Energy Barrier For Phase Transition Research Articles

A new type of pentagonal structure HgS2 monolayer with abundant active sites and low Gibbs free energy for photocatalytic water splitting

Discovery of new two-dimensional (2D) materials not only has important fundamental research significance but also has promising application prospects. Through systematic structure searching combined with density functional theory calculations and simulations, we predict a new 2D monolayer HgS2 material featuring with a previously unreported type of pentagonal structure with orthorhombic P21212 symmetry. The penta-HgS2 monolayer shows good thermal, thermodynamic, mechanical and dynamic stabilities, exhibiting ferroelastic phase transition with an ultralow switching energy barrier (about 1 meV/atom), high ultimate strength of 12 N/m, moderate indirect band gap of 2.25 eV. In addition, the penta-HgS2 monolayer shows significantly anisotropic carrier mobility with a large anisotropy ratio of 98.5 along the y direction. More importantly, the penta-HgS2 monolayer exhibits abundant catalytic active sites, low Gibbs free energy (ΔGH ranging from 0.656 to 1.687 eV) for hydrogen evolution reactions, excellent solar light absorption capacity (∼105 cm−1) with the solar-to-hydrogen efficiency reaching up to 11.83%. The excellent ultimate tensile ability and the ultralow ferroelastic phase transition energy barrier implies penta-HgS2 monolayer material can be used to manufacture flexible mechanical and nanoelectronic devices. The suitable band edge alignments, ultrahigh carrier mobility anisotropy, high catalytic activity and excellent visible light adsorption performance indicate that penta-HgS2 monolayer is a promising candidate photocatalyst for high-performance photocatalytic water splitting. The present work not only supplements a new member to the 2D pentagonal structure material family, but also points out its promising applications in nanoscale devices and photocatalytic hydrogen productions.

Investigation of phase transformation model, densification mechanism, and mechanical properties of TiH2 powder metallurgy materials

TiH2 has gradually gained attention in powder metallurgy because of its unique properties. This study systematically investigated the porosity, density, mechanical tensile properties, and fracture toughness of sintered samples of TiH2 as a powder metallurgy starting material. The results showed that, compared with hydrogenation-dehydrogenation titanium (HDH Ti), the density, elongation, and fracture toughness of the sintered TiH2 samples significantly improved. In addition, the contributions of grain size, porosity, and oxygen content to the yield strength of the samples are discussed, and the results revealed that a lower oxygen content and porosity are the main reasons for the differences in the mechanical properties between HDH Ti and TiH2. Finally, the experimental results are combined with first-principles calculations and simulations to construct a TiH2 phase transition model. The contribution of H atoms to the TiH2 phase transition energy barrier and activation sintering densification was investigated and elucidated, revealing the TiH2 sintering densification mechanism from the perspective of phase transition. The derived results contribute to a deeper understanding of the intrinsic mechanism of TiH2 activation sintering densification, which is highly important for the development of advanced titanium materials.

Achieving High Operating-Temperature Self-powered X-Ray Detection in Multilayered Hybrid Perovskites through Arylamine Intercalation.

Polar metal halide hybrid perovskites (PHPs) that exhibit outstanding bulk photovoltaic effect (BPVE), excellent semiconductor features, and strong radiation absorption ability, have shown prominent advantages in highly sensitive direct X-ray detection. However, it is still a challenge to explore PHPs with high BPVE temperature ranges, answering the demand of developing thermally stable passive X-ray detection. Herein, by intercalating arylamine into lead tribromide and inducing order-disorder phase transition, a 2D multilayered PHPs (BZA)2(MA)Pb2Br7 (BZPB, BZA = benzylamine, MA = methylamine) is synthesized. BZPB crystallizes in a polar space group Aea2 at a low-temperature phase and demonstrates a significant open-circuit of 0.3V deriving from BPVE under X-ray irradiation. Meanwhile, the strong X-ray absorption coefficient and outstanding carrier transport capability of the bilayered lead halide framework associated with the polar BPVE give BZPB excellent X-ray detection abilities. At 0V bias, the impressive sensitivity of BZPB is 98 µC Gy-1 cm-2. Importantly, the introduction of the rigid BZA ring increases the energy barrier of phase transition and thus dramatically enhances the X-ray detection operating temperature of BZPB up to 409 K without significant performance degradation. This work strongly reveals the great potential of rational design of metal halide hybrid perovskites for X-ray detection applications.

Photodoping-Modified Charge Density Wave Phase Transition in WS2/1T-TaS2 Heterostructure

Controlling collective electronic states hold great promise for development of innovative devices. Here, we experimentally detect the modification of the charge density wave (CDW) phase transition within a 1T-TaS2 layer in a WS2/1T-TaS2 heterostructure using time-resolved ultrafast spectroscopy. Laser-induced charge transfer doping strongly suppresses the commensurate CDW phase, which results in a significant decrease in both the phase transition temperature (T c) and phase transition stiffness. We interpret the phenomenon that photo-induced hole doping, when surpassing a critical threshold value of ∼ 1018 cm−3, sharply decreases the phase transition energy barrier. Our results provide new insights into controlling the CDW phase transition, paving the way for optical-controlled novel devices based on CDW materials.

Phase transition mechanism of CsPbI2Br perovskite films induced by moisture

The humidity stability and phase transition mechanism of the all-inorganic perovskite CsPbI2Br based on an optimized dual-source co-evaporation preparation process are investigated at the film interface level. It is found that the CsPbI2Br films annealed at 300 °C for several minutes exhibit a best crystallinity and photoelectric properties. The as-grown CsPbI2Br film is confirmed to be a α phase with a dark brown cubic crystal structure and an average visible transparency of 35.9%. But it will be transformed into its δ phase with a transparent orthorhombic crystal structure and an average visible transparency of 80.3% after a certain amount of moisture exposure. Compared with the α phase film, the electronic structure of the δ phase has also changed significantly with a VBM shift of about 0.32 eV to high binding energy. The results of AR-XPS show that the water molecules in perovskite CsPbI2Br after a moisture exposure only adsorb on the surface rather than penetrate the interior of the lattice. When water molecules adsorb on the lattice surface, halide ions should migrate towards the lattice surface due to their high hydration enthalpy, resulting in halide vacancies within the lattice and causing the reduction of energy barrier for phase transition from α phase to δ phase. So the CsPbI2Br film will transform from its α phase to δ phase induced by water vapor, and this phase transition will be reversed to some extent after another annealing.

The Effect of Self‐Assembled Bridging Layer on the Performance of Pure FAPbI3‐Based Perovskite Solar Cells

AbstractPure FAPbI3‐based, with FA being formamidinium, perovskite solar cells (PSCs) have garnered worldwide recognition for their exceptional efficiency. However, the phase stability of FAPbI3 is still a big obstacle in this area, because the ordinary strategy using MA+, Br−, Cs+ to stabilize α‐FAPbI3 phase can cause the bandgap change and ion migration. Herein, a new strategy is introduced to improve the α‐FAPbI3 phase stability by using a self‐assembled bridging layer at the buried interface of FAPbI3 perovskite in the n–i–p solar cell structure. A series of multidentate bisphosphonic acid molecules are screened and demonstrate that etidronic acid (EA) with the smallest steric hindrance behaves the best. The four P‐OH groups can first form multidentate anchors on SnO2 while the remaining unanchored ─OH and P═O groups can form strong interaction between I− and Pb2+. Thus, a strong and stable bridging layer is formed, which greatly increases the energy barrier of phase transition of FAPbI3. As a result, the pure FAPbI3‐based (MA+, Br+, Cs+‐free system) n–i–p device reached an impressive power conversion efficiency of 24.2% with good stability. Furthermore, the strong interaction between EA and Pb2+ can greatly reduce lead leakage in harsh conditions.

Renewing Halogen Substitution Strategy for the Rational Design of High‐Curie Temperature Metal‐Free Molecular Antiferroelectrics

AbstractMetal‐free molecular antiferroelectric (AFE) holds a promise for energy storage on account of its unique physical attributes. However, it is challenging to explore high‐curie temperature (Tc) molecular AFEs, due to the lack of design strategies regarding the rise of phase transition energy barriers. By renewing the halogen substitution strategy, we have obtained a series of high‐Tc molecular AFEs of the halogen‐substituted phenethylammonium bromides (x‐PEAB, x=H/F/Cl/Br), resembling the binary stator‐rotator system. Strikingly, the p‐site halogen substitution of PEA+ cationic rotators raises their phase transition energy barrier and greatly enhances Tc up to ~473 K for Br‐PEAB, on par with the record‐high Tc values for molecular AFEs. As a typical case, the member 4‐fluorophenethylammonium bromide (F‐PEAB) shows notable AFE properties, including high Tc (~374 K) and large electric polarization (~3.2 μC/cm2). Further, F‐PEAB also exhibits a high energy storage efficiency (η) of 83.6 % even around Tc, catching up with other AFE oxides. This renewing halogen substitution strategy in the molecular AFE system provides an effective way to design high‐Tc AFEs for energy storage devices.

Renewing Halogen Substitution Strategy for the Rational Design of High-Curie Temperature Metal-Free Molecular Antiferroelectrics.

Metal-free molecular antiferroelectric (AFE) holds a promise for energy storage on account of its unique physical attributes. However, it is challenging to explore high-curie temperature (Tc) molecular AFEs, due to the lack of design strategies regarding the rise of phase transition energy barriers. By renewing the halogen substitution strategy, we have obtained a series of high-Tc molecular AFEs of the halogen-substituted phenethylammonium bromides (x-PEAB, x=H/F/Cl/Br), resembling the binary stator-rotator system. Strikingly, the p-site halogen substitution of PEA+ cationic rotators raises their phase transition energy barrier and greatly enhances Tc up to ~473 K for Br-PEAB, on par with the record-high Tc values for molecular AFEs. As a typical case, the member 4-fluorophenethylammonium bromide (F-PEAB) shows notable AFE properties, including high Tc (~374 K) and large electric polarization (~3.2 μC/cm2). Further, F-PEAB also exhibits a high energy storage efficiency (η) of 83.6 % even around Tc, catching up with other AFE oxides. This renewing halogen substitution strategy in the molecular AFE system provides an effective way to design high-Tc AFEs for energy storage devices.

First-principles prediction of ferroelectric Janus Si2XY (X/Y = S/Se/Te, X ≠ Y) monolayers with negative Poisson's ratios.

Nowadays, two-dimensional (2D) materials with Janus structures evoke much attention due to their unique mechanical and electronic properties. In this work, Janus Pma2-Si2XY (X/Y = S/Se/Te, X ≠ Y) ferroelectric monolayers are firstly proposed and systematically investigated by first-principles calculations. These monolayers exhibit remarkable mechanical properties, including small Young's modulus values, negative Poisson's ratios (NPRs) and large critical strains, reflecting their exceptional flexibility and stretchability. More strikingly, the novel structures of Si2STe and Si2SeTe also endow them with in-plane spontaneous polarization (Ps) and low energy barrier for phase transition, with Ps and energy barrier values being 1.632 × 10-10 C m-1 and 159 meV for Si2STe and 1.149 × 10-10 C m-1 and 196.6 meV for Si2SeTe. The ab initio molecular dynamics (AIMD) simulations reveal high Curie temperatures (Tc) for Si2STe and Si2SeTe, ranging between 1300 K and 1400 K. Additionally, Si2XY monolayers exhibit high anisotropic carrier mobility (∼103 cm2 V-1 s-1) and an extraordinary light absorption coefficient (∼105 cm-1). Our research not only broadens the family of 2D Janus ferroelectric materials, but also demonstrates their potential applications in nanomechanical, nanoelectronic and optoelectronic devices.

(Invited) Achieving Stable Black-CsPbI3 Thin-Films for Opto-Electronic Applications

Halide perovskite materials, particularly CsPbI3, have emerged as promising candidates for optoelectronic applications, including solar cells, due to their favorable bandgap of ~1.7 eV for tandem solar cells with silicon-based counterparts. However, their widespread adoption is hindered by their instability and reactivity under ambient conditions, especially to moisture and oxygen. The black phase CsPbI3 polymorphs (α, β, and γ) are only stable at elevated temperatures, and at room temperature (RT), they transform to a yellow, nonperovskite phase (δ) with a wider bandgap of ~2.8 eV, leading to a loss of device performance. To address this challenge, various approaches have been explored to increase the stability of the black phase of CsPbI3 thin films under ambient conditions.[1]One approach is based on interface engineering to induce crystal strain, which increases the stabilization time of the black phase. Thin films of CsPbI3 are prepared on substrates with different thermal expansion coefficients, leading to interfacial strain when quenched from high temperatures (> 320 °C) to RT. This interfacial strain increases the stability of the black phase from a few seconds in bulk polycrystalline samples to a few minutes in thin films, as shown in Fig. 1(a).[2] Additionally, black phase stabilization has been enhanced to a few hours by introducing minimal amounts (< 5%) of dopant elements in the Pb site of CsPbI3, which modifies the texture and generates microstrain in the polycrystalline perovskite films (see Fig. 1(b)).[3] The dopants locally disrupt the normal bonding arrangement and manipulate strains/distortions, and structural relaxation around the dopants is mediated by dynamic disorder and the relatively soft elastic constants of halide perovskite, resulting in the stabilization of the required crystallographic phase.Furthermore, annealing of CsPbI3 thin films in the presence of oxygen has been explored as another approach to increase the stability of the black phase (stable for a few days). Heating the films under oxygen leads to surface oxidation and the formation of Pb-O bonds, resulting in the gathering of Pb and O atoms and the formation of lead oxide. The replacement of I atoms in the inorganic frameworks by O atoms tends to form volatile iodine (I2), but PbI2 is typically detected as the dominant product of degradation during heating in a dry air environment (Fig. 1(c)).[4] The oxidation products on the surface could potentially serve as a protective layer to inhibit further oxidation.Another highly effective approach to enhance the stability of the black phase CsPbI3 in perovskite thin films and devices is through the implementation of coarse photolithography to embed a PbI2-based interfacial microstructure.[5] The resulting films, adorned with a tessellating microgrid ((Fig. 1(d))), display remarkable resistance to moisture-induced decay and demonstrate prolonged stability of the black phase, persisting beyond 2.5 years even in dry environments. This remarkable stability can be attributed to the significant increase in the phase transition energy barrier and the effective limitation of potential yellow phase formation to structurally isolated domains within the microgrid.In summary, our laboratory has effectively implemented various methods to enhance the durability of black phase CsPbI3 thin films when exposed to ambient conditions. These methods comprise inducing interfacial strain, introducing bulk strain through doping, embedding interfacial microstructures, and surface oxidation. These techniques have demonstrated encouraging outcomes in maintaining the black phase of CsPbI3 for extended durations, ranging from a few minutes to several months, and exhibit significant potential for the advancement of practical applications of CsPbI3-based perovskite solar cells. Further exploration and advancement in this direction are anticipated to contribute to achieving long-lasting and efficient perovskite devices.[1] Acc. Mater. Res., 2020, 1, 1, 3–15[2] Science, 2019, 365, 679-684[3] J. Am. Chem. Soc., 2021, 143, 28, 10500–10508[4] unpublished results[5] Nature Commun., 2022, 13, 7513. Figure 1

Inhibition of defect-induced α-to-δ phase transition for efficient and stable formamidinium perovskite solar cells

Defects passivation is widely devoted to improving the performance of formamidinium lead triiodide perovskite solar cells; however, the effect of various defects on the α-phase stability is still unclear. Here, using density functional theory, we first reveal the degradation pathway of the formamidinium lead triiodide perovskite from α to δ phase and investigate the effect of various defects on the energy barrier of phase transition. The simulation results predict that iodine vacancies are most likely to trigger the degradation, since they obviously reduce the energy barrier of α-to-δ phase transition and have the lowest formation energies at the perovskite surface. A water-insoluble lead oxalate compact layer is introduced on the perovskite surface to largely suppress the α-phase collapse through hindering the iodine migration and volatilization. Furthermore, this strategy largely reduces the interfacial nonradiative recombination and boosts the efficiency of the solar cells to 25.39% (certified 24.92%). Unpackaged device can maintain 92% of its initial efficiency after operation at maximum power point under simulated air mass 1.5 G irradiation for 550 h.

Construction of Stable Oxygen Redox by Electrochemical Activation O–TM–Se in Nickel‐Rich Layered Oxides for Lithium‐Ion Batteries

The irreversible oxygen redox and structural degradation of LiNi0.8Co0.1Mn0.1O2 (NCM811) at a 4.5 V high voltage cause a severe decline in cycling performance for lithium‐ion batteries. In this study, a novel approach is proposed to enhance the anionic redox chemistry and stability of NCM811 cathode material by introducing gaseous selenium. Seβ+ species are selectively adsorbed within oxygen vacancies, leading to the continuous replacement of Oα− to form a stable O–TM–Se bond during deep charging. Furthermore, Selenium modification improves cationic redox efficiency and alleviates Oα− (α &lt; 2) outward migration, increases oxygen vacancy formation energy. The redox activity of oxygen is diminished, facilitating improved reversibility of oxygen redox and effectively inhibiting irreversible oxygen escape. Additionally, Selenium increases the energy barrier for phase transition, effectively suppressing irreversible phase transition and Ni migration. Selenium reacts with escaping oxygen to form SeO2, effectively reducing side reactions during cycling. As a result, the proposed approach significantly inhibits irreversible oxygen release, leading to remarkable cyclic stability with 87.5% capacity retention after 300 cycles at 1C at 4.5 V and maintained 192.9 mAh g−1 after 150 cycles under 60C. The Se modification realizes stability anionic redox strategy to design novel high‐energy‐density cathode materials with superior cycling performance.

Modulation of capacitive energy storage performance in 0.9(Na0.5Bi0.5)(Fe0.02Ti0.98)O3-0.1SrTiO3 relaxor ferroelectric thin film via sol-gel optimizing strategy

0.9(Na0.5Bi0.5)(Fe0.02Ti0.98)O3-0.1SrTiO3 (NBSFT) precursor solutions with varying ratios (1:0, 2:1, 1:1 and 1:2) of C2H6O2 to C3H8O2 are modulated and phase-pure thin films (marked as NBSFT10, NBSFT21, NBSFT11 and NBSFT12) are deposited onto Pt(111)/Ti/SiO2/Si substrate. The hydrolysis of titanate is enhanced with the addition of C3H8O2, which is beneficial for the formation of three-dimension network structure in the sol-gel. The wettability of sol-gel onto the substrate is improved and both the critical radius of new phase and phase transition energy barrier from liquid to solid phases are decreased. All these contribute to fine grain size, even and dense microstructure, and smooth surface for thin films. Besides, the low phase transition energy barrier causes the ion migration with high-efficiency and the increased degree of ion disorder, which is highly relevant to the relaxation behavior of the thin films. Note that the NBSFT11 thin film possesses higher recoverable energy storage density (Wrec) and efficiency (η) of 41.0 J/cm3 and 71.6%, respectively under 3207.6 kV/cm. Excellent thermal stability within the temperature range of 20–220 °C, frequency stability in the range of 1–20 kHz, and fatigue resistance up to 1 × 108 cycles are obtained. These findings provide a novel approach and valuable guidance for designing ferroelectric thin films for energy storage applications.

An embedded interfacial network stabilizes inorganic CsPbI3 perovskite thin films

The black perovskite phase of CsPbI3 is promising for optoelectronic applications; however, it is unstable under ambient conditions, transforming within minutes into an optically inactive yellow phase, a fact that has so far prevented its widespread adoption. Here we use coarse photolithography to embed a PbI2-based interfacial microstructure into otherwise-unstable CsPbI3 perovskite thin films and devices. Films fitted with a tessellating microgrid are rendered resistant to moisture-triggered decay and exhibit enhanced long-term stability of the black phase (beyond 2.5 years in a dry environment), due to increasing the phase transition energy barrier and limiting the spread of potential yellow phase formation to structurally isolated domains of the grid. This stabilizing effect is readily achieved at the device level, where unencapsulated CsPbI3 perovskite photodetectors display ambient-stable operation. These findings provide insights into the nature of phase destabilization in emerging CsPbI3 perovskite devices and demonstrate an effective stabilization procedure which is entirely orthogonal to existing approaches.

α-BaF2 Nanoparticle Substrate-Enabled γ-CsPbI3 Heteroepitaxial Growth for Efficient and Bright Deep-Red Light-Emitting Diodes.

All-inorganic CsPbI3 perovskite is attractive for deep-red light-emitting diodes (LEDs) because of its excellent carrier mobility, high color purity, and solution processability. However, the high phase transition energy barrier of optically active CsPbI3 black phase hinders the fabrication of efficient and bright LEDs. Here, we report a novel α-BaF2 nanoparticle substrate-promoted solution-processable heteroepitaxial growth to overcome this hindrance and obtain high-quality optically active γ-CsPbI3 thin films, achieving efficient and bright deep-red LEDs. We unravel that the highly exposed planes on the α-BaF2 nanoparticle-based heteroepitaxial growth substrate have a 99.5% lattice matching degree with the (110) planes of γ-CsPbI3. This ultrahigh lattice matching degree initiates solution-processed interfacial strain-free epitaxial growth of low-defect and highly oriented γ-CsPbI3 thin films on the substrate. The obtained γ-CsPbI3 thin films are uniform, smooth, and highly luminescent, based on which we fabricate efficient and bright deep-red LEDs with a high peak external quantum efficiency of 14.1% and a record luminance of 1325 cd m-2.

Harnessing Phase Transitions in Antiferroelectric ZrO2Using the Size Effect

AbstractThe unique nonlinear dielectric properties of antiferroelectric (AFE) oxides are promising for advancements in solid state supercapacitor, actuator, and memory technologies. AFE behavior in high‐k ZrO2is of particular technological interest, but the origin of antiferroelectricity in ZrO2remains questionable. The theory of reversible electric field‐induced phase transitions between the nonpolar P42/nmc tetragonal phase and the polarPca21orthorhombic phase is experimentally tested with local structural and electromechanical characterization of AFE ZrO2thin films. Piezoresponse force microscopy identifies signature evidence of a field‐induced phase transition. A significant size effect in AFE ZrO2is experimentally observed as film thickness is scaled down from 14.7 to 4.3 nm. The size effect is explained by modifications to the phase transition energy barrier heights ranging from 0.6 to 7.6 meV f.u−1depending on crystallite size and in‐plane compressive strain with decreasing ZrO2film thickness. Using the size effect, it is possible to double the energy storage density in ZrO2from 20 J cm−3to greater than 40 J cm−3, thus highlighting a feasible route for superior performance in AFE fluorite supercapacitors.

High-Curie Temperature Multilayered Hybrid Double Perovskite Photoferroelectrics Induced by Aromatic Cation Alloying

Due to the breakthrough development of layered hybrid perovskites, the multilayered hybrid double perovskites have emerged as outstanding semiconducting materials owing to their environmental friendliness and superior stability. Despite recent booming advances, the realization of above-room temperature ferroelectricity in this fascinating family remains a huge challenge. Herein, when the molecular design strategy of aromatic cation alloying is applied, an above-room temperature "green" bilayered hybrid double perovskite photoferroelectric, (C6H5CH2NH3)2CsAgBiBr7 (BCAB), is successfully developed with a notable saturation polarization of 10.5 μC·cm-2 and high-Curie temperature (Tc ∼ 483 K). Strikingly, such a Tc achieves a new record in multilayered hybrid perovskite ferroelectrics, which extends the ferroelectric working temperature to a high level. Further computational investigation reveals that the high-Tc originated from the high phase-transition energy barrier switched by the rotation of the aromatic cation in the confined environment of the inorganic layers. In addition, benefiting from the attractive polarization and remarkable photoelectric properties, a bulk photovoltaic effect (BPVE) with a prominent zero-bias photocurrent (2.5 μA·cm-2) is achieved. As far as we know, such a high-Tc multilayered hybrid double perovskite ferroelectric is unprecedented, which sheds light on the rational design of an environmental photoferroelectric for high performance photoelectric devices.

Flexible PLZT antiferroelectric film capacitor for energy storage in wide temperature range

Flexible energy-storage capacitor has attracted great attention due to deformable and lightweight, which could be applied to wearable electronics, bendable smartphones. It is urgent to manufacture a capacitor combining excellent electrical properties with mechanical bending capacity. Here, flexible Pb0.97La0.02Zr0.95Ti0.05O3 (PLZT 2/95/5) films are prepared by controlled spalling technology (CST) and exhibit outstanding electrical properties with polarization about 86.3 µC/cm2 at various tensile or compressive bending radii, which indicates excellent mechanical stability of films. It is worth mentioning that recoverable energy-storage density (Wre) of films has increased by 21% at 500 kV/cm compared to the original substrate, which is caused by change in stress. Meanwhile, flexible films were measured under wide temperature range from −70–200 °C with Wre fluctuating from 9.2 J/cm3 to 17.1 J/cm3, which is related to free energy barrier of phase transition. These studies provide reference for preparation of flexible capacitors which have great potential applications for future flexible micro-devices.

Efficient and Stable All‐Inorganic Perovskite Solar Cells

The large‐scale commercial application of organic–inorganic hybrid perovskite solar cells (PSCs) based on organic hole transport material (HTM) is still hindered by poor long‐term operational stability, although a certified record power conversion efficiency (PCE) as high as 25.2% can be achieved. In the recent several years, all‐inorganic PSCs have received tremendous attention due to their superb thermal and moisture stability and considerable progresses have been witnessed. Herein, the recent advancements of all‐inorganic PSCs are reviewed comprehensively. First, the recent progresses of the strategies for stabilizing the black phase of inorganic perovskites through either increasing tolerance factor or enhancing the energy barrier of phase transition from black to yellow phase are summarized and discussed. Second, the deposition and growth techniques of inorganic perovskite films are discussed. Third, the effective inorganic HTMs in normal all‐inorganic PSCs are described. Fourth, HTM‐free normal all‐inorganic PSCs are discussed. Afterward, the effective inorganic electron transport materials in inverted all‐inorganic PSCs are discussed. Subsequently, the advancements of interface engineering for increasing the PCE and stability of all‐inorganic PSCs are reviewed. Finally, a brief summary and outlook are presented to push up the PCE of all‐inorganic PSCs to over 20% in the near future.

Efficient and Stable CsPbI3 Solar Cells via Regulating Lattice Distortion with Surface Organic Terminal Groups.

All-inorganic cesium lead iodide perovskites (CsPbI3 ) are promising wide-bandgap materials for use in the perovskite/silicon tandem solar cells, but they easily undergo a phase transition from a cubic black phase to an orthorhombic yellow phase under ambient conditions. It is shown that this phase transition is triggered by moisture that causes distortion of the corner-sharing octahedral framework ([PbI6 ]4- ). Here, a novel strategy to suppress the octahedral tilting of [PbI6 ]4- units in cubic CsPbI3 by systematically controlling the steric hindrance of surface organic terminal groups is provided. This steric hindrance effectively prevents the lattice distortion and thus increases the energy barrier for phase transition. This mechanism is verified by X-ray diffraction measurements and density functional theory calculations. Meanwhile, the formation of an organic capping layer can also passivate the surface electronic trap states of perovskite absorber. These modifications contribute to a stable power conversion efficiency (PCE) of 13.2% for the inverted planar perovskite solar cells (PSCs), which is the highest efficiency achieved by the inverted-structure inorganic PSCs. More importantly, the optimized devices retained 85% of their initial PCE after aging under ambient conditions for 30 days.