Stable Perovskite Solar Cells Research Articles

Efficient and stable perovskite solar cells via oxalic acid doped SnO2 nanocrystals with surface-defect passivation

The electron extraction and transfer play a crucial role in high performance of perovskite solar cells (PSCs). Tin dioxide (SnO2), with the high electrical conductivity and low photocatalytic activity, has been reported to be one of the most advantageous electron-transporting layers (ETL) in PSCs. However, a large number of non-radiative recombination defects have been reported in SnO2, which are attributed to the low tunability and lower dispersibility. Here, we propose a ligand-assisted tuning strategy based on the oxalic acid (OA) modification to control the SnO2 film and interfacial structure. This strategy can effectively inhibit the particle aggregation of SnO2 film. In addition, the bonding interaction between CO in the ligand and Sn in SnO2 and Pb atoms in the perovskite reduces the interfacial contact impedance and enhances the electron extraction. As a result, an impressive PCE of 22.68 %, a fill factor exceeding 0.82 and a Voc of 1.15 V were successfully obtained. In addition, the unencapsulated PSCs can maintain an initial efficiency of 93 % upon exposure to ambient air for 500 h.

Ultrafast hole transfer mediated by a conjugated self-assembled molecule enables efficient and stable wide-bandgap perovskite solar cells

Charge accumulations and electron recombination at the interfaces between perovskites and charge transporting materials are two critical factors significantly hindering the power conversion efficiency (PCE) and device stability of wide-bandgap perovskite solar cells (WBG PSCs). Herein, we tailor-made a self-assembled molecule (SAM), termed XS13, featuring an enlarged π-donor and a π-linker, to regulate the interface carrier dynamics in ∼1.8 eV WBG PSCs. Ultrafast spectroscopy clearly demonstrated that the XS13 facilitated the rapid extraction and transfer of photo-generated holes compared to the reference SAM-2PACz. Consequently, WBG PSCs based on XS13 achieved an outstanding PCE of up to 19.20 %, surpassing that of control devices (16.41 %). Furthermore, XS13-based WBG PSCs exhibited a remarkable suppression of light/electricity-induced halide ions migration, leading to significantly improved device stability. Our findings offer a new strategy for the rational design of hole transporting molecules with controlled properties to enhance device performance of PSCs.

Composites electron transport layer of PVA-regulated SnO2 for high-efficiency stable perovskite solar cells

As a new and efficient solar cell, perovskite solar cell has attracted wide attention due to its excellent performance. The electron transport layer in perovskite solar cells has a significant impact on device performance. SnO2 films that can be prepared by solution method have become the first choice for electron transport layer due to their simple process and excellent performance. However, the defects in SnO2 thin films and non-radiative recombination sites at the SnO2/Perovskite interface will lead to potential losses in the performance of photovoltaic devices. Therefore, in order to improve the interface loss and interface characteristics and prepare more efficient perovskite solar cells. In this work, a functional polymer, polyvinyl alcohol (PVA), is introduced to regulate the arrangement of SnO2 nanocrystals. The SnO2-PVA composite electron transport layer not only improves carrier transport, but also further affects the growth of perovskite films. PVA inhibits the agglomeration of tin dioxide particles by adding it to the aqueous solution of tin dioxide. Meanwhile, the oxygen vacancy defects in the SnO2 layer have also improved. Correspondingly, SnO2-PVA-based PSCs can be obtained a maximum efficiency of 23.73 %. Attributed to the strengthened interface binding and the improved perovskite crystallization process, the devices obtain good long-term stability, retaining 90 % of their initial performance after 1000 h operation at their maximum power point under 1 sun illumination.

Perovskite Quantum Dots for Solar Cells and Beyond

Halide perovskite solar cells have witnessed great successes recently while their instability is a big hurdle for practical application. Herein we discuss our recent progress in addressing the stability of perovskite solar cells, including introduction of capping layers to improve the stability against moisture and heat, and perovskite size engineering to suppress phase segregation. In particular, quantum dots (QDs) have the advantages of quantum confinement effect, defect-tolerant nature, and processability for flexible devices. We discuss a new surface ligand engineering strategy in designing new hybrid perovskite QDs with controllable compositions and sizes The QDs have been used as building blocks in quantum dot solar cells delivering a certified record efficiency of 16.6% with excellent long-term operation stability. By using QDs as light absorbing materials, the QD based photocatalysts also exhibited good stable performance in photocatalytic hydrogen production. The combination of perovskite QDs with Metal-Organic Framework (MOF) materials to form new composites led to ultrastable photoluminescent property for > 10,000 hours. The integration of perovskite solar cells and rechargeable batteries have led to a single module type rechargeable solar batteries with an overall storable solar energy conversion efficiency of >12%.

Enhancing Charge Transport and Stability in Perovskite Solar Cells via Integration with Porous Copper-Based Metal-Organic Frameworks

Enhancing Charge Transport and Stability in Perovskite Solar Cells via Integration with Porous Copper-Based Metal-Organic Frameworks

Unraveling Differences in the Effects of Ammonium/Amine-Based Additives on the Performance and Stability of Inverted Perovskite Solar Cells.

Additive engineering, with its excellent ability to passivate bulk or surface perovskite defects, has become a common strategy to improve the performance and stability of perovskite solar cells (PVSCs). Among the various additives reported so far, ammonium salts are considered an important branch. It is worth noting that although both ammonium-based additives (R-NH3 +) and amine-based additives (R-NH2) are derivatives of ammonia (NH3), the functions of the two can be easily confused due to their structural similarities. Moreover, there is no comprehensive comparative analysis of them in the literature. Here, the differences between phenethylammonium iodide (PEA+) and phenethylamine (PEA) additives are revealed experimentally and theoretically. The results clearly show that PEA outperforms PEA+ in terms of device performance and stability based on the following three factors: i) PEA's defect passivation capability is superior to that of PEA+; ii) PEA has better hydrophobicity to hinder water ingress; and iii) PEA completely improves the stability of PVSCs by enhancing thermal stability and inhibiting iodide migration in perovskite more effectively than PEA+. As a result, the power conversion efficiency (PCE) of the inverted methylammonium triiodide (MAPbI3) device using PEA increases by ≈15% to over 21%. More importantly, this device exhibits greater ability to prevent water invasion, thermal-induce degradation, and inhibit iodide ion migration, resulting in better long-term stability.

(Invited) Ion Migration Influencing Perovskite Solar Cell Performance and Stability

The thermodynamic and redox properties of halide perovskites provide a strong driving force for hole trapping and oxidation of iodide species. When in contact with a non-polar solvent, the migration of iodine species is further extended to expulsion of iodine from the perovskite film. Thus, the mobility of halides and their susceptibility to hole-induced oxidation play a crucial role in determining the long-term stability of metal halide perovskite solar cells. When Ruddlesden-Popper 2D mixed-halide perovskite films with spacer cations such as butylammonium are introduced into three-dimensional (3D) perovskite films, they can stabilize them against moisture-induced degradation at room temperature. While such passivation of 3D perovskites using 2D perovskites has been reported widely, the instability of the 2D/3D interface during long term solar cell operation can be problematic, especially at higher temperatures. The cation migration under light and heat can significantly alter the 2D/3D interface, thus affecting the solar cell performance. We have now probed the cation migration between 2D and 3D perovskites by physically pairing X PbI (X=butylammonium BA, oleylammonium OA, or phenethylammonium PEA) 2D film and (CH3)PbI3 3D film at different temperatures by recording changes in the absorption and emission spectra. Thus, suppression of halide ion migration as well as cation migration remains a key factor in achieving long term stability and improving efficiency of perovskite solar cells and light emitting devices.

Nitrogen-rich carbon dots as the antisolvent additive for perovskite-based photovoltaic devices

Solution-processed perovskite solar cells (PSCs) have demonstrated a tremendous growth in power conversion efficiency (PCE). A high-quality, defect-free perovskite-based active layer is a key point to enhance PSC performance. Introduction of additives and interlayers have proved to be an effective tool to passivate surface defects, control crystal growth, and improve PSC stability. Antisolvent engineering has emerged recently as a new approach, which aims to adjust perovskite layer properties and enhance the PCE and stability of PSC devices. Here, we demonstrate that carbon dots (CDs) may serve as a prospective additive for antisolvent engineering. Nitrogen-rich amphiphilic CDs were synthesized from amines by a solvothermal method and used as an additive to chlorobenzene for a perovskite layer fabrication. The interaction between perovskite and functional groups in CDs promotes improved crystallization of an active perovskite layer and defects passivation, bringing higher PSCs efficiency, stability, and suppressed hysteresis. Under optimized CD concentration, the maximum PCE increased by 34% due to the improved short-circuit current and fill factor, and the device maintains 87% of its initial efficiency after 6 d of storage under ambient conditions.

Understanding different oxidation methods for the hole transport layer Spiro-OMeTAD to improve perovskite solar cell performance

The preparation of a high-performance hole transport layer is a pivotal factor in achieving efficiency and stable perovskite solar cells. 2,2’,7,7’-Tetrakis[N, N-di(4-methoxyphenyl)amino]−9,9’-spirobifluorene (Spiro-OMeTAD) currently stands as the most widely employed hole transport material in high-performance perovskite solar cells. The current methodologies for its preparation primarily revolve around three techniques: O2 oxidation, cobalt salt doping, and CO2 bubbled doping. In this study, we systematically investigated and analyzed Spiro-OMeTAD prepared through these three methods, from solution and film to device. The CO2-bubbled method and Co-doped method allow for faster and more complete oxidation of Spiro-OMeTAD while maintaining conductivity and energy level matching. Therefore, the film of both methods shows better carrier extract capabilities and defect states than that of O2-oxidized. In particular, the film of the CO2-bubbled method had better hydrophobicity and thermal stability, showing the least degradation at 85 °C annealing, which can be attributed to the removal of hydrophilic Li+. This study could inspire further optimization of Spiro-OMeTAD film fabrication processes in perovskite solar cells.

Enhancing photovoltaic efficiency in perovskite solar cells through synergistic blending of polyvinyl alcohol and F-127 polymer in a sandwich architecture

In the field of photovoltaics, perovskite solar cells (PSCs) have become increasingly popular because of their cost-effective processing and competitive efficiency when compared to silicon solar cells. This work presents a novel design of a PSC based on methyl ammonium lead iodide (CH3NH3PbI3) and investigates the possibilities of organic-inorganic metal halides in the field of PSCs. The device has a sandwich architecture, where the hole transport material (HTM) operates at room temperature using a blend of polyvinyl alcohol (PVA) and F-127 polymer. Under typical solar conditions, the built-in PSC, which has the architecture FTO/TiO2/Perovskite/PVA & F-127/Pt, exhibits a remarkable efficiency of 1.29 %. Interestingly, PSC stability at room temperature is still a major problem, yet our design demonstrates a remarkable 2-h stability in ambient circumstances. This accomplishment is ground breaking because it introduces a high-efficiency PSC in a sandwich construction operating in ambient settings for the first time. The fact that this novel technique is solution-based and does not require vacuum deposition lends even more credence to its viability and scalability.

Suppressing the phase separation in FAMA mixed perovskite solar cells via the preloading of A site cations within the lattice

The incorporation of MA as a dopant is highly advantageous for stabilizing the lattice structure of α-phase FAPbI3. However, achieving a homogeneous phase mixing is only feasible at elevated MA doping levels, which significantly compromises both the efficiency and stability of FA-dominated perovskite solar cells (PSCs). In this study, it is found that in the nucleation stage of FAMA mixed perovskite, MA+ exhibit a significant kinetic advantage over FA+ in their reaction with PbI3−. The rapid crystallization of MAPbI3 not only induces FA-MA separation but also hinders the crystallization of perovskite due to strains induced by the bulky FA+ cations. To address this issue, we introduced FA0.8MA0.2PbI3 single crystals as the material source to prepare the precursor solutions, which achieved a delicate balance between lattice stability and bandgap (Eg = 1.54 eV). The preloaded A-site cations within the PbI3− cages make the bare FA-dominated perovskite films by blade coating maintain the phase stability in wild ambient for over one year. The final PSCs (0.09 cm2) achieved a highest power conversion efficiency (PCE) of 23.66 %, among the highest efficiency records for blade coated PSCs. The unpackaged PSCs show efficiency loss of < 10 % as being aged in air with a relative humidity of 10 % for over 1000 h.

Lattice Strain Regulation and Halogen Vacancies Passivation Enable High-Performance Formamidine-Based Perovskite Solar Cells.

Formamidinium lead iodide (FAPbI3) perovskite has lately surfaced as the preferred contender for highly proficient and robust perovskite solar cells (PSCs), owing to its favorable bandgap and superior thermal stability. Nevertheless, volatilization and migration of iodide ions (I-) result in non-radiating recombination centers, and the presence of large formamidine (FA) cations tends to cause lattice strain, thereby reducing the power conversion efficiency (PCE) and stability of PSCs. To solve these problems, the lead formate (PbFa) is added into the perovskite solution, which effectively mitigates the halogen vacancy and provides tensile strain outside the perovskite lattice, thereby enhancing its properties. The strong coordination between the C═O of HCOO- and Pb-I backbones effectively immobilizes anions, significantly increases the energy barrier for anion vacancy formation and migration, and reduces the risk of lead ion (Pb2+) leakage, thereby improving the operation and environmental safety of the device. Consequently, the champion PCE of devices with Ag electrodes can be increased from 22.15% to 24.32%. The unencapsulated PSCs can still maintain 90% of the original PCE even be stored in an N2 atmosphere for 1440h. Moreover, the target devices have significantly improved performance in terms of light exposure, heat, or humidity.

Supramolecular Cucurbit[5]uril Modulates the Buried SnO2/Perovskite Interface for Efficient and Stable Perovskite Solar Cells

AbstractReducing non‐radiative recombination caused by defects at buried interfaces is crucial to the development of efficient and stable perovskite solar cells (PSCs). Herein, supramolecular cucurbit[5]uril (CB[5]) is introduced into the SnO2 layer, where it engages in host–guest interactions to suppress oxygen vacancies in SnO2, prevent particle aggregation, and enhance the electron mobility of SnO2. By serving as a bridging agent at the buried interface between SnO2 and the perovskite layer, CB[5] reduces the defect density and improves the carrier extraction efficiency. It also reduces the surface energy of the SnO2 substrate, facilitates the formation of large grains in the perovskite film, alleviates residual lattice stresses, and enhances the film quality. Consequently, the PSC with CB[5] shows a champion power conversion efficiency of 24.83%. Moreover, an unencapsulated device incorporating CB[5] retains more than 87% of its initial PCE under continuous illumination at the maximum power point tracking for 1000 h. This study pioneers the utilization of cucurbiturils in PSCs and provides insights into how supramolecular compounds can regulate buried interfaces.

Stearic acid as a potential interlayer at the FAPI/hole transport layer interface

In this study, we explore the potential of using an ultra-thin film of stearic acid (SA) as an interlayer at the interface between the active material and the hole transport layer (HTL) in perovskite solar cells (PSCs). The FAPbI3 active material thin film was fabricated under ambient conditions using the antisolvent method, followed by the deposition of stearic acid overlayers of varying coverages/thicknesses. By adjusting the coverage/thickness of the SA overlayer, the electronic structure of the perovskite surface can be finely tuned, which may potentially lead to favorable energy level alignment at the perovskite/HTL interface. The interaction between the perovskite thin film and the stearic acid overlayer is expected to involve coordination between defects on the perovskite surface and the carboxyl group of stearic acid. The presence of the nonpolar alkyl chain of stearic acid on the perovskite surface enhances material stability by preventing water and oxygen ingress. Our findings suggest that introduction of SA interlayer at the perovskite/HTL interface may enhance operational stability and efficiency of PSCs by improving the charge transfer across the interface through optimization of energy level alignment and reduction of recombination sites, and protect the absorber from environmental factors like water and oxygen.

Photocontrolled interfacial defect passivation of coumarin 151 with enhanced hydrophobicity for stable perovskite solar cell

Defect passivation has been recognized as an efficient strategy to boost the performance of perovskite solar cells (PSCs) for commercial applications. However, most reported strategies overly emphasize passivation of undesirable defects, while ignoring the inherent instability of perovskite materials caused by environmental risks. In this study, we explore a groundbreaking strategy to integrate various functions of defect passivation, photoresponsivity and photocontrolled hydrophobicity in one device via the surface engineering of 7-amino-4-trifluoromethylcoumarin (C151). The detailed experiments demonstrate that C151 based PSCs have regulated power conversion efficiency and stability responding to UV illumination due to the photodimerization of coumarin. On the one hand, the photodimer of C151 (C151-L) can form stronger chelation with various defect sites in comparison with C151, resulting in optimized energy level arrangement, superior charge extraction/transport and significantly inhibited nonradivation recombination. One the other hand, morphological changes of the perovskite film triggered by UV illumination also bring convertible surface hydrophobicity transition. As a result, the unpackaged C151-L modified device exhibits excellent stability maintaining 91% of its initial PCE after aging for 1000 h under a relative humidity of 30%–40% at 20 °C. Moreover, C151-L plays a positive role in improving the operation stability against high humidity, continuous UV radiation, and heating stress. This work may offer more choices for materials with tunable properties in high-efficiency optoelectronic devices.

Synergistic effects of MOF 545 and inorganic additives synchronously for enhanced performance of low-cost carbon-based perovskite solar cells

Perovskite solar cells (PSCs) hold significant promise for the future of renewable energy, with their commercial viability highly anticipated. However, their limited long-term stability, mainly due to degradation from moisture, humidity, elevated temperatures, and UV-A light exposure, remains a significant obstacle. This study addresses these challenges by employing a multifaceted approach involving additive engineering and surface passivation. A novel method was used to synthesize CZTS nanoparticles, which were incorporated as an additive within the perovskite precursor solution. Additionally, MOF 545 was successfully integrated into the perovskite precursor solution, and a CdS layer was deposited at the ETL/perovskite interface. XRD analysis revealed that the combined addition of MOF 545 and CZTS enhanced the perovskite's crystallinity and surface morphology, leading to an increase in grain size and a reduction in grain boundary defects. Furthermore, these additives effectively restricted Pb2+ ion migration within the perovskite absorber layer. The champion cell, incorporating all three additives, achieved a notable power conversion efficiency (PCE) of 10.32 %, representing a significant 70.58 % increase compared to the pristine PSC. The use of additive-treated cells demonstrated improved thermal stability compared to untreated cells, as confirmed through stress testing. These results highlight the potential of additive engineering to significantly enhance the performance and stability of PSCs. Further exploration and optimization of synergistic additive combinations to achieve even greater performance enhancements and long-term stability in PSCs can pave the way for their successful commercialization.

Configurational design of NiPc derivative as electron transport material for stable and efficient perovskite solar cell: DFT and SCAPS-1D framework

In the present work electron transport layer is optimized to achieve the high stability and efficiency of Formamidinium tin iodide (FASnl3) perovskite solar cells (PSCs). Optical and electronic characteristics of designed ETLs were investigated by implying density functional theory. The designed ETLs show improved charge mobility over the nickel phthalocyanines (NiPcs). It has been observed that NiPc, a material for a hole-hole-transporting layer, acts as an electron transport layer in a modified configuration implying electron-withdrawing groups on the hydrogen site. In this study, the electron-withdrawing group (F−, Cl−, Br−, and I−) were substituted in the configuration X8Y8 (X and y are halide ions where X ≠ Y). Among various configurations, F8Br8NiPc demonstrates the maximum charge mobility 50 cm2/Vs Furthermore, the designed ETLs show improved stability over the NiPcs, due to their hydrophobic nature. Optimal characteristics for both the HTL and ETL were achieved to ensure enhanced efficiency. Furthermore, to investigate the impact of various parameters such as thickness, doping density, and defect density of the ETL layer SCAPS-1D numerical simulation was employed. The obtained electron affinity for designed HTL and ETL were found to be 2.4 eV and 4.247 eV respectively. The optimized photovoltaic (PV) characteristics including power conversion efficiency, short-circuit current density (Jsc), and open-circuit voltage (Voc) were found as 30.58 mA/cm2, 1.09 V, and 29.12 % respectively.

Semiconductor heterojunctions coated with reduced graphite oxide as electron transfer materials for high-performance perovskite solar cells

Exploring and insight into the relationship between the microstructure, light absorption performance, and carrier transport of perovskite light absorption layer materials and carrier transport layer materials is crucial for obtaining efficient and stable perovskite solar cells. We adopted a simple strategy to prepare a composite material known as reduced graphene oxide wrapped mesoporous hierarchical TiO2–CdS semiconductor heterojunctions (TiO2–CdS-RGO) as the electron transport layer in formamidine lead iodide perovskite solar cells. Compared with single TiO2 and binary composite, this composite material exhibits enhanced photoluminescence quenching, reduced photo generated carrier recombination rate, and improved electron transfer capability. Photovoltaic devices based on TiO2–CdS-RGO composite material showed a 14.5 % increase in short-circuit current density (JSC) and a 36.3 % increase in photoelectric conversion efficiency (PCE) compared to those with only TiO2. The improved optoelectronic properties observed with the TiO2–CdS-RGO as electron transfer layers can be attributed to several factors. On the one hand, mesoporous TiO2 with a high specific surface area is beneficial for perovskite infiltration and enhances electron transfer rate. On the other hand, the well-matching energy level structure among the three components aids in electrons extraction and reduces the recombination rate of photo generated charge carriers; In addition, RGO nanosheets with high conductivity serve as an efficient electron transfer network, providing a rapid charge transfer pathways, which is crucial for enhancing the photoelectric conversion performance of perovskite solar cells.

Surface passivation enables efficient and stable inverted perovskite solar cells by 6-(Trifluoromethyl)pyridine-3-amidinehydrochloride

The inverted p-i-n PSCs are gradually gaining more attention since they are generally more stable and can employ low-cost transport materials. However, the interfaces between the perovskite and the charge transport layers contribute to major power conversion efficiency (PCE) loss and instability. Here, we use a material of 6-(Trifluoromethyl)pyridine-3-amidinehydrochloride (CF3-PyFACl) to molecularly engineer the interface between the perovskite and electron transport layer. The interface modification results in suppressed nonradiative recombination, and improved interfacial contact. A PCE of 23.17 % is demonstrated, with open-circuit voltage (Voc) and fill factor (FF) of 1.169 V and 84.1 %, respectively. The unencapsulated device retains >80 % of the initial performance after 400 h continuous light soaking.

NiOx Passivation in Perovskite Solar Cells: From Surface Reactivity to Device Performance.

Nonstoichiometric nickel oxide (NiOx) is one of the very few metal oxides successfully used as hole extraction layer in p-i-n type perovskite solar cells (PSCs). Its favorable optoelectronic properties and facile large-scale preparation methods are potentially relevant for future commercialization of PSCs, though currently low operational stability of PSCs is reported when a NiOx hole extraction layer is used in direct contact with the perovskite absorber. Poorly understood degradation reactions at this interface are seen as cause for the inferior stability, and a variety of interface passivation approaches have been shown to be effective in improving the overall solar cell performance. To gain a better understanding of the processes happening at this interface, we systematically passivated specific defects on NiOx with three different categories of organic/inorganic compounds. The effects on NiOx and the perovskite (MAPbI3) deposited on top were investigated using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Here, we find that the perovskite's structural stability and film formation can be significantly affected by the passivation treatment of the NiOx surface. In combination with density functional theory (DFT) calculations, a likely origin of NiOx-perovskite degradation interactions is proposed. The surface passivated NiOx layers were incorporated into MAPbI3-based PSCs, and the influence on device performance and operational stability was investigated by current-voltage (J-V) characterization, impedance spectroscopy (IS), and open circuit voltage decay (OCVD) measurements. Interestingly, we find that a superior structural stability due to interface passivation must not relate to high operational stability. The discrepancy comes from the formation of excess ions at the interface, which negatively impacts all solar cell parameters.