Original Power Conversion Efficiency Research Articles

Improving the Efficiency, Stability, and Adhesion of Perovskite Solar Cells Using Nanogel Additive Engineering.

Additive engineering has been applied widely to improve the efficiency and/or stability of perovskite solar cells (PSCs). Most additives used to date are difficult to locate within PSCs as they are small molecules or linear polymers. In this work, we introduce, for the first time, carboxylic acid-functionalized nanogels (NGs) as additives for PSCs. NGs are swellable sub-100 nm gel particles. The NGs consist of poly(2-(2-methoxyethoxy) ethyl methacrylate)-co-methacrylic acid-co-ethylenegylcol dimethacrylate (PMEO2MA-MAA-EGD) particles prepared by a scalable synthesis, which have a diameter of 40 nm. They are visualized in the perovskite films using SEM and are located at the grain boundaries. X-ray photoelectron and FTIR spectroscopy reveal that the NGs coordinate with Pb2+ via the -COOH groups. Including the NGs within the PSCs increased the grain size, decreased nonradiative recombination, and increased the power conversion efficiency (PCE) to 20.20%. The NGs also greatly increase perovskite stability to ambient storage, elevated temperature, and humidity. The best system maintained more than 80% of its original PCE after 180 days of storage under ambient conditions. Tensile cross-cut tape adhesion tests are used to assess perovskite film mechanical integrity. The NGs increased both the adhesion of the perovskite to the substrate and the mechanical stability. This study demonstrates that NGs are an attractive alternative to molecularly dispersed additives for providing performance benefits to PSCs. Our study indicates that the NGs act as a passivator, stabilizer, cross-linker, and adhesion promoter.

Dual Interface Protection for High Performance and Excellent Long-Term Stability of Organic Solar Cells.

Stability is still the main barrier to the commercial application of organic solar cells (OSCs), although the maximal power conversion efficiency (PCE) value has exceeded 19%. The encapsulation technique is an effective and vital way to guarantee the long-term stabilities of OSCs, but it can only avoid the penetration of water and oxygen from the environment. Herein, we introduced a structure that provides dual interface protection by using commercially available and chemically stable polyvinylidene fluoride (PVDF) as the cathode interface protection layer working as the cathode interlayer (CIL) and poly(styrene-comethyl-methacrylate) (PS-r-PMMA) as the anode interface protection layer between the poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate) (PEDOT:PSS) and the active layer. With this structure, both the migration of impurities caused by degradation of the interfacial layer and the infiltration of oxygen and water in the air can be prevented. PVDF can effectively provide optimal electron transfer by improving the surface potential of active layers and lowering the work function of the Al electrode. PS-r-PMMA can improve the hydrophobicity of PEDOT:PSS and induce optimized phase separation, facilitating charge transfer. After storage in an air environment with a humidity of approximately 60% for 3600 h, the device based on the PM6:IT-4F blend film with dual interface protection showed a decrease in its PCE value from 13.43 to 10.90%, retaining 81.2% of its original PCE value, in contrast to the sharp decrease in the PCE value from 13.66 to 0.74% of the device without dual interface protection. The dual interface protection design could also be useful in the high-performance PM6:Y6 system, which shows a champion PCE of 15.39% and shows potential for the effective fabrication of stable OSCs in the future.

In Situ Interfacial Passivation of Sn-Based Perovskite Films with a Bi-functional Ionic Salt for Enhanced Photovoltaic Performance.

Environment-friendly Tin (Sn)-based perovskite solar cells (PSCs) have lately made significant development, showing tremendous promise in addressing the hazardous problems associated with Pb-based PSCs. However, even in N2 atmospheres, the thermodynamic stability of Sn-based perovskite films and long-term stability of Sn-based PSCs are demonstrated to be poor due to the presence of interfacial defect trap states. Here, we demonstrate the post-treatment of Sn-based perovskite films with ethylenediamine formate (EDAFa2) ion salt, serving as a bi-functional interface layer to in situ passivate the interfacial defect and improve the stability of Sn2+ by creating a thermodynamic chemical environment pathway. Moreover, the presence of EDAFa2 is shown to promote the interfacial energy level alignment, which is beneficial for the charge extraction at the interface. As a result, PSC devices with a bi-functional interface achieve a champion power conversion efficiency (PCE) as high as 9.40% and enhanced stability, retaining ∼95% of the original PCE stored in a N2 environment after ∼1960 h without encapsulation. This work highlights the significant role of an interfacial design in efficient and stable Sn-based PSCs.

Interface and Grain Boundary Passivation by PEA-SCN Double Ions via One-Step Crystal Engineering for All Air-Processed, Stable Perovskite Solar Cells

The degeneration of organic–inorganic hybrid perovskite solar cells (PSCs) under ambient air is a serious challenge that prevents the commercialization of PSCs. The introduction of hydrophobic long-chain organic cations into the perovskite film is a promising way to improve the long-term stability of devices. However, this approach always comes with the sacrifice of the power conversion efficiency (PCE). In this work, we introduce a novel one-step double ion passivation route together using phenylethylamine ion (PEA+) and SCN– to passivate the grain boundary and surface of the perovskite polycrystalline film by crystal engineering to fabricate all air-processed, stable PSCs. Compared with three-dimensional (3D) MAPbI3 perovskite films, the PEA+ and SCN– codoped MAPbI3 perovskite films from the single crystal engineering have a larger grain size and better stability with a longer carrier lifetime and lower electron trap state density. The champion PCE of 18.04% with negligible hysteresis was achieved for the 0.05 M PEA+ and SCN– codoped PSCs, which exhibit 25% higher efficiency than the MAPbI3 solar cell fabricated using the traditional precursor solution mixing method. The devices without encapsulation still maintain 82% of their original PCE when stored over 750 h under ambient air conditions with a relative humidity of 50%.

Favorable grain growth of thermally stable formamidinium-methylammonium perovskite solar cells by hydrazine chloride

Formamidinium methylammonium lead iodine (FAMAPbI3) based perovskite solar cells have reached phenomenal efficiencies recently. However, it is difficult to form pure black α-phase perovskite by solution method. Meanwhile, the formed polycrystalline FAMAPbI3 film often has large amount of grain boundaries, which can consist dangling bonds and iodide ions. Under illumination and heat, iodide ions can easily migrate and oxidize to form iodine, thus decompose the structure of perovskite and reduce the device performance. Herein, hydrazine chloride (HACl) as an additive is employed to promote favorable grain orientation during the growth of perovskite crystals. From grazing incidence wide-angle X-ray scattering (GIWAXS) and scanning electron microscope (SEM), HACl can facilitate strong diffraction signals along crystallographic planes (100) and (200) indicating a strengthened lattice structure for α-phase FAPbI3 and significantly decrease the grain boundaries for reduced carrier recombination. Consequently, the perovskite solar cells (PSCs) with optimized content of HACl lead to a champion power conversion efficiency (PCE) of 22.32% (certified PCEs of 21.59%) in a mesoporous device based on (FAPbI3)0.95(MAPbBr3)0.05 perovskite solar cells. Furthermore, from UV–vis and XPS spectrum, HACl can reduce iodine (I0) to iodide (I-) effectively, meaning the process of decomposition of FAMAPbI3-based perovskite has been greatly inhibited. As a result, unencapsulated device can retain 95% of its original power conversion efficiency after 1400 h of continuous one-sun illumination. Meanwhile, thermal (60 °C) stability is also greatly improved by maintaining 90% of initial efficiency after aging for 1400 h.

Construction of Polyoxometalate‐Based Material for Eliminating Multiple Pb‐Based Defects and Enhancing Thermal Stability of Perovskite Solar Cells

AbstractThe high‐quality perovskite film with few defects plays an important role in the power conversion efficiency (PCE) and long‐term stability of perovskite solar cells. Here, an efficient strategy is proposed to eliminate Pb0 and passivate Pb2+ simultaneously by employing a stable polyoxometalate‐based material CoW12@MIL‐101(Cr) in the precursor solution of perovskite. The controllable oxidation ability of CoW12 is optimized through the interaction with metal–organic frameworks, resulting in a doped perovskite film with regular morphology, large grain size, and low defects density. The solvent effects and formation of intermediate materials in the precursor solution are further investigated by an in situ thermogravimetry‐Fourier transform infrared spectroscopy analysis. In addition, the champion doped‐device showed enhanced PCE to 21.39% and excellent stability, maintaining 85% and 89% of the original PCE after heating at 85 °C in N2 atmosphere and stored in ambient conditions (25 °C, 40% humidity) for 1000 h, respectively.

Phenylformamidinium-enabled quasi-2D Ruddlesden-Popper perovskite solar cells with improved stability

Two-dimensional (2D)/quasi-2D perovskite solar cells (PSCs) incorporating organic spacer cations exhibit appealing ambient stability in comparison with their 3D analogs. Most reported organic spacer cations are based on ammonium, whereas formamidinium (FA+) has been seldom applied despite that FA has been extensively used in high-efficiency 3D PSCs. Herein, a novel FA-based organic spacer cation, 4-chloro-phenylformamidinium (CPFA+), is applied in quasi-2D Ruddlesden-Popper (RP) PSCs for the first time, and methylammonium chloride (MACl) is employed to promote crystal growth and orientation of perovskite film, resulting in high power conversion efficiency (PCE) with improved stability. Upon incorporating CPFA+ organic spacer cation and MACl additive, high-quality quasi-2D CPFA2MAn−1Pbn(I0.857Cl0.143)3n+1 (n = 9) perovskite film forms, exhibiting improved crystal orientation, reduced trap state density, prolonged carrier lifetime and optimized energy level alignment. Consequently, the CPFA2MAn−1Pbn(I0.857Cl0.143)3n+1 (n = 9) quasi-2D RP PSC devices deliver a highest PCE of 14.78%. Moreover, the un-encapsulated CPFA-based quasi-2D RP PSC devices maintain ∼ 80% of its original PCE after exceeding 2000 h storage under ambient condition, whereas the 3D MAPbI3 counterparts retain only ∼ 45% of its original PCE. Thus, the ambient stability of quasi-2D RP PSC devices is improved obviously relative to its 3D MAPbI3 counterpart.

Synergistic Effect of Defect Passivation and Crystallization Control Enabled by Bifunctional Additives for Carbon-Based Mesoscopic Perovskite Solar Cells.

The emerging carbon-based mesoscopic perovskite solar cells (MPSCs) are known as one of the most promising candidates for photovoltaic applications thanks to their screen-printing process and excellent stability. Unfortunately, they usually suffer from serious defects because it is challenging to realize sufficient mesopore filling of the perovskite precursor solution throughout the triple-mesoporous scaffold. Herein, a bifunctional additive, biuret, endowed with both carbonyl and amino groups, was designed to realize a convenient fabrication approach for controllable crystallization of the precursor solution. Owing to the strong coordination ability with perovskite components, the incorporation of biuret can not only regulate crystallization kinetics allowing for the growth of high-quality perovskite crystals but also associate with uncoordinated ions for defect passivation to enhance the overall photovoltaic performance of MPSCs. A champion power conversion efficiency (PCE) of 13.42% with an enhanced short-circuit current density of 19.49 mA cm-2 and a much higher open-circuit voltage of 0.96 V was achieved for the device doped with 3 mol % biuret, which is 26% higher than that of the control device (10.66%). Moreover, the unencapsulated devices with biuret incorporation demonstrated superior stability, maintaining over 90% of the original PCE after 50 days of storage under ambient conditions. This work helps exploit bifunctional additive strategies for simultaneous defect passivation and crystallization control toward high-efficiency and long-term stability of carbon-based MPSCs.

Significant performance enhancement of all‐inorganic CsPbBr3 perovskite solar cells enabled by Nb‐doped SnO2 as effective electron transport layer

All‐inorganic CsPbBr3‐based perovskite solar cells (PSCs) have attracted great attention because of their high chemical and thermal stabilities in ambient air. However, the short‐circuit current density (Jsc) of CsPbBr3‐based PSCs is inadequate under solar illumination because of the wide bandgap, inefficient charge extraction and recombination loss, leading to lower power‐conversion efficiencies (PCEs). It is envisaged that in addition to narrowing the bandgap by alloying, Jsc of the PSCs could be enhanced by effective improvement of electron transportation, suppression of charge recombination at the interface between the perovskite and electron transporting layer (ETL), and tuning of the space charge field in the device. In this work, Nb‐doped SnO2 films as ETLs in the CsPbBr3‐based PSCs have been deposited at room temperature by high target utilization sputtering (HiTUS). Through optimizing the Nb doping level alone, the Jsc was increased by nearly 19%, from 7.51 to 8.92 mA·cm−2 and the PCE was enhanced by 27% from 6.73% to 8.54%. The overall benefit by replacing the spin‐coated SnO2 with sputtered SnO2 with Nb doping was up to 39% increase in Jsc and 62% increase in PCE. Moreover, the PCE of the optimized device showed negligible degradation over exposure to ambient environment (T ˜ 25 °C, RH˜45%), with 95.4% of the original PCE being maintained after storing the device for 1200 h.

Constructing All‐Inorganic Perovskite/Fluoride Nanocomposites for Efficient and Ultra‐Stable Perovskite Solar Cells

AbstractOrganic‐inorganic hybrid perovskite solar cells (PSCs) have rapidly developed over the past decade and have achieved the latest certified power conversion efficiency (PCE) up to 25.5%. However, unsatisfactory long‐term operational stability for these hybrid PSCs remains a huge obstacle to further development and commercialization. Herein, a unique hetero‐structured CsPbI3/CaF2 perovskite/fluoride nanocomposites (PFNCs) is fabricated via a newly developed facile two‐step hetero‐epitaxial growth strategy to deliver efficient and ultra‐stable PSCs. After being incorporated into the crystal lattice of α‐phase CsPbI3 perovskite, the cubic‐phase CaF2 in the resultant CsPbI3/CaF2 PFNCs can not only passivate the intrinsic defects of CsPbI3 perovskite itself but also effectively suppress the notorious ion migration in hybrid perovskite Cs0.05FA0.81MA0.14PbI2.55Br0.45 (CsFAMA) thin‐films of PSCs. As such, the CsFAMA PSC devices based on CsPbI3/CaF2‐deposited perovskite thin‐film achieve a mean PCE of 20.45%, in sharp contrast to 19.33% of the control devices without deposition. Specifically, the CsPbI3/CaF2‐deposited PSC retains 85% of its original PCE after 1000 h continuous operation at the maximum power point under AM 1.5G solar light, far better than those of the control and CsPbI3‐deposited PSCs with a device T85 lifetime of 315 and 125 h, respectively.

Synergistic Effects of Eu-MOF on Perovskite Solar Cells with Improved Stability.

Enhancing device lifetime is one of the essential challenges in perovskite solar cells. The ultrathin Eu-MOF layer is introduced at the interface between the electron-transport layer and the perovskite absorber to improve the device stability. Both Eu ions and organic ligands in the MOF can reduce the defect concentration and improve carrier transport. Moreover, due to the Förster resonance energy transfer effect, Eu-MOF in perovskite films can improve light utilization and reduce the decomposition under ultraviolet light. Meanwhile, Eu-MOF also turns tensile strain to compressive strain in the perovskite films. As a result, the corresponding devices achieve a champion power conversion efficiency (PCE) of 22.16%. In addition, the devices retain 96% of their original PCE after 2000 h under the relative humidity of 30% and 91% of their original PCE after 1200 h after continuous 85°C aging condition in N2 .

PEDOT:PSS: CuNW-based transparent composite electrodes for high-performance and flexible organic photovoltaics under indoor lighting

Highly efficient and mechanically resilient transparent electrodes for indoor organic photovoltaics (OPVs) have attracted significant interest based on the emergence of the internet of things. In this study, transparent composite electrodes (TCEs) were fabricated by blending copper nanowires (CuNWs) with the conductive polymer poly (3, 4-ethylenedioxythiophene): poly (styrene-sulfonic acid) (PEDOT:PSS, PH1000). The optimized PEDOT:PSS: CuNW-based TCEs exhibited a high transmittance of approximately 90% at a wavelength of 460 nm, excellent flexibility with a change in resistance < 1.0%, and a smooth surface morphology with a root-mean-squared roughness value of 1.85 nm. As a result, the TCE-based flexible OPVs demonstrated an outstanding power conversion efficiency (PCE) of 17.6% ± 0.2% under 1000-lx light-emitting diode illumination, which is approximately 25% higher than that of OPVs with a reference indium-tin-oxide (ITO) electrode. Additionally, they exhibited exceptional mechanical durability while retaining 85% of their original PCE after bending 500 times with a bending radius of 3.8 mm. These results suggest that the excellent optoelectronic properties of the proposed TCEs should make them promising alternatives to costly ITO electrodes, thereby improving the economic feasibility and stability of indoor OPVs.

Defect Passivation Effect of Chemical Groups on Perovskite Solar Cells.

Defect passivation is a key strategy to prepare high-performance perovskite solar cells (PVSCs). Even though abundant passivation molecules have been applied, the absence of detailed researches with regard to different functional groups in polymer additives may inevitably impede the establishment of passivation molecules selection rules. In this work, three passivation molecules including poly(vinyl alcohol) (PVA), polymethyl acrylate (PMA), and poly(acrylic acid) (PAA) are employed to systematically analyze the passivation effect from hydroxyl, carbonyl, and carboxyl groups. In general, PVA (-OH) can form hydrogen bonds with perovskite and PMA (-C═O) can complex with uncoordinated Pb2+. Specifically, PAA (-COOH) can interact selectively with MA+ and I- ions via hydrogen bonding and complex with uncoordinated Pb2+ to passivate defects more effectively. Hence, the PAA-incorporated PVSCs based on MAPbI3 achieve the champion power conversion efficiency (PCE) of 20.29% with open-circuit voltage up to 1.13 V. In addition, PAA cross-linking perovskite grains can relieve mechanical stress, as well as occupy the major channels to suppress ion migration and water/oxygen erosion. The corresponding unencapsulated devices demonstrate a superior light soaking stability, retaining more than 80% of the original PCE under one sun illumination for 1000 h.

Photostable electron-transport-layer-free flexible graphene quantum dots/perovskite solar cells by employing bathocuproine interlayer

Electron transport layer (ETL)-free perovskite solar cells (PSCs) are very useful for the low-temperature process that can reduce the instability caused by the ETL such as TiO2 layer. There are several publications on ETL-free PSCs, but most of them are based on transparent conductive oxides, not suitable for flexible applications. Here, we first report photostable ETL-free PSCs of maximum 15.72% power conversion efficiency (PCE) by employing an insulating interlayer of bathocuproine (BCP) between the graphene (GR) transparent conductive electrode (TCE) and the graphene quantum dots-added perovskite layer. The BCP interlayer effectively enhances the electron carrier injection by reducing the recombination centers at the active layer/GR TCE interface. Only 8 or 17% of the original PCE is lost under ambient conditions or under light soaking, respectively for 500 h. A flexible-type of the PSC shows a PCE comparable to that of the rigid-type counterpart, and 83% of the initial PCE is maintained even after 1000 repeated bending tests at a radius of 4 mm. These results suggest that the ETL-free PSCs exhibit excellent long-term and mechanical stabilities.

Water-Repellent Perovskites Induced by a Blend of Organic Halide Salts for Efficient and Stable Solar Cells.

Despite tremendous progress in the power conversion efficiency (PCE) of perovskite solar cells (PeSCs), the long-term stability issue remains a significant challenge for commercialization. In this study, by blending organic halide salts, phenylethylammonium halide (PEAX, X = I, Br), with CH3NH3PbI3 (MAPbI3), we achieved remarkable enhancements in the water-repellency of perovskite films and long-term stability of PeSCs, together with enhanced PCE. The hydrophobic aromatic PEA+ group in PEAX protects the perovskite film from destruction by water. In addition, the smaller halide Br- in PEABr restructures MAPbI3 to form MAPbI3-xBrx during post-annealing, leading to lattice contraction with beneficial crystallization quality. The perovskite films modified by PEAX exhibited excellent water resistance. When the perovskite films were directly immersed in water, no obvious decompositions were observed, even after 60 s. The PEAX-decorated PeSCs exhibited considerable long-term stability. Under high-humidity conditions (60 ± 5%), the PEAX-decorated PeSCs held 80.5% for PEAI and 85.2% for PEABr of their original PCE after exposure for 100 h, whereas the pristine PeSC device lost more than 99% of its initial PCE after exposure for 60 h under the same conditions. Moreover, compared to the pristine device with a PCE of 13.28%, the PEAX-decorated PeSCs exhibited enhanced PCEs of 17.33% for the PEAI device and 17.18% for the PEABr device.

Room‐Temperature‐Processed, Carbon‐Based Fully Printed Mesoscopic Perovskite Solar Cells with 15% Efficiency

Methylamine (MA) and methylamine hydrochloride (MACl) are widely used to prepare highly efficient and stable perovskite solar cells (PSCs). However, MA, as a gas, is difficult to handle and inevitably leads to a large amount of escape, and it is difficult to quantitatively calculate. Herein, selecting a mixture solvent of methylamine ethanol solution (MA‐EtOH sol) and acetonitrile (ACN) as a solvent, a new strategy for preparing fully printed mesoscopic perovskite solar cells (MPSCs) at room temperature is first proposed. With the introduction of 20 mol% MACl as additive, the fully printed MPSCs are fabricated without any posttreatment at room temperature via a one‐step drop‐coating method. As a consequence, the average power conversion efficiency (PCE) of 14.73 ± 0.3% (0.1 cm2) with almost no hysteresis is achieved. Most importantly, the device also exhibits excellent long‐term stability when it is unencapsulated. Specifically, the unencapsulated device still retains nearly 100% of its original PCE after 64 days and 88% after 81 days of storage in the dark with a humidity of 50 ± 5% in an atmospheric environment. It provides a new idea for constructing fully printed MPSCs at room temperature in the future.

High‐Performance ITO‐Free Perovskite Solar Cells Enabled by Single‐Walled Carbon Nanotube Films

AbstractThe unprecedented advancement in power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) has rendered them a promising game‐changer in photovoltaics. However, unsatisfactory environmental stability and high manufacturing cost of window electrodes are bottlenecks impeding their commercialization. Here, a strategy is introduced to address these bottlenecks by replacing the costly indium tin oxide (ITO) window electrodes via a simple transfer technique with single‐walled carbon nanotubes (SWCNTs) films, which are made of earth‐abundant elements with superior chemical and environmental stability. The resultant devices exhibit PCEs of ≈19% on rigid substrates, which is the highest value reported to date for ITO‐free PSCs. The facile approach for SWCNTs also enables application in flexible PSCs (f‐PSCs), delivering a PCE of ≈18% with superior mechanical robustness over their ITO‐based counterparts due to the excellent mechanical properties of SWCNTs. The SWCNT‐based PSCs also deliver satisfactory performances on large‐area (1 cm2 active area in this work). Furthermore, these SWCNT‐based PSCs can retain over 80% of original PCEs after exposure to air over 700 h while ITO‐based devices only sustain ≈60% of initial PCEs. This work paves a promising way to accelerate the commercialization of ITO‐free PSCs with reduced material cost and prolonged lifetimes.

Dopant-free Hole-transporting Materials for CH3NH3PbI3 Inverted Perovskite Solar Cells with an Approximate Efficiency of 20%

A D-π–A-π–A-π-D structure-based small organic molecule (YJ01) has been demonstrated as an efficient dopant-free hole-transporting material (HTM) for inverted perovskite solar cells (iPSCs). The conjugation and twisted angles are balanced by the 1,4-di((E)-styryl)benzene core that bears two electron-withdrawing cyan groups. The cyan positions on the central core have a significant impact on the HTM properties. The outstanding performance of the iPSC device employing indium-doped tin oxide/pristine HTM/CH3NH3PbI3/PCBM/BCP/Ag based on YJ01 yielded an efficiency of 19.85% with a Voc of 1.08 V, Jsc of 22.53 mA cm–2, and FF of 0.815. The device which was based on YJ02 yielded power conversion efficiency (PCE) of 17.5%. The devices retained 80% of their original PCE after 500 h in an ambient environment. The hole motilities of YJ01 and YJ02 were determined to be 5.68 × 10–3 cm2 V–1 s–1 and 1.55 × 10–3 cm2 V–1 s–1, respectively. The large efficiency difference between YJ01 and YJ02 is attributed to the enlargement of the substitution distance between the two cyan units given the much greater reduction of solid-state fluorescence emission for YJ01 compared with YJ02. Thus, it is hoped to provide a good strategy for the HTM design, facilitating highly efficient and stable iPSCs.

Fabricating efficient and stable quasi-3D and 3D/2D perovskite solar cells with 2D-sheets connected by inorganic type ionic-bond

In this work, we report a novel two-dimensional (2D) (SrBr)2PbI4 perovskite layered architecture, which were formed by the reaction of strontium bromide (SrBr2), strontium iodide (SrI2) and lead iodide (PbI2). Formation of 2D (SrBr)2PbI4 was verified by small angle XRD peak at 6.4°, which corresponds to the layer distance of 13.78 Å. The best one of solar cells fabricated with Quasi-3D perovskite, (SrBr)2FA59Pb60I181 (n = 60), showed a power conversion efficiency (PCE) of 18.46% and retained 95% of the initial PCE at 1000 h in the dry air. Further, the 2D (SrBr)2PbI4 as the surface passivation layer on the 3D FAPbI3 perovskite greatly reduced the defects at the perovskite/Spiro-OMeTAD interface, and the corresponding solar cells with FAPbI3/(SrBr)2PbI4 3D/2D structure achieved a PCE of 22.14% and over 90% retention of the original PCE at 1000 h. In short, this work provides an example of inorganic complex cations that can form 2D perovskites and achieve perovskite solar cells with high PCE and stabilization at the same time.

Perovskites on Ice: An Additive-Free Approach to Increase the Shelf-Life of Triple-Cation Perovskite Precursor Solutions.

The development of stable perovskite precursor solutions is critical if solution‐processable perovskite solar cells (PSCs) are to be practically manufacturable. Ideally, such precursors should combine high solution stability without using chemical additives that might compromise PSC performance. Here, it was shown that the shelf‐life of high‐performing perovskite precursors could be greatly improved by storing solutions at low‐temperature without the need to alter chemical composition. Devices fabricated from solutions stored for 31 days at 4 °C achieved a champion power conversion efficiency (PCE) of 18.6 % (97 % of original PCE). The choice of precursor solvent also impacted solution shelf‐life, with DMSO‐based solutions having enhanced solution stability compared to those including DMF. The compositions of aged precursors were explored using NMR spectroscopy, and films made from these solutions were analysed using X‐ray diffraction. It was concluded that the improvement in precursor solution stability is directly linked to the suppression of an addition‐elimination reaction and the preservation of higher amounts of methylammonium within solution.