Perovskite Films Research Articles

Multi-Functional Interface Engineering for Monolithic Perovskite/Perovskite/Crystalline Silicon Triple-Junction Tandem Solar Cells.

Perovskite/perovskite/silicon triple-junction tandem solar cells (TSCs) hold significant potential for achieving higher efficiencies while lowering the levelized cost of electricity. The top subcell utilizing wide-bandgap (WBG) perovskite is crucial for improving the efficiency of TSCs. However, the defects caused by poorly crystallized WBG perovskite films and suboptimal energy level alignment lead to significant energy loss. Herein, we present a multifunctional interface engineering utilizing piperazinium bromide (PZBr) for enhancing the property of 2.03-eV perovskite films. The unique molecular structure of PZBr enables it to effectively passivate defects in perovskite films, to suppress photoinduced phase segregation, and to improve the energy band alignment between perovskite films and contact layers. Additionally, the PZBr modification facilitates the crystal ripening process in perovskite polycrystalline films. These functions result in suppressed non-radiative recombination and accelerated carrier extraction. Consequently, single-junction 2.03-eV perovskite solar cells (PSCs) achieved a remarkable efficiency of 13.82%, one of the highest efficiencies reported for PSCs with a bandgap exceeding 2.0 eV. In further, a monolithic triple-junction TSC was fabricated, achieving a photovoltage of 2.96 V and a champion efficiency of 20.05% (aperture area: 1 cm2). This work underscores the critical role of PZBr-based interface engineering in advancing WBG PSCs and triple-junction TSCs.

Strain Release via Glass Transition Temperature Regulation for Efficient and Stable Perovskite Solar Cells.

Thermally induced tensile strain that remains in perovskite films after annealing is one of the key reasons for diminishing the performance and operational stability of perovskite solar cells (PSCs). Herein, a glass transition temperature (Tg) regulation (TR) strategy is developed by introducing two polymerizable monomers, 2-(N-3-Sulfopropyl-N,N-dimethyl ammonium)ethyl methacrylate (SBMA) and 2-Hydroxyethyl acrylate (HEA), into the perovskite layer. SBMA and HEA undergo in situ polymerization, which regulates the nucleation and crystal growth of the perovskite film. In addition, adjusting the ratio of SBMA and HEA to lower the Tg of the resulting polymer effectively releases the strain in the perovskite film. The modified film exhibits significantly reduced tensile strain, decreased trap density and improved stability. As a result, the optimized PSCs achieve a champion power conversion efficiency (PCE) of 26.15% (certified as 25.59%). Furthermore, the encapsulated device demonstrates prominent enhanced operation stability, maintaining 90.3% of its initial efficiency after 500h of continuous sunlight exposure.

Chemical passivation and grain-boundary manipulation via in situ cross-linking strategy for scalable flexible perovskite solar cells.

Flexible perovskite solar cells (f-PSCs) are considered the most promising candidates in portable power applications. However, high sensitivity of crystallization on the substrate and the intrinsic brittleness usually trade off the performance of f-PSCs. Herein, we introduced an initiator-free cross-linkable monomer (2,5-dioxopyrrolidin-1-yl) 5-(dithiolan-3-yl)pentanoate (FTA), which can chemically passivate defects and enable real-time fine regulation of crystallization. The resulting perovskite film exhibited higher crystallinity, enlarged grain size, and reduced dependence on the substrate. In addition, the cross-linked FTA [CL(FTA)] distributed along the grain boundaries effectively released the residual stress and securely bound the grains together. Consequently, the CL(FTA)-modified flexible PSCs achieved a record-breaking efficiency of 24.64% (certified 24.08%). Moreover, the scalable potential has been verified by the corresponding rigid and flexible modules, delivering impressive efficiencies of 19.53 and 17.13%, respectively. Furthermore, the optimized device demonstrated bending durability and improved operational stability, thereby advancing the progress of f-PSCs toward industrialization.

Inhibiting ion migration in strontium-lead halide perovskite for pure-blue emission: a first-principle and experimental study.

Bromide-chloride mixed perovskites have garnered significant attention as a direct and efficient material for achieving pure-blue emission. However, the complex problem of halide migration in mixed halide perovskites presents a significant obstacle to achieving stable electroluminescence (EL) spectra. Here, we investigate the mechanism of partially replacing the B-site Pb2+ with the non-toxic Sr2+ to achieve pure-blue emission based on first principles. The ion mobility activation energy of Sr2+ is 1.23 eV, which is an order of magnitude greater than that of halogens. Meanwhile, the incorporation of Sr2+ triples the activation energy for halogen migration. Furthermore, the halide defect formation energy increases from 4.75 eV to 5.62 eV, thereby reducing ion migration channels. Transient absorption spectroscopy demonstrates that suppressing the ion mobility pathway and enhancing ion mobility activation energy promotes the perovskite film to exhibit excellent spectral stability under laser pumping. Our work provides insights for the development of highly stable and eco-friendly perovskite devices.

Predicting Perovskite Photovoltaics Performance.

Wide band gap FA0.8Cs0.2Pb(I0.6Br0.4)3 perovskite photovoltaic (PV) devices are measured by spectroscopic ellipsometry in the through-the-glass configuration and analyzed to determine the complex optical property spectra of the perovskite absorber as well as the structural properties of all constituent layers. This information is used to simulate external quantum efficiency (EQE) spectra, to calculate PV device performance parameters such as short circuit current density, open circuit voltage, fill factor, and power conversion efficiency, and to develop strategies for increasing the accuracy of predictions. Simulations and calculations tend to overestimate PV device performance parameters, undermining the accuracy and usefulness of those simulations. Mapping spectroscopic ellipsometry measurements of an incomplete device are also collected from the perovskite film side to obtain layer thicknesses, perovskite band gap energies, and Urbach energies at each mapping point. The incomplete device stacks feature the perovskite absorber as the final deposited layer, while the complete devices add electron transport layers and silverback electrical contacts. When simulations are based on structural and optical properties obtained from spectroscopic ellipsometry measurements of incomplete PV device stacks, further inaccuracies arise as characteristics of the exposed perovskite film are not necessarily the same as those of an absorber in a complete, protected PV device. Predictions for PV performance parameters fall within 5% of the experiment for three of four baseline devices. The usefulness of this is apparent in situations where experimentally measuring PV device performance is unfeasible or overly tedious, as well as during intermediate steps during production.

In-situ Polymerization Induced Seed-Root Anchoring Structure for Enhancing Stability and Efficiency in Perovskite Solar Modules.

The escape of organic cations over time from defective perovskite interface leads to non-stoichiometric terminals, significantly affecting the stability of perovskite solar cells (PSCs). How to stabilize the interface composition under environmental stress remains a grand challenge. To address this issue, we utilize thiol-functionalized particles as a "seed" and conduct in situ polymerization of 2,2,3,4,4,4-hexafluorobutyl methacrylate (HFMA) as a "root" at the bottom of the perovskite layer. In this process, the thiol group acts as the initiation site for the polymerization of HFMA, while the fluorine groups in HFMA firmly anchor the organic cations of the perovskite through multiple hydrogen bonds. This strategy resembles how seeds take root in soil to prevent soil erosion. This bionic seed-rooting structure effectively stabilizes the stoichiometry of the perovskite, thus suppressing the escape of organic cations. As a result, the perovskite films with seed-rooting structures exhibit enhanced stability under harsh vacuum thermal conditions (150 °C, < 10 Pa). The resulting PCS achieves an efficiency of 25.64% and a 22.4 cm2 module efficiency of 22.61%. After 1300 hours of 1-sun illumination at 85% relative humidity and 65 °C (ISOS-L-3 protocol), the perovskite solar module maintains 90% of its initial efficiency.

SN2-Reaction-Driven Bonding-Heterointerface Strengthens Buried Adhesion and Orientation for Advanced Perovskite Solar Cells.

Traditionally weak buried interaction without customized chemical bonding always goes against the formation of high-quality perovskite film that highly determines the efficiency and stability of perovskite solar cells. To address this issue, herein, we propose a bimolecular nucleophilic substitution reaction (SN2) driving strategy to idealize the robust buried interface by simultaneously decorating underlying substrate and functionalizing [PbX6]4- octahedral framework with iodoacetamide and thiol molecules, respectively. Theoretical and experimental results demonstrate that a strong SN2 reaction between exposed halogen and thiol group in two molecules occurs, which not only benefits the reinforcement of buried adhesion, but also triggers target-point-oriented crystallization, synergistically upgrading the upper perovskite film quality and accelerating interfacial charge extraction-transfer behavior. Benefiting from the suppressed nonradiative recombination, as a result, an all-air-processed carbon-based all-inorganic CsPbI2Br device achieves an enhanced efficiency of 15.14%, more importantly, with significantly prolonged long-term stability under harsh conditions. This unique reaction-driven buried interface provides a new path for manipulating perovskite growth and obtaining advanced perovskite photovoltaics.

SN2‐Reaction‐Driven Bonding‐Heterointerface Strengthens Buried Adhesion and Orientation for Advanced Perovskite Solar Cells

Traditionally weak buried interaction without customized chemical bonding always goes against the formation of high‐quality perovskite film that highly determines the efficiency and stability of perovskite solar cells. To address this issue, herein, we propose a bimolecular nucleophilic substitution reaction (SN2) driving strategy to idealize the robust buried interface by simultaneously decorating underlying substrate and functionalizing [PbX6]4‐ octahedral framework with iodoacetamide and thiol molecules, respectively. Theoretical and experimental results demonstrate that a strong SN2 reaction between exposed halogen and thiol group in two molecules occurs, which not only benefits the reinforcement of buried adhesion, but also triggers target‐point‐oriented crystallization, synergistically upgrading the upper perovskite film quality and accelerating interfacial charge extraction‐transfer behavior. Benefiting from the suppressed nonradiative recombination, as a result, an all‐air‐processed carbon‐based all‐inorganic CsPbI2Br device achieves an enhanced efficiency of 15.14%, more importantly, with significantly prolonged long‐term stability under harsh conditions. This unique reaction‐driven buried interface provides a new path for manipulating perovskite growth and obtaining advanced perovskite photovoltaics.

In‐situ Polymerization Induced Seed‐Root Anchoring Structure for Enhancing Stability and Efficiency in Perovskite Solar Modules

The escape of organic cations over time from defective perovskite interface leads to non‐stoichiometric terminals, significantly affecting the stability of perovskite solar cells (PSCs). How to stabilize the interface composition under environmental stress remains a grand challenge. To address this issue, we utilize thiol‐functionalized particles as a "seed" and conduct in situ polymerization of 2,2,3,4,4,4‐hexafluorobutyl methacrylate (HFMA) as a "root" at the bottom of the perovskite layer. In this process, the thiol group acts as the initiation site for the polymerization of HFMA, while the fluorine groups in HFMA firmly anchor the organic cations of the perovskite through multiple hydrogen bonds. This strategy resembles how seeds take root in soil to prevent soil erosion. This bionic seed‐rooting structure effectively stabilizes the stoichiometry of the perovskite, thus suppressing the escape of organic cations. As a result, the perovskite films with seed‐rooting structures exhibit enhanced stability under harsh vacuum thermal conditions (150 °C, &lt; 10 Pa). The resulting PCS achieves an efficiency of 25.64% and a 22.4 cm2 module efficiency of 22.61%. After 1300 hours of 1‐sun illumination at 85% relative humidity and 65 °C (ISOS‐L‐3 protocol), the perovskite solar module maintains 90% of its initial efficiency.

Efficient Spin-Light-Emitting Diodes With Tunable Red to Near-Infrared Emission at Room Temperature.

Spin light-emitting diodes (spin-LEDs) are important for spin-based electronic circuits as they convert the carrier spin information to optical polarization. Recently, chiral-induced spin selectivity (CISS) has emerged as a new paradigm to enable spin-LED as it does not require any magnetic components and operates at room temperature. However, CISS-enabled spin-LED with tunable wavelengths ranging from red to near-infrared (NIR) has yet to be demonstrated. Here, chiral quasi-2D perovskites are developed to fabricate efficient spin-LEDs with tunable wavelengths from red to NIR region by tuning the halide composition. The optimized chiral perovskite films exhibit efficient circularly polarized luminescence from 675 to 788nm, with a photoluminescence quantum yield (PLQY) exceeding 86% and a dissymmetry factor (glum) ranging from 8.5 × 10-3 to 2.6 × 10-2. More importantly, direct circularly polarized electroluminescence (CPEL) is achieved at room temperature in spin-LEDs. This work demonstrated efficient red and NIR spin-LEDs with the highest external quantum efficiency (EQE) reaching 12.4% and the electroluminescence (EL) dissymmetry factors (gEL) ranging from 3.7 × 10-3 to 1.48 × 10-2 at room temperature. The composition-dependent CPEL performance is further attributed to the prolonged spin lifetime as revealed by ultrafast transient absorption spectroscopy.

Regulation of Perovskite Nucleation and Orientated Crystal Growth via In Situ Self‐Crosslinking Polymer for Bright Perovskite Light‐Emitting Diodes

AbstractHybrid halide perovskite films are becoming increasingly efficient in various applications, but several challenges still remain to be overcome. In this study, thermally polymerized additive N‐vinyl‐2‐pyrrolidone (NVP) is utilized to tune the crystallization and orientation of mixed organo‐metal perovskite films. Using in situ spectroscopy, it is demonstrated that NVP plays a crucial role in prolonging the crystallization process and separating the nucleation and crystal growth by forming an NVP‐precursor intermediate phase. Additionally, the intermediate adduct effectively passivates defects, reduces nonradiative recombination, improves crystallinity, and enhances the transmission of charge carriers. NVP‐containing perovskite light‐emitting diodes (PeLEDs) are subsequently developed that exhibit stable and bright green luminance exceeding 240 000 cd m−2. These findings provide valuable insights into manipulating the crystallization behavior of mixed organo‐metal perovskite films.

Multifunctional Graphdiyne Enables Efficient Perovskite Solar Cells via Anti-Solvent Additive Engineering

Finding ways to produce dense and smooth perovskite films with negligible defects is vital for achieving high-efficiency perovskite solar cells (PSCs). Herein, we aim to enhance the quality of the perovskite films through the utilization of a multifunctional additive in the perovskite anti-solvent, a strategy referred to as anti-solvent additive engineering. Specifically, we introduce ortho-substituted-4'-(4,4″-di-tert-butyl-1,1':3',1″-terphenyl)-graphdiyne (o-TB-GDY) as an AAE additive, characterized by its sp/sp2-cohybridized and highly π-conjugated structure, into the anti-solvent. o-TB-GDY not only significantly passivates undercoordinated lead defects (through potent coordination originating from specific high π-electron conjugation), but also serves as nucleation seeds to effectively enhance the nucleation and growth of perovskite crystals. This markedly reduces defects and non-radiative recombination, thereby increasing the power conversion efficiency (PCE) to 25.62% (certified as 25.01%). Meanwhile, the PSCs exhibit largely enhanced stability, maintaining 92.6% of their initial PCEs after 500h continuous 1-sun illumination at ~ 23°C in a nitrogen-filled glove box.

Efficient defect passivation and charge extraction with 2-cyano-5-fluorobenzyl bromide interface modification for hole-transporting layers-free CsPbIXBr3−X perovskite solar cells

Abstract Fully inorganic metal halide perovskite solar cells (PSCs) have become an emerging research hotspot in photovoltaics due to their high efficiency and excellent thermal stability. Unfortunately, HTL-free CsPbIXBr3−X devices suffer from surface traps on the perovskite films, which severely limits the power conversion efficiency and operational stability of the devices. In this work, we propose a multifunctional passivator, 2-cyano-5-fluorobenzene bromide molecule (2-C-5-FB), to passivate perovskite films by post-treatment, aiming to improve the quality of perovskite films, reduce interfacial defects and non-radiative complexes, enhance carrier separation kinetics, and improve the extraction of carriers, thus improving device performance. The C≡N in the molecular structure immobilizes the undercoordinated Pb2+ ions, thus passivating the defects in the perovskite films. In addition, the Br atoms on the ring can with the [PbI6]4− backbone through halogen bonding, and the F atoms form Pb-F and Cs-F, which can effectively reduce the film defects. We prepared passivated devices with the structure of FTO/TiO2/CsPbIXBr3−X/2-C-5-FB/Carbon, and the PCE of the passivated devices was improved compared with the pristine devices, and the cell efficiency was increased from 7.84% to 9.21% with a light intensity of 100 mW cm−2, and the stability of the devices was also improved. The experimental results indicate that the use of 2-cyano-5-fluorobenzene bromide passivation strategy has a positive effect on the performance enhancement of the perovskite devices, and is an effective way to realize efficient and stable PSCs.

Surface Template Realizing Oriented Perovskites for Highly Efficient Solar Cells.

Formamidinium lead iodide (FAPbI3) perovskite films, ensuring optically active phase purity with uniform crystal orientation, are ideal for photovoltaic applications. However, the optically active α-FAPbI3 phase is easy to degrade into δ-phase due to numerous defects within randomly oriented films. Here, a "quasi-2D" perovskite template is pre-deposited on the film surface within the crystallization process based on the two-step preparation technology, which directly induced pure and highly orientated crystallization of α-FAPbI3 across the downward growth process. Furthermore, the enlarged interaction between 2D components with colloidal properties and lead iodide delayed the crystallization process effectively, yielding high crystallinity with low trap state density. The resulting perovskite photovoltaic devices exhibited a champion efficiency as high as 25.79% with comprehensively improved device stability. This work provides new insights into the utilization of 2D components and the formation mechanism behind 2D perovskites.

A Review on Recent Advances in Flexible Perovskite Solar Cells

Flexible perovskite solar cells (FPSCs), featured with lightweight, high efficiency, and low cost, have attracted much attention anticipating in applications on wearable electronics, near‐space vehicles, and internet of things. High efficiency and mechanical stability are two main factors in the study of FPSCs toward practical applications. In recent few years, many breakthroughs in materials modification and device innovation make the power conversion efficiency of FPSCs reach over 25%. A comprehensive review thus is conducted to elucidate the critical issues including flexible substrates, transparent electrodes, charge transport layers, perovskite films, and modifications for mechanical enhancement of FPSCs, which is expected to promote the future development of FPSCs.

Solvent-dripping modulated 3D/2D heterostructures for high-performance perovskite solar cells

The controlled growth of two-dimensional (2D) perovskite atop three-dimensional (3D) perovskite films reduces interfacial recombination and impedes ion migration, thus improving the performance and stability of perovskite solar cells (PSCs). Unfortunately, the random orientation of the spontaneously formed 2D phase atop the pre-deposited 3D perovskite film can deteriorate charge extraction owing to energetic disorder, limiting the maximum attainable efficiency and long-term stability of the PSCs. Here, we introduce a meta-amidinopyridine ligand and the solvent post-dripping step to generate a highly ordered 2D perovskite phase on the surface of a 3D perovskite film. The reconstructed 2D/3D perovskite interface exhibits reduced energetic disorder and yields cells with improved performance compared with control 2D/3D samples. PSCs fabricated with the meta-amidinopyridine-induced phase-pure 2D perovskite passivation show a maximum power conversion efficiency of 26.05% (a certified value of 25.44%). Under damp heat and outdoor tests, the encapsulated PSCs maintain 82% and 75% of their initial PCE after 1000 h and 840 h, respectively, demonstrating improved practical durability.

Organic Molecule Vapor‐Assisted Passivation for Efficient and Stable Perovskite Solar Cells

AbstractEffective suppression of non‐radiative recombination caused by surface defects in perovskite is crucial for achieving high‐efficiency perovskite solar cells (PSCs). However, conventional passivators such as organic amine salts are prone to deprotonation to amines and rapid reaction with formamidine, leading to device degradation. Meanwhile, the solvent processing of the organic amine salts can also decompose the surface of the perovskite layer due to the dissolution of the organic amine salts. In this work, an organic small molecule, 2‐Thiophenacetamide (TAM), features multiple active sites is presented. TAM demonstrates the ability to passivate perovskite thin films through sublimation deposition. It is demonstrated that this solvent‐free method and the effect of thiophene and the carbonyl group efficiently passivate the uncoordinated Pb2+, while the amino group aids in stabilizing perovskite structures by forming hydrogen bonds with iodide ions. As a result, the TAM vapor treatment device demonstrates an enhanced efficiency of 25.33%, and the operational stability is maintained at 95% of the original efficiency after continuous operation for over 1000 h. Additionally, perovskite submodules with an active area of 14 cm2 are successfully assembled with a efficiency of up to 22.17%.

Designing Robust Quasi-2D Perovskites Thin Films for Stable Light-Emitting Applications.

Quasi-2D perovskite made with organic spacers co-crystallized with inorganic cesium lead bromide inorganics is demonstrated for near unity photoluminescence quantum yield at room temperature. However, light emitting diodes made with quasi-2D perovskites rapidly degrade which remains a major bottleneck in this field. In this work, It is shown that the bright emission originates from finely tuned multi-component 2D nano-crystalline phases that are thermodynamically unstable. The bright emission is extremely sensitive to external stimuli and the emission quickly dims away upon heating. After a detailed analysis of their optical and morphological properties, the degradation is attributed to 2D phase redistribution associated with the dissociation of the organic spacers departing from the inorganic lattice. To circumvent the instability problem, a diamine is investigated spacer that has both sides attached to the inorganic lattice. The diamine spacer incorporated perovskite film shows significantly improved thermal tolerance over maintaining a high photoluminescence quantum yield of over 50%, which will be a more robust material for lighting applications. This study guides designing quasi-2D perovskites to stabilize the emission properties.

Impact of Spin-Coating Temperature on Morphology of Pb-Based Mixed Ion Perovskite Films and Their Solar Cell Performance

Impact of Spin-Coating Temperature on Morphology of Pb-Based Mixed Ion Perovskite Films and Their Solar Cell Performance

Enhanced Efficiency and Stability in Blade-Coated Perovskite Solar Cells through Using 2,3,4,5,6-Pentafluorophenylethylammonium Halide Additives.

The power conversion efficiency (PCE) of perovskite solar cells is sensitive to their method of fabrication as well as the combination of materials in the perovskite layer. Air knife-assisted blade coating enables good quality perovskite films to be formed but the device efficiencies still tend to lag behind those fabricated using spin-coated perovskite layers. Herein we report the use of three 2,3,4,5,6-pentafluorophenylethylammonium halides (FEAX, where X = I-, Br- or Cl-) as additives in nitrogen knife-assisted blade-coated methylammonium lead iodide (MAPbI3) perovskite solar cells. The additives were all found to passivate defects in the MAPbI3 films. The use of chloride as the counteranion led to additive containing films with the largest crystal size and fewest defects and consequently the FEACl film was found to have the highest photoluminescence (PL) intensity, longest average PL lifetime and lowest trap density. These features led to the devices having a high open-circuit voltage (Voc) of 1.17 V and a PCE of 21.4%. In addition, the hydrophobic fluorinated cations led to the additive containing devices being more stable, with those containing FEACl having the best thermal stability and performance under maximum-power-point (MPP) tracking in a humid (≈65%) environment at 50 ± 1 °C.