the way for scalable large-area production, advancing the possible commercialization of PSCs.

In this work, resonance Raman spectroscopy (RRS) together with a spectrally resolved analysis by transmittance and efficiency mapping (SATEM) have been applied as a powerful tool to detect and to understand deeply the degradation mechanisms suffered by a series-connected dye-sensitized solar cell (DSC) in a module under real working condition. When shadowing phenomena occur on the module, the shadowed cell works as a load rather than as a generator and suffers reverse bias (RB) condition that induces a progressive degradation until the complete device⬢s breakdown. The reported analysis follows the degradation processes involving both the electrolyte solution and the sensitizer during the aging time. In particular, polyiodides formation has been pointed out as crucial triiodide depletion mechanism in the electrolyte solution leading to a strong unbalance in the redox couple and to a slowdown in dye regeneration process. The final device breakdown occurs when hydrogen production within the electrolyte solution causes the breaking of the sealing and the partial electrolyte leakage from the active area. RRS demonstrated the irreversible structural changes suffered by dye molecules during this final stage by identifying the main degradation products. Finally, a spectrally resolved comparison between incident to photon current conversion efficiency (IPCE) for photo (PE) and counter electrode (CE) illumination were used, along with transmittance analysis, in order to derive detailed information about the structural modification suffered by the cell constituents. The combination between SATEM and RRS techniques exhaustively provided a deep comprehension of the DSC degradation processes by giving a route to further stabilize the devices for a feasible next commercialization.

Producing active thin films coated on supports resolves many issues of powder-based photo catalysis and energy harvesting. In this study, thin films of C-N-TiO2 were prepared by dynamic spin coating of C-N-TiO2 sol-gel on glass support. The effect of spin speed and sol gel precursor to solvent volume ratio on the film thickness was investigated. The C-N-TiO2-coated glass was annealed at 350 &deg, C at a ramping rate of 10 &deg, C/min with a holding time of 2 hours under a continuous flow of dry N2. The C-N-TiO2 films were characterised by profilometry analysis, light microscopy (LM), and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS). The outcomes of this study proved that a spin coating technique followed by an annealing process to stabilise the layer could be used for immobilisation of the photo catalyst on glass. The exposure of C-N-TiO2 films to UV radiation induced photocatalytic decolouration of orange II (O.II) dye. The prepared C-N-TiO2 films showed a reasonable power conversion efficiency average (PCE of 9%) with respect to the reference device (15%). The study offers a feasible route for the engineering of C-N-TiO2 films applicable to wastewater remediation processes and energy harvesting in solar cell technologies.

In this work, the successful application of graphene and related 2D materials in the field of perovskite solar cells (PSCs) has been demonstrated by engineering the standard mesoscopic n-i-p structure. The use of 2D materials has the dual role in improving both the stability and the overall efficiency of the proposed 2D-engineered PSC structure with respect to existing devices. The easy and successfully demonstrated device scaling-up allowed the realization of efficient large area graphene/perovskite modules.