Grain Boundary and Interface Passivation with Core–Shell Au@CdS Nanospheres for High‐Efficiency Perovskite Solar Cells

The plasmonic characteristic of core–shell nanomaterials can effectively improve exciton‐generation/dissociation and carrier‐transfer/collection. In this work, a new strategy based on core–shell Au@CdS nanospheres is introduced to passivate perovskite grain boundaries (GBs) and the perovskite/hole transport layer interface via an antisolvent process. These core–shell Au@CdS nanoparticles can trigger heterogeneous nucleation of the perovskite precursor for high‐quality perovskite films through the formation of the intermediate Au@CdS–PbI₂ adduct, which can lower the valence band maximum of the 2,2,7,7‐tetrakis(N,N‐di‐p‐methoxyphenyl‐amine)9,9‐spirobifluorene (Spiro‐OMeTAD) for a more favorable energy alignment with the perovskite material. With the help of the localized surface plasmon resonance effect of Au@CdS, holes can easily overcome the barrier at the perovskite/Spiro‐OMeTAD interface (or GBs) through the bridge of the intermediate Au@CdS–PbI₂, avoiding the carrier accumulation, and suppress the carrier trap recombination at the Spiro‐OMeTAD/perovskite interface. Consequently, the Au@CdS‐based perovskite solar cell device achieves a high efficiency of over 21%, with excellent stability of ≈90% retention of initial power conversion efficiencies after 45 days storage in dry air.     

Sulfate‐Assisted Interfacial Engineering for High Yield and Efficiency of Triple Cation Perovskite Solar Cells with Alkali‐Doped TiO2 Electron‐Transporting Layers

Facile electron injection and extraction are two key attributes desired in electron transporting layers to enhance the efficiency of planar perovskite solar cells. Herein it is demonstrated that the incorporation of alkali metal dopants in mesoporous TiO₂ can effectively modulate electronic conductivity and improve the charge extraction process by counterbalancing oxygen vacancies acting as nonradiative recombination centers. Moreover, sulfate bridges (SO₄^2?) grafted on the surface of K‐doped mesoporous titania provide a seamless integration of absorber and electron‐transporting layers that accelerate overall transport kinetics. Potassium doping markedly influences the nucleation of the perovskite layer to produce highly dense films with facetted crystallites. Solar cells made from K:TiO₂ electrodes exhibit power conversion efficiencies up to 21.1% with small hysteresis despite all solution coating processes conducted under ambient air conditions (controlled humidity: 25–35%). The higher device efficiencies are attributed to intrinsically tuned electronic conductivity and chemical modification of grain boundaries enabling uniform coverage of perovskite films with large grain size.     

Origin of Hysteresis in CH3NH3PbI3 Perovskite Thin Films

Organic–inorganic hybrid perovskite solar cells are attracting the attention of researchers owing to the high level of performance they exhibit in photovoltaic device applications. However, the attainment of an even higher level of performance is hindered by their anomalous current–voltage (I–V) hysteresis behavior. Even though experimental and theoretical studies have suggested that the perovskite materials may have a ferroelectric nature, it is still far from being fully understood. In this study, the origin of the hysteresis behavior in CH₃NH₃PbI₃ perovskite thin films is investigated. The behavior of ferroelectricity using piezoresponse force microscopy is first examined. Then, by comparing the scan‐rate‐dependent nano/macroscopic I–V curves, it is found that ion migration assisted by the grain boundaries is a dominant origin of I–V hysteresis from a macroscopic viewpoint. Consequently, the observations suggest that, even though ferroelectricity exists in the CH₃NH₃PbI₃ perovskite materials, ion migration primarily contributes to the macroscopic I–V hysteresis. The presented results can provide fundamental guidelines to the resolution of hysteresis issues in organic–inorganic hybrid perovskite materials.     

Nucleation and Crystallization Control via Polyurethane to Enhance the Bendability of Perovskite Solar Cells with Excellent Device Performance

Solar cells based on mixed organic–inorganic halide perovskites are promising photovoltaic technologies with low‐cost and fantastic power conversion efficiency (PCE). Enhancing the nucleation and regulating the crystallization rate of perovskite films and improving the bendability of brittle hybrid grains are crucial to improving the photovoltaic performance of flexible perovskite solar cells (PVSCs). Here, a simple approach is first introduced for fabricating perovskite films with full coverage and larger crystalline size by incorporating the elastomer polyurethane (PU) into the perovskite precursor solution to both retard the crystallization rate and improve the bendability. Shiny, smooth perovskite films are obtained with compact, micrometer‐sized crystalline grains that exhibit excellent photoelectric performances. The PVSCs fabricated by incorporating PU into the perovskite precursor offer an impressive PCE of 18.7% with almost no photocurrent hysteresis and excellent stability in ambient air. More importantly, the elastomer PU additive crosslinks the grain boundaries between neighboring perovskite crystals to form a PU network that effectively improves the bendability of the perovskite films.     

Self‐Additive Low‐Dimensional Ruddlesden–Popper Perovskite by the Incorporation of Glycine Hydrochloride for High‐Performance and Stable Solar Cells

The recent rise of low‐dimensional Ruddlesden–Popper (RP) perovskites is notable for superior humidity stability, however they suffer from low power conversion efficiency (PCE). Suitable organic spacer cations with special properties display a critical effect on the performance and stability of perovskite solar cells (PSCs). Herein, a new strategy of designing self‐additive low‐dimensional RP perovskites is first proposed by employing a glycine salt (Gly⁺) with outstanding additive effect to improve the photovoltaic performance. Due to the strong interaction between C?O and Pb²⁺, the Gly⁺ can become a nucleation center and be beneficial to uniform and fast growth of the Gly‐based RP perovskites with larger grain sizes, leading to reduced grain boundary and increased carrier transport. As a result, the Gly‐based self‐additive low‐dimensional RP perovskites exhibit remarkable photoelectric properties, yielding the highest PCE of 18.06% for Gly (n = 8) devices and 15.61% for Gly (n = 4) devices with negligible hysteresis. Furthermore, the Gly‐based devices without encapsulation show excellent long‐term stability against humidity, heat, and UV light in comparison to BA‐based low‐dimensional PSCs. This approach provides a feasible design strategy of new‐type low‐dimensional RP perovskites to obtain highly efficient and stable devices for next‐generation photovoltaic applications.     

Octadecylamine‐Functionalized Single‐Walled Carbon Nanotubes for Facilitating the Formation of a Monolithic Perovskite Layer and Stable Solar Cells

Organic–inorganic lead halide perovskites have shown great future for application in solar cells owing to their exceptional optical and electronic properties. To achieve high‐performance perovskite solar cells, a perovskite light absorbing layer with large grains is desirable in order to minimize grain boundaries and recombination during the operation of the device. Herein, a simple yet efficient approach is developed to synthesize perovskite films consisting of monolithic‐like grains with micrometer size through in situ deposition of octadecylamine functionalized single‐walled carbon nanotubes (ODA‐SWCNTs) onto the surface of the perovskite layer. The ODA‐SWCNTs form a capping layer that controls the evaporation rate of organic solvents in the perovskite film during the postthermal treatment. This favorable morphology in turn dramatically enhances the short‐circuit current density of the perovskite solar cells and almost completely eliminates the hysteresis. A maximum power conversion efficiency of 16.1% is achieved with an ODA‐SWCNT incorporated planar solar cell using (FA_0.83MA_0.17)_0.95Cs_0.05Pb(I_0.83Br_0.17)₃ as light absorber. Furthermore, the perovskite solar cells with ODA‐SWCNT demonstrate extraordinary stability with performance retention of 80% after 45 d stability testing under high humidity (60–90%) environment. This work opens up a new avenue for morphology manipulation of perovskite films and enhances the device stability using carbon material.     

Native Defect‐Induced Hysteresis Behavior in Organolead Iodide Perovskite Solar Cells

Despite the high power conversion efficiency and ease of fabrication, planar‐junction organolead halide perovskite solar cells often exhibit anomalous hysteretic current–voltage (I–V) characteristics. In this work, the origin of the I–V hysteresis is studied by fine‐tuning the precursor ratio of methylammonium lead iodide and thus varying the native defects in the material. It is shown that the perovskites synthesized from “PbI₂ excess,” “methylammonium iodide excess,” and “stoichiometric” precursors exhibit identical film morphology but different I–V hysteresis in a planar solar cell configuration. Through a comparative analysis on the temperature‐dependent continuous and stepwise‐stabilized I–V responses of the three devices, a model involving transport and trapping of the ionic native defects is proposed. The active energy of the transport process is estimated to be between 0.10 and 0.18 eV, most likely associated with the vacancy‐mediated iodide ion migration. The lower activation energy of the “PbI₂ excess” and “Stoichiometric” samples indicates that the presence of methylammonium vacancies may provide a favorable pathway for the migration of iodide ions due to reduced steric hindrance. Furthermore, the slow trapping and release processes of iodide ions at the TiO₂/perovskite interface are accounted for the long time scale current decay (or raise) following a voltage change.     

2D Perovskite Seeding Layer for Efficient Air‐Processable and Stable Planar Perovskite Solar Cells

Despite the record power conversion efficiencies, inverted perovskite solar cells (PSCs) are still looking to overcome the challenge of moisture instability. This is mitigated by introducing 2D perovskite at the base of a 3D perovskite via coating of ethylenediamine bications on top of the hole transport layer of p–i–n planar configured devices. The cations induce thin 2D perovskite growth beneath the 3D perovskite to create a 2D/3D hybrid active layer. This 2D layer in turn acts as a template for the growth of relatively large grains compared to that of pure 3D perovskite films. This stems from the merging of grain boundaries. The hydrophobicity of the 2D/3D perovskite film consequently improves, as evidenced by a large contact angle of 93.1°, compared to 68.9° for the 3D perovskite film. Because there are fewer defects sourced from grain boundaries, the air‐processed 2D/3D perovskite devices yield a high power conversion efficiency of 15.02%, compared to 13.10% from 3D perovskite devices. When stored in moderately humid environment of 55% relative humidity, the 2D/3D devices exhibit longer stabilities, with 75% of their power conversion efficiencies maintained after 150 h, compared to a total loss in efficiency for 3D device in the same time frame.     

Electron‐Transport‐Layer‐Assisted Crystallization of Perovskite Films for High‐Efficiency Planar Heterojunction Solar Cells

Crystal engineering of CH₃NH₃PbI₃ perovskite materials through template‐directed nucleation and growth on PbI₂ nuclei dispersed in a polar fullerene (C₆₀ pyrrolidine tris‐acid, CPTA) electron transport layer (ETL) (CPTA:PbI₂) is proposed as a route for controlling crystallization kinetics and grain sizes. Chemical analysis of the CPTA:PbI₂ template confirms that CPTA carboxylic acid groups can form a monodentate or bidentate chelate with Pb(II), resulting in a lower nucleation barrier that promotes rapid formation of the tetragonal perovskite phase. Moreover, it is demonstrated that a uniform CH₃NH₃PbI₃ film with highly crystalline and large domain sizes can be realized by increasing the spacing between nuclei to retard perovskite crystal growth via careful control of the preferred nucleation site distribution in the CPTA:PbI₂ layer. The improved perovskite morphology possesses a long photoluminescence lifetime and efficient photocarrier transport/separation properties to eliminate the hysteresis effect. The corresponding planar heterojunction photovoltaic yields a high power conversion efficiency (PCE) of 20.20%, with a high fill factor (FF) of 81.13%. The average PCE and FF values for 30 devices are 19.03% ± 0.57% and 78.67% ± 2.13%, respectively. The results indicate that this ETL template‐assisted crystallization strategy can be applied to other organometal halide perovskite‐based systems.     

Cover Picture: Bilayer Organic–Inorganic Gate Dielectrics for High‐Performance,Low‐Voltage,Single‐Walled Carbon Nanotube Thin‐Film Transistors,Complementary Logic Gates,and p–n Diodes on Plastic Substrates (Adv. Funct. Mater. 18/2006)

Low‐voltage, hysteresis‐free, flexible thin‐film‐type electronic systems based on networks of single‐walled carbon nanotubes and bilayer organic–inorganic nanodielectrics are detailed in work by Rogers and co‐workers reported on p. 2355. The cover image shows a schematic array of such thin‐film transistors (TFTs) on a plastic substrate. The structure of the bilayer nanodielectric, which consists of a film of HfO₂ formed by atomic layer deposition and an ultrathin layer of epoxy formed by spin‐casting, is also illustrated schematically. High‐capacitance bilayer dielectrics based on atomic‐layer‐deposited HfO₂ and spin‐cast epoxy are used with networks of single‐walled carbon nanotubes (SWNTs) to enable low‐voltage, hysteresis‐free, and high‐performance thin‐film transistors (TFTs) on silicon and flexible plastic substrates. These HfO₂–epoxy dielectrics exhibit excellent properties including mechanical flexibility, large capacitance (up to ca. 330 nF cm^–2), and low leakage current (ca. 10^–8 A cm^–2); their low‐temperature (ca. 150 °C) deposition makes them compatible with a range of plastic substrates. Analysis and measurements of these dielectrics as gate insulators in SWNT TFTs illustrate several attractive characteristics for this application. Their compatibility with polymers used for charge‐transfer doping of SWNTs is also demonstrated through the fabrication of n‐channel SWNT TFTs, low‐voltage p–n diodes, and complementary logic gates.     

Bilayer Organic–Inorganic Gate Dielectrics for High‐Performance,Low‐Voltage,Single‐Walled Carbon Nanotube Thin‐Film Transistors,Complementary Logic Gates,and p–n Diodes on Plastic Substrates

High‐capacitance bilayer dielectrics based on atomic‐layer‐deposited HfO₂ and spin‐cast epoxy are used with networks of single‐walled carbon nanotubes (SWNTs) to enable low‐voltage, hysteresis‐free, and high‐performance thin‐film transistors (TFTs) on silicon and flexible plastic substrates. These HfO₂–epoxy dielectrics exhibit excellent properties including mechanical flexibility, large capacitance (up to ca. 330 nF cm^–2), and low leakage current (ca. 10^–8 A cm^–2); their low‐temperature (ca. 150 °C) deposition makes them compatible with a range of plastic substrates. Analysis and measurements of these dielectrics as gate insulators in SWNT TFTs illustrate several attractive characteristics for this application. Their compatibility with polymers used for charge‐transfer doping of SWNTs is also demonstrated through the fabrication of n‐channel SWNT TFTs, low‐voltage p–n diodes, and complementary logic gates.     

Pseudohalide‐Induced Recrystallization Engineering for CH3NH3PbI3 Film and Its Application in Highly Efficient Inverted Planar Heterojunction Perovskite Solar Cells

High crystallinity and compactness of the active layer is essential for metal‐halide perovskite solar cells. Here, a simple pseudohalide‐induced film retreatment technology is developed as the passivation for preformed perovskite film. It is found that the retreatment process yields a controllable decomposition‐to‐recrystallization evolution of the perovskite film. Corresponding, it remarkably enlarges the grain size of the film in all directions, as well as improving the crystallinity and hindering the trap density. Meanwhile, owing to an intermediate catalytic effect of the pseudohalide compound (NH₄SCN), no crystal orientation changing and no impurity introduction in the modified film. By integrating the modified perovskite film into the planar heterojunction solar cells, a champion power conversion efficiency of 19.44% with a stabilized output efficiency of 19.02% under 1 sun illumination is obtained, exhibiting a negligible current density–voltage hysteresis. Moreover, such a facile and low‐temperature film retreatment approach guarantees the application in flexible devices, showing a best power conversion efficiency of 17.04%.     

Dual Interfacial Modification Engineering with 2D MXene Quantum Dots and Copper Sulphide Nanocrystals Enabled High‐Performance Perovskite Solar Cells

The performance of perovskite solar cells (PSCs) strongly depends on the electron transport layer (ETL), perovskite absorber, hole transport layer (HTL), and their interfaces. Herein, the first approach to utilize ultrathin 2D titanium‐carbide MXenes (Ti₃C₂T_x quantum dots, TQD) by engineering the perovskite/TiO₂ ETL interface and perovskite absorber and introducing Cu_1.8S nanocrystals to perfect the Spiro‐OMeTAD HTL is represented. A significant hysteresis‐free power conversion efficiency improvement from 18.31% to 21.64% of PSCs is achieved after modifications with the enhanced short‐circuit current density, open‐circuit voltages, and fill factor. Various advanced characterizations, including femtosecond transient absorption spectroscopy, electrochemical impedance spectroscopy, and ultraviolet photoelectron spectroscopy, elucidate that the TQD/Cu_1.8S significantly contribute to the improved crystalline quality of the perovskite film with its large grain size and improved electron/holes extraction efficiencies at perovskite/ETL and perovskite/HTL interfaces. Furthermore, the long‐time ambient and light stability of PSCs are largely boosted through the TQD and/or Cu_1.8S nanocrystals doping, originating from the better crystallization of perovskite, suppressing the film aggregation and crystallization of HTL, and inhibiting the ultraviolet‐induced photocatalysis of the ETL. The findings highlight the TQD and Cu_1.8S can act as a superfast electrons and holes tunnel for the optoelectronic devices.     

Fullerene Polymer Complex Inducing Dipole Electric Field for Stable Perovskite Solar Cells

Lead halide perovskite solar cells (PSCs) have demonstrated great potential for realizing low‐cost and easily fabricated photovoltaics. At this juncture, power conversion efficiency and long‐term stability are two important factors limiting their transition. PSCs exhibit rapid environmental degradation since the perovskite layer is very sensitive to factors such as humidity, temperature, and ultraviolet light. Here, a novel successful approach is demonstrated that simultaneously improves the efficiency and stability of PSCs. This approach relies on incorporation of a dual‐functional polymethyl methacrylate (PMMA)–fullerene complex into the perovskite layer. The fullerene within perovskite layer forms a localized dipole‐like electric field that favors electron–hole separation, resulting in significant improvement in current density and fill factor with conversion efficiency reaching 18.4%. The molecular‐scale coating of hydrophobic PMMA on the perovskite grain boundary effectively blocks moisture penetration into the perovskite, thereby, significantly improving the stability against moisture, heat, and light. The PSCs with PMMA–fullerene complex showed no photovoltaic performance degradation for 250 d and exhibited 60 times higher stability compared to the state‐of‐the‐art devices under continuous 1 sun illumination in ambient air.     

Perovskite Photovoltaics for Dim‐Light Applications

The use of photovoltaic cells with an organometallic perovskite as the active layer for indoor dim‐light energy harvesting is evaluated. By designing the electron‐transporting materials and fabrication processes, the traps in the perovskite active layers and carrier dynamics can be controlled, and efficient devices are demonstrated. The best‐performing small‐area perovskite photovoltaics exhibit a promising high power conversion efficiency up to ≈27.4%, no hysteresis behavior, and an exceptionally low maximum power point voltage variation of ≈0.1 V under fluorescent lamp illumination at 100–1000 lux. The 5.44 cm² large‐area device also shows a high efficiency of 20.4% and a promising long‐term stability. Compared with the most efficient inorganic and organic solar cells nowadays, the competitive efficiency, low fabrication cost, and low raw material costs make perovskite photovoltaics ideal for indoor light harvesting and as Internet of Things power provider.     

Polar Cation Ordering: A Route to Introducing >10% Bond Strain Into Layered Oxide Films

The 3d transition metal (M) perovskite oxides exhibit a remarkable array of properties, including novel forms of superconductivity, magnetism and multiferroicity. Strain can have a profound effect on many of these properties. This is due to the localized nature of the M 3d orbitals, where even small changes in the M–O bond lengths and M–O–M bond angles produced by strain can be used to tune the 3d– O 2p hybridization, creating large changes in electronic structure. A new route is presented to strain the M–O bonds in epitaxial two‐dimensional perovskite films by tailoring local electrostatic dipolar interactions within every formula unit via atomic layer‐by‐layer synthesis. The response of the O anions to the resulting dipole electric fields distorts the M–O bonds by more than 10%, without changing substrate strain or chemical composition. This distortion is largest for the apical oxygen atoms (O_ap), and alters the transition metal valence state via self‐doping without chemical substitution.     

Copper(I) Iodide as Hole‐Conductor in Planar Perovskite Solar Cells: Probing the Origin of J–V Hysteresis

Organic–inorganic lead halide perovskite solar cells are promising alternatives to silicon‐based cells due to their low material costs and high photovoltaic performance. In this work, thin continuous perovskite films are combined with copper(I) iodide (CuI) as inorganic hole‐conducting material to form a planar device architecture. A maximum conversion efficiency of 7.5% with an average efficiency of 5.8 ± 0.8% is achieved which, to our knowledge, is the highest reported efficiency for CuI‐based devices with a planar structure. In contrast to related planar 2,2′,7,7′‐tetrakis‐(N,N ‐di‐4‐methoxyphenylamino)‐9,9′‐spirobifluorene (spiro‐OMeTAD)‐based devices, the CuI‐based devices do not show a pronounced hysteresis when tested by scanning the potential in a forward and backward direction. The strong quenching of photoluminescence (PL) signal and comparatively fast decay of open‐circuit voltage demonstrates a more rapid removal of positive charge carriers from the perovskite layer when in contact with CuI compared to spiro‐OMeTAD. A slow response on a timescale of 10–100 s is observed for the spiro‐OMeTAD‐based devices. In comparison, the CuI‐based device displays a significantly faster response as determined through electrochemical impedance spectroscopy (EIS) and open‐circuit voltage decays (OCVDs). The characteristically slow kinetics measured through EIS and OCVD are linked directly to the current–voltage hysteresis.     

Passivated Perovskite Crystallization via g‐C3N4 for High‐Performance Solar Cells

Organometallic halide perovskite films with good surface morphology and large grain size are desirable for obtaining high‐performance photovoltaic devices. However, defects and related trap sites are generated inevitably at grain boundaries and on surfaces of solution‐processed polycrystalline perovskite films. Seeking facial and efficient methods to passivate the perovskite film for minimizing defect density is necessary for further improving the photovoltaic performance. Here, a convenient strategy is developed to improve perovskite crystallization by incorporating a 2D polymeric material of graphitic carbon nitride (g‐C₃N₄) into the perovskite layer. The addition of g‐C₃N₄ results in improved crystalline quality of perovskite film with large grain size by retarding the crystallization rate, and reduced intrinsic defect density by passivating charge recombination centers around the grain boundaries. In addition, g‐C₃N₄ doping increases the film conductivity of perovskite layer, which is beneficial for charge transport in perovskite light‐absorption layer. Consequently, a champion device with a maximum power conversion efficiency of 19.49% is approached owing to a remarkable improvement in fill factor from 0.65 to 0.74. This finding demonstrates a simple method to passivate the perovskite film by controlling the crystallization and reducing the defect density.     

Boosting the Efficiency of SnO2‐Triple Cation Perovskite System Beyond 20% Using Nonhalogenated Antisolvent

Solution‐processed triple‐cation perovskite solar cells (PSCs) rely on complex compositional engineering or delicate interfacial passivation to balance the trade‐off between cell efficiency and long‐term stability. Herein, the facile fabrication of highly efficient, stable, and hysteresis‐free tin oxide (SnO₂)‐based PSCs is demonstrated with a champion cell efficiency of 20.06% using a green, halogen‐free antisolvent. The antisolvent, composed of ethyl acetate (EA) solvent and hexane (Hex) in different proportions, works exquisitely in regulating perovskite crystal growth and passivating grain boundaries, leading to the formation of a crack‐free perovskite film with enlarged grain size. The high quality perovskite film inhibits carrier recombination and substantially improves the cell efficiency, without requiring an additional enhancer/passivation layer. Furthermore, these PSCs also demonstrate remarkable long‐term stability, whereby unencapsulated cells exhibit a power conversion efficiency (PCE) retention of ≈71% after >1500 hours of storage under ambient condition. For encapsulated cells, an astounding PCE retention of >98% is recorded after >3000 hours of storage in air. Overall, this work realizes the fabrication of SnO₂‐based PSCs with a performance greater or comparable to the state‐of‐the‐art PSCs produced with halogenated antisolvents. Evidently, EA–Hex antisolvent can be an extraordinary halogen‐free alternative in maximizing the performance of PSCs.     

From Black Phosphorus to Phosphorene: Basic Solvent Exfoliation,Evolution of Raman Scattering,and Applications to Ultrafast Photonics

Although phosphorene has attracted much attention in electronics and optoelectronics as a new type of two‐dimensional material, in‐depth investigations and applications have been limited by the current synthesis techniques. Herein, a basic N‐methyl‐2‐pyrrolidone (NMP) liquid exfoliation method is described to produce phosphorene with excellent water stability, controllable size and layer number, as well as in high yield. Phosphorene samples composed of one to four layers exhibit layer‐dependent Raman scattering characteristics thus providing a fast and efficient means for the in situ determination of the thickness (layer number) of phosphorene. The linear and nonlinear ultrafast absorption behavior of the as‐exfoliated phosphorene is investigated systematically by UV–vis–NIR absorption and Z‐scan measurements. By taking advantage of their unique nonlinear absorption, ultrashort pulse generation applicable to optical saturable absorbers is demonstrated. In addition to a unique fabrication technique, our work also reveals the large potential of phosphorene in ultrafast photonics.