Hysteresis In Perovskite Solar Cells Research Articles

Accelerating the Assessment of Hysteresis in Perovskite Solar Cells.

Halide perovskite materials have reached important milestones in the photovoltaic field, positioning them as realistic alternatives to conventional solar cells. However, unavoidable kinetic phenomena have represented a major concern for reliable steady-state performance assessment from standard current-voltage measurements. In particular, the dynamic hysteresis of current-voltage curves requires relatively long stabilization to achieve a credible figure for the power conversion efficiency. Hysteresis is caused by complex current transient phenomena that become active during staircase voltammetry. Here, we address the root of this problem. We pinpoint the dynamic characteristics behind the slow transient responses to strategically predict a minimum time delay and thus estimate the power conversion efficiency under steady-state conditions. Circuit-element analysis and impedance spectroscopy confirm our predictions based on an advanced transient study. Our results fundamentally explore the possibility of reducing data time acquisition in a reliable performance assessment, providing disruptive solutions and perspectives toward systematic production of photovoltaic perovskites.

Effect of TiO2 structure on hysteretic behaviors in CH3NH3PbI3 perovskite solar cells

This work explores a mechanism behind hysteresis in CH3NH3PbI3 perovskite solar cells. The solar cells in this work employed either compact TiO2, mesoporous TiO2, or a combination of compact and mesoporous TiO2 as an electron transport layer. The solar cells using compact TiO2 layer displayed the most pronounced hysteresis compared to those which made use of mesoporous TiO2. Different hysteretic behavior is attributed to difference in the built-in electric fields present in the architecture of perovskite solar cell. The solar cells with a compact TiO2 layer have a built-in field which allows for iodide ions to migrate and accumulate near to the interface of indium-tin-oxide electrode, ultimately causing a reduction in the measured power conversion efficiency for forward bias scans. In case of the cells with a mesoporous TiO2 layer, they have the built-in fields configured in such a way that iodide ions are blocked from migrating on a large scale to the vicinity of the ITO electrode. This results in the reduced hysteresis in perovskite solar cells when a mesoporous TiO2 electron transport layer is employed.

Inhibiting hysteresis and optimizing the performance of perovskite solar cells

We developed a comprehensive Poisson and drift-diffusion solver coupled with a time-dependent ion migration model in the COMSOL simulation software to analyze hysteresis effects and efficiency in perovskite solar cells (PSCs). Initial simulations on PSCs with the structure ITO/SnO2/CH3NH3PbI3/Spiro-OMeTAD/Au revealed suboptimal efficiency of 10.31% due to hysteresis loops near the open-circuit voltage (Voc) caused by interface recombination. Next, we explored the influence of the transport layer's dielectric constant on PSCs performance and hysteresis. The modeling results emphasized the vital role of the transport layer's dielectric constant in determining PSCs hysteresis and power conversion efficiency (PCE). To investigate further, we replaced the hole transport layer (HTL) material with NiO, CuSCN, and CuI. Studied four different transport layer combinations for n-i-p PSCs: SnO2-Spiro-OMeTAD, SnO2–NiO, SnO2–CuSCN, and SnO2–CuI. Notably, the SnO2–CuSCN combination achieved an impressive efficiency of 21.30%. The p-i-n PSCs with a matched dielectric constant PCBM-PTAA transport layer combination achieves higher PCE. It attains a reverse-scan PCE of up to 21.22% with a fill factor (FF) of 85.04%. Our findings underscore the importance of dielectric constant matching in both electron transport layer (ETL) and HTL, highlighting the potential of SnO2–CuSCN and PCBM-PTAA as transport layer materials for achieving high efficiency and minimizing hysteresis in PSCs.

Impact of compact TiO2 interface modification on the crystallinity of perovskite solar cells

The effect of TiO2 interfacial morphology on perovskite crystallinity was investigated by modifying the micro and nanoscale surface roughness of compact TiO2. While surface treatments of the compact TiO2 layer are recognized as effective strategies to enhance the photovoltaic performance of perovskite solar cells, the discussion regarding the crystallinity of perovskite atop TiO2 has been limited. In this study, we explored the impact of micro and nano scale interface morphology on perovskite crystal formation and its subsequent effects on device performance. Surprisingly, despite the absence of noticeable voids at the interface between the compact TiO2 and perovskite layers, the perovskite crystal morphology exhibited significant improvement following either micro or nanoscale interfacial modification. This enhancement ultimately led to improved photoconversion efficiency and reduced I–V hysteresis. These results emphasize the importance of underlayer surface morphology in the perovskite crystallization and suggest that the presence of grain boundaries within the perovskite layer may also contribute to I–V hysteresis in perovskite solar cells.

Role of Dipolar Organic Cations on Light-triggered Charge Transfer at TiO2 /CH3 NH3 PbI3 Interfaces.

The TiO2 /MAPbI3 (MA=CH3 NH3 ) interfaces have manifested correlation with current-voltage hysteresis in perovskite solar cells (PSCs) under light illumination conditions, but the relations between the photo-induced charge transfer and the collective polarization response of the dipolar MA cations are largely unexplored. In this work, we adopt density functional theory (DFT) and time-dependent DFT approach to study the light-triggered charge transfer across the TiO2 /MAPbI3 interfaces with MAI- and PbI-exposed terminations. It is found that regardless of the surface exposure of the MAPbI3 , the photo-induced charge transfer varies when going from the ground-state geometries to the excited-state configurations. Besides, thanks to the electrostatic interactions between the ends of MA cations and the photogenerated electrons, the photo-induced charge transfer across the interfaces is enhanced (weakened) by the negatively (positively) charged CH3 (NH3 ) moieties of the MA species. Resultantly, the positively charged iodine vacancies at the TiO2 /MAPbI3 interfaces tend to inhibit the charge transfer induced by light. Combining with the energy level alignment which is significantly modulated by the orientation of the MA species at the interfaces, the dipolar MA cations might be a double-edge sword for the hysteresis in PSCs with the TiO2 /MAPbI3 interfaces.

Inverted hysteresis as a diagnostic tool for perovskite solar cells: Insights from the drift-diffusion model

Despite current–voltage hysteresis in perovskite solar cells (PSCs) having been the subject of significant research over the past decade, inverted hysteresis (IH), although frequently observed, is still not properly understood. Several mechanisms, based on numerical simulations, have been proposed to explain it but a satisfactory description of the underlying cause remains elusive. To rectify this omission, we analyze a drift-diffusion model of a planar three-layer PSC, using asymptotic techniques, to show how inverted hysteresis comes about. The asymptotic analysis of the drift-diffusion model yields a simple approximate model that shows excellent agreement with numerical simulations of the full drift-diffusion model provides fundamental insights into the causes of IH and reconciles the alternative explanations found in the literature. This approximate model is analyzed further to isolate the material properties and external conditions that contribute to inverted hysteresis and constitutes a diagnostic tool in which the appearance of IH can be used to infer properties of the cell.

The Influence of Different Recombination Pathways on Hysteresis in Perovskite Solar Cells with Ion Migration

The impact of hysteresis on the power conversion efficiency (PCE) of perovskite solar cells (PSCs) still faces uncertainties despite the rapid development of perovskite photovoltaics. Although ion migration in perovskites is regarded as the chief culprit for hysteresis, charge carrier recombination pathways in PSCs are proposed to be necessary for the occurrence of hysteresis. Here, the impact of both bulk recombination and interface recombination on hysteresis in PSCs is investigated via drift–diffusion modeling. The simulation results demonstrate a direct correlation between recombination pathways and hysteresis in PSCs with ion migration. The simulation reveals that recombination pathways in PSCs will react to the variation in charge carrier distribution under different voltage scanning directions induced by ion migration in absorber layers, which leads to hysteresis in PSCs. Moreover, the hysteresis in normal (N-I-P) PSCs with different electron transport layers (ETLs) including sintered SnO2, SnO2 nano crystals and TiO2 is experimentally explored. The results demonstrate that multiple recombination pathways coupled with ion migration can lead to obvious hysteresis in fabricated PSCs which is consistent with simulation results. This work provides great insight into hysteresis management upon composition, additive and interface engineering in PSCs.

Correlation between hysteresis dynamics and inductance in hybrid perovskite solar cells: studying the dependency on ETL/perovskite interfaces.

In this study, to elucidate the origin of inductance and its relationship with the phenomenon of hysteresis in hybrid perovskite solar cells (PSCs), two electron transport layer (ETL) structures have been utilized: (a) rutile titania nanorods grown over anatase titania (AR) and (b) anatase titania covering the rutile titania nanorods (RA). The rutile and anatase phases are prepared via hydrothermal synthesis and spray pyrolysis, respectively. PSCs based on an ETL with an RA structure attain higher short-circuit current density (JSC) and open-circuit voltage (VOC) while showing a slightly lower fill factor (FF) compared with their AR counterparts. Using electrochemical impedance spectroscopy (EIS) measurements, we show that the ETL plays a major role in setting the tone for ionic migration speed and consequent accumulation. Moreover, we consider the conductivity of transport layers as a determining factor in not only giving rise to inductive features but also dictating the bias region under which recombination takes place, ultimately influencing hysteresis locus.

Optoelectronic properties and ion diffusion mechanism in 2D perovskites Cs3BX5 (B = Ge, Sn, and Pb; X = Cl, Br, and I): A first–principles investigation

Mitigating ion migration is a big challenge for optoelectronic perovskite materials. In this work, we investigate a novel family of layered halide perovskites Cs3BX5 (B = Ge, Sn, and Pb; X = Cl, Br, and I) by first–principles calculations. These compounds exhibit direct bandgap and small effective masses of electrons and holes. The optical absorption and spectroscopic limited maximum efficiency suggest the promising potential for these materials in solar energy conversion. The suppressed ionic conductivity has also been demonstrated by the higher energy barriers of halide ions migrations, which would be conducive to mitigate the hysteresis in perovskite solar cells.

Slow Shallow Energy States as the Origin of Hysteresis in Perovskite Solar Cells

Organic-inorganic metal halide perovskites have attracted a considerable interest in the photovoltaic scientific community demonstrating a rapid and unprecedented increase in conversion efficiency in the last decade. Besides the stunning progress in performance, the understanding of the physical mechanisms and limitations that govern perovskite solar cells are far to be completely unravelled. In this work, we study the origin of their hysteretic behaviour from the standpoint of fundamental semiconductor physics by means of technology computer aided design electrical simulations. Our findings identify that the density of shallow interface defects at the interfaces between perovskite and transport layers plays a key role in hysteresis phenomena. Then, by comparing the defect distributions in both spatial and energetic domains for different bias conditions and using fundamental semiconductor equations, we can identify the driving force of hysteresis in terms of slow recombination processes and charge distributions.

Influences of dielectric constant and scan rate on hysteresis effect in perovskite solar cell with simulation and experimental analyses

In this work, perovskite solar cells (PSCs) with different transport layers were fabricated to understand the hysteresis phenomenon under a series of scan rates. The experimental results show that the hysteresis phenomenon would be affected by the dielectric constant of transport layers and scan rate significantly. To explain this, a modified Poisson and drift-diffusion solver coupled with a fully time-dependent ion migration model is developed to analyze how the ion migration affects the performance and hysteresis of PSCs. The modeling results show that the most crucial factor in the hysteresis behavior is the built-in electric field of the perovskite. The non-linear hysteresis curves are demonstrated under different scan rates, and the mechanism of the hysteresis behavior is explained. Additionally, other factors contributing to the degree of hysteresis are determined to be the degree of degradation in the perovskite material, the quality of the perovskite crystal, and the materials of the transport layer, which corresponds to the total ion density, carrier lifetime of perovskite, and the dielectric constant of the transport layer, respectively. Finally, it was found that the dielectric constant of the transport layer is a key factor affecting hysteresis in perovskite solar cells.

Current-voltage hysteresis reduction of CH3NH3PbI3 planar perovskite solar cell by multi-layer absorber

In this paper, we present two structures with two and three-layer absorber to reduce the current density-voltage (J-V) characteristics hysteresis of the planar perovskite solar cell. The quantity of hysteresis has significantly decreased by adjusting precursor ratios and thickness of devices layers. The main factor of hysteresis in perovskite solar cells is built-in field screening resulting from ion migration and minority carriers' recombination. In the proposed structures, the reduction of minority carriers decreases recombination in the forward scan. The thickness of the absorber layer of a primary (single-layer) solar cell is 450 nm as the same as the proposed structures in which aggregate thickness is 450 nm. In the single-layer absorber structure, the least quantity of the hysteresis was obtained by 0.0508 with the most precursor quantity. The optimization of thickness and precursor ratio demonstrated the reduction of hysteresis by ∼64% in two-layer absorber structures and ∼88.3% in three-layer absorber structures compared to the single-layer structure.

Assessment of Lead‐Free Tin Halide Perovskite Solar Cells Using J–V Hysteresis

Perovskite solar cells (PSCs) are considered as one of the most promising alternatives for existing solar cells due to its excellent optoelectronic properties and high efficiency. However, lead has posed a serious issue due to its toxicity which may hinder the commercial use of lead‐based perovskite solar panels/arrays. There has been substantial work progress to find an environment‐friendly alternative metal ion to replace lead. Tin (Sn)‐based PSCs have been successfully synthesized and optimized with high efficiency, making it the most promising active material for lead‐free PSCs. In this review, the role of J–V hysteresis in tin halide PSCs is discussed from the perspective of system structure, working concepts, and interfacial carrier dynamics in detail. The problem of hysteresis in PSCs is closely linked to ion migration, ferroelectric effects, capacitive effects, and trap‐assisted recombination processes, which are highlighted in this review. Further, remediation to reduce the hysteresis by various strategies is explained for tin‐based perovskites. The core focus of this review is to analyze the deterioration of device performance and stability caused due to the generation of defects in the perovskite films, leading to a time‐dependent hysteresis of the current–voltage curves.

Relationship between ion vacancy mobility and hysteresis of perovskite solar cells

The relation between ion vacancy mobility and hysteresis of perovskite solar cells (PSCs) is investigated by computer simulation. Due to the ion vacancy migration, the hysteresis in PSCs strongly depends on the scan rate of J-V sweeps. The hysteresis only occurs in certain regime of scan rate. We calculate the evolution of ionic charge density stored within the Debye layers to discuss the process of ion vacancy migration and the variation of ion vacancy accumulation during the J-V sweeps. Based on this discussion, we give the physical picture of hysteresis. We discover that the regime of scan rate where hysteresis shows up moves towards higher value with increasing mobility of ion vacancy.

Methods of Hysteresis Reduction in Perovskite Solar Cells

Maniell workmanElectrochemical SocietyPerovskite Solar cells have shown much promise in a relatively short time. Power conversion efficiencies have increased from 3.8% to 24.2 % in a span of ten years. Perovskite solar cells have attracted much attention in research because of the relatively low cost in manufacturing and production. Current silicon photovoltaic devices are more expensive than conventional fossil fuel. Perovskites are typically analyzed by assessing their current voltage relationship. Under test conditions emulating standard environmental conditions the voltage is incrementally increased in one scan in decreased in another. hysteresis, the variance between the scans, is a common issue amongst perovskites. large hysteresis creates instability in operation. There are currently a number of efforts in order to reduce hysteresis in Perovskite solar cells. The capacitive element innate to perovskites makes addressing this issue complicated. Hysteresis has many sources such as the interfacial boundary, morphology, perovskite chemistry, and defects. In this presentation some of the current methods of hysteresis reduction for perovskite solar cells are examines for their effectiveness. The electrical and quantum mechanical characteristics play a critical role in hysteresis and device performance.

Fundamentals of Hysteresis in Perovskite Solar Cells: From Structure-Property Relationship to Neoteric Breakthroughs.

Perovskite solar cells (PSC) have shown a rapid increase in efficiency than other photovoltaic technology. Despite its success in terms of efficiency, this technology is inundated with numerous challenges hindering the progress towards commercial viability. The crucial one is the anomalous hysteresis observed in the photocurrent density-voltage (J-V) response in PSC. The hysteresis phenomenon in the solar cell presents a challenge for determining the accurate power conversion efficiency of the device. A detailed investigation of the fundamental origin of hysteresis behavior in the device and its associated mechanisms is highly crucial. Though numerous theories have been proposed to explain the causes of hysteresis, its origin includes slow transient capacitive current, trapping, and de-trapping process, ion migrations, and ferroelectric polarization. The remaining issues and future research required toward the understanding of hysteresis in PSC device is also discussed.

Numerical modelling of ion-migration caused hysteresis in perovskite solar cells

We presented one dimensional defect model to simulate hysteresis in perovskite solar cells. It can be numerically simulated in perovskite devices with p+-i-n+ configuration by considering ions migration under influence of different voltage biasing. The availability of mobile ion which contribute towards ion migration, ion accumulation at interfaces and near interface regions are observed to be generating I–V hysteresis in simulations. To simulate ion migration under positive poling we have taken a defect model and reverse the defect polarity for simulating ion migration under negative poling. The hysteresis is observed when the device has either of the condition (a) defects at the interfacial traps at the junction, or (b) defects in p+ or n+ layer in vicinity of the interface region. Both the conditions have yielded I–V hysteresis when we switched polarity of defect to simulate positive and negative poling. This study brings out the prominent role of mobile ions and carrier dynamics in controlling device working. Band diagram and capacitance variation visibly showed the impacts of charge reversal and capacitance simulations of perovskite device. 1D modelling shows that the ionic migration is one of the responsible mechanisms behind the I–V hysteresis in the perovskite solar cell devices

Work function engineering to enhance open-circuit voltage in planar perovskite solar cells by g-C3N4 nanosheets

Enhancement of open-circuit voltage (Voc) is an effective way to improve power conversion efficiency (PCE) of the perovskite solar cells (PSCs). Theoretically, work function engineering of TiO2 electron transport layer can reduce both the loss of Voc and current hysteresis in PSCs. In this work, two-dimensional g-C3N4 nanosheets were adopted to modify the compact TiO2 layers in planar PSCs, which can finely tune the work function (WF) and further improve the energy level alignment at the interface to enhance the Voc and diminish the hysteresis. Meanwhile, the quality of perovskite films and charge transfer of the devices were improved by g-C3N4 nanosheets. Therefore, the PCE of the planar PSCs was champed to 19.55% without obvious hysteresis compared with the initial 15.81%, mainly owing to the remarkable improvement of VOC from 1.01 to 1.11 V. In addition, the stability of the devices was obviously improved. The results demonstrate an effective strategy of WF engineering to enhance Voc and diminish hysteresis phenomenon for improving the performance of PSCs.

Investigating physical origin of dominant hysteresis phenomenon in perovskite solar cell

The progress of perovskite solar cell (PSC) technology is held back due to the presence of anomalous hysteresis in its current–voltage (J–V) characteristics. Understanding the physical origin of J–V hysteresis is crucial for the development of hysteresis-free solar cell. We computationally explore the relative contribution of dominant physical phenomenon that could cause hysteresis in PSC. We explore that accumulation of mobile ions at the interfaces of the cell inside perovskite produces a space charge which in combination with charge trapping/detrapping in deep traps results in hysteresis which is often characterized by an S shaped behavior of J–V curve. We further explore that shallow traps at the interfaces of carrier-extraction layers alone exhibit the combined effects of ion accumulation and deep charge traps, and lead to J–V hysteresis in PSCs. Moreover, we investigate the effect of energy level of deep/shallow traps and show that the energy level of deep/shallow traps plays an important role in J–V characteristics of the cell. Lastly, we explore that high minority carrier lifetime in the bulk of the perovskite mitigates the effects of ion accumulation and/or charge trapping/detrapping and leads to hysteresis-free cell. The results presented in this work are beneficial for the development of hysteresis-free PSCs.

Efficient and Stable Perovskite Solar Cells Enabled by Dicarboxylic Acid-Supported Perovskite Crystallization.

Defect states at surfaces and grain boundaries as well as poor anchoring of perovskite grains hinder the charge transport ability by acting as nonradiative recombination centers, thus resulting in undesirable phenomena such as low efficiency, poor stability, and hysteresis in perovskite solar cells (PSCs). Herein, a linear dicarboxylic acid-based passivation molecule, namely, glutaric acid (GA), is introduced by a facile antisolvent additive engineering (AAE) strategy to concurrently improve the efficiency and long-term stability of the ensuing PSCs. Thanks to the two-sided carboxyl (-COOH) groups, the strong interactions between GA and under-coordinated Pb2+ sites induce the crystal growth, improve the electronic properties, and minimize the charge recombination. Ultimately, champion-stabilized efficiency approaching 22% is achieved with negligible hysteresis for GA-assisted devices. In addition to the enhanced moisture stability of the devices, considerable operational stability is achieved after 2400 h of aging under continuous illumination at maximum power point (MPP) tracking.