Search

Perovskite solar cells (PSCs) longevity is nowadays the bottleneck for their full commercial exploitation. Although lot of research is ongoing, the initial decay of the output power - an effect known as "burn-in" degradation happening in the first 100 h - is still unavoidable, significantly reducing the overall performance (typically of20%). In this paper, the origin of the "burn-in" degradation in n-i-p type PSCs is demonstrated that is directly related to Li

Although perovskite solar cells have achieved great development in the device performance, the device stability is still a crucial issue hinder the further development. The ion migration is a main reason for the poor stability of the perovskite solar cells. Here, we use a cross-linking material, polydimethylsiloxane (PDMS) to dope the perovskite layer to improve the operational stability. We systematically studied the effect of curing agent content in PDMS on the device performance and stability. The characterization of perovskite film indicates that PDMS primarily doped in the perovskite layer and as well as enriched at the surface of perovskite film. Doping of PDMS promoted the crystallization of perovskite phase, leading to increase of short circuit density (JSC) and fill factor (FF) of the solar cells. In addition, PDMS doping improved the operational stability of device due to the suppressing the migration of iodide ions during aging. Moreover, the higher content of curing agents used in PDMS, the better stability of the devices. This work indicates PDMS doping the perovskite layer with a suitable content of curing agent can produce a better operational stability of the perovskite solar cells.

n–i–p Type perovskite solar cells generally require air oxidation of the Spiro-OMeTAD layer to achieve high power conversion efficiency (PCE). However, the detailed oxidation mechanism is still not fully understood. In this paper, oxidation of Spiro-OMeTAD was demonstrated via a non-contact electrochemical route using UV-Vis absorption, laser beam induced current (LBIC) imaging and secondary ion mass spectrometry (SIMS) profiling of the Spiro-OMeTAD films. At the cathode, oxygen is reduced to form OH− with the help of H2O, while the anodic reaction is the oxidation of Spiro-OMeTAD to form Spiro-OMeTAD+. Diffusion of Li+ towards the surface of the Ag electrode completes the electrochemical cycle and increases the conductivity of the hole-transporting layer. SIMS analyses of the completed devices demonstrate that the oxidation of Spiro-OMeTAD also leads to migration of Li+ through the perovskite layer into SnO2, which supposedly leads to an increase of the built-in voltage. We verify these results by incorporation of the experimentally measured Li+ concentration into a numerical drift-diffusion simulation, to replicate solar cell J–V-curves. This work provides a new insight into the oxidation of Spiro-OMeTAD in perovskite solar cells, and demonstrates that Li+ migration is involved in the oxidation of Spiro-OMeTAD.

Transparent conductive electrode (TCE) is an essential part of modern optoelectronic devices. Silver nanowire (AgNW) is regarded as the most promising TCEs, owing to its balanced conductivity and transparency, and solution processability. The use of insulating polyvinyl pyrrolidone (PVP) surfactant limits the conductivity of the final AgNW networks. Herein, by introducing a small amount of deionized water into the AgNWs dispersion in isopropanol (IPA), the conductivity of the spray-coated AgNW electrode was significantly improved. Sheet resistance (Rs) of 27.0 Ω □−1 with transparency of 92% (at 550 nm) was obtained for the AgNW films spray coated from the AgNW ink with 20% water, which is much lower than the IPA-only AgNW film (120.9 Ω □−1 with similar transparency). Morphology analysis confirmed that water is able to wash PVP away from the AgNW surface and promote the formation of AgNW bundles, which increase the conductivity. The optimized AgNW ink was then used for perovskite and polymer solar cells. High power conversion efficiencies of 14.04% for perovskite solar cell and 6.44% for organic solar cells with averaged light transmittance of 21.7% and 33.12% are achieved, respectively, which are among the highest values for all solution-processed semi-transparent perovskite and polymer solar cells.

Silver nanowires (Ag NWs) network is an excellent candidate as flexible transparent electrode applying in flexible perovskite solar cells, owing to their excellent electrical and optical properties. However, several problems including large surface roughness, chemical reaction between Ag and perovskite precursor, and migration of Ag limited the application in high performance perovskite solar cells. Aiming to solve these problems, the composite electrode combining the spray coated Ag nanowires and the low-temperature sol-gel zinc oxide was developed in this work. The optimized concentration and annealing temperature of sol-gel ZnO were 0.45 M and 150 °C. The introduction of zinc oxide with suitable concentration caused slight impact on the transmittance and sheet resistant of transparent composite electrode, and promoted mechanical and chemical stability in air relative to the pristine Ag NWs electrode. The use of the composite flexible electrode could decrease the surface roughness of the Ag NWs electrode, passivate the reaction of perovskite and silver electrode, and prevent the migration of Ag. As a consequence, the performance of the flexible device significantly improved from 9.51% to 13.12%. Under the AM 1.5G constant illumination, the optimization device has a remarkably improved stability than pristine device. This study demonstrates that spray Ag NWs as bottom electrode is suitable for flexible perovskite solar cells. Meanwhile, it's an effective method using sol-gel ZnO to construct composite electrode to promote the device performance and stability.

Thermal spray coatings are widely applied as antiwear solutions in a variety of industries. In such applications, the coatings are frequently susceptible to two competing mechanical responses, (a) indentation deformation and (b) fracture, caused by erodent, abrasive, and debris originated from the environment or produced during use [1–4]. Microhardness and fracture toughness can quantify the resistance to deformation and fracture, respectively [5]. Thus indentation tests, especially Vickers indentation tests for determining the microhardness and fracture toughness of materials, are commonly used as quality control tools. Correspondingly, the Vickers hardness of thermal spray coatings considering measurement locations, directions, and indenter loads were studied [6–8]. The fracture toughness values of some coatings were measured employing the Vickers indentation technique and correlated with the friction and wear behaviors of the coatings [4, 9, 10]. However, no attempt was made so far to combine the Vickers hardness and fracture toughness into a common description for thermal spray coatings. Thermal sprayed Cr3C2-NiCr coatings are often used in high temperature applications such as in turbine engine and steel industry [2, 4, 11, 12]. Several studies have contributed to the processing, characterization, mechanical, and tribological properties of this type of coating [2, 4, 8, 11–18]. Plastic deformation [15], interlamellar boundary sliding [8, 17, 18], and intralamellar cracking, [19] were proposed to explain the mechanical properties and wear behavior of these coatings. In the present study, a universal deformation/fracture diagram, based on the methodology developed by Lawn and Marshall [5], has been presented for plasmasprayed Cr3C2-NiCr coatings using several feedstock materials. The threshold loads and crack dimensions that the coatings might sustain in a contact event, without the onset of fracture, are obtained from the universal deformation/fracture diagram. The purpose of this paper is to assess the susceptibilities to deformation and fracture of the coatings with respect to the starting powders, coating microstructure, and indentation direction, so as to provide a physical insight into the mechanical and tribological properties of the coatings.

Three kinds of nanostructured alumina coatings were prepared by air plasma spraying (APS). The microstructure of these coatings was characterized by SEM and X-ray diffraction (XRD). The surface roughness, porosity and microhardness of as-sprayed coatings were measured. The results indicated that the smaller the size of starting powder was, the better properties the coating possessed. The differences among phase analysis of these as-sprayed coatings could explain it.

Wear of plasma sprayed Cr2O3 TiO2, Cr3C2-NiCr and WC-Co coatings have been evaluated with a block-on-ring arrangement under dry and lubricated conditions. The results indicated that the wear of the coatings was interpreted in term of subsurface grain fracture which was related to the special microstructure of the coatings such as size, shape and distribution of pore as well as crack. Among the four kinds of coating, Cr2O3 coating possesses the lowest wear coefficient. Water accelerated cracking and fracturing and deteriorated the wear resistance of both Cr3C2-NiCr and TiO2 coatings. Ethanol reduced the wear of Cr3C2-NiCr coating, which was attributed to the formation of a smooth surface film mainly consisting of Cr2O3. Wear of Cr2O3, coating against an Al2O3 ball at high temperature has been also produced. The wear of Cr2O3 coating against Al2O3 ceramics decreased with increase in temperature and load. The reaction between Cr2O3 coating and Al2O3, ceramics at high temperature and the formation of a protective film consisting of Cr2O3, Al2O3 and SiO2 glass on the surface of Cr2O3 coating improved the wear resistance of Cr2O3 coating.

Defect‐mediated recombination losses limit the open‐circuit voltage (VOC) of perovskite solar cells (PSCs), negatively affecting the device's performance. Bulk and dimensional engineering have both been reported as promising strategies to passivate shallow defects, thus improving the photovoltaic conversion efficiency (PCE). Here, a combined bulk and surface treatment employing chlorine‐based compounds is employed. Methylammonium chloride (MACl) is used as a bulk additive, while 4‐methylphenethylammonium chloride (MePEACl) is deposited onto the perovskite surface to produce a low‐dimensional perovskite (LDP) and reduce nonradiative recombination. Through structural and morphological investigations, it can be confirmed that bulk and surface doping have a beneficial effect on the film morphology and its overall quality, while electroluminescence (EL) and photoluminescence (PL) analyses demonstrate an increased and more homogeneous emission. Applying this double passivation strategy in PSC fabrication, a boost is observed in both the short‐circuit current density and the VOC of the devices, achieving a champion 21.4% PCE while improving device stability.