Instability Of Perovskite Solar Cells Research Articles

Enhanced carbon-based back contact electrodes for perovskite solar cells: Effect of carbon paste composition on performance and stability

To address the issue of cost and instability in perovskite solar cells (PSCs), it is promising to substitute the regular hole collecting electrode i.e., spiro-OMeTAD/Au with inorganic hole transport layer (HTL)/carbon electrode. In this study, three carbon pastes were investigated with different binders: polymethyl methacrylate (PMMA), styrene-butadiene-styrene (SBS) and ethyl cellulose (EC). Carbon layers were compared in terms of mechanical stability, conductivity and performance as back contact electrodes in PSCs with an inorganic HTM composed of CuInS2 nanoparticles. To assess mechanical properties of the carbon pastes, adhesion tests by using tape, ultrasonication in the media of deionized water and acidic deionized water, and also flexibility test were performed. The carbon layer based on SBS carbon paste (SBS-CP) was intact after adhesion tests and over 1017 cycles of flexibility test. The one based on PMMA carbon paste (PMMA-CP) didn't tolerate all mechanical tests and disintegrated. The carbon layer based on EC carbon paste (EC-CP) partly damaged after adhesion tests and didn't pass the flexibility test. The best efficiency of 18.6 % was obtained for a device based on SBS-CP and significant shelf-life stability over 172 days stored in relative humidity of 40 % and dark.

Thermal Stability Analysis of Formamidinium–Cesium‐Based Lead Halide Perovskite Solar Cells Fabricated under Air Ambient Conditions

The instability of perovskite solar cells (PSCs) remains a major bottleneck for their commercialization, with thermal instability posing a major concern, given the inevitable presence of heat in photovoltaic devices. Mixed‐cation/halide perovskites demonstrate enhanced stability and efficiency compared to single‐cation/halide perovskites. Identifying the optimal perovskite composition capable of withstanding high temperatures for longer durations is crucial for the development of thermally stable PSCs. This study provides valuable insights into the optimization of mixed‐cation/halide perovskites to enhance the thermal and structural stability of perovskite films. By systematically varying the Cs content in FA1−yCsyPb(I0.85Br0.15)3 (0 < y < 25)‐based perovskite, it is observed that controlling the Cs content allows precise modulation of crystal orientation in perovskite film with 10% Cs obtained as the optimal value. The perovskite film containing 10% Cs not only exhibits reduced microstrain but also demonstrates enhanced thermal stability during testing at 85 °C under controlled humidity. Furthermore, planar PSCs are fabricated using FA0.90Cs0.10Pb(I0.85Br0.15)3 as the absorber layer and TOP‐3 as the hole‐transporting material, achieving a promising power conversion efficiency (PCE) of 17.70%. Impressively, the unencapsulated devices retain 95% of their initial PCE after 1000 h of dark storage under ambient conditions.

Temperature dependence of iodine vacancies concentration in [formula omitted] perovskite: A theoretical analysis

In this study, we investigate the temperature dependence of iodine vacancies in the organic-inorganic hybrid perovskite CH3NH3PbI3 through theoretical analysis. Iodine vacancies, as point defects, play a crucial role in the instability of perovskite solar cells. By employing molecular dynamics (MD) simulations, we calculate the formation energy of vacancies and examine its relationship with temperature. Our results reveal that the formation energy remains constant irrespective of temperature. However, elevated temperatures facilitate the provision of energy necessary for vacancy formation. To accurately determine the vacancy concentration, it is essential to consider the associated entropy changes. Analytical methods are employed to assess these entropy changes, offering valuable insights into the vacancy formation process. Utilizing the derived values, we quantify the concentration of vacancies and analyze their dependence on temperature. The findings obtained from this research contribute significant insights into the behavior of iodine vacancies within the studied CH3NH3PbI3 perovskite system.

A Comprehensive Review on Defects-Induced Voltage Losses and Strategies toward Highly Efficient and Stable Perovskite Solar Cells

The power conversion efficiency (PCE) of single-junction perovskite solar cells (PSCs) has reached 26.1% in small-scale devices. However, defects at the bulk, surface, grain boundaries, and interfaces act as non-radiative recombination centers for photogenerated electron-hole pairs, limiting the open-circuit voltage and PCE below the Shockley–Queisser limit. These defect states also induce ion migration towards interfaces and contribute to intrinsic instability in PSCs, reducing the quasi-Fermi level splitting and causing anomalous hysteresis in the device. The influence of defects becomes more prominent in large-area devices, demonstrating much lower PCE than the lab-scale devices. Therefore, commercializing PSCs faces a big challenge in terms of rapid decline in working performance due to these intrinsic structural defects. This paper provides a comprehensive review of recent advances in understanding the nature and the classification of defects, their impact on voltage losses, device parameters, intrinsic stability, and defect quantification and characterization techniques. Novel defect passivation techniques such as compositional engineering, additive engineering, post-treatments, dimensionality engineering, and interlayer engineering are also reviewed, along with the improvements in PCE and stability based on these techniques for both small-area devices and large-area roll-to-roll coated devices.

Design and Synthesis of Fluorinated Quantum Dots for Efficient and Stable 0D/3D Perovskite Solar Cells

AbstractDimensionality engineering involving the low‐dimensional and 3D perovskites has been demonstrated as an efficient promising strategy to modulate interfacial energy loss as well as instability in perovskite solar cells (PSCs). Herein, the use of fluorinated Cesium Lead Iodide (CsPbI3) perovskite quantum dot (PQD) is first reported as interface modification layer for PSCs. The binding between the CsPbI3 PQD surface and native oleic acid (OLA)/oleylamine (OAm) ligands is governed by a dynamic adsorption–desorption equilibrium. Perfluorooctanoic acid (PFA) with stronger binding affinity and more hydrophobic nature is explored to partially replace OLA to prepare the fluorinated ligand capped CsPbI3 PQDs (F‐CsPbI3). Through optimization of the addition of PFA during hot‐injection synthesis, the in situ treated F‐CsPbI3 PQDs display reduced surface defect states, higher photoluminescence quantum yields together with improved stability. Subsequently, both CsPbI3 and F‐CsPbI3 PQDs are utilized as interface engineering layer in PSCs, delivering the best efficiency values of 21.99% and 23.42%, respectively, which is significantly enhanced compared to the control device (20.37%). More importantly, benefiting from its more hydrophobic properties, the F‐CsPbI3 PQD treated device exhibits excellent ambient storage stability (25 °C, relative humidity: 35–45%), retaining over 80% of its initial efficiency after 1500 h aging.

Stable and efficient perovskite solar cells via hydrogen bonding and coordination.

The instability of perovskite solar cells (PSCs) is primarily caused by the unavoidable ion migration in the perovskite layer. Ion migration and accumulation influence the properties of perovskite and functional layers, resulting in severely degraded device performance. Herein, we introduced an n-type, low optical gap-conjugated organic molecule (i.e., COTIC-4F or COTIC-4Cl) to serve as the perovskite photoactive layer in a perovskite precursor solution for broadening the near-infrared spectral response and enhancing the efficiency of PSCs. Various characterization studies have determined that COTIC-4F forms hydrogen bonds with perovskites, thereby remarkably enhancing the anchoring ability of MA+, suppressing ion migration, and reducing photocurrent hysteresis. Meanwhile, the carbonyl (CO) group of COTIC-4F and COTIC-4Cl can donate a lone electron pair to passivate the Pb trap, avoiding possible carrier recombination. The COTIC-4F- and COTIC-4Cl-treated perovskite films exhibit an optical response in the near-infrared region and an excellent morphology. Through ultraviolet photoelectron spectroscopy, it has been determined that COTIC-4F can facilitate more charge transfer than COTIC-4Cl, which results in a larger photocurrent from the PSCs. The PSCs of the COTIC-4F-treated perovskite films demonstrate a maximum power conversion efficiency of 21.72%. They exhibit a high fill factor of 82.02% and possess long-term stability under an air atmosphere.

The influence of A-site dipole moment on iodine migration in perovskite films revealed by transient ion drift

Ion migration is regarded as the chief culprit for the long-term instability in perovskite solar cells (PSCs), and iodine ions are the most subjects to migration in PSCs. Strategies, such as grain size engineering, chemical bonding engineering, steric impediment effect, and interface passivation, are employed to suppress the iodine migration but unfortunately are unable to completely eliminate it. Here, the influence of the dipole moment of A-site ions on iodine migration has been comprehensively investigated for perovskite films based on different A-site cations via a transient ion drift (TID) method. TID results demonstrate that the decrease in the strength of the dipole moment of A-site ions can lead to a decrease in the activation energy (EA) of iodine ions. Therefore, this work suggests that increasing the strength of dipole moment of A-site ions can be utilized as an effective strategy for suppressing iodine migration in perovskite films providing critical insight for enhancing the long-term stability for PSCs.

Ionic Liquid Gating in Perovskite Solar Cells with Fullerene/Carbon Nanotube Collectors

Metallic cathodes are one of reasons for instability in perovskite solar cells due to reaction with halogens I−, Br−, and it is desirable to have stable carbon‐based cathodes, particularly carbon nanotubes (CNTs), and transport layers such as C60/C70. In this work, we show that gating of such top CNT cathode in ionic liquid by changing gate voltage (V g) tunes the Fermi level of CNT by electrical double layer charging and causes lowering of the barrier at C60/C70 electron transport layer (ETL). Moreover, at higher V g the ions further propagate into fullerene ETL by electrochemical n‐doping, which increases dramatically performance by further raising mostly two parameters: short‐circuit current and fill factor, resulting in solar cell efficiency growth from 3% to 11%. Surprisingly, open‐circuit voltage (V oc) is not sensitive to V g in the perovskite solar cells, on the contrary to strongly enhanced V oc in ionically gated organic solar cells, where it is the main effect for ionic gating. This insensitivity of V oc to lowering of the work function of CNT electrode is a clear indication that V oc in the perovskite solar cell is determined by inner p‐i‐n junction formation in the perovskite layer itself.

Tracking the evolution of materials and interfaces in perovskite solar cells under an electric field

What causes the instability of perovskite solar cells has been a puzzling problem impeding the development of commercial panels. So far there is limited evidence on the link between device instability and the various materials in each of the stacked layers. Here, we study the chemistry and distribution of various species and the integrity of the functional layers in high-performance inverted perovskite solar cells, with and without an electric field. The distribution of the diffusion species and its impact on the chemical and electronic structures through the transporting layers are measured by photoemission spectroscopy combined with damage-free ion beam sputtering. We find that various species, such as I2 and PbI2, are distributed throughout the organic transporting layers toward the electrode interface. These species are found to be charge neutral, have no impact on the Fermi level, and react little with copper. An electric field, however, can catalyze the electro-decomposition of the perovskite, causing chemical heterogeneity and degradation in device performance.

A high\u2010efficiency and stable perovskite solar cell fabricated in ambient air using a polyaniline passivation layer

Over the past number of years, the power conversion efficiency of perovskite solar cells has remained at 25.5%, reflecting a respectable result for the general incorporation of organometallic trihalide perovskite solar cells. However, perovskite solar cells still suffer from long-term stability issues. Perovskite decomposes upon exposure to moisture, thermal, and UV-A light. Studies related to this context have remained ongoing. Recently, research was mainly conducted on the stability of perovskite against non-radiative recombination. This study improved a critical instability in perovskite solar cells arising from non-radiative recombination and UV-A light using a passivation layer. The passivation layer comprised a polyaniline (PANI) polymer as an interfacial modifier inserted between the active layer and the electron transport layer. Accordingly, the UV-A light did not reach the active layer and confined the Pb2+ ions at PANI passivation layer. This study optimized the perovskite solar cells by controlling the concentration, thickness and drying conditions of the PANI passivation layer. As a result, the efficiency of the perovskite solar cell was achieved 15.1% and showed over 84% maintain in efficiency in the ambient air for one month using the 65 nm PANI passivation layer.

Reformation of thiophene-functionalized phthalocyanine isomers for defect passivation to achieve stable and efficient perovskite solar cells

Lewis acid–base passivation is a significant technique to achieve structural stability of perovskite solar cells (PSCs) by overcoming the issues of wide grain boundaries, crystal defects, and the instability of PSCs. In this work, the combined effects of thiophene with phthalocyanine (Pc) as isomers (S2 and S3) on the photovoltaic performance of PSCs were studied for the first time. Through density functional theory calculations, we confirmed that the position of the S atom in the structure affects Lewis acid–base interactions with under-coordinated Pb2+ sites. The morphology of methylammonium lead iodide (MAPbI3) for passivated devices was improved and thin dense layers with compact surface and large grain size were observed, leading to improvement of the charge extraction ability and reduction of non-radiative recombination and the trap density. A highest power conversion efficiency of 18% was achieved for the Pc S3 passivated device, which was 6.69% more than that of the controlled device. Furthermore, the Pcs passivated devices demonstrated remarkable stability under high-moisture and high-temperature conditions.

Achieving Resistance against Moisture and Oxygen for Perovskite Solar Cells with High Efficiency and Stability

Realization of high efficiency along with long-term stability of perovskites solar cells has been a goal of researchers in this field. Breakthroughs in efficiency have been achieved in the past decade, exceeding those of most thin film solar cells. However, the challenge of degradation and instability of perovskite solar cells is currently the bottleneck for their real-life application. Extensive research has been conducted to achieve simultaneously high efficiency and high stability, leading to considerable progress in device performance. A significant source causing degradation is the ingression of external materials, such as moisture and oxygen. In this review, the mechanisms of moisture and oxygen degradation occurring in perovskite absorber and charge transporting layers are interpreted. Primary approaches to simultaneously achieve high efficiency and high stability focus on encapsulation, interfacial layer engineering, process engineering, ion engineering, and dopant and alternative engineering. In brief, we review the materials development and engineering strategies to improve performance and identify the obstacles that hinder the realization of high stability along with high efficiency.

High efficient and stable Tin-based perovskite solar cells via short-chain ligand modification

Sn-based perovskite material has been selected as a strong contender for perovskite solar cells (PSCs) application compared with Pb-based perovskite, due to its more suitable bandgap and excellent optoelectronic characteristics. However, the poor quality of Sn-based perovskite film and the oxidation of Sn 2+ still lead to the unsatisfactory efficiency and instability of PSCs. In our work, a type of ligand “Trifluoroethylamine iodide (3FEAI)” was developed to achieve the crystallization regulation of FASnI 3 perovskite films, which could effectively improve the film quality while restricting the film defects. Moreover, it is found that the short-chain 3FEAI exhibited the better assistance of charge transport effect compared with the conventional ligand PEAI, which further contributed to the efficiency of PSCs. At last, with the introduction of 3FEAI, the prepared device shows the considerable efficiency (9.34%) and long-term stability (~10% PCE loss after 500 h of aging). • Considerable efficiency and light aging stability performance in Sn-based PSCs application. • Perovskite films with improved crystallinity and morphology were obtained by introducing 3FEAI ligands. • Less resistance for charge-exchanging on perovskite GBs/surface compared with the previous long-chain ligand.

Influence of grain size on the photo-stability of perovskite solar cells

Organometallic perovskite solar cells have recently attracted huge attention as one of the most promising photovoltaic technologies. Despite higher efficiency achieved in recent years, the instability of perovskite solar cells remains as the biggest problem to be solved. Recently, researchers have developed several encapsulation techniques to enhance the device stability against moisture, but the stability of the device under light soaking did not receive that much attention. Previously, we had studied the device physics behind photo-induced degradation of the perovskite solar cells, and we found that the performance degradation during light exposure is attributed to the generation and migration of mobile ions. In this paper, we investigated the effect of the grain size on the photo-stability and mobile ion generation in perovskite solar cells. We found that with larger perovskite film grain size, the ion generation rate decreased significantly under light exposure, which leads to less performance degradation. This result was further confirmed by our ion density measurement using transient ionic current.

Simultaneously Passivating Cation and Anion Defects in Metal Halide Perovskite Solar Cells Using a Zwitterionic Amino Acid Additive.

Ionic defects (e.g., organic cations and halide anions), preferably residing along grain boundaries (GBs) and on perovskite film surfaces, are known to be a major source of the notorious environmental instability of perovskite solar cells (PeSCs). Although passivating ionic defects is desirable, previous approaches using Lewis base or acid molecules as additives suppress only the negatively or positively charged defects, thus leaving oppositely charged defects. In this work, both the cationic and anionic defects inside methyl ammonium lead tri-iodide (MAPbI3 ) are simultaneously passivated by introducing a zwitterionic form of the amino acid, L-alanine, into the precursor solution as an additive. L-alanine has both positive (NH3+ ) and negative (COO- ) functional groups at a specific solvent pH, thereby passivating both the cation and anion defects in MAPbI3 . The addition of L-alanine increases the grain size of the perovskite crystals and lengthens the charge carrier lifetime (τ>1 µs), leading to improved power conversion efficiencies (PCEs) of 20.3% (from 18.3% without an additive) for small-area (4.64 mm2 ) devices and 15.6% (from 13.5%) for large-area submodules (9.06 cm2 ). More importantly, the authors' approach also significantly enhances the shelf storage and photoirradiation stabilities of PeSCs.

Ambient air-processed mesoscopic solar cells based on methylammonium and phenethylammonium quasi-2D/3D perovskites

The instability of perovskite solar cells under ambient conditions leads many scientific groups to produce their solar cell devices under controllable, yet, expensive conditions. In this work, a mesoscopic solar cell device produced under ambient air/temperature conditions and relatively high humidity is presented. The active material is based on methylamine, phenethylamine, lead(II) iodide and lead(II) chloride. Furthermore, a bis(trifluoromethane)sulfonimide lithium (Li-TFSI) salt layer was used as a dopant onto mesoscopic TiO2, while the hole-transport material used was the popular poly(3-hexylthiophene-2,5-diyl) (P3HT) polymer. All layers were deposited by simple spin coating technique, while the whole process took place under 40–60% relative humidity–ambient conditions. The sequential deposited perovskite layer was built by a 3D mixed halide (CH3NH3)3PbI3Cl2 layer on top of a mixed 3D/Quasi-2D perovskite (CH3NH3)3PbI3Cl2–(C8H9NH3)2(CH3NH3)2Pb3I10 layer. These specific perovskites were used to take advantage of the well-known power conversion efficiency (PCE) of the mixed halide perovskite based on methylamine, and the proven reproducibility and stability of the phenethylamine-based perovskites, especially under non-controllable conditions. The champion mesoscopic device presented a PCE of 13.22%, with short circuit current density (JSC) of 23.67 mA/cm2, open circuit voltage (VOC) of 1034 mV and fill factor (FF) 0.54.

Steric Impediment of Ion Migration Contributes to Improved Operational Stability of Perovskite Solar Cells.

The operational instability of perovskite solar cells (PSCs) is known to mainly originate from the migration of ionic species (or charged defects) under a potential gradient. Compositional engineering of the "A" site cation of the ABX3 perovskite structure has been shown to be an effective route to improve the stability of PSCs. Here, the effect of size-mismatch-induced lattice distortions on the ion migration energetics and operational stability of PSCs is investigated. It is observed that the size mismatch of the mixed "A" site composition films and devices leads to a steric effect to impede the migration pathways of ions to increase the activation energy of ion migration, which is demonstrated through multiple theoretical and experimental evidence. Consequently, the mixed composition devices exhibit significantly improved thermal stability under continuous heating at 85 °C and operational stability under continuous 1 sun illumination, with an extrapolated lifetime of 2011 h, compared to the 222 h of the reference device.

Oxidation states in perovskite layers formed using various deposition techniques

Organic–inorganic halide perovskites have rapidly become emerging materials for photovoltaic applications, but a major factor causing instability in perovskite solar cells could be the elemental shift due to oxygen. The present work demonstrates the oxidation states of perovskite layers formed by (i) one-step deposition, (ii) solvent-to-solvent extraction, (iii) hot casting, and (iv) mixed-cation solution processing. X-ray photoelectron spectroscopy is used to investigate the compositional changes due to oxygen, and the spectra confirm the diffusion of oxygen in the perovskite layer. Mixed-cation perovskites show the most promising results among the four deposition techniques. The best photovoltaic performance is achieved by an SnO2-based mixed-cation perovskite solar cell with a power conversion efficiency of 18.75%. A power conversion efficiency of 16.74% is obtained by a TiO2-based mixed-cation perovskite solar cell when the optimum thickness of the TiO2 blocking layer is 60–65 nm.

Cesium[sbnd]lead based inorganic perovskite quantum-dots as interfacial layer for highly stable perovskite solar cells with exceeding 21% efficiency

Despite the excellent photovoltaic performances of perovskite solar cells (PSCs), the instability of PSCs under severe environment (e.g. humidity, light-induced, etc.) limits further commercialization of such devices. Therefore, in recent years, research on the long-term stability improvement of PSCs has been actively carried out in perovskite field. To address these issues, we demonstrated the incorporation of ultra-thin interfacial layer of inorganic CsPbBr1.85I1.15 perovskite quantum-dots (PQDs) that can effectively passivate defects at or near to the perovskite/hole transport material (HTM) interface, significantly suppressing interfacial recombination. This passivation layer increased the open circuit voltage (Voc) of triple-cation perovskite cells by as much as 50 mV, with champion cells achieving Voc ∼ 1.14 V. As a result, we obtained hysteresis-free cells with the efficiency beyond 21%. More importantly, devices based on such architecture are capable of resisting humidity and light-induced. Remarkably, the device employing CsPbBr1.85I1.15 demonstrated a superb shelf-stability aganist to humidity under ambient conditions (R.H.≥40%), retaining nearly 91% of initial efficiency after 30 days, while the efficiency of control device rapidly dropped to 45% from its initial value under the same conditions. Besides benefiting from the high moisture resistivity as well as supressed ion migration, PSCs based on PQDs showed better operational stability (retaining 94% of their initial performance) than that of the PQDs-free one under continuous light irradiation over 400 h. In addition, a faster PL decay time of 4.66 ns was attained for perovskite/PQDs structure (5.77 ns for only PQDs structure) due to the favorable energy transfer at the interface, indicating a Förster resonance energy transfer (FRET) mechanism. This work indicates that inorganic PQDs are important materials as interlayer in PSCs to supremely enhance the device stability and efficiency.

Potassium ions as a kinetic controller in ionic double layers for hysteresis-free perovskite solar cells

This work highlights the clear correlation of ion migration and a fast generation of the double layer with severe hysteresis and long-term instability in perovskite solar cells and the importance of K+ ions in reducing the kinetics affecting the ionic attachment to the contact surface.