TiO2 Nanocolumn Arrays for More Efficient and Stable Perovskite Solar Cells.

Influence of Charge Transport Layers on Capacitance Measured in Halide Perovskite Solar Cells

Decoupling the effects of defects on efficiency and stability through phosphonates in stable halide perovskite solar cells

ABX<sub>3</sub> crystalline perovskite material has many advantages: good photoelectric absorption property, high charge carrier mobility, good film formation, long charge carrier lifetime, and easy bandgap adjustment for absorption layer of perovskite solar cells. As a result, the power conversion efficiency (PCE) of the organic-inorganic halide perovskite solar cells (PSCs) has taken a tremendous step forward, from 3.9% in 2009 to a recently reported value over 25.5%. Thus, it shows great potential to compete with traditional silicon solar cells. However, PSCs preparing conditions are harsh and susceptible to environmental influences, thus leading to instability. Therefore, it is essential to prepare high-performance and stable PSCs in an air environment. This study aims to use the ion doping method to improve the performance and stability of PSCs and analyze the mechanism. This work focuses on enhancing PSCs efficiency and stability by performing FA<sup>+</sup> and Cl<sup>–</sup> doping experiments on MAPbI<sub>3</sub> films in air. The results show that a single Cl<sup>–</sup>-doping increases the carrier diffusion length, reducing the recombination of electrons and holes, and inducing the perovskite intermediate hydrate (CH<sub>3</sub>NH<sub>3</sub>)<sub>4</sub>PbI<sub>6</sub>·2H<sub>2</sub>O to form, promoting the crystallization of the thin film, and improving the device performance. On the other hand, a single FA<sup>+</sup>-doping will reduce the bandgap of perovskite and increase the short-circuit current density (<i>J</i><sub>SC</sub>) of the device, and FA<sup>+</sup> is susceptible to the influence of water vapor to induce a yellow <i>δ</i>-FAPbI<sub>3</sub> perovskite film to form, which leads the device performance to degrade. However, the prepared co-doping Cl<sup>–</sup>, FA<sup>+</sup> significantly improves overall PSCs device performance, yielding the highest PCE of 17.29%, and showing excellent stability by maintaining over 80% of the original PCE without any encapsulation after 1000-hour storage in ambient air.

In recent years, organic-inorganic hybrid perovskite solar cells have aroused the interest of a large number of researchers due to the advantages of large optical absorption coefficient, tunable bandgap and easy fabrication. Recently, the power conversion efficiency of organic-inorganic hybrid perovskite solar cells has been enhanced to more than 23% in laboratory. In solution processed perovskite solar cells, perovskite and charge transport layer are stacked together, due to the different crystallization rates leading to lattice mismatch near the surface region of perovskite film, resulting in a lot of interface defects, especially at the interface between perovskite and charge transport layer. What is more, the photo-induced free carriers must transfer across the interfaces to be collected. But the defects near the interface can trap photogeneration electrons, thus reducing the carrier lifetime and causing the charges to be recombined, which greatly influence the performance and stability of perovskite solar cells. Therefore, reducing and passivating these defects is critical for obtaining the high performance perovskite solar cells. Now, there have been made tremendous efforts devoting to advancing passivation techniques, such as doping and surface modification, for high efficiency perovskite solar cell with improved stability and reduced hysteresis. These approaches also contribute to improving the energy band alignment between carrier transport layers and perovskite absorber improving device performance, or resistance moisture to enhance device stability. In this review we mainly introduce the formation and the effect of defects on perovskite solar cells, analyze the mechanism for passivating the interfacial defects between charge transport layer and perovskite photo absorption layer for different materials, compare the effects of different passivation materials on the photovoltaic performance of perovskite solar cells, and summarize the role of these materials in passivating the defects. Finally we discuss the research trend and development direction of passivation defects in perovskite solar cells.

An efficient guanidinium isothiocyanate additive for improving the photovoltaic performances and thermal stability of perovskite solar cells

High-performance methylammonium-free ideal-band-gap perovskite solar cells

Organometal hybrid perovskite material has emerged as an attractive competitor in the field of photovoltaics due to its promising potential of low-cost and high-efficiency photovoltaic applications. Although organometal halide perovskite solar cell shows great potential to meet future energy needs, the degradation raises serious questions about its commercialization viability. At present, the stability of perovskite solar cells has been studied in various environmental conditions. Nonetheless, an understanding of the degradation and its performance of CH3NH3PbI3-xClx perovskite solar cell is limited. Herein, we report the mechanical and structural degradation of CH3NH3PbI3-xClx perovskite films at room temperature as a function of time and thermal instability of perovskite solar cells during the heating and cooling processes. For mechanical degradation measurement, we used nanoindentation for CH3NH3PbI3-xClx perovskite films fabricated on FTO/PEDOT:PSS substrate. The hardness and elastic modulus of perovskite films were measured as a function of time. In addition, the mechanical degradation of perovskite thin films was correlated with X-ray diffraction, steady-state and time-resolved photoluminescence (PL). We also investigated the thermal instability of perovskite thin films and the irreversible performance of perovskite solar cells. Particularly, the irreversible performance of CH3NH3PbI3-xClx was analyzed by measuring the development of crystallinity, charge trapping/detrapping, trap depth, and PbI- phase while varying the temperature of perovskite films and solar cells between room temperature and 82 °C. Surprisingly, we found that the degradation of both perovskite films and solar cells occurred at ~70°C. Remarkably, even after the perovskite solar cell temperature cooled down to room temperature, the performance of solar cells continuously degraded. The underlying mechanism of irreversibly degraded performance of perovskite films and solar cells were explained in terms of the development of phase separation, increased trapping rates and deep trap depth of defect states of perovskite films.

Lead-free tin perovskite solar cells

Carrier Dynamics Engineering for High-Performance Electron-Transport-Layer-free Perovskite Photovoltaics

Perovskite solar cells based on methylammonium iodide (MAPbI3) as active material have been intensively investigated for low cost and high power conversion efficiency (PCE). Todays, the PCE beyond 20% have been obtained using different structures of solar cells. However, there are still many problems needed to be solved prior to mass production and commercialization, in particular the stability of solar cells. The PCE decreases significantly in high humidity due to the decomposition of organic methylammonium iodide with water vapor from air-humid into lead iodide. Many researchers are now paying a lot of attentions to improve the stability of perovskite solar cells, including device structures, interfaces engineering and materials engineering. Recently, perovskite solar cell based on methylammonium lead(II) thiocyanate [MA(PbSCN)2] improved the humidity-stability of solar cells, due to higher binding energy of thiocyanate (SCN) ions to Pb ions as than that of iodide (I) ions to Pb ions. However, the PCE is lower than that of commonly used MAPbI3 solar cells, because the large bandgap leads to low light absorption. In this work, we present our recent study on J-V characteristic of solar cells using lead(II) thiocyanate Pb(SCN)2 doped lead(II) iodide as active materials of perovskite solar cells. We prepared perovskite films using two-step spin-coating method. We used two different structures of solar cells, mesoporous device and inverted planar structure. The best PCE of solar cells is 7% obtained with inverted planar structure. The mesoporous device structure shows lower performance than that of inverted planar structure, which is due to poor quality of electron transport layer, both titanium dioxide (TiO2) both blocking and mesoporous layers.

A compromise between high power conversion efficiency and long-term stability of hybrid organic-inorganic metal halide perovskite solar cells is necessary for their outdoor photovoltaic application and commercialization. Herein, a method to improve the stability of perovskite solar cells under water and moisture exposure consisting of the encapsulation of the cell with an ultrathin plasma polymer is reported. The deposition of the polymer is carried out at room temperature by the remote plasma vacuum deposition of adamantane powder. This encapsulation method does not affect the photovoltaic performance of the tested devices and is virtually compatible with any device configuration independent of the chemical composition. After 30 days under ambient conditions with a relative humidity (RH) in the range of 35-60%, the absorbance of encapsulated perovskite films remains practically unaltered. The deterioration in the photovoltaic performance of the corresponding encapsulated devices also becomes significantly delayed with respect to devices without encapsulation when vented continuously with very humid air (RH > 85%). More impressively, when encapsulated solar devices were immersed in liquid water, the photovoltaic performance was not affected at least within the first 60 s. In fact, it has been possible to measure the power conversion efficiency of encapsulated devices under operation in water. The proposed method opens up a new promising strategy to develop stable photovoltaic and photocatalytic perovskite devices.

To solve the energy crisis, humans are actively searching for renewable energy to replace fossil fuels. Solar energy has attracted much attention due to its clean and inexhaustible characteristics. The photovoltaic effect can be used to convert solar energy into electrical energy for human use; thus, it is important to develop high-performance, stable solar cells. Perovskite solar cells have been the subject of attention since the first perovskite solar cell was reported in 2009. The power conversion efficiency of perovskite solar cells has increased from 3.8% to 22.1% at present. Perovskite is considered a candidate material for a new generation of solar cells because of its high-power conversion efficiency, its simple fabrication process, its flexible characteristics and its controllable band gap. Several methods exist for the fabrication of perovskite solar cells, such as the one-step method and the two-step method as well as vapor deposition. Herein, we used a novel method, the flash method, to deposit perovskite film. After the perovskite precursor was deposited onto an electron transport layer by spin coating, the substrate was transferred into a vacuum chamber. The solvent was removed, and an interphase was formed after pumping. In this work, we fabricated perovskite devices by the flash method through a homemade vacuum flash system. The structure of the devices was ITO/SnO2/perovskite/spiro-OMeTAD/Ag, where spiro-OMeTAD is 2,2′,7,7′-tetrakis( N , N -di- p -methoxyphenylamine)- 9,9′-spirobifluorene. The fabrication parameters for depositing a perovskite active layer were studied. Through the analysis of the results, we show that the pumping pressure should be controlled under 20 Pa and that the time for laying up precursor solution needs to be less than 1 h. The open-circuit voltage decreased, and the short-circuit current density increased, with pumping. The filling factor reached a maximum at approximately 20 Pa. The films were observed by a scanning electron microscope to recognize the growth process. It was found that the perovskite begins to crystallize following pumping and that the surface of the perovskite film is relatively rough at this time, and defect pinholes can be observed. The film became uniform and showed no defect pinholes when decreasing pressure in the vacuum chamber. The interphase was formed when the pressure reached 20 Pa. After optimization, the highest power conversion efficiency reached was 18.09%. In addition, it was possible to control the perovskite bandgap width, to reduce the leakage current and to increase the carrier diffusion length by doping other halogen ions. Therefore, this work demonstrates improved performance of perovskite solar cells by doping of CH3NH3Cl into a perovskite precursor. A series of perovskite devices was fabricated by adjusting the doping ratio of CH3NH3Cl. The doping of the Cl element significantly improved the short circuit current density and fill factor of the devices. To further explore the influence of Cl doping, we observed the morphology of perovskite films with varying doping ratios with a scanning electron microscope. It was found that perovskite grains were enlarged after Cl doping, which increased the length of carrier diffusion. The highest power conversion efficiency of 18.69% was reached when the Cl doping ratio was 10%. For flexible devices, the highest power conversion efficiency obtained was 15.10%. This work has value for researchers in terms of the use of the vacuum flash method to fabricate perovskite devices.

. This review analyzes current research on perovskite solar cells as an alternative to traditional silicon-based solar cells. The paper discusses various types of solar cell architectures, including different combinations of the main layers, materials for electron and hole transport, as well as the anode, cathode, and conductive substrates. Different approaches to improving the stability and efficiency of these cells are examined through the use of new innovative materials for electron and hole transport layers (ETL and HTL), such as organic and inorganic analogs, as well as tandem and heterostructural elements. A review of the performance and limitations of solar cells with various perovskite materials, including hybrid ones, is also provided. A key issue discussed in the paper is the enhancement of the stability of perovskite solar cells, which can degrade significantly under the influence of moisture, ultraviolet light, and heat. The conclusion is drawn that the use of coatings, additives, and innovative materials contributes to the improvement of the stability of high-efficiency perovskite solar cells. The role of ETL and HTL in enhancing the efficiency and stability of solar cells is also analyzed. The paper emphasizes the importance of research in the field of perovskite solar cells for the development of new efficient, stable cell structures for mass production and commercialization.

Perovskite solar cells are one of the most promising photovoltaic technologies and have made extraordinary advances in production efficiency and simple processes. The possibility of replacing the extensively used silicon-based solar cell nowadays by perovskite solar cell has triggered a surge of interest in researching this unprecedented photovoltaic. The quality of the buried interface plays a crucial role in determining high performance perovskite solar cells (PSCs). Large defect density in perovskite solar cells has a destructive effect on device performance and modification of electron transport material is therefore considered as a feasible solution to this problem since it can not only passivate defects but also enhance the electrical property of electron transport material. However, it is challenging to guarantee its quality, performance and stability, which is pivotal for the commercialization of PSCs.A popular seasoning and flavor enhancer, AJI-NO-MOTO, an MSG (monosodium glutamate) product, is the purest form of AJI-NO-MOTO, the fifth taste, altogether different from sweet, salty, sour and bitter. AJI-NO-MOTO is widely used to intensify and enhance AJI-NO-MOTO flavors in sauces, broths, soups and many more foods. AJI-NO-MOTO is used around the world to bring out the delicious flavor of foods. Herein, we have identified that this AJI-NO-MOTO element makes not only food but also PSC "tastier". A facile strategy is developed to modify the SnO2/perovskite buried interface by incorporating different amount of AJI-NO-MOTO into SnO2 colloidal dispersion to improve performance and stability. AJI-NO-MOTO (monosodium glutamate) is a cheap and common material with multidentate ligands can coordinate with Sn to form stable dispersion, inhibiting the agglomeration of nanoparticles at the buried interface. In addition, the coordination between AJI-NO-MOTO and SnO2 nanoparticles in turn promotes the uniform distribution of AJI-NO-MOTO, which facilitates the uniform and effective passivation of the buried defects. The AJI-NO-MOTO modified SnO2 colloidal dispersion was utilized as electron transport material to fabricate perovskite solar cells. Throughout the experiment, AJI-NO-MOTO modified SnO2 colloidal dispersion as an electron transport layer was found that could considerably enhance the performance of the device compared to the pristine tin oxide. The conductivity of the as-spun AJI-NO-MOTO modified tin oxide layer was enhanced because of its dense and well-distributed film quality. Defect density in perovskite layer was also reduced due to the enlarged perovskite crystal and a suitable amount of non-reacted lead iodide passivating grain boundaries of perovskite crystal when a portion of AJI-NO-MOTO was dissolved in the perovskite precursor solution. Both the enhanced conductivity of the electron transport layer and reduced defect density in the perovskite layer led to a significantly promoted electron transfer efficiency from the perovskite layer to the electron transport layer.Employing a planar structure of FTO/SnO2/perovskite/OABr/Spiro-OMeTAD/Au, perovskite solar cells (PSCs) were systematically fabricated to explore the impact of AJI-NO-MOTO doping incorporation on J-V performance. Fig 1. illustrates the power conversion efficiencies (PCEs) for PSCs with varying AJI-NO-MOTO doping concentrations. Photovoltaic parameters, including Voc, Jsc, and FF are also depicted. Notably, the higher photovoltaic performance was achieved with AJI-NO-MOTO doping, with the higher Voc. Consequently, the conversion efficiency of AJI-NO-MOTO treated perovskite solar cell displayed an 7.7% remarkable improvement from 19.4 ± 1.4% to 20.9 ± 1.0% on average and an 5.0% improvement from 22.1% to 23.2% in champion devices when AJI-NO-MOTO modified tin oxide as electron transport layer was used in comparison with pristine tin oxide. This facile AJI-NO-MOTO modification strategy to tin oxide had achieved great success and may provide an opportunity for improving the performance and enhances the operation stability of perovskite solar cells. Figure 1

Revealing fundamentals of charge extraction in photovoltaic devices through potentiostatic photoluminescence imaging