Non-encapsulated Devices Research Articles

Three-Dimensional (3D) Fluoride Molecular Glue to Improve the SnO2/Perovskite Interface for Efficient Perovskite Solar Cells.

Aiming at numerous defects at SnO2/perovskite interface and lattice mismatch in perovskite solar cells (PSCs), we design a kind of three-dimensional (3D) molecular glue (KBF4-TFMSA), which is derived from strong intramolecular hydrogen bonding interaction between potassium tetrafluoroborate (KBF4) and trifluoromethane-sulfonamide (TFMSA). A remarkable efficiency of 25.8 % with negligible hysteresis and a stabilized power output of 25.0 % have been achieved, in addition, 24.57 % certified efficiency of 1 cm2 device is also obtained. Further investigation reveals that this KBF4-TFMSA can interact with oxygen vacancies and under-coordinated Sn(IV) from the SnO2, in the meantime, FA+ (NH2-C=NH2 +) and K+ cations can be well fixed by hydrogen bonding interaction between FA+ and BF4 -, and electrostatic attraction between sulfonyl oxygen and K+ ions, respectively. Thereby, FAPbI3 crystal grain sizes are increased, interfacial defects are significantly reduced while carrier extraction/ transportation is facilitated, leading to better cell performance and excellent stabilities. Non-encapsulated devices can maintain 91 % of their initial efficiency under maximum-power-point (MPP) tracking while continuous illumination (~100 mW cm-2) for 1000 h, and retain 91 % of the initial efficiency after 1000 h "double 60" damp-heat stability testing (60 °C and 60 %RH (RH, relatively humidity)).

Interfacial modification by 2-fluoroisonicotinic acid enabling high-efficiency and stable n-i-p perovskite solar cells

The power conversion efficiency (PCE) of organic-inorganic halide perovskite solar cells (PSCs) developed rapidly in recent years. However, the defects at the bulk grain boundaries and heterojunction interfaces acting as non-radiative recombination centres and the ion-migration channels severely hinder the charge transport and stability of the PVKs, resulting in low PCE and poor stability. One of the principal impediments to the commercialization of PSCs resides in the challenge posed by this particular aspect. In this work, we employed 2-fluoroisonicotinic acid (2-FINA) as a passivation agent to improve the PCE and stability of n-i-p PSCs by interfacial modification strategy. Owing to the presence of carboxyl (COOH) functional groups and pyridine groups, 2-FINA can strongly interact with uncoordinated Pb2+ and regulate the growth of perovskite crystals, which in turn reduces ion migration and suppress non-radiative recombination along with improves optical properties. Thanks to these improvements, the champion n-i-p PSC solar cell, treated with 2-FINA, showed a PCE of 20.92 %, whereas the untreated one in the same batch exhibited a PCE of 17.13 %. In long-term stability tests, we demonstrated that 2-FINA treatment significantly increases the moisture resistance of non-encapsulated devices.

Multifunctional buried interface engineering via phenyl-phosphonic acid for efficient and stable SnO2-based planar perovskite solar cells

Tin dioxide (SnO2) is widely used as an electron transport layer (ETL) in efficient and stable perovskite solar cells (PSCs) due to its excellent optoelectronic properties and low-temperature solution preparation process. However, SnO2 ETLs fabricated by the conventional solution method have many defects, among which Sn dangling bonds (i.e., oxygen vacancies) are particularly prominent. Herein, a simple buried interface engineering is employed to introduce phenyl-phosphinic acid (PPA) into the surface of SnO2 film for the preparation of highly efficient PSCs. A series of test results have shown that the phosphate group (PO) in PPA can not only passivate oxygen vacancy defects on the surface of SnO2, but also improve the film-forming quality of the upper perovskite, thereby exhibiting better photoelectric conversion efficiency (PCE) and stability. Ultimately, the optimized device achieves a maximum PCE of 22.81 %, an improvement of about 15 % over the control device (19.82 %). Meanwhile, the nonencapsulated device based on SnO2-PPA ETL shows much better storage and light stability than the control SnO2.

Julolidine functionalized benzimidazoline‐doped fullerene derivatives for efficient and stable perovskite solar cells

AbstractFullerene derivatives are highly attractive materials in solar cells, organic thermoelectrics, and other devices. However, the intrinsic low electron mobility and electrical conductivity restrict their potential device performance, such as perovskite solar cells (PSCs). Herein, we successfully enhanced the electric properties and morphology of phenyl‐C61‐butyric acid methyl ester (PCBM) by n‐doping it with a benzimidazoline derivative, 9‐(1,3‐dimethyl‐2,3‐dihydro‐1H‐benzoimidazol‐2‐yl)‐julolidine (JLBI‐H) via a solution process. We found the n‐doping can not only improve the conductivity and optimize the band alignment but also enable the PCBM to have a constantly strong charge extraction ability in a wide temperature from 173 to 373 K, which guarantees a stable photovoltaic performance of the corresponding PSCs under a wide range of operating temperatures. With the JLBI‐H‐doped PCBM, we improved the efficiency from 17.9% to 19.8%, along with enhanced stability of the nonencapsulated devices following the aging protocol of ISOS‐D‐1.

Triple-junction perovskite-perovskite-silicon solar cells with power conversion efficiency of 24.4.

The recent tremendous progress in monolithic perovskite-based double-junction solar cells is just the start of a new era of ultra-high-efficiency multi-junction photovoltaics. We report on triple-junction perovskite-perovskite-silicon solar cells with a record power conversion efficiency of 24.4%. Optimizing the light management of each perovskite sub-cell (∼1.84 and ∼1.52 eV for top and middle cells, respectively), we maximize the current generation up to 11.6 mA cm-2. Key to this achievement was our development of a high-performance middle perovskite sub-cell, employing a stable pure-α-phase high-quality formamidinium lead iodide perovskite thin film (free of wrinkles, cracks, and pinholes). This enables a high open-circuit voltage of 2.84 V in a triple junction. Non-encapsulated triple-junction devices retain up to 96.6% of their initial efficiency if stored in the dark at 85 °C for 1081 h.

Crossover between rigid and reconstructed moiré lattice in h-BN-encapsulated twisted bilayer WSe2 with different twist angles.

A moiré lattice in a twisted-bilayer transition metal dichalcogenide (tBL-TMD) exhibits a complex atomic reconstruction effect when its twist angle is less than a few degrees. The influence of the atomic reconstruction on material properties of the tBL-TMD has been of particular interest. In this study, we performed scanning transmission electron microscopy (STEM) imaging of a moiré lattice in h-BN-encapsulated twisted bilayer WSe2 with various twist angles. Atomic-resolution imaging of the moiré lattice revealed a reconstructed moiré lattice below a crossover twist angle of ∼4° and a rigid moiré lattice above this angle. Our findings indicate that h-BN encapsulation has a considerable influence on lattice reconstruction, as the crossover twist angle was larger in h-BN-encapsulated devices compared to non-encapsulated devices. We believe that this difference is due to the improved flatness and uniformity of the twisted bilayers with h-BN encapsulation. Our results provide a foundation for a deeper understanding of the lattice reconstruction in twisted TMD materials with h-BN encapsulation.

Ionic liquid optimized buried interface between spray-coated NiOX and perovskite for efficient solar cells

Spray-coated nickel oxide (NiOX) has great potential as hole transport layer for the fabrication of efficient, stable metal halide perovskite solar cells (PSCs). However, emerging evidences demonstrate that the inferior contact and the redox reaction at the NiOX|perovskite buried interface limit the performance of the devices. Herein, a series of ionic liquids were selected to modulate this interface as well as the perovskite film morphology. The results show that 1-butyl-3-methylimidazole tetrafluoroborate (BMIMBF4) exhibits a strong interfacial coupling effect between NiOX and perovskite, which facilitates the perovskite crystallization and charge transfer at the interface. As a result, the BMIMBF4 enables an efficiency improvement from 17.7% to 20.1% (aperture area: 0.16 cm2). More importantly, the non-encapsulated devices retain 90% of their initial performance after aging under ambient conditions for 700 h (ISOS-D-1).

Analysis of the stability of organic photovoltaic cells under indoor illumination

In this study, we analyze the degradation behavior of conventional polymeric solar cells
 (PSCs) under constant indoor light illumination. A LED lamp with a color temperature of 2700 K, was used for the indoor light illumination conditions. We compare the results obtained with encapsulated and non-encapsulated devices. The performance of the PTB7:PC70BM-based cell showed an initial maximum power conversion efficiency (PCE) of 12.0% under the luminance of 1000 lux and maximum power density (MPP) of 45.7 μW/cm2. The work describes the results of the measurements and analysis of the degradation process, performed by a current density – voltage (J–V) characteristic curve study under LED light. The analyzed performance parameters were PCE, short circuit current density (JSC), open-circuit voltage (VOC) and fill factor (FF). The PCE of encapsulated devices remained above 80% of the initial value after 624 h.

Improved Power Conversion Efficiency and Stability of Perovskite Solar Cells Induced by Molecular Interaction with Poly(ionic liquid) Additives.

Ionic liquid (IL) additives proved to have a positive effect on the device efficiency and stability of perovskite solar cells. However, since ILs are small molecules and undergo Coulomb interactions, they can easily aggregate and evaporate over long times, which would cause instabilities during a long-term device operation. To overcome these problems, we polymerize ILs into macromolecules and incorporate them into perovskite films as well as into the corresponding solar cells. Both cations and anions of the used poly[1-(2-acryloylethyl)-3-methylimidazolium] bis (trifluoromethane) sulfonamides (PAEMI-TFSIs) are designed to coordinate with the Pb and I of PbI62- octahedra, respectively, which changes the crystallization behavior of the perovskite films. Importantly, the PAEMI-TFSI efficiently passivates electronic defects on the grain boundaries and thereby enhances the charge-carrier transport in the perovskite film. As a result, PAEMI-TFSI-modified MAPbI3 solar cells show a high power conversion efficiency of 22.4% and an excellent storage stability (92% of the initial efficiency remains after 1200 h operation in a nitrogen atmosphere for nonencapsulated devices).

Surface-bulk-passivated perovskite films via 2-thiophenemethylammonium bromide and PbBr2 for air-processed perovskite solar cells with high-stability

Suppressing non-radiative recombination induced by defect is of much concern to efficient and stable perovskite solar cells (PSCs). We report a cooperative strategy to passivate both interfacial and bulk defects in perovskite layer by coupling interface engineering and additive engineering. 2-Thiophenemethylammonium bromide (2-ThMAB) is synthesized by recrystallization. PbBr2 used as an additive is introduced into the perovskite precursor solution. 2-ThMAB features with an electron-rich π-system and 2-thiophene group. Br− ions have an impact on perovskite lattice reorganization. The synergistic modification of 2-ThMAB and PbBr2 enables the external electronic state modulation and internal bandgap adjustment of perovskite, which is beneficial to passivate defect and inhibit ion migration. As a result, a modified PSC exhibits a high-power conversion efficiency of 20.01% with negligible hysteresis for an all-air-processed device. More importantly, a non-encapsulated device exhibits excellent long-term stability of T98 of > 720 h. This study thus provides a new way to obtain highly stable all-air-processed PSCs..

Ionic liquids tailoring crystal orientation and electronic properties for stable perovskite solar cells

The crystallization behavior of perovskite films has a profound influence on the resulting defect densities, charge carrier dynamics and photovoltaic performance. Herein, we introduce ionic liquids into the perovskite component to tailor the crystal growth of perovskite films from a disordered to a preferential corner-up orientation and accordingly increase the charge carrier mobility to accelerate electron transport and extraction. Using time-resolved measurements, we probe the charge carrier generation, transport and recombination behavior in these films and related devices. We find the ionic liquid-containing samples exhibit lower defects, faster charge carrier transport and suppressed non-radiative recombination, contributing to higher efficiency and fill factor. Via operando grazing-incidence small- and wide-angle X-ray scattering measurements, we observe a light-induced lattice compression and grain fragmentation in the control devices, whereas the ionic liquid-containing devices exhibit a slight light-induced crystal reconstitution and stronger tolerance against illumination. Under ambient conditions, the non-encapsulated device with the pyrrolidinium-based ionic compound (Pyr14BF4) maintains 97% of its initial efficiency after 4368 h.

Ultrahigh fill-factor all-inorganic CsPbBr3 perovskite solar cells processed from two-step solution method and solvent additive strategy

All-inorganic CsPbBr3 perovskite solar cells (PSCs) have attracted more attentions due to the excellent environmental stability, however, the wide bandgap and relatively poor crystallinity of CsPbBr3 have been the main obstacle to improve their power conversion efficiency (PCE). Herein, we proposed an efficient and simple strategy of precursor additive in the two-step aqueous-solution method, the resulted CsPbBr3 film has achieved more uniform grain size, almost pure perovskite phase, smoother surface, less defects, enhanced light absorption and longer carrier lifetime. This is due to the rapid evaporation of additive (IPA and CH3OH) in the CsBr/H2O precursor leads to a relatively higher local CsBr concentration on the surface of PbBr2, which can provide more nucleation sites and accelerate the crystallization of perovskite. Further, when utilizing the optimal additive of 5% (in volume) IPA, the HTM-free carbon-based CsPbBr3 PSCs obtained a PCE improvement from 9.09% to 10.29%, and an ultrahigh fill factor (FF) of 85.21%. What is more, by adding 0.1 mol/L PbCl2 into the PbBr2 solution in the first step, the open circuit voltage of device has increased from 1.36 V to 1.48 V, the champion PCE reached 10.37% (steady output PCE of 10.17%), and the non-encapsulated device could maintain 85% of its initial efficiency after 50 d in the air. This work provides a cost-effective approach to grow CsPbBr3 film and boosts the efficiency benchmark of the CsPbBr3 PSCs to more than 10%, it is desirable that the highly efficient and stable CsPbBr3 PSCs can be developed in future.

Enhanced power conversion efficiency of perovskite solar cells using dopant-free carbon nanotubes-Spiro-OMeTAD

Paintable carbon-based perovskite solar cells (PSCs) are of tremendous attention due to their structural stability and low fabrication cost. However, the poor interfacial contact and unsatisfied energy band alignment between carbon and perovskite lead to relatively low efficiency of carbon-based perovskite solar cells. Herein, we employed a multi-functional holes transfer layer, a dopant-free Spiro-OMeTAD composited with CNTs (CNTs-spiro), to bridge the interface between carbon and perovskite and optimize the energy band alignment in carbon-based PSCs. The power conversion efficiency of the PSCs with the CNTs-spiro layer (10.45%) has an enhancement of 17.51% compared with the PSC without the CNTs-spiro layer (8.62%). Our non-encapsulated devices showed excellent stability under light, air, or ambient conditions. The CNTs-spiro composition may be a promising hole transfer material for PSCs with high efficiency and high stability.

High Mobility and Quantum Oscillations in Semiconducting Bi2O2Te Nanosheets Grown by Chemical Vapor Deposition.

Bi2O2Te has the smallest effective mass and preferable carrier mobility in the Bi2O2X (X = S, Se, Te) family. However, compared to the widely explored Bi2O2Se, the studies on Bi2O2Te are very rare, probably attributed to the lack of efficient ways to achieve the growth of ultrathin films. Herein, ultrathin Bi2O2Te crystals were successfully synthesized by a trace amount of O2-assisted chemical vapor deposition (CVD) method, enabling the observation of ultrahigh low-temperature Hall mobility of >20 000 cm2 V-1 s-1, pronounced Shubnikov-de Haas quantum oscillations, and small effective mass of ∼0.10 m0. Furthermore, few nm thick CVD-grown Bi2O2Te crystals showed high room-temperature Hall mobility (up to 500 cm2 V-1 s-1) both in nonencapsulated and top-gated device configurations and preserved the intrinsic semiconducting behavior with Ion/Ioff ∼ 103 at 300 K and >106 at 80 K. Our work uncovers the veil of semiconducting Bi2O2Te with high mobility and brings new blood into Bi2O2X family.

Fluorinated Interfaces for Efficient and Stable Low‐Temperature Carbon‐Based CsPbI2Br Perovskite Solar Cells

AbstractCarbon‐based inorganic perovskite solar cells (C‐PSCs) have attracted intensive attention owing to their low cost and superior thermal stability. However, the bulk defects in perovskites and interfacial energy level mismatch seriously undermine their performance. To overcome these issues, a multifunctional dual‐interface engineering is proposed with a focus on low‐temperature CsPbI2Br C‐PSCs, where the potassium trifluoroacetate (KTFA) and the 4‐trifluorophenyl methylammonium bromide (CF3PMABr) are introduced beneath and on top of the perovskite layer, respectively. It is found that TFA‐ ions locate at the SnO2/CsPbI2Br interface, whereas a small amount of K+ ions diffuse into perovskite lattice to participate in nucleation and crystallization, resulting in more favored interfacial energy level alignment, improved film quality, passivated interfacial defects, released interfacial strain, as well as suppressed charge recombination and ion migration. Meanwhile, the CF3PMABr passivates I/Br vacancies and forms 2D perovskite capping layer to facilitate hole extraction at the CsPbI2Br/carbon interface. As a result, a remarkable power conversion efficiency (PCE) of 14.05% with an open‐circuit voltage of 1.273 V is achieved. To the best of the authors’ knowledge, it is currently the highest PCE reported for low‐temperature CsPbI2Br C‐PSCs. Furthermore, the nonencapsulated device exhibits improved moisture, thermal, and illumination stability in ambient air.

Lead Sequestration from Halide Perovskite Solar Cells with a Low-Cost Thiol-Containing Encapsulant.

Perovskite solar cells (PSCs) are being studied and developed because of the outstanding properties of halide perovskites as photovoltaic materials and high conversion efficiencies achieved with the best PSCs. However, leaching out of lead (Pb) ions into the environment presents potential public health risks. We show that thiol-functionalized nanoparticles provide an economic way of minimizing Pb leaching in the case of PSC module damage and subsequent water exposure (at most, ∼2.5% of today’s crystal silicon solar panel production cost per square meter). Using commercial materials and methods, we retain ∼90% of Pb without degrading the photovoltaic performance of the cells, compared with nonencapsulated devices, yielding a worst-case scenario of top-soil pollution below natural Pb levels and well below the U.S. Environmental Protection Agency limits.

Dual-Resistance of Ion Migration and Moisture Erosion via Hydrolytic Crosslinking of Siloxane Functionalized Poly(Ionic Liquids) for Efficient and Stable Perovskite Solar Cells

Dual-Resistance of Ion Migration and Moisture Erosion via Hydrolytic Crosslinking of Siloxane Functionalized Poly(Ionic Liquids) for Efficient and Stable Perovskite Solar Cells

Characterization of a New Low Temperature Encapsulation Method with Ethylene-Vinyl Acetate under UV Irradiation for Perovskite Solar Cells

In this work, the performance of a new ethylene-vinyl acetate-based low temperature encapsulation method, conceived to protect perovskite samples from UV irradiation in ambient conditions, has been analyzed. To this purpose, perovskite samples consisting of a set of MAPbI3 (CH3NH3PbI3) films and MAPbI3 with an ETL layer were deposited over glass substrates by spin-coating techniques and encapsulated using the new method. The samples were subjected to an UV lamp or to full solar irradiation in ambient conditions, with a relative humidity of 60–80%. Microscope imaging, spectroscopic ellipsometry and Fourier-transform infrared spectroscopy (FTIR) techniques were applied to analyze the samples. The obtained results indicate UV energy is responsible for the degradation of the perovskite layer. Thus, the cut-UV characteristics of the EVA encapsulate acts as an efficient barrier, allowing the laminated samples to remain stable above 350 h under full solar irradiation compared with non-encapsulated samples. In addition, the FTIR results reveal perovskite degradation caused by UV light. To extend the study to encompass whole PSCs, simulations were carried out using the software SCAPS-1D, where the non-encapsulated devices present a short-circuit current reduction after exposure to UV irradiation, while the encapsulated ones maintained their efficiency.

Plasmonic Local Heating Induced Strain Modulation for Enhanced Efficiency and Stability of Perovskite Solar Cells

AbstractThe residual strain induced during the growth of perovskite film is an intrinsic issue that significantly affects the efficiency and stability of perovskite solar cells (PVSCs). Inspired by the flipped annealing method to release strain in perovskite thin films, SiO2‐coated gold nanorods (GNR@SiO2) are introduced into perovskite film and advantage of the plasmonic local heating effect is taken for in situ strain relaxation. The GNR@SiO2‐incorporated inverted PVSCs exhibit a champion power conversion efficiency (PCE) over 23%, which is the highest PCE in plasmonic‐incorporated PVSCs. Moreover, the intrinsic stability of the resulting PVSCs is greatly improved for the nonencapsulated device and retains 84% of its initial PCE after 2800 h aging under continuous illumination at 65 ± 5 °C in an N2 glove box and nearly 90% after 1000 h repetitive 12 h light on–off cycles. This work provides an efficient yet easy‐to‐implement plasmonic heating strategy for simultaneously enhancing the efficiency and stability of PVSCs.

ZrSnO4: A Solution-Processed Robust Electron Transport Layer of Efficient Planar-Heterojunction Perovskite Solar Cells

A robust electron transport layer (ETL) is an essential component in planar-heterojunction perovskite solar cells (PSCs). Herein, a sol-gel-driven ZrSnO4 thin film is synthesized and its optoelectronic properties are systematically investigated. The optimized processing conditions for sol-gel synthesis produce a ZrSnO4 thin film that exhibits high optical transmittance in the UV-Vis-NIR range, a suitable conduction band maximum, and good electrical conductivity, revealing its potential for application in the ETL of planar-heterojunction PSCs. Consequently, the ZrSnO4 ETL-based devices deliver promising power conversion efficiency (PCE) up to 19.05% from CH3NH3PbI3-based planar-heterojunction devices. Furthermore, the optimal ZrSnO4 ETL also contributes to decent long-term stability of the non-encapsulated device for 360 h in an ambient atmosphere (T~25 °C, RH~55%,), suggesting great potential of the sol-gel-driven ZrSnO4 thin film for a robust solution-processed ETL material in high-performance PSCs.