Intensity-modulated Photovoltage Spectroscopy Research Articles

Fabrication of TiO2 photoelectrodes doped with copper and zirconium to improve electron generation and flow in dye-sensitized solar cell

Dye-sensitized solar cell (DSSC) are devices that convert solar light into electricity using a semiconductor substance, e.g. TiO2. Although DSSC are environmentally friendly and economical, they exhibit a low energy conversion efficiency. In this study, to improve its energy conversion efficiency, a DSSC in which TiO2 was doped with transition metals (TMs) such as Cu and Zr was fabricated by a sol–gel method. Doping with TMs extended the light-absorption range of TiO2 to the visible-light region, generating more electrons and improving electrical conductivity. The successful doping of Cu, Zr in the fabricated photoelectrode was confirmed by X-ray diffraction (XRD) and FESEM–energy dispersive X-ray spectroscopy (EDS) analyses, and doping with Cu, Zr increased the dye adsorption amount and current density of DSSC. In addition, the electron-transfer resistance was confirmed to be reduced by electrochemical impedance spectroscopy (EIS) analysis, and the electron movement, speed, and lifetime were improved by Intensity-modulated photocurrent spectroscopy (IMPS) and intensity-modulated photovoltage spectroscopy (IMVS) analyses. The electrical properties of the Cu, Zr-doped TiO2 photoelectrodes were determined from the chemical capacitance and recombination resistance calculations, and the results revealed that the efficiency was improved by Cu, Zr doping. In conclusion, the Cu, Zr doping of the photoelectrode improved the electron generation and flow of TiO2, thereby increasing the energy conversion efficiency of the DSSC by up to 3.28%

P-Type DSSCs by sensitizing a benzofuran[b]-fused BODIPY with cyanoacrylic acid

We found that a benzofuran[b]-fused 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) with cyanoacrylic acid (1) served as a photosensitizer for p-type dye-sensitized solar cells (DSSCs). The photovoltaic parameters (short circuit current density = 3.57 mA cm2, open circuit voltage = 0.12 V, fill factor = 0.33, and power conversion efficiency = 0.14%) were obtained with a 1-loaded NiO photocathode under AM 1.5 conditions. The incident photon-to-current efficiency spectrum showed excellent photo-harvesting capability, with a significant band at approximately 600 nm. Time-dependent density functional theory (TD-DFT)/DFT calculations indicated that electron distributions of both the HOMO and LUMO levels spread over the benzofuran-fused BODIPY core, mainly owing to π-π* transition. It is noteworthy that 1 served as a photosensitizer for p-type DSSC, despite almost no push-pull sensitizers. The hole transport and recombination processes were investigated by using intensity-modulated photocurrent spectroscopy and intensity-modulated photovoltage spectroscopy. This study demonstrates that the local excitation (LE) character of dye is significantly workable for p-type sensitization, which may contribute to surpass recombination.

Influence of impregnation time on TiO2 films sensitized with N719 and 2-Mercaptobenzothiazole: An electrochemical analysis

Dye sensitized solar cells (DSSC) are low-cost photovoltaic devices with easy production. They operate with a photoanode, a photocathode, and an electrolyte responsible for charge permeation within the cell. Recent research focus in DSSCs has aimed at enhancing their energy conversion properties, such as the insertion of new materials to reduce electronic recombination, utilization of gel electrolytes, dye synthesis, and studying cell assembly parameters. This study examined the effects of various immersion durations (6, 12, and 24 h) on TiO2 semiconductor films immersed in solutions containing charge carriers (N719 and 2-Mercaptobenzothiazole). To characterize the electrochemical properties, analyses such as current density versus potential curves (j-V), Electrochemical Impedance Spectroscopy (EIS), charge extraction, Intensity-Modulated Photovoltage (IMVS), and Photocurrent Spectroscopy (IMPS) were performed. It was found that the cell with 24 h of impregnation, presented a higher current density, consequently increasing efficiency (η = 5.76%). Impedance analyses showed that the 24-h samples facilitated charge transport, reducing cell resistance, consistent with charge extraction measurements. Lastly, IMPS and IMVS tests revealed that 24 h of immersion generated shorter collection times (τc = 0.016 ± 0.01) and longer electronic recombination times (τr = 0.07 ± 0.007), aiding the charge transport process.

Electrostatic [FeFe]-hydrogenase-carbon nitride assemblies for efficient solar hydrogen production.

The assembly of semiconductors as light absorbers and enzymes as redox catalysts offers a promising approach for sustainable chemical synthesis driven by light. However, achieving the rational design of such semi-artificial systems requires a comprehensive understanding of the abiotic-biotic interface, which poses significant challenges. In this study, we demonstrate an electrostatic interaction strategy to interface negatively charged cyanamide modified graphitic carbon nitride (NCNCNX) with an [FeFe]-hydrogenase possessing a positive surface charge around the distal FeS cluster responsible for electron uptake into the enzyme. The strong electrostatic attraction enables efficient solar hydrogen (H2) production via direct interfacial electron transfer (DET), achieving a turnover frequency (TOF) of 18 669 h-1 (4 h) and a turnover number (TON) of 198 125 (24 h). Interfacial characterizations, including quartz crystal microbalance (QCM), photoelectrochemical impedance spectroscopy (PEIS), intensity-modulated photovoltage spectroscopy (IMVS), and transient photocurrent spectroscopy (TPC) have been conducted on the semi-artificial carbon nitride-enzyme system to provide a comprehensive understanding for the future development of photocatalytic hybrid assemblies.

Experimental and theoretical studies on improving the efficiency of ZnO-based dye-sensitized solar cells using single-layer anti-reflective coating

The effect of a single-layer anti-reflective coating (ARC) on ZnO-based dye-sensitized solar cells (DSSCs) is theoretically predicted and verified by experimental fabrication. By the transfer matrix method (TMM), the absorption of the DSSC with and without the single-layer ARC is calculated and the improvement in short-circuit current density (∆ Jsc%) is estimated. The optimized thickness of the ARC required to obtain maximum improvement in the short-circuit current density (∆ Jsc%) is determined. By employing ARC with the calculated optimized thickness, the fabrication of spin-coated ZnO-based DSSCs is carried out. The structural and optical parameters are studied using XRD analysis and UV absorption spectra. The efficiency of the DSSC with and without the ARC is measured by intensity-modulated photocurrent and photovoltage spectroscopy. The theoretically predicted efficiency of the DSSC with and without ARC agrees well with the experimental values that provide insights about improving the electrical performance of the DSSC by the ARC.

Retinomorphic Motion Detector Fabricated with Organic Infrared Semiconductors.

Organic retinomorphic sensors offer the advantage of in-sensor processing to filter out redundant static backgrounds and are well suited for motion detection. To improve this promising structure, here, the key role of interfacial energetics in promoting charge accumulation to raise the inherent photoresponse of the light-sensitive capacitor is studied. Specifically, incorporating appropriate interfacial layers around the photoactive layer is crucial to extend the carrier lifetime, as confirmed by intensity-modulated photovoltage spectroscopy. Compared to its photodiode counterpart, the retinomorphic sensor shows better detectivity and response speed due to the additional insulating layer, which reduces the dark current and the RC time constant. Lastly, three retinomorphic sensors are integrated into a line array to demonstrate the detection of movement speed and direction, showing the potential of retinomorphic designs for efficient motion tracking.

Nb/TiO2 oxides: A study of synthesis and electron transport mechanism as an ETL in a solar device

Efficient solar devices to energy conversion are the key to a sustainable future. TiO2 dye solar cells are systems that present limited energy conversion efficiency due to recombination reactions. An alternative to reduce the back-electron recombination is the insertion of new oxides in electron transport material, such as Nb. However, what are the changes in electron lifetime and collection time caused by Nb insertion in TiO2 photoanodes? This work aims to analyze TiO2 dye solar devices with different Nb proportions synthesized by an easy and low-cost particle preparation methodology, Pechini. The techniques performed were X-ray Diffraction (XRD), Scanning Electronic Microscopy (SEM), and X-ray fluorescence to particle characterization. To the electrochemical analysis of the cells, j-V curves, Electrochemical Impedance Spectroscopy (EIS), charge extraction, Intensity Modulated Photovoltage Spectroscopy (IMVS), and Intensity-Modulated Photocurrent Spectroscopy (IMPS) were performed. The results showed a mix of anatase and rutile phase to TiO2 with Nb insertion and at the 5% of Nb proportion has been able to generate a cell with better electrochemical parameters (PCE = 5.43 %; j = 6.34 mA cm−2). The creation of energy substates below the conduction band has been able to increase the collection time (0.1748 s) and electron lifetime (0.15514 s) when compared to the cell with bare TiO2, suppressing the back-electron recombination but also difficulting the collection reaction.

Blackberries dye-sensitized solar cells with poly(vinyl alcohol) based gel polymer electrolytes

Dye-sensitized solar cells (DSSCs) have been constructed using fluoride tin oxide (FTO) glass deposited with TiO2 and anthocyanin dye extracted from blackberries as the photoanode, platinum coated cathode, and gel polymer electrolytes (GPEs) comprising poly(vinyl alcohol) (PVA) dissolved in two different solvents, viz., dimethyl formamide (DMF) and dimethyl sulfoxide (DMSO). GPE employing DMF solvent exhibits the highest ambient conductivity of 14.05 mS cm−1. Charge transport properties of DSSCs were studied via intensity-modulated photocurrent spectroscopy (IMPS), intensity-modulated photovoltage spectroscopy (IMVS) and electrochemical impedance spectroscopy (EIS). The highest efficiency of 0.54% is recorded for DSSC with GPE containing DMF and TBP.

New Views on Carrier Diffusion and Recombination by Combining Small Perturbation Techniques: Application to BiVO4 Photoelectrodes

Impedance spectroscopy (IS), intensity‐modulated photocurrent spectroscopy (IMPS), and intensity‐modulated photovoltage spectroscopy (IMVS) are well‐established powerful modulated techniques to characterize optoelectronic devices. Their combined use has proven to provide an understanding of the behavior and performance of these systems, far beyond the output obtained from their independent analysis. However, this combination is shown to be challenging when applied to complex systems. Herein, IS, IMPS, and IMVS are cooperatively used, for the first time, to study the distributed photogeneration, diffusion, and recombination processes in a photoanode of zircon‐doped bismuth vanadate. The use of this methodology reveals that the carriers that determine the response of the device are the electrons when the device is illuminated from the hole‐collector side (electrolyte) and the holes when the illumination reaches the device from the electron‐collector side. Detailed quantitative information is obtained for each carrier, including recombination lifetime, diffusion coefficient and collectrion and separation efficiencies, identifying the latter as the main limitation of this device. This methodology is a powerful tool that can be used for the characterization and understanding of the operating processes of other photoconversion devices.

Electrochemical investigation of PEDOT:PSS and Nb2O5 composites as counter electrodes for dye-sensitized solar cells

Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) has attracted considerable interest to replace expensive and rare platinum (Pt) in counter electrodes (CEs) of dye-sensitized solar cells (DSC). The use of niobium pentoxide (Nb2O5) combined with this polymer has not yet been reported. In the present paper, the DSC performance was compared with five different types of CEs Pt, PEDOT:PSS, PEDOT:PSS with Nb2O5 and Nb2O5 deposited via spin coating and doctor blading. For the characterization of the device, open-circuit voltage (Voc), short-circuit current density (Jsc), current density versus potential curves, electrochemical impedance spectroscopy (EIS), intensity-modulated photovoltage spectroscopy (IMVS), and intensity-modulated photocurrent spectroscopy (IMPS) measurements were applied. The performance of DSC with CE of PEDOT:PSS (j = 4.59 ± 0.70 mA cm−2; ɳ = 0.89 ± 0.19%) was significantly improved by the incorporation of Nb2O5 with photoelectrochemical parameters of j = 8.35 ± 0.30 mA cm−2; ɳ = 2.65 ± 0.61%. This behavior is attributed to a reduction of the charge transfer resistance in the film as shown by EIS. The electron transport time was shorter for the PEDOT:PSS_Nb (ԏtr = 0.002522 s) CE when compared to Pt standard counter electrode with a ԏtr = 0.006336 s, but the electron lifetime was superior, which resulted in collection efficiency of ɳc = 84.15% when PEDOT:PSS_Nb was used.

The use of 2-Mercaptobenzothiazole as a new co-adsorbent in dye-sensitized solar cells

Using co-adsorbents is an efficient strategy to improve the photoconversion energy efficiency of dye-sensitized solar cells (DSSC). Some organic molecules might be used as these dye additives, suppressing the back-electron recombination by some changes in TiO2/dye/electrolyte interfase. In this perspective, the literature shows the use of 2-Mercaptobenzothiazole in some papers as a passivator to electrode process reactions. This work aims to study the influence of 2-MBT in DSSc produced with TiO2 as a scaffold material. A complete electrochemical characterization was performed, by j-V curves, Electrochemical Impedance Spectroscopy, and Intensity-Modulated Photovoltage and Photocurrent Spectroscopy. It was verified that in 20 mg mL−1 of additive inserted in a dye, lead to a higher photoconversion energy efficiency (PCE = 4.20 ± 0.61), with a superior electron lifetime (ԏr = 0.054 s) when compared to bared cell (PCE = 2.65 ± 0.65 ԏr = 0.0311 s). Regarding the charge transfer process of collection reaction, 2-MBT difficult the charge transportation, due to oxide coverage proportional to dye additive amounts added.

Limited information of impedance spectroscopy about electronic diffusion transport: The case of perovskite solar cells

Impedance Spectroscopy (IS) has proven to be a powerful tool for the extraction of significant electronic parameters in a wide variety of electrochemical systems, such as solar cells or electrochemical cells. However, this has not been the case with perovskite solar cells, which have the particular ionic-electronic combined transport that complicates the interpretation of experimental results due to an overlapping of different phenomena with similar characteristic frequencies. Therefore, the diffusion of electrons is indistinguishable on IS, and there appears the need to use other small perturbation experimental techniques. Here, we show that voltage-modulated measurements do not provide the same information as light-modulated techniques. We investigate the responses of perovskite solar cells to IS, Intensity-Modulated Photocurrent Spectroscopy (IMPS) and Intensity-Modulated Photovoltage Spectroscopy (IMVS). We find that the perturbations by light instead of voltage can uncover the electronic transport from other phenomena, resulting in a loop in the high-frequency region of the complex planes of the IMPS and IMVS spectra. The calculated responses are endorsed by the experimental data that reproduce the expected high frequency loops. Finally, we discuss the requirement to use a combination of small perturbation techniques for successful estimation of diffusion parameters of perovskite solar cells.

Charge dynamics in CuInS2 photovoltaic devices with In2S3 as buffer layer

The charge carrier dynamics of photovoltaic devices composed of FTO/TiO2/In2S3/CuInS2/graphite (FTO=Fluorine doped Tin Oxide) is investigated by Intensity Modulated Photocurrent Spectroscopy (IMPS) and Intensity Modulated Photovoltage Spectroscopy (IMVS). Characteristic lifetimes and transport times are obtained. The dependence of the lifetime with light intensity can be explained by multitrapping processes, which justify the rather long lifetimes. Moreover, typical spectral features in the Nyquist plots are obtained by a model based on the continuity equation where diffusion is the major transport process, as confirmed by the dependence of the transport times on the externally applied potential. Changes from a kinetically limited process to a diffusion limited process are observed by modifying the excitation wavelength. Moreover, the existence of a potential barrier or a similar limitation process at the In2S3/CuInS2 interface could be inferred by comparing of the experimental IMPS measurements with data derived from. The existence of defect states at the In2S3 can be deduced from the IMVS dependence with wavelength. Also, different capacitive effects in the samples can be discriminated due to the spectroscopic nature of the techniques here employed.

Improved dye-sensitized solar cell performance with hedgehog-like shaped ZnO nanorods grown using ZnO nanoparticles seed layer

We have investigated the preparation of ZnO nanorods (ZnO-NRs) with a hedgehog-like structure by hydrothermal method and the working performance of dye-sensitized solar cell (DSSC) based on this ZnO-NRs electrode. ZnO-NRs were grown from ZnO nanoparticles (ZnO-NPs) seed layer. Scanning Electron Microscopy (SEM) images show that ZnO-NPs seed layer produced a hedgehog-like shape ZnO-NRs. The X-Ray Diffraction (XRD) characterization results show that the resulted ZnO-NRs have a good crystallinity with the diffraction pattern of hexagonal wurtzite ZnO. The optical absorbance spectra show a high dye absorption for ZnO-NRs with a hedgehog-like shaped structure. The power conversion efficiency of the cell using a hedgehog-like ZnO-NRs is around 2.35%, which is larger than the cell with all-vertically aligned ZnO-NRs that produce efficiency of about 1.86%. The intensity-modulated photovoltage spectroscopy (IMVS) characterization indicates that the effective total diffusion length to reach FTO becomes smaller and the recombination loss is reduced for DSSC with a hedgehog-like ZnO-NRs. This study shows that hedgehog-like ZnO-NRs can improve the cell perfomace of DSSC based on ZnO-NRs.

Plasmon-Enhanced Photoresponse of Self-Powered Si Nanoholes Photodetector by Metal Nanowires.

In this work, we report the development of self-powered photodetectors that integrate silicon nanoholes (SiNHs) and four different types of metal nanowires (AgNWs, AuNWs, NiNWs, PtNWs) applied on the SiNHs’ surface using the solution processing method. The effectiveness of the proposed architectures is evidenced through extensive experimental and simulation analysis. The AgNWs/SiNHs device showed the highest photo-to-dark current ratio of 2.1 × 10−4, responsivity of 30 mA/W and detectivity of 2 × 1011 Jones along with the lowest noise equivalent power (NEP) parameter of 2.4 × 10−12 WHz−1/2 in the blue light region. Compared to the bare SiNHs device, the AuNWs/SiNHs device had significantly enhanced responsivity up to 15 mA/W, especially in the red and near-infrared spectral region. Intensity-modulated photovoltage spectroscopy (IMVS) measurements revealed that the AgNWs/SiNHs device generated the longest charge carrier lifetime at 470 nm, whereas the AuNWs/SiNHs showed the slowest recombination rate at 627 nm. Furthermore, numerical simulation confirmed the local field enhancement effects at the MeNWs and SiNHs interface. The study demonstrates a cost-efficient and scalable strategy to combine the superior light harvesting properties of SiNHs with the plasmonic absorption of metallic nanowires (MeNWs) towards enhanced sensitivity and spectral-selective photodetection induced by the local surface plasmon resonance effects.

Combining Modulated Techniques for the Analysis of Photosensitive Devices.

Small-perturbation techniques such as impedance spectroscopy (IS), intensity-modulated photocurrent spectroscopy (IMPS), and intensity-modulated photovoltage spectroscopy (IMVS) are useful tools to characterize and model photovoltaic and photoelectrochemical devices. While the analysis of the impedance spectra is generally carried out using an equivalent circuit, the intensity-modulated spectroscopies are often analyzed through the measured characteristic response times. This makes the correlation between the two methods of analysis generally unclear. In this work, by taking into consideration the absorptance and separation efficiency, a unified theoretical framework and a procedure to combine the spectral analysis of the three techniques are proposed. Such a joint analysis of IS, IMPS, and IMVS spectra greatly reduces the sample space of possible equivalent circuits to model the device and allows obtaining parameters with high reliability. This theoretical approach is applied in the characterization of a silicon photodiode to demonstrate the validity of this methodology, which shows great potential to improve the quality of analysis of spectra obtained from frequency domain small-perturbation methods.

From Frequency Domain to Time Transient Methods for Halide Perovskite Solar Cells: The Connections of IMPS, IMVS, TPC, and TPV.

The correlation of different methods of measurement can become an important tool to identify the dominant physical elements that govern the electronic and ionic dynamics in perovskite solar cells. The diverse phenomena underlying the response of halide perovskite materials to different stimuli are reflected in time-domain measurements, where transients appear with time scales spanning orders of magnitude, from nanoseconds to hours. We discuss the connection between different frequency- and time-domain methods to probe the voltage and current response of halide perovskite solar cells to different small perturbations. To solve the frequency-to-time transformation, we start from models of the transfer function of intensity-modulated photocurrent spectroscopy (IMPS) and derive the associated impulse response function, the transient photocurrent (TPC), in response to a short light pulse. Similarly, we determine the transient photovoltage (TPV) starting from the intensity-modulated photovoltage spectroscopy (IMVS) transfer function. We also discuss the open-circuit voltage decays (OCVD). We first show the response of simple equivalent circuit models, and then we treat the full model for generation–diffusion–recombination of electrons that shows a spiraling loop in IMPS. This model gives rise to overshoots in the time domain.

Tailored ZnO Nanostructure Based Quasi-Solid-State Electrolyte and Mesoporous Carbon Electrocatalyst for Solar Energy Conversion

We have investigated the photoelectrochemical influence of quasi-solid-state electrolytes based on tailored ZnO nanostructures and mesoporous carbon electrocatalyst in the solar conversion performance of dye-sensitized solar cells (DSSCs). Tailored ZnO nanostructures with rod-shaped petals (ZnO nanorod) and almond-shaped petals (ZnO nanoalmond), were prepared using the hydrothermal method, respectively. Mesoporous carbon electrocatalyst with a high surface area is obtained by the carbonization of the PVDC-g-POEM double comb copolymer. The phase and structure of tailored ZnO nanostructures were investigated using scanning electron microscopy (SEM) and wide angle X-ray scattering (WAXS). Diffuse reflectance, intensity-modulated photocurrent spectroscopy (IMPS)/intensity-modulated photovoltage spectroscopy (IMVS), electrochemical impedance spectroscopy (EIS) measurements were used to investigate the optical and electrochemical properties of quasi-solid-state electrolytes. The quasi-solid-state electrolytes based on ZnO nanorod significantly improved the solar conversion performance owing to its enhanced scattering effect, ion diffusion, effective path for redox couple transfer, and sufficient penetration of quasi-solid-state electrolytes into the electrode. The quasi-solid-state electrolytes based on ZnO nanorod, ZnO nanoalmond and mesoporous carbon electrocatalyst showed a solar conversion efficiency of 6.4%, 5.4%, respectively, which is higher than that of the polymer gel electrolytes (4.7%).

The influences of interfacial recombination loss on the perovskite solar cell performance studied by transient photovoltage spectroscopy

The charge-carrier transport and recombination loss in MAPbI3-based perovskite solar cells (PSCs) have been investigated by transient photovoltage (TPV) spectroscopy measurements. The TPV decays exhibit multi-exponential decay characteristics, where the fast decay seems to be correlated with both the cell performance (J-V characteristics) and the presence of low arc in the Nyquist plot obtained from the intensity-modulated photovoltage spectroscopy (IMVS) measurements. This fast decay exhibits the characteristic of a stretched exponential decay, which is a typical non-simple first-order trapping and recombination process, in the present case, by involving electron transport among defect states on the surface of grain boundaries or interlayer interface. Temperature dependence of TPV decays may also lead to a suggestion that the process can be also accompanied by local lattice distortion. Furthermore, the present experimental data also indicate the interplay between electronic processes in the fast time scale (microseconds in TPV data) and unpaired/mobile ion migration in the slow time scale (hundreds of milliseconds in IMVS data) on the overall cell performance (J-V characteristics). In addition, in practical viewpoints, the results may also demonstrate the potential application of this TPV spectroscopy, in conjunction with IMVS measurement, as a simple tool for identifying the fabricated perovskites solar cells that exhibit a good cell performance with low recombination loss due to surface defect states and ion migration.

Origin of Degradation in Perovskite Solar Cells by Intensity Modulated Photovoltage Spectroscopy Measurement (IMVS)

Perovskite solar cells (PSCs) based on lead halide perovskite have attracted much attention owing to the fast development of their power conversion efficiency (PCE) from 3.8% to 25%. Various factors play important roles in affecting the conversion efficiency of PSCs, such as charge carrier generation, transport, recombination, and collection. In addition, the presence of interfacial defects has also a crucial effect in charge carrier transfer and recombination processes. However, the origin and mechanism of interfacial charge recombinations in PSCs are still not comprehensively investigated. For that purpose, we have performed intensity-modulated photovoltage spectroscopy (IMVS) and transient photovoltage (TPV) measurements of PSCs, which were fabricated with FTO/c-TiO2/mp-TiO2/Perovskite/PTAA/Au cell structure. The solar cell (J-V) characteristics of the PSCs on the day-1, day-2, day-3, and day-6 after the cell fabrication, indicating a significant degradation of the cell with time. The Nyquist plots of IMVS measurement on the same day as the J-V measurement seem to be composed of two semicircles at a lower frequency range and a higher frequency range. The semicircle at the lower frequency range enlarged on the day-6 measurement, but the semicircle at higher frequency decreased. The change of this Nyquist plot is in agreement with a significant decrease in the J-V curves. The semicircle at lower frequency may be assigned to the ion diffusion or migration. Therefore, cell degradation may be caused by the liberation of ions (including iodide) from the surface of the perovskite crystal structure. It then increases recombination loss due to back charge transfer from TiO2 to perovskite as indicated by the changing of the semicircle at high frequency into a smaller semicircle. Therefore, the present results reemphasize that the improvement of PSC stability needs the prevention of ions liberations from the surface by introducing passivation substances. In addition, the results also show the practical usefulness of IMVS for inspecting PSC degradation due to such an ion liberation process.