Field-Induced Antiferroelectric-Ferroelectric Transformation in Organometallic Perovskite Displaying Giant Negative Electrocaloric Effect.

Antiferroelectric materials with an electrocaloric effect (ECE) have been developed as promising candidates for solid-state refrigeration. Despite the great advances in positive ECE, reports on negative ECE remain quite scarce because of its elusive physical mechanism. Here, a giant negative ECE (maximum ΔS ∼ -33.3 J kg-1 K-1 with ΔT ∼ -11.7 K) is demonstrated near room temperature in organometallic perovskite, iBA2EA2Pb3I10 (1, where iBA = isobutylammonium and EA = ethylammonium), which is comparable to the greatest ECE effects reported so far. Moreover, the ECE efficiency ΔS/ΔE (∼1.85 J cm kg-1 K-1 kV-1) and ΔT/ΔE (∼0.65 K cm kV-1) are almost 2 orders of magnitude higher than those of classical inorganic ceramic ferroelectrics and organic polymers, such as BaTiO3, SrBi2Ta2O9, Hf1/2Zr1/2O2, and P(VDF-TrFE). As far as we know, this is the first report on negative ECE in organometallic hybrid perovskite ferroelectric. Our experimental measurement combined with the first-principles calculations reveals that electric field-induced antipolar to polar structural transformation results in a large change in dipolar ordering (from 6.5 to 45 µC/cm2 under the ΔE of 18 kV/cm) that is closely related to the entropy change, which plays a key role in generating such giant negative ECE. This discovery of field-induced negative ECE is unprecedented in organometallic perovskite, which sheds light on the exploration of next-generation refrigeration devices with high cooling efficiency.

Mixing cage cations in 2D metal-halide ferroelectrics enhances the ferro-pyro-phototronic effect for self-driven photopyroelectric detection.

The ferro-pyro-phototronic (FPP) effect, coupling photoexcited pyroelectricity and photovoltaics, paves an effective way to modulate charge-carrier behavior of optoelectronic devices. However, reports of promising FPP-active systems remain quite scarce due to a lack of knowledge on the coupling mechanism. Here, we have successfully enhanced the FPP effect in a series of ferroelectrics, BA2Cs1-xMAxPb2Br7 (BA = butylammonium, MA = methylammonium, 0 ≤ x ≤ 0.34), rationally assembled by mixing cage cations into 2D metal-halide perovskites. Strikingly, chemical alloying of Cs+/MA+ cations leads to the reduction of exciton binding energy, as verified by the x = 0.34 component; this facilitates exciton dissociation into free charge-carriers and boosts photo-activities. The crystal detector thus displays enhanced FPP current at zero bias, almost more than 10 times higher than that of the x = 0 prototype. As an innovative study on the FPP effect, this work affords new insight into the fundamental principle of ferroelectrics and creates a new strategy for self-driven photodetection.

Building Block-Inspired Hybrid Perovskite Derivatives for Ferroelectric Channel Layers with Gate-Tunable Memory Behavior.

Ferroelectric photovoltaics driven by spontaneous polarization (Ps ) holds a promise for creating the next-generation optoelectronics, spintronics and non-volatile memories. However, photoactive ferroelectrics are quite scarce in single homogeneous phase, owing to the severe Ps fatigue caused by leakage current of photoexcited carriers. Here, through combining inorganic and organic components as building blocks, we constructed a series of ferroelectric semiconductors of 2D hybrid perovskites, (HA)2 (MA)n-1 Pbn Br3n+1 (n=1-5; HA=hexylamine and MA=methylamine). It is intriguing that their Curie temperatures are greatly enhanced by reducing the thickness of inorganic frameworks from MAPbBr3 (n=∞, Tc =239 K) to n=2 (Tc =310 K, ΔT=71 K). Especially, on account of the coupling of room-temperature ferroelectricity (Ps ≈1.5 µC/cm2 ) and photoconductivity, n=3 crystal wafer was integrated as channel field effect transistor that shows excellent a large short-circuit photocurrent ≈19.74 µA/cm2 . Such giant photocurrents can be modulated through manipulating gate voltage in a wide range (±60 V), exhibiting gate-tunable memory behaviors of three current states ("-1/0/1" states). We believe that this work sheds light on further exploration of ferroelectric materials toward new non-volatile memory devices.

A molecular pyroelectric enabling broadband photo-pyroelectric effect towards self-driven wide spectral photodetection.

Broadband spectral photoresponse has shown bright prospects for various optoelectronic devices, while fulfilling high photoactivity beyond the material bandgap is a great challenge. Here, we present a molecular pyroelectric, N-isopropylbenzylaminium trifluoroacetate (N-IBATFA), of which the broadband photo-pyroelectric effects allow for self-driven wide spectral photodetection. As a simple organic binary salt, N-IBATFA possesses a large polarization (~9.5 µC cm-2), high pyroelectric coefficient (~6.9 µC cm-2 K-1) and figures-of-merits (FV = 187.9 × 10-2 cm2 µC-1; FD = 881.5 × 10-5 Pa-0.5) comparable to the state-of-art pyroelectric materials. Particularly, such intriguing attributes endow broadband photo-pyroelectric effect, namely, transient currents covering ultraviolet (UV, 266 nm) to near-infrared (NIR, 1950 nm) spectral regime, which breaks the restriction of its optical absorption and thus allows wide UV-NIR spectral photodetection. Our finding highlights the potential of molecular system as high-performance candidates toward self-powered wide spectral photodetection.

Polarization-Dependent Large Photorefractive Effect In A Wide Bandgap 2D Metal Halide Ferroelectric.

Photorefractive effect of ferroelectrics refers to the light-induced change of refractive index, which is an optical controlling avenue in holographic storage and image processing. For most ferroelectrics, however, the small photorefractive effect (10-5 -10-4 ) hinders their practical application and it is urgent to exploit new photorefractive system. Here, for the first time, strong photorefractive effects are achieved in a 2D metal-halide ferroelectric, [CH3 (CH2 )3 NH3 ]2 (CH3 NH3 )Pb2 Cl7 (1), showing large spontaneous polarization (≈4.1 µC cm-2 ) and wide optical bandgap (≈3.20 eV). Notably, under light irradiation, 1 enables a large variation of refractive indices up to ≈ 1× 10-3 , being one order higher than the existing materials and comparable to the state-of-the-art inorganic ferroelectrics. This intriguing photorefractive behavior involves with the sharp variation of polarization caused by photo-pyroelectricity. As the first report of 2D metal-halide photorefractive ferroelectric, this work sheds light on optical controlling of physical properties in electric-ordered materials.

Giant Polarization Sensitivity via the Anomalous Photovoltaic Effect in a Two-Dimensional Perovskite Ferroelectric.

Polarization sensitivity, which shows great potential in photoelectric detection, is expected to be significantly improved by the ferroelectric anomalous photovoltaic (APV) effect. However, it is challenging to explore new APV-active ferroelectrics due to severe polarization fatigue induced by the leakage current of photoexcited carriers. For the first time, we report a strong APV effect in a 2D hybrid perovskite ferroelectric assembled by alloying mixed organic cations, (HA)2(EA)2Pb3Br10 (1, where HA+ is n-hexylammonium and EA+ is ethylammonium), which has a large spontaneous polarization ∼3.8 µC/cm2 and high a Curie temperature ∼378 K. Its ferroelectricity allows a strong APV effect with an above-bandgap photovoltage up to 7.4 V, which exceeds its bandgap (∼2.7 eV). Most strikingly, based on the dependence on polarized-light angle, this strong APV effect renders the highest level of polarization sensitivity with a giant current ratio of ∼25, far beyond other 2D single-phase materials. This study sheds light on the exploration of APV-active ferroelectrics and inspires their future high-performance optoelectronic device applications.

Improper High-Tc Perovskite Ferroelectric with Dielectric Bistability Enables Broadband Ultraviolet-to-Infrared Photopyroelectric Effects.

The photopyroelectric effect in ferroelectrics has shown great potential for application in infrared detection and imaging. One particular subclass is broadband with dielectric bistability, which allows for large pyroelectric figures-of-merit (FOMs). Herein, an improper high-Tc perovskite ferroelectric, (IA)2 (EA)2 Pb3 Cl10 (1, where IA is isoamylammonium and EA is ethylammonium) is presented, in which spontaneous polarization (Ps ) stems from the dynamic ordering of organic cations and the tilting of distorted PbCl6 octahedra. Notably, 1 displays unusual dielectric bistability with small variations in the temperature-dependent dielectric constants near Tc  = 392 K; this bistable attribute endows large pyroelectric FOMs with peak voltage efficiency (FV  = 1.7×10-2  cm2 µC-1 ) and sensitivity (FD  = 3.9×10-4 Pa-1/2 ). These FV and FD parameters, beyond those of their proper counterparts, make 1 a promising candidate for infrared photodetection. As expected, the broadband photopyroelectric effects observed in 1 covered the ultraviolet to infrared-II spectral region (266-1950 nm). Such Ps -directed photoactivities overcome the optical bandgap limitation and allow for wide-wave photodetection. As an innovative study on improper ferroelectricity, light is shaded here on the targeted engineering of new electrically ordered candidate materials for smart optoelectronic devices.

A high-temperature double perovskite molecule-based antiferroelectric with excellent anti-breakdown capacity for energy storage.

Halide double perovskites have recently emerged as an environmentally green candidate toward electronic and optoelectronic applications owing to their non-toxicity and versatile physical merits, whereas study on high-temperature antiferroelectric (AFE) with excellent anti-breakdown property remains a huge blank in this booming family. Herein, we present the first high-temperature AFE of the lead-free halide double perovskites, (CHMA)2CsAgBiBr7 (1, where CHMA+ is cyclohexylmethylammonium), by incorporating a flexible organic spacer cation. The typical double P-E hysteresis loops and J-E curves reveal its concrete high-temperature AFE behaviors, giving large polarizations of ~4.2 µC/cm2 and a high Curie temperature of 378 K. Such merits are on the highest level of molecular AFE materials. Particularly, the dynamic motional ordering of CHMA+ cation contributes to the formation of antipolar alignment and high electric breakdown field strength up to ~205 kV/cm with fatigue endurance over 104 cycles, almost outperforming the vast majority of molecule counterparts. This is the first demonstration of high-temperature AFE properties in the halide double perovskites, which will promote the exploration of new "green" candidates for anti-breakdown energy storage capacitor.

Centimeter-Sized Single Crystals of Dion-Jacobson Phase Lead-Free Double Perovskite for Efficient X-ray Detection.

2D Dion-Jacobson (DJ) phase hybrid perovskites have shown great promise in the photoelectronic field owing to their outstanding optoelectronic performance and superior structural rigidity. However, DJ phase lead-free double perovskites are still a virgin land with direct X-ray detection. Herein, we have designed and synthesized a new DJ phase lead-free layered double perovskite of (HIS)2 AgSbBr8 (1, HIS2+  = histammonium). Centimeter-sized (18 × 10 × 5 mm3 ) single crystals of 1 are successfully grown via the temperature cooling technique, exhibiting remarkable semiconductive characteristics such as a high resistivity (2.2 × 1011  Ω cm), a low trap state density (3.56 × 1010 cm-3 ), and a large mobility-lifetime product (1.72 × 10-3 cm2 V-1 ). Strikingly, its single-crystal-based X-ray detector shows a high sensitivity of 223 µC Gy-1 air cm-2 under 33.3 V mm-1 , a low detection limit (84.2 nGyair s-1 ) and superior anti-fatigue. As far as we know, we firstly demonstrates the potential of 2D DJ phase lead-free hybrid double perovskite in X-ray detection, showing excellent photoelectric response and operational stability. This work will pave a promising pathway to the innovative application of hybrid perovskites for eco-friendly and efficient X-ray detection.

Electrically Switchable Persistent Spin Texture in a Two-Dimensional Hybrid Perovskite Ferroelectric.

As a momentum-independent spin configuration, persistent spin texture (PST) could avoid spin relaxation and play an advantageous role in spin lifetime. Nevertheless, manipulation of PST is a challenge due to the limited materials and ambiguous structure-property relationships. Herein, we present electrically switchable PST in a new 2D perovskite ferroelectric, (PA)2 CsPb2 Br7 (where PA is n-pentylammonium), which has a high Curie temperature of 349 K, evident spontaneous polarization (3.2 µC cm-2 ) and a low coercive electric field of 5.3 kV cm-1 . The combination of symmetry-breaking in ferroelectrics and effective spin-orbit field facilitates intrinsic PST in the bulk and monolayer structure models. Strikingly, the directions of spin texture are reversible by switching the spontaneous electric polarization. This electric switching behavior relates to the tilting of PbBr6 octahedra and the reorientation of organic PA+ cations. Our studies on ferroelectric PST of 2D hybrid perovskites afford a platform for electrical spin texture manipulation.

Acquiring Bulk Anomalous Photovoltaic Effect in Single Crystals of a Lead-Free Double Perovskite with Aromatic and Alkali Mixed-Cations.

The bulk anomalous photovoltaic (BAPV) effect of acentric materials refers to a distinct concept from traditional semiconductor-based devices, of which the above-bandgap photovoltage hints at a promise for solar-energy conversion. However, it is still a challenge to exploit new BAPV-active systems due to the lacking of knowledge on the structural origin of this concept. BAPV effects in single crystals of a 2D lead-free double perovskite, (BBA)2 CsAgBiBr7 (1, BBA = 4-bromobenzylammonium), tailored by mixing aromatic and alkali cations in the confined architecture to form electric polarization are acquired here. Strikingly, BAPV effects manifested by above-bandgap photovoltage (VOC ) show unique attributes of directional anisotropy and positive dependence on electrode spacing. The driving source stems from orientations of the polar aromatic spacer and Cs+ ion drift, being different from the known built-in asymmetry photovoltaic heterojunctions. As the first demonstration of the BAPV effect in the double perovskites, the results will enrich the family of environmentally green BAPV-active candidates and further facilitate their new optoelectronic application.

X-ray-Induced Pyroelectric Effect in a Perovskite Ferroelectric Drives Low Detection Limit Self-Powered Responses.

The light-induced pyroelectric effect (LPE) has shown a great promise in the application of optoelectronic devices, especially for self-powered detection and imaging. However, it is quite challenging and scarce to achieve LPE in the X-ray region. For the first time, we report X-ray LPE in a single-phase ferroelectric of (NPA)2(EA)2Pb3Br10 (1, NPA = neopentylamine, EA = ethylamine), adopting a two-dimensional trilayered perovskite motif, which has a large spontaneous polarization of ∼3.7 µC/cm2. Its ferroelectricity allows for significant LPE in the wavelength range of ordinary visible light. Strikingly, the X-ray LPE is observed in 1, which endows remarkable self-powered X-ray responses at 0 bias, including sensitivity up to 225 µC Gy-1 cm-2 and a low detection limit of ∼83.4 nGy s-1, being almost 66 times lower than the requirement for medical diagnostics (∼5.5 µGy s-1). This work not only develops a new mode for X-ray detection but also provides valuable insights for future photoelectric device application.

A room-temperature antiferroelectric in hybrid perovskite enables highly efficient energy storage at low electric fields.

Molecular antiferroelectrics (AFEs) have taken a booming position in the miniaturization of energy storage devices due to their low critical electric fields. However, regarding intrinsic competitions between dipolar interaction and steric hindrance, it is a challenge to exploit room-temperature molecular AFEs with high energy storage efficiency. Here, we present a new 2D hybrid perovskite-type AFE, (i-BA)2(FA)Pb2Br7 (1), which shows ultrahigh energy storage efficiencies at room temperature. Most strikingly, the typical double P-E hysteresis loops afford an ultrahigh storage efficiency up to ∼91% at low critical electric fields (E cr = 41 kV cm-1); this E cr value is much lower than those of state-of-the-art AFE oxides, revealing the potential of 1 for miniaturized energy-storage devices. In terms of the energy storage mechanism, the dynamic ordering and antiparallel reorientation of organic cations trigger its AFE-type phase transition at 303 K, thus giving a large spontaneous electric polarization of ∼3.7 µC cm-2, while the increasement of steric hindrance of the organic branched-chain i-BA+ spacer cations stabilizes its antipolar sublattices. To the best of our knowledge, this exploration of achieving ultrahigh energy storage efficiency at such a low critical electric field is unprecedented in the AFE family, which paves a pathway for miniaturized energy storage applications.

Broadband Photoresponses from Ultraviolet to Near-Infrared (II) Region through Light-induced Pyroelectric Effects in a Hybrid Perovskite.

Broadband photodetection has shown a great promise for diverse applications, while the realization of plateau photoresponse from ultraviolet (UV) to near-infrared (NIR) spectral region is very challenging. Herein, we exploit photoexcited pyroelectric effect in a chiral hybrid perovskite, (N, N-dimethylcyclohexylammonium)PbBr3 (1), serving as a new pathway to drive broadband photoactivities. It is a room-temperature pyroelectric with large polarization of ≈6.4 µC cm-2 and high pyroelectric figure-of-merits (FV =1.0×10-2  cm2 µC-1 and FD =7.1×10-5  Pa-1/2 ). Strikingly, light-induced pyroelectric effect arising from spontaneous polarization is observed in 1, which cover UV (266 nm) to NIR-II (1950 nm) full spectral region. The broadband photoresponses actualized by pyroelectricity break the limit of optical band gap. As the first demonstration of photo-pyroelectricity covering UV-to-NIR spectral region in hybrid perovskites, this work paves a pathway to assemble high-performance smart devices.

Record high-Tc and large practical utilization level of electric polarization in metal-free molecular antiferroelectric solid solutions.

Metal-free antiferroelectric materials are holding a promise for energy storage application, owing to their unique merits of wearability, environmental friendliness, and structure tunability. Despite receiving great interests, metal-free antiferroelectrics are quite limited and it is a challenge to acquire new soft antiferroelectric candidates. Here, we have successfully exploited binary CMBrxI1-x and CMBrxCl1-x solid solution as single crystals (0 ≤ x ≤ 1, where CM is cyclohexylmethylammonium). A molecule-level modification can effectively enhance Curie temperature. Emphatically, the binary CM-chloride salt shows the highest antiferroelectric-to-paraelectric Curie temperature of ~453 K among the known molecular antiferroelectrics. Its characteristic double electrical hysteresis loops provide a large electric polarization up to ~11.4 µC/cm2, which endows notable energy storage behaviors. To our best knowledge, this work provides an effective solid-solution methodology to the targeted design of new metal-free antiferroelectric candidates toward biocompatible energy storage devices.

Incorporating an Aromatic Cationic Spacer to Assemble 2D Polar Perovskite Crystals toward Self-Powered Detection of Quite Weak Polarized Light.

Two-dimensional (2D) hybrid perovskites with intrinsic attributes of structural and optical anisotropy are holding a bright promise for polarization-sensitive photodetection. However, studies on self-powered detection to quite weak polarized light remain scarce in this 2D family. By incorporating an aromatic spacer into the 3D cubic prototype, we have successfully assembled a new 2D hybrid perovskite with a polar motif, (FPEA)2(MA)Pb2I7 (FMPI, where FPEA is 4-fluorophenethylammonium and MA is methylammonium). Its unique 2D quantum-well structure allows optical absorption dichroism with a large ratio of ∼3.15, and the natural polarity results in a notable bulk photovoltaic effect. Further, centimeter-size crystals (10 × 10 × 3 mm3) of FMPI were facilely obtained by the temperature cooling method, and its crystal-based detectors enable excellent self-powered detection of quite weak polarized light, showing a notable polarization-sensitive ratio (∼1.5), extremely low detection limit (∼100 nW/cm2), and antifatigued stability. The alloyed aromatic cationic spacers facilitate the polarity and enhanced phase stability. This study paves a way for further exploration of new 2D perovskite candidates toward optoelectronic device applications.

A Metal-Free Molecular Antiferroelectric Material Showing High Phase Transition Temperatures and Large Electrocaloric Effects.

Antiferroelectric (AFE) materials, featuring an antiparallel alignment of electric dipoles in the adjacent sublattices, are keeping a great promise toward solid-state refrigeration applications on account of their electrocaloric (EC) effects. Although extensive studies have been performed on inorganic oxide counterparts (e.g., PbZrO3 and AgNbO3), metal-free molecular AFE alternatives with the above-room-temperature EC activities are quite scarce but urgently demanded in terms of environmental issues. Herein, we present a new metal-free molecular AFE, cyclohexylmethylammonium bromide (CMB), which exhibits the unusual antiferroelectric-ferroelectric-paraelectric phase transitions around 364 and 368 K upon heating. The phase transition temperatures are much higher than the majority of known molecular AFE materials. The practical utilization level of electric polarization (∼6 µC/cm2) is clearly evidenced by the typical double polarization-electric field hysteresis loops. Strikingly, large positive and negative EC responses with the temperature changes (ΔT) of 4.2 and -3 K are achieved under an electric field of 20 kV/cm. The origin of its antiferroelectricity and EC properties is elucidated by the antipolar reorientation of cations along with displacement of bromine anions, being distinct from the known mechanism of inorganic oxides. Such intriguing AFE behaviors, including large polarization and EC effects, reveal great potentials of CMB for the solid-state refrigeration. This study sheds light on further exploration of new AFE candidates toward environmentally friendly solid-state cooling devices.

Incorporating Guanidinium as Perovskitizer-Cation of Two-Dimensional Metal Halide for Crystal-Array Photodetectors.

Two-dimensional (2D) hybrid perovskites are recently emerging as a potential family of semiconductors for versatile optoelectronic applications. Currently, the "perovskitizer" moieties are rigidly limited to small-size cations, while few 2D metal-halides containing guanidinium cations inside perovskite cages have been studied for photodetection. Herein, we present a new 2D hybrid perovskite, (i-BA)2 (G)Pb2 I7 (where G is guanidinium and i-BA is isobutylammonium), which adopts a bilayered framework of {GPb2 I7 }. Single-crystal structure analyses disclose that G cations act as the perovskitizer, confined in the flexible perovskite cages formed by the distorted PbI6 octahedra. Such inorganic sheets are crucial to the superior semiconducting properties and optical bandgap, as verified by the density functional theory calculation. Furthermore, its planar crystal-array photodetector shows fascinating photoelectric performance, including a quite low dark current (∼4.6×10-11  A), a large current switching ratio (∼1.0×103 ), and a notable photo-responsivity of ∼0.72 A W-1 , suggesting great potential of (i-BA)2 (G)Pb2 I7 for photodetection.

Two-Dimensional Guanidine-Based Hybrid Perovskites with Strong Dichroism for Multiwavelength Polarization-Sensitive Detection.

Two-dimensional (2D) organic-inorganic hybrid perovskites, benefiting from their natural anisotropy of quantum-well motifs and optical properties, have shown remarkable polarization-dependent responses superior to the 3D counterparts. Here, for the first time, multiwavelength polarization-sensitive detectors were fabricated by using single crystals of a guanidine-based 2D hybrid perovskite, (BA)2 (GA)Pb2 I7 (where BA+ is n-butylammonium and GA+ is guanidium). Its unique 2D quantum-well structure results in strong crystallographic-dependence of optical absorption. Strikingly, our crystal-based photodetector exhibits a prominent photocurrent dichroic ratio (Imax /Imin ) of ∼2.2 at 520 nm, higher than the typical 2D inorganic materials (GeSe, ∼1.09, PdSe2 , ∼1.8). In addition, notable dichroic ratios of 1.29 and 1.23 at 405 nm and 637 nm are also created for the multiwavelength polarized-light detection. The prominent detecting performances, including low dark current (1.6×10-11  A), considerable on/off ratio (∼2×103 ), high photodetectivity (∼3.3×1011 Jones) and responsivity (∼12.01 mA W-1 ), make (BA)2 (GA)Pb2 I7 a promising candidate for polarized-light detection. This work sheds light on the rational engineering of new 2D hybrid perovskites for the high-performance optoelectronic device applications.

Tailoring of a visible-light-absorbing biaxial ferroelectric towards broadband self-driven photodetection.

In terms of strong light-polarization coupling, ferroelectric materials with bulk photovoltaic effects afford a promising avenue for optoelectronic devices. However, due to severe polarization deterioration caused by leakage current of photoexcited carriers, most of ferroelectrics are merely capable of absorbing 8-20% of visible-light spectra. Ferroelectrics with the narrow bandgap (<2.0 eV) are still scarce, hindering their practical applications. Here, we present a lead-iodide hybrid biaxial ferroelectric, (isopentylammonium)2(ethylammonium)2Pb3I10, which shows large spontaneous polarization (~5.2 µC/cm2) and a narrow direct bandgap (~1.80 eV). Particularly, the symmetry breaking of 4/mmmFmm2 species results in its biaxial attributes, which has four equivalent polar directions. Accordingly, exceptional in-plane photovoltaic effects are exploited along the crystallographic [001] and [010] axes directions inside the crystallographic bc-plane. The coupling between ferroelectricity and photovoltaic effects endows great possibility toward self-driven photodetection. This study sheds light on future optoelectronic device applications.