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Perovskite solar cells (PSCs) are currently the leading thin-film photovoltaic technology owing to their high power conversion efficiency (PCE), as well as their low-cost and facile manufacturing process. Two-dimensional (2D) materials have been reported to improve both the PCE and the stability of PSCs when incorporated across the device's layered configuration. Hereby, a two-fold engineering approach is implemented in inverted PSCs by using ultra-thin Bi2Te3 flakes, i.e.: (1) to dope the electron transport layer (ETL) and (2) to form a protective interlayer above the ETL. Thorough steady-state and time-resolved transport analyses reveal that our first engineering approach improves the electron extraction rate and thus the overall PCE (+6.6% vs. reference cells), as a result of the favourable energy level alignment between the perovskite, the ETL and the cathode. Moreover, the Bi2Te3 interlayer, through the second engineering approach, facilitates further the electron transport and in addition protects the underlying structure against chemical instability effects, leading to enhanced device performance and stability. By combining the two engineering approaches, our optimised PSCs reach a PCE up to 19.46% (+15.2% vs. reference cells) and retain more than 80% of their initial PCE, after the burn-in phase, over 1100 h under continous 1 sun illumination. These performances are among the highest reported in the literature for inverted PSCs.

An analytical rheological model capable of describing the loading speed dependent in-plane shear behavior of the unreinforced masonry (URM) walls with a multi-layer bed joint subjected to static-cyclic shear loading is presented. Such joints consist of a core soft layer protected by two thin extruded elastomer membranes, which in turn are placed in a bed mortar joint. The extruded elastomer membranes are employed to prevent and/or limit the deterioration of the core soft layer during the cyclic action. Joint behavior is assumed to be linear elastic-perfectly viscoplastic and has been captured by a uniaxial model consisting of three elements: an elastic spring connected in series with the frictional slider and a dashpot (viscous damper). Assuming a linear elastic behavior of masonry, the model was able to describe the in-plane horizontal force-displacement behavior of URM walls with multi-layer bottom bed joints and was validated against the experimental results.

Methylammonium (MA) and formamidinium (FA) mixed perovskites have been widely utilized in invert planar perovskite solar cell (PSC) applications due to their great potentials such as solution processing, high power conversion efficiency, high absorption, and low cost. To commercialize the PSCs, further improving the device performance without detrimentally changing the device configuration is important at present. Herein, small amount (5%) of CsI is introduced to form a pinhole-free mixed perovskite light absorption layer in a flexible photovoltaic system with enhanced main photovoltaic parameters of the device, resulting in a ~ 36% enhancement of power conversion efficiency (PCE) from 8.9% to 12.1% (from 11.3% to 14.6% for rigid device). The origins of the enhancement have been studied by exploring the crystal structures, optical absorption, and crystal morphlogies of the synthesised perovskite layers and charge carrier behaviors of the devices. Through small perturbation transient photovoltage (TPV) measurements, the lifetime of the charge carriers are found remarkably increased after the small amount of CsI doping. These characteristics make cation doping of the mixed perovskite layer a promising method in facile tuning of the film quality of the perovskite layer for efficient charge carriers transporting and further boosting the PCE of the devices.

Low-temperature optoelectrical studies of perovskite solar cells using MAPbI3 and mixed-perovskite absorbers implemented into planar and mesoporous architectures reveal fundamental charge transporting properties in fully assembled devices operating under light bias. Both types of devices exhibit inverse correlation of charge carrier lifetime as a function of temperature, extending carrier lifetimes upon temperature reduction, especially after exposure to high optical biases. Contribution of bimolecular channels to the overall recombination process should not be overlooked because the density of generated charge surpasses trap-filling concentration requirements. Bimolecular charge recombination coefficient in both device types is smaller than Langevin theory prediction, and its mean value is independent of the applied illumination intensity. In planar devices, charge extraction declines upon MAPbI3 transition from a tetragonal to an orthorhombic phase, indicating a connection between the trapping/detrapping mechanism and temperature. Studies on charge extraction by linearly increasing voltage further support this assertion, as charge carrier mobility dependence on temperature follows multiple-trapping predictions for both device structures. The monotonously increasing trend following the rise in temperature opposes the behavior observed in neat perovskite films and indicates the importance of transporting layers and the effect they have on charge transport in fully assembled solar cells. Low-temperature phase transition shows no pattern of influence on thermally activated electron/hole transport.

An analytical rheological model capable of describing the loading speed dependent in-plane shear behaviour of a masonry multi-layer bed joint is presented in this paper. Such joints consist of a core soft layer protected by two thin extruded elastomer membranes, which in turn are placed in a bed mortar joint. The extruded elastomer membranes are employed to prevent and/or limit the deterioration of the core soft layer during the cyclic action observed in previous investigations. Joint behaviour is assumed to be linear elastic-perfectly viscoplastic and has been captured by a uniaxial model consisting of three elements: an elastic spring connected in series with the frictional slider and a dashpot (viscous damper). The rheological model is characterized by three material parameters that have been assessed from several series of monotonic and static-cyclic tests on small masonry specimens (triplets). In addition to these three parameters, the contraction of the thickness of multi-layer bed joint due to pre-compression has been considered too. Although model parameters are determined for the multi-layer bed joint with a rubber granulate core soft layer, the parameter space can be extended to the other types of core soft layer once the appropriate test data becomes available.

Planar inverted lead halide photovoltaics demonstrate remarkable photoconversion properties when employing poly(triarylamine) (PTAA) as a hole transporting layer. Herein, we elucidate the effect of ambient ultraviolet (UV) degradation on the structural and operational stability of the PTAA hole transporter through a series of rigorous optoelectrical characterization protocols. Due attention was given to the interplay between the polymer and perovskite absorber, both within the framework of a bilayer structure and fully assembled solar cells. The obtained results imply that UV degradation exerts a major influence on the structural integrity of PTAA, rather than on the interface with the perovskite light harvester. Moreover, UV exposure induced more adverse effects on tested samples than environmental humidity and oxygen, contributing more to the overall reduction of charge extraction properties of PTAA, as well as increased defect population upon prolonged UV exposure.

PbI2-enriched mixed perovskite film [FA0.81MA0.15Pb(I0.836Br0.15)3] has been widely studied due to its great potential in perovskite solar cell (PSC) applications. Herein, a FA0.81MA0.15Pb(I0.836Br0.15)3 film has been fabricated with the temperature-dependent optical absorption spectra utilized to determine its exciton binding energy. A ∼13 meV exciton binding energy is estimated, and a near-unity fraction of free carriers out of the total photoexcitons has been obtained in the solar cell operating regime at equilibrium state. PSCs are fabricated with this mixed perovskite film, but a significant electron transport barrier at the TiO2–perovskite interface limited their performance. Cs2CO3 and CsI are then utilized as functional enhancers with which to substantially balance the electron and hole transport and increase the carriers (both electrons and holes) mobilities in PSCs, resulting in much-improved solar-cell performance. The modified PSCs exhibit reproducible power conversion efficiency (PCE) values ...

Titanium dioxide (TiO2) nanoporous hemispheres (NHSs) with a radius of ∼200 nm are fabricated by electrospraying a hydrothermally synthesized TiO2 nanoparticle (NP) suspension solution. The resulting TiO2 NHSs are highly porous, which are beneficial to the infiltration of perovskites and provide a larger contact area, as building blocks to construct a mesoporous TiO2 layer for FA0.81MA0.15Pb(I0.836Br0.15)3 based perovskite solar cells (PSCs). By varying the TiO2 NHS collecting period (15 s, 30 s, 60 s and 90 s) during the electrospraying process, the performance of PSCs changes with different TiO2 NHS distribution densities. The optimized PSC employing TiO2 NHSs (60 s) exhibits a photovoltaic conversion efficiency (PCE) as high as 19.3% with a Jsc of 23.8 mA cm−2, a Voc of 1.14 V and a FF of 0.71. Furthermore, the PSC possesses a reproducible PCE value with little hysteresis in its current density–voltage (J–V) curves. The small perturbation transient photovoltage (TPV) measurement reveals a longer free carrier lifetime within the TiO2 NHS based PSC than that in the TiO2 NP based PSC, and the time of flight (TOF) photoconductivity measurement shows that charge mobilities in this system are also enhanced. These characteristics make TiO2 NHSs a promising electron transport material for efficient photovoltaic devices.

Organometallic lead-halide solar cells exhibited immense potential over the past years and reached the transition point from lab to industry-scale fabrication. However, bridging this gap and establishing perovskites as a viable competitor to conventional Si-based photovoltaics, hinges on the success of cost-effective upscaling process. The key factor impeding this transition is operational stability of solar cells under realistic photoconversion conditions. To this extent, reducing the dimensionality of cell constituents appears as a promising and very attractive approach to tackle this issue. The beneficial influence of such materials on device stability, which is explicitly tied to the engineered interface quality with underlying layers, comes as a result of complex interplay between energy alignment, strain-induced interactions and barrier-like properties of 2D components. The aim of this perspective is to briefly outline key challenges regarding the exploitation of 2D materials within the framework of perovskite photovoltaics, as well as to suggest further development directions.

Bismuth ferrite (BFO) is one of the most popular multiferroic oxides and has recently attracted interest of scientific community as a suitable material for light harvesting applications, due to its efficient polarization-governed mechanism of charge separation and ability to generate above-bandgap voltages. Identified as a promising photoferroic material, BFO has been a subject of various photoconversion studies in conjunction with other oxides and polymers commonly found in organic photovoltaics. In this report, we examined fundamental device parameters such as carrier lifetime, charge transport and diffusion coefficient within BFO/polymer bilayer, utilizing transient photovoltage and photocurrent spectroscopy techniques. Tested devices were fabricated via simple and inexpensive solution processing route, using nitrate precursors for BFO synthesis. Obtained results suggest formation of space-charge region within the device causing charge carrier lifetimes extension up to 350 μs in the absence of external voltage bias, as well as fast charge extraction (

Recent advancements in the area of perovskite photovoltaics have drawn wide attention of scientific community, mainly because of exceptional light absorbing properties exhibited by these organometallic halides. One of the main advantages perovskites have is their ability to be processed from solutions at relatively low temperatures. This paper briefly describes main structural, optical and electrical properties of perovskite materials, as well as the most popular solution processing techniques. We reflect on current progress in fabrication of solar cells containing organic–inorganic perovskites, device inner workings and effect of cell architecture on efficiency, along with prospective fine tuning of device properties through alteration of organometallic halide structure. Over the span of only three years, reported photoconversion efficiencies of such devices went from 3.8% to over 19%, with further increase being expected in near future. Finally, we describe other prospective applications for different perovskite materials. There is no doubt that perovskite photovoltaics possess great potential to provide bright future for the field of solar cells research, but whether they are going to live up to their expectations, remains to be seen.

The goal of the research project presented here is to investigate the effect of multi-layer bed joints on the shear behaviour of unreinforced masonry elements subjected to cyclic actions, and to assess the shear mechanical characteristics of multi-layer bed joints. Such joints consist of a core soft layer protected with two thin extruded elastomer membranes, which in turn are placed in a bed mortar joint. The extruded elastomer membranes are employed to prevent and/or limit the deterioration of the core soft layer during the cycling action, which has been observed in previous investigations. Five different core soft layer materials, namely rubber granulate, cork-rubber granulate, cork, bitumen and polyvinylchloride were employed. A total of 57 clay block masonry triplets were subjected to both monotonic and static-cyclic loading under varying levels of pre-compression. The shear behaviour of the specimens was greatly influenced by the applied pre-compression level and by the loading speed. Increasing the level of pre-compression leads to the higher values of shear strength. The same is true for increasing loading speed. Further, for the prediction of the failure shear force a Mohr–Coulomb failure criterion with zero cohesion can be applied. Finally, experimental findings showed that extruded elastomer layers largely fulfilled the intended protective role. The results indicate that multi-layer bed joints with adequate material properties have the potential to change the typical brittle shear response of unreinforced masonry walls to a more desirable quasi-ductile behaviour. Moreover, based on the observed hysteretic behaviour, considerable energy dissipation could be expected in masonry structures with multi-layer bed joints. Such behaviour would be desirable for enhanced seismic performance.

In recent years, organic–inorganic lead halides attracted widespread interest, mainly due to their impressive photoconversion properties and low-cost solution processing. In this study, we employed small amplitude transient photovoltage and photocurrent spectroscopy to investigate charge transport and recombination properties of perovskite CH3NH3PbI3–xClx solar cell under realistic light harvesting conditions (

In order to extend the latest findings on the in-plane shear behavior of rectangular unreinforced masonry (URM) wallettes with soft-layer bed joints and gain insight into the possible influ...

A series of static-cyclic shear tests on full-scale unreinforced masonry (URM) walls with multi-layer bed joints have been performed within a research project on the seismic behaviour of unreinforced masonry walls with soft layer membrane placed in the bed joint to induce sliding. Walls were made using typical perforated Swiss clay blocks and standard cement mortar and the so-called multi-layer bottom bed joints, which comprise a core soft layer protected by two layers of extruded elastomer and placed in the middle of mortar joint. The preliminary testing phase was aimed at choosing the most suitable core soft layer type among the four types considered (rubber granulate, cork, cork-rubber granulate and bitumen). The main testing phase comprised five tests on storey-high URM specimens with rubber granulate core soft layers performed to investigate the influence of the size, the pre‐compression level and the aspect ratio on the seismic behaviour of URM walls with a multi‐layer bed joint. Sliding occurred in all tested specimens. However, the final failure mode as well as the displacement capacity of test specimens were governed by the extent of shear and tensile (vertical) cracks that developed from the bottom brick course. The response of specimens can be interpreted using a multilinear horizontal force-displacement response idealization, whose parameters can be estimated using the proposed equations.

Photoinduced charge selective carrier extraction by linearly increasing voltage technique allows straightforward assessment of charge transport properties within planar and mesostructured perovskite solar cells with respect to light intensity and signal delay time. Charge sensitive device architecture is realized through implementation of insulating layer between the anode or cathode to prevent extraction of unwanted type of carriers. Resulting behavior of comparatively efficient mesoporous and planar solar cells exhibits well balanced charge transport with slight dependence of charge mobility on applied laser pulse fluence, for given pulse delay times. Very similar charge carrier mobilities are present within mesoporous devices, whereas holes trail approximately half an order of magnitude behind electrons in planar structured specimens. Moreover, dispersive transport is identified in the electron selective devices with titanium oxide electron transporter, suggesting considerable presence of trapping states at the perovskite interface, whereas no such behavior characterizes planar samples. Variation in delay time between laser pulse and extraction ramp only affects initial charge concentration present within the device, while transient outlay remains unchanged, indicating absence of film charging effect.