Hysteresis Index Research Articles

Thermal Annealing Influence on the Properties of Heterostructure Based on 2 at.%Eu Doped SnO2 and Cu1.8S

Aiming at optoelectronic applications, a heterostructure based on Eu-doped tin oxide (SnO2) and copper sulfide (Cu2−xS) is built. SnO2 thin films doped with 2 at.% Eu were obtained by the sol–gel dip-coating and spin-coating techniques, whereas the Cu2−xS film was obtained by resistive evaporation. Samples were prepared using three distinct thermal annealing temperatures of the SnO2 bottom layer: 150°C, 250°C and 500°C. Transmittance and absorption spectra of the heterostructure shows high transparency in the visible to near infrared range (600–1800 nm), and considering the dominance of SnO2 on light absorption, it was possible to evaluate the sample indirect bandgap around 3.5 eV, independently of the thermal annealing temperature. Cyclic voltammetry and impedance spectroscopy, in conjunction with calculation of the hysteresis index, show that the heterostructure presents a behavior highly capacitive, and the higher annealing temperature leads to higher capacitance at low frequencies, similar to the observed qualitative behavior of supercapacitive devices. Besides, the sample with the SnO2 bottom layer annealed at 500°C yielded a higher current density.

Hysteresis Index: A Figure without Merit for Quantifying Hysteresis in Perovskite Solar Cells

Hysteresis Index: A Figure without Merit for Quantifying Hysteresis in Perovskite Solar Cells

Charge Injection and Electrical Response in Low-Temperature SnO2-Based Efficient Perovskite Solar Cells.

Defining low-temperature engineering protocols for efficient planar perovskite solar cell (PSC) preparation is important for fabrication simplification and low-cost production. In the present work, we have defined a low-temperature (123 °C) protocol for the preparation from a solution of SnO2 layers which are efficient for an application as an electron transporting layer (ETL) in PSCs. Thin, conformal, and transparent layers have been obtained. The related PSCs have shown best devices with a power conversion efficiency of 18.22% and low-hysteresis J- V curves (a hysteresis index of 6.7%). Charge injection has been thoroughly studied by photoluminescence decay measurements. The decay curves followed a biexponential function. The injection of holes into the spiro-OMeTAD layer was found very fast and is a no-limiting step. On the other side, the charge injection into the oxide ETLs depends on its structure and on the oxide. The time constant for the low-temperature SnO2 layers is close to that of the mesoporous benchmark layers with a fast (surface) and a slow (bulk) component at 11 and 129 ns with relative contributions calculated at 13% and 87%, respectively. The phenomena occurring at a longer time scale have been investigated by impedance spectroscopy. The SnO2 cell spectra showed no intermediate-frequency inductive loop. The very low frequency part of the spectra was characterized by the beginning of an arc of a circle at the origin of a very large resistance over a large applied potential range. This resistance, along with an intermediate-frequency resistance, has been assigned to a recombination resistance and explains the very large Voc achievable with SnO2 PSCs. The existence of a capacitance at the intermediate frequency with a noticeable low value at about 0.2 mF·cm-2 is linked with the low hysteresis of the devices.

Evaluation of applicability of filling materials in permeable reactive barrier (PRB) system to remediate groundwater contaminated with Cd and Pb at open solid waste dump sites

Abstract This study aimed to identify appropriate filling materials for a permeable reactive barrier (PRB) system to treat groundwater contaminated with trace metals in the vicinity of solid waste landfills in Sri Lanka. Mixtures of alluvial loamy soil, coconut shell biochar, and laterite clay brick in different proportions were tested as easily-available PRB adsorbents. A series of adsorption and desorption experiments were carried out to investigate the effects of initial concentration, pH, ionic strength, and multiple competitive trace elements on Cd and Pb adsorption onto the tested adsorbents. In addition, hydraulic conductivities (Ks) of the tested adsorbents under different compaction levels were measured to examine a suitable packing condition for the PRB system. Results showed that the Langmuir model performed well for fitting Cd and Pb adsorption isotherms and maximum adsorption capacities (Qm) for Pb (2.1–15.3 mg/g) became higher than those for Cd (0.8–6.8 mg/g). All tested adsorbents showed low leaching of adsorbed metals with high hysteresis indices in desorption studies. In the multiple trace element solution, the existence of other trace metals (Cu, Zn, Ni) had a significant effect on Cd adsorption but less on Pb adsorption. The three mixed adsorbents had no dependency on the initial pH and ionic strength of the solution, while the single material showed a low dependency in both Cd and Pb adsorption. The inclusion of brick was effective to improve the hydraulic property and measured Ks values for the 75% brick mixed materials resulted of >10−4 cm/s at high compaction levels (Dr = 90% and 100%). Three mixed materials can be strongly recommended as a PRB filling material to treat landfill leachate based on their reactivity and hydraulic properties.

Investigation of hysteresis during anesthetic-induced unconsciousness by using brain functional networks

Abstract Hysteresis exists during the induction of and emergence from the anesthetic induced unconsciousness. Earlier researches considered this hysteresis as a pharmacokinetic delay, and its elimination has been the target of pharmacokinetics-pharmacodynamics (PK PD) model for anesthetic agents. However, recent animal studies suggested that the observed hysteresis may be an intrinsic characteristic of the neural system. Thus, investigating the anesthetic-induced hysteresis in human subjects during the full course of general anesthesia was needed. In this work, we employed bispectral index (BIS) as the index for anesthetic effect-site concentration. The anesthetic effect was tracked by the graph theory-based measures obtained from the brain functional networks that was estimated from 60-channel EEG data. The hysteresis in this work is defined as the discrepancy between the estimated graph theory-based measures at the same BIS level during the process of anesthesia induction and emergence. Our results showed that the hysteresis quantified by graph theory-based measures exists in both delta and beta bands. Further, the frontal lobe and parietal lobe were identified to be responsible for the observed hysteresis. Moreover, it was observed that the proposed hysteresis index was significantly correlated with the time duration of the anesthesia induction and emergence. These findings suggested that the hysteresis might be an intrinsic characteristic of the human neural system, and it should be taken into consideration when designing PK PD models for the anesthetics such as Propofol.

How measurement protocols influence the dynamic J-V characteristics of perovskite solar cells: Theory and experiment

The dynamic effects observed in the J-V measurements represent one important hallmark in the behavior of the perovskite solar cells. Proper measurement protocols (MPs) should be employed for the experimental data reproducibility, in particular for a reliable evaluation of the power conversion efficiency (PCE), as well as for a meaningful characterization of the type and magnitude of the hysteresis. We discuss here several MPs by comparing the experimental J-V characteristics with simulated ones using the dynamic electrical model (DEM). Pre-poling conditions and bias scan rate can have a dramatic influence not only on the apparent solar cell performance, but also on the hysteretic phenomena. Under certain measurement conditions, a hysteresis-free behavior with relatively high PCEs may be observed, although the J-V characteristics may be far away from the stationary case. Furthermore, forward-reverse and reverse-forward bias scans show qualitatively different behaviors regarding the type of the hysteresis, normal and inverted, depending on the bias pre-poling. We emphasize here that correlated double-scans, forward-reverse or reverse-forward, where the second scan is conducted in the opposite sweep direction and begins immediately after the first scan is complete, are essential for a correct assessment of the dynamic hysteresis. In this context, we define a hysteresis index which consistently assigns the hysteresis type and magnitude. Our DEM simulations, supported by experimental data, provide further guidance for an efficient and accurate determination of the stationary J-V characteristics, showing that the type and magnitude of the dynamic hysteresis may be affected by unintentional pre-conditioning in typical experiments.

Effect of functional group position change of pyridinesulfonic acid as interface-modified layer on perovskite solar cell

There are fewer researches on the effect of functional group position change on device performance for highly efficient perovskite solar cell. In this work, we take pyridinesulfonic acid as an example, and study the effect of the isomeride: 2- and 3-pyridinesulfonic acid self-assembled monolayer on device performance for highly efficient perovskite solar cell. The efficiency of control device is 14.65% (Hysteresis Index = 0.31) under illumination of a simulated sunlight (AM 1.5G, 100 mW cm−2). Through use of the 3-pyridinesulfonic acid self-assembled monolayer, the device exhibits striking improvements to reach the efficiency of 16.88% (Hysteresis Index = 0.02), which constitutes an enhancement compared to those of 2-pyridinesulfonic acid self-assembled monolayer modified device (16.54%, Hysteresis Index = 0.02). The enhanced photovoltaic performances can be attributed to the larger perovskite grain sizes, and easier passivation of electron transporting layer/perovskite interface, which promote the charge separation, transport and collection.

Stable high-performance perovskite solar cells based on inorganic electron transporting bi-layers

As one of the significant electron transporting materials (ETMs) in efficient planar heterojunction perovskite solar cells (PSCs), SnO2 can collect/transfer photo-generated carriers produced in perovskite active absorbers and suppress the carrier recombination at interfaces. In this study, we demonstrate that a mild solution-processed SnO2 compact layer can be an eminent ETM for planar heterojunction PSCs. Here, the device based on chemical-bath-deposited SnO2 electron transporting layer (ETL) exhibits a power conversion efficiency (PCE) of 16.10% and with obvious hysteresis effect (hysteresis index = 19.5%), owing to the accumulation and recombination of charge carriers at the SnO2/perovskite interface. In order to improve the carrier dissociation and transport process, an ultrathin TiO2 film was deposited on the top of the SnO2 ETL passivating nonradiative recombination center. The corresponding device based on the TiO2@SnO2 electron transporting bi-layer (ETBL) exhibited a high PCE (17.45%) and a negligible hysteresis effect (hysteresis index = 1.5%). These findings indicate that this facile solution-processed TiO2@SnO2 ETBL paves a scalable and inexpensive way for fabricating hysteresis-less and high-performance PSCs.

Dependence of power conversion properties of hole-conductor-free mesoscopic perovskite solar cells on the loading of perovskite crystallites

Effect of the loading of perovskite crystallites on the power conversion properties of carbon based hole-conductor-free mesoscopic perovskite solar cells is studied by varying the concentration of the perovskite precursor from 0.3 to 1.0 mol/L (at given volume of 30 μL). It is observed that, when the concentration is 0.3 mol/L, poor filling is obtained due to relatively low loading of perovskite, and the perovskite solar cells suffer from huge dispersion in efficiencies and large hysteresis index (averaged at 18.29% and up to 34.61%). With increment of the concentration (from 0.4 to 1.0 mol/L), crystallinity of perovskite crystallites is improved according to X-ray diffraction studies, and the lifetime of photo-generated charge carriers is prolonged as reflected by transient photovoltaic (TPV) detection. Meanwhile, the open circuit voltage rises up from 0.86 (±0.03) V to 0.91 (±0.01) V, and the hysteresis index is reduced from 10.02 (±4.67)% to 1.45 (±2.21)%. However, the film conductance of carbon film is decreased due to the loading of perovskite, which deteriorates the fill factor of the devices. Finally, optimized power conversion efficiency is achieved at moderate concentration or 0.6 mol/L, which is 12.59 (±0.40) %, compared to 11.81 (±0.36) % at 1.0 mol/L. Due to the barrier provided by the carbon film against H2O/O2, all of the devices showed good shelf-stability, though loading of perovskite is varied in these devices.

Using Qmsax* to evaluate the reasonable As(V) adsorption on soils with different pH

As a toxic metalloid element, arsenic (As) derived from human activities can pose hazardous risks to soil and water. The bioavailability of arsenic is influenced by its behavior, in particular its adsorption-desorption in the soil environment. The maximum adsorption amount (Qmax) calculated from Langmuir equation is an important parameter to estimate the adsorption capacity of adsorbents. However, the soil is a more complicated system compared with specific adsorbents. Thus, in this study, we tried to find a more reasonable parameter (Qmax*) to evaluate the adsorption capacity of soils. Eighteen Chinese soil samples with different pH were used for adsorption-desorption experiments. The maximum As(V) adsorption capacity calculated through Langmuir fitting for 18 samples were ranged from 50.25 (S13) to 312.50 (S4) mg kg−1. Besides, Qmax was highly related with soil pH. Using the difference value of adsorption amount and desorption amount to indicate the amount of non-electrostatic adsorption of As(V) onto soils, calculated the maximum adsorption amount of non-electrostatic adsorption (Qmax*). The average Qmax* of acidic and neutral soils was 162.18 mg kg−1 whereas that for alkaline soils it was only 79.52 mg kg−1. The result from multiple linear regression analysis showed Qmax* was strongly influenced by Feox and clay contents. Furthermore, hysteresis index (HI) in the As(V) desorption varied from 0.83 (S13) to 1.82 (S6). The results further indicated the risk of secondary pollution originating from the desorption process cannot be ignored.

Accelerated electron extraction and improved UV stability of TiO2 based perovskite solar cells by SnO2 based surface passivation

Abstract TiO2 is a famous electron-transport-material (ETM) that used widely in perovskite solar cells. Photo-catalysis effect is a highly concerned issue for such TiO2 based devices because of its impact on device stability. To deal with the problem, a strategy was proposed to passivate the surface of TiO2 by a thin layer of in-situ formed SnO2, and then perovskite solar cells (PSCs) were prepared using such modified TiO2. It was observed that, after the surface passivation, photo-to-electric power conversion efficiency, hysteresis as well as stability of the TiO2 based PSCs were all improved. For example, efficiency increased from 14.92 (±1.86)% (AM 1.5G, 100 mW/cm2) to 16.33 (±0.26)%; hysteresis index decreased from 20.49 (±11.85)% to 1.40 (±0.01)%. As for stability, after being stored for 25 days (relative humidity of about 45%, no encapsulation), efficiency could preserve 73.99% of the original value, comparing to 47.55% for device based on bare TiO2. Moreover, the passivation was found to accelerate electron extraction, while retard charge recombination between perovskite and TiO2. The improvement was ascribed to the enhanced contact between perovskite and bottom electron-transport-material, passivated surface defects of TiO2 by SnO2, as well as the high mobility of SnO2. Finally, designated ultraviolet (UV) illumination experiment showed that SnO2 passivation could obviously retard the photo-catalysis activity of TiO2, thus improve the UV stability of the devices.

Electron extraction mechanism in low hysteresis perovskite solar cells using single crystal TiO2 nanorods

This study compares the photovoltaic performance of perovskite solar cells PSCs which use different types of TiO2 mesoporous scaffold; nanoparticle (NP) film and nanorod (NR) array. In PSCs of TiO2 NRs, the hysteresis of current density–voltage (J-V) curves is reduced significantly. The hysteresis index of PSCs of 670 nm long NRs is only 0.014. A difference in the charge accumulation at the TiO2-perovskite interface and the trapping site density is responsible for the smaller hysteresis of PSCs of TiO2 NRs. In PSCs of TiO2 NRs, mobile ions migrate longer and less electrons are trapped on the surface of TiO2 NRs. This leads to a unique columnar space charge polarization at the TiO2-perovskite interface, which facilitates electron extraction and suppresses the hysteresis of J-V curve. Our study shows a new way to design the microstructure of the mesoporous TiO2 layer for hysteresis-free high performance perovskite solar cells.

ANALYSIS OF THE EFFECTIVENESS OF SCLEROPLASTIC OPERATIONS IN CHILDREN WITH PROGRESSIVE MYOPIA WITH LONG-TERM FOLLOW-UP. NEW POSSIBILITIES OF DRUG TREATMENT OF PROGRESSIVE MYOPIA

There were performed a retrospective study of scleroplasty results in patients with progressive myopia (1282 eyes) and a prospective study of patients with myopia after scleroplasty (192 eyes). The age of patients is from 5 to 17 years, mean age is (12,5 ± 0,07) years. The observation period is from 1 to 7 years. The studies showed slowing rate of myopia progression after sclera operations in the majority of operated patients - in 92 % of cases. The maximum stabilizing effect of scleroplasty is observed one year after the operation. After 4 years and 7 years after operation the stabilizing effect is reduced. The combination of weakness of accommodation, constantly redundant tension of accommodation (CRTA) and finding intraocular pressure values in the upper normal range indicate the progression of myopia. The use of 0,005 % solution of Latanoprost (Prolatan) in the complex treatment of patients with myopia leads to normalization of intraocular pressure, increase of corneal hysteresis and rigidity index of corneoscleral membrane, as well as increase in the coefficient of accommodative response and decrease in the coefficient of the ciliary body microfluctuations.

Characterization of adsorption and desorption of lawn herbicide siduron in heavy metal contaminated soils

Siduron is a widely used herbicide in urban lawn and has been frequently detected in urban and suburban surface water. However, characteristics of its environmental behavior in soil are seldom reported. The combined pollution of heavy metals, especially for Cu, Pb, Cd, Zn and siduron would be common because of the widely existence of heavy metal pollution in urban soils. In this study, four soils with similar physicochemical properties but different levels of preexisting heavy metals were selected to investigate the adsorption and successive desorption of siduron using batch experiments. The results revealed a low sorption of siduron to all the tested soils. The organic carbon normalized distribution coefficient (Koc) of siduron in the studied soils ranged from 117 to 137 L kg−1 and was not significantly correlated to heavy metal levels. No apparent desorption hysteresis was observed with the hysteresis index (HI) ranging from 0.921 to 1.11. More than 50% of the sorbed siduron was readily released into soil solution. Results suggested that siduron was highly mobile and bioavailable in the studied soils. Significant correlation was found between adsorption/desorption parameters and soil organic carbon (SOC) in four soils. soil organic matter was thus considered as the dominant factor determining the adsorption and desorption of siduron in soils. Different from most of reported studies conducted by laboratory-amended soils, the influence of preexisting heavy metals on the adsorption-desorption of siduron was not significant in this work.

Correlation of ETL in perovskite light-emitting diodes and the ultra-long rise time in time-resolved electroluminescence

Here, two series CH3NH3PbI3 based perovskite light-emitting diodes (Pe-LEDs) were synthesized with TiO2 and SnO2 as electron transport layer (ETL), respectively. An exceptional ultra-long rise time (Tr) persisting to tens of seconds was observed in time-resolved electroluminescence (EL) characteristics from the Pe-LEDs as driven with constant voltage, which might be intrinsic to the MAPbI3 perovskite layer regardless of the ETL materials. Qualitatively, SnO2 based ETL was preferred than the TiO2 ETL counterpart for faster response Pe-LED devices with lower Tr. Moreover, the Tr of Pe-LED can be adjusted in the range of 10–28 s by precisely controlling the thickness of SnO2 ETL. In addition, the similar trend was also confirmed in the SnO2 ETL thickness dependent hysteresis index deduced from current-voltage (J-V) characteristics. The mechanism was interpreted by means of dynamics of carrier injection and transport at the perovskite/ETL interface. These achievement may contribute to better understanding of the origin and mechanism of the slow process in EL characteristics, and hence favorable for minimizing this detrimental effects.

Quantifying the Vegetation Health Based on the Resilience in an Arid System

Abstract Proper management of natural ecosystems is not possible without the knowledge of the health status of its components. Vegetation, as the main component of the ecosystem, plays an important role in its health. One of the key determinants of vegetation health is its resilience in the face of environmental disorders. This research was conducted in parts of the Namakzar-e Khaf watershed in Northeast of South Khorasan Province with the aim of quantifying the vegetative resilience on behalf of the ecosystem health in response to long-term precipitation changes. First, the annual precipitation standardization was performed during a thirty-year period by the SPI method. Then, the average variation in TNDVI index obtained from the Landsat satellite images was examined and the resilience was tested by calculating the four effective factors (amplitude, malleability, damping and hysteresis). According to the results, the amplitude in the survey period was 6.04% and the vegetation has had different values of damping over the years. The most prominent example of vegetation resilience occurred between 1986 and 1996, with malleability of 0.7 and damping of zero. Vegetation in this period, after the elimination of drought effects (1986), has not only returned to the amount of vegetation of reference year with severe precipitation (1996) but also increased by 0.25%. This increase, as the index of hysteresis, has been presented for the first time in the ecosystem health discussion quantitatively in the present study. A set of quantitative calculations showed that despite reduced annual precipitation and drought events, the vegetation has been able to maintain its resilience, which indicates the health of vegetation in the studied ecosystem.

Sorption and desorption of atrazine on soils: The effect of different soil fractions

The study of atrazine (AT) sorption and desorption was carried out, employing three Brazilian soils (Typic Acrudox, Typic Argiudoll and Oxic Argiudoll), using horizons A and B, as well as their clay fractions – natural clay, clay after H2O2 treatment, clay after iron removal and after treatment to concentrate iron oxides. A contact time of 12 h was defined as adequate for sorption studies. Sorption and desorption curves were adjusted by the Freundlich equation, and satisfactory linear responses were observed, between 0.8332 and 0.9998 for the sorption process. Multiple regression analyses were performed considering the mineralogy, organic carbon content, specific surface area and texture of the soils, and the Freundlich parameter Kf. The principal influence for AT sorption was attributed to organic carbon content and physical bonding on quartz for soil samples. Positive correlation with goethite was observed for clay fractions. The Kf values for sorption (Kf(S)) obtained for soil samples were between 0.60 and 3.9, and for clay fractions were between 1.90 and 5.30, suggesting an important role of the mineral phase in the sorption of AT. Environmental risks of groundwater contamination were evaluated using the partition coefficient normalized by the soil organic carbon content (Koc), hysteresis index (HI), groundwater ubiquity score (GUS) and leachability index (LIX). Both horizons for the three soils presented leaching potential for AT based on GUS and LIX parameters.

Effects of Fulvic Acid on TNT Adsorption in Soil

abstractIn order to study the effect of fulvic acids (FA) on the migration of TNT in soil, batch experiments in which 2%, 5%, and 10% (w/w) of FA were added to soils were conducted. Adsorption kinetics and adsorption-desorption isotherms of TNT in soils were investigated, with results of the kinetics tests showing that the adsorption process could be divided into a fast and a slow stage and that FA could extend the adsorption time. Kinetic data were fit to pseudo first-order, pseudo second-order, Elovich, and intra-particle diffusion kinetic models. The fitting results showed that a pseudo second-order kinetic model best described the adsorption process, while Elovich and intra-particle diffusion kinetic models could accurately predict the adsorption at higher FA content. The adsorption-desorption isotherms were predicted using Linear, Freundlich, and Langmuir isotherm models. Results showed that the Freundlich model best described the adsorption-desorption process, and that FA increased adsorption capacity and enhanced the adsorption affinity. The hysteresis index suggested that FA could reduce the desorption of TNT in soil.

Seasonal variability of stream water quality response to storm events captured using high-frequency and multi-parameter data

The response of stream chemistry to storm is of major interest for understanding the export of dissolved and particulate species from catchments. The related challenge is the identification of active hydrological flow paths during these events and of the sources of chemical elements for which these events are hot moments of exports. An original four-year data set that combines high frequency records of stream flow, turbidity, nitrate and dissolved organic carbon concentrations, and piezometric levels was used to characterize storm responses in a headwater agricultural catchment. The data set was used to test to which extend the shallow groundwater was impacting the variability of storm responses. A total of 177 events were described using a set of quantitative and functional descriptors related to precipitation, stream and groundwater pre-event status and event dynamics, and to the relative dynamics between water quality parameters and flow via hysteresis indices. This approach led to identify different types of response for each water quality parameter which occurrence can be quantified and related to the seasonal functioning of the catchment. This study demonstrates that high-frequency records of water quality are precious tools to study/unique in their ability to emphasize the variability of catchment storm responses.

Improvement of current characteristic of perovskite solar cells using dodecanedioic acid modified TiO2 electron transporting layer

In the classical planar heterojunction perovskite solar cells (PSCs), the electron conducting TiO2 layer shows lower conductivity than the hole transporting materials such as spiro-OMeTAD, which becomes one of the key problems in improving the power conversion efficiency (PCE) of PSCs. In this study, the surface of compact TiO2 layer is modified by a thin self-assembled dodecanedioic acid (DDDA) molecular layer. The TiO2 substrates are immersed into the DDDA solution for 0.5, 2.5, 4.5, 22 h, respectively. It is found that the PCE of PSCs is improved when using the DDDA modified TiO2, showing optimized PCE of 15.35%0.75% under AM 1.5G illumination at 100 mWcm-2 after 4.5 h modification. The short current density (JSC) of the best device is improved from 20.34 mA cm-2 to 23.28 mA cm-2, with the PCE increasing from 14.17% to 15.92%. And it is found that the hysteresis of the PSC is also reduced remarkably with hysteresis index decreasing from 0.4288 to 0.2430. In the meantime, the device with DDDA modification shows a significant improvement in light stability, keeping 71% of its initial PCE value after 720 min exposure under AM 1.5G illumination at 100 mW cm-2 without encapsulation. As a contrast, the device without DDDA modification keeps 59% of its initial PCE value under the same condition. To reveal the mechanism, we investigate the surface energy level change using ultraviolet photoemission spectroscopy. It is found that after DDDA modification, the valence-band maximum energy (EVBM) of TiO2 decreases from -7.25 eV to -7.32 eV, and the conduction-band minimum energy (ECBM) of TiO2 from -4.05 eV to -4.12 eV. The shifting of energy level optimizes the energy level alignment at the interface between the TiO2 and perovskite. It promotes the transport of electrons from perovskite layer to compact TiO2 layer and obstructs the transport of holes from perovskite layer to compact TiO2 layer more effectively. In addition, the decrease of ECBM implies the increase of conductivity of TiO2. We further design a series of electrical experiments, and confirm that the modification improves the conductivity of TiO2 obviously with both contact resistance and thin-film resistance decreasing. In summary, our results indicate the enormous potential of the compact TiO2 layer with a thin self-assembled DDDA molecular layer modification to construct efficient and stable planar heterojunction PSCs for practical applications.