Two near-infrared- (NIR-) emitting cationic iridium(III) complexes, [Ir(pbq-g)2(Bphen)]+PF6– (1) and [Ir(mpbqx-g)2(Bphen)]+PF6– (2), were synthesized and characterized, where pbq-g, mpbqx-g, and Bphen represent phenylbenzo[g]quinoline, 2-methyl-3-phenylbenzo[g]quinoxaline, and 4,7-diphenyl-1,10-phenanthroline, respectively. By employing sp2-hybridized N opposite the chelating N atom in the cyclometalated ligand, we succeeded in expanding the emission of iridium complexes with simple structures to the truly NIR region of the spectrum. This subtle structural adjustment significantly lowered the LUMOs of the iridium complexes, leading to a 60–80-nm emission red shift of complex 2 relative to complex 1. Based on these solution-processable phosphors, NIR organic light-emitting devices (OLEDs) were fabricated with the emission covering the range 690–850 nm. Compared with common OLEDs, these NIR-emitting electrophosphorescent devices demonstrate exclusive small efficiency roll-off with increasing current density. For complex 1, the external quantum efficiency (EQE) was 0.67% at a current density of 6 mA/cm2, and the value held at 0.61% at a current density of 20 mA/cm2. In particular, the EQEs of devices based on complex 2 remained almost constant even up to 100 mA/cm2. Such unique characteristics are desirable for the practical application of OLEDs in terms of energy savings. They can be ascribed to the bulky aromatic cyclometalated and ancillary ligands, together with the octahedral configuration of Ir(III) complexes, thereby hindering molecular aggregation and triplet–triplet annihilation under high populations of triplet excitons.

Despite the great potential for applications spanning from military night-vision displays and information-secured devices to civilian medical diagnostics and phototherapy, the development of highly efficient, stable, and low-cost near-infrared (NIR) emitting lumophores is still a formidable challenge. Herein, we report two novel NIR-emitting homoleptic facial Ir(III) complexes based on extended π-conjugated benzo[g]phthalazine ligands, namely, tris[1,4-di(thiophen-2-yl)benzo[g]phthalazine] iridium(III) (Ir(dtbpa)3, 1) and tris[1-(2,4-bis(trifluoromethyl)phenyl)-4-(thiophen-2-yl)benzo[g]phthalazine] iridium(III) (Ir(Ftbpa)3, 2). Actually, these two ligands not only enable simple one-pot synthesis of homoleptic Ir(III) complexes without any catalyst under mild conditions, but also contribute to intense NIR-emission with high photoluminescence quantum yield up to 5.2% at 824 nm for 1 and 17.3% at 765 nm for 2, respectively. Single-crystal structure of 1 demonstrates desired facial form with short Ir–N and Ir–C bonds because of strong coordination and small steric hindrance of those highly conjugated C^N═N ligands. Importantly, the incorporation of CF3 groups in 2 further leads to high thermal stability and a good ability to sublime, thus resulting in ultrapurity for highly efficient NIR-organic light-emitting diodes (NIR-OLEDs) with a high maximum external quantum efficiency of 4.5% at 760 nm and small efficiency roll-off remaining of 3.5% at 100 mA cm–2, values which rank with those of the most efficient NIR-OLEDs with small roll-off and peak emission over 750 nm. Notably, the content percentages of the noble metal in these two complexes (∼10% Ir) are markedly lower by about two-thirds than that of typical green-emitting tris(2-phenylpyridine)iridium (∼30% Ir). The findings may provide a new strategy to develop robust NIR emitters and achieve high efficiency, small roll-off, and low cost simultaneously in NIR-OLEDs for practical applications.

AbstractThe simultaneous realization of high quantum yield and exciton utilizing efficiency (ηr) is still a formidable challenge in near-infrared (NIR) fluorescent organic light-emitting diodes (FOLEDs). Here, to achieve a high quantum yield, a novel NIR dye, 4,9-bis(4-(diphenylamino)phenyl)-naphtho[2,3-c][1,2,5]selenadiazole, is designed and synthesized with a large highest occupied molecular orbital/lowest unoccupied molecular orbital overlap and an aggregation-induced emission property, which demonstrates a high photoluminescence quantum yield of 27% at 743 nm in toluene and 29% at 723 nm in a blend film. For a high ηr, an orange-emitting thermally activated delayed fluorescent material, 1,2-bis(9,9-dimethyl-9,10-dihydroacridine)-4,5-dicyanobenzene, is chosen as the sensitizing host to harvest triplet excitons in devices. The optimized devices achieve a good ηr of 45.7% and a high external quantum efficiency up to 2.65% at 730 nm, with a very small efficiency roll-off of 2.41% at 200 mA cm−2, which are among the most efficient values for NIR-FOLEDs over 700 nm. The effective utilization of triplet excitons via the thermally activated delayed fluorescence-sensitizing host will pave a way to realize high-efficiency NIR-FOLEDs with small efficiency roll-off.

AbstractDesigning probes for real-time imaging of dynamic processes in living cells is a continuous challenge. Herein, a novel near-infrared (NIR) photoluminescence probe having a long lifetime was exploited for photoluminescence lifetime imaging (PLIM) using an iridium-alkyne complex. This probe offers the benefits of deep-red to NIR emission, a long Stokes shift, excellent cell penetration, low cytotoxicity, and good resistance to photobleaching. This example is the first PLIM probe applicable to the click reaction of copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) with remarkable lifetime shifts of 414 ns, before and after click reaction. The approach fully eliminates the background interference and distinguishes the reacted probes from the unreacted probes, thus enabling the wash-free imaging of the newly synthesized proteins within single living cells. Based on the unique properties of the iridium complexes, it is anticipated to have applications for imaging other processes within living cells.

AbstractDesigning probes for real-time imaging of dynamic processes in living cells is a continuous challenge. Herein, a novel near-infrared (NIR) photoluminescence probe having a long lifetime was exploited for photoluminescence lifetime imaging (PLIM) using an iridium-alkyne complex. This probe offers the benefits of deep-red to NIR emission, a long Stokes shift, excellent cell penetration, low cytotoxicity, and good resistance to photobleaching. This example is the first PLIM probe applicable to the click reaction of copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) with remarkable lifetime shifts of 414 ns, before and after click reaction. The approach fully eliminates the background interference and distinguishes the reacted probes from the unreacted probes, thus enabling the wash-free imaging of the newly synthesized proteins within single living cells. Based on the unique properties of the iridium complexes, it is anticipated to have applications for imaging other processes within living cells.

Organometal halide perovskites are emerging as potential materials for light-emitting diodes (LEDs) and lasers due to their superior color purity, tunable band gaps, low cost and solution processability. However, the performance of perovskite LEDs (PeLEDs) is intrinsically limited by the poor morphology and undesirable trap states of the perovskite film, resulting in electric losses. Herein, we demonstrate a unique strategy to obtain high quality perovskite films through the integrated utilization of solvent engineering and moisture exposure. The synergistic effects of solvent engineering and moisture exposure could contribute to uniform and dense morphology meanwhile significantly reducing the trap density of the perovskite films. Strikingly, the controlled exposure to a relative humidity (RH) around 65% significantly improved the photoluminescence lifetime of the formamidinium lead iodide (FAPbI3) film with α/δ phase junction from 14 ns to 35 ns. For the first time, we revealed that moisture treatment could be exploited in PeLEDs for significantly decreasing the trap density of perovskite films, thus enabling a fortyfold increase of external quantum efficiency from 0.03% up to 1.20% as well as a low turn-on voltage at 2.4 V. It is anticipated that this approach could be extended from FAPbI3 to other compositional perovskites and provide guidelines for optimum combination of moisture post-treatment to realize high-performance perovskite devices.

Shape memory polymers (SMPs) have been widely used in our daily life (e.g. shrinkable tubes) and are expected to play more important roles in soft robotics, biomedical devices and other high-tech areas. Due to the energy shortage the world is facing now, it would be ideal to convert normal heat-driven SMPs into sunlight-responsive SMPs, so that solar energy could be converted into mechanical work. It is even more desirable to make SMPs flexibly switch between photo-responsiveness and photo-inertness. However, these objectives have not been realised so far. Here, we come up with a straightforward and low-cost method to do so by coating thermal-responsive SMPs with CH3NH3PbI3 perovskite. We find that CH3NH3PbI3 has excellent photo-thermal effect. As it can effectively convert solar energy into heat, the shape change of SMPs can be controlled by sunlight. The CH3NH3PbI3 layer can be easily washed off with water. The coating–erasing can be repeated many times to make the SMPs photo-responsive and photo-inert alternatively. The concept introduced here will not only expand the application of many currently available thermal-responsive SMPs, but also provide a practical method to make good use of solar energy.

Though urgently needed, high-performance near-infrared organic light-emitting diodes (NIR-OLEDs) are still rare. NIR-OLEDs based on conventional NIR fluorescent materials usually suffer from low external quantum efficiencies (EQEs) because of the intrinsic obstacles according to the spin-statistics limit and energy-gap law. Herein, we realized high-efficiency and low efficiency roll-off fluorescent NIR-OLEDs through efficient triplet fusion of a bipolar host doped with a special naphthoselenadiazole emitter (4,9-bis(4-(2,2-diphenylvinyl)phenyl)-naphtho[2,3-c][1,2,5]selenadiazole, NSeD). Unlike typical NIR organic donor–acceptor (D–A) chromophores, NSeD features a non-D–A structure and a very large HOMO/LUMO overlap and displays a strong deep-red to NIR fluorescence and unique ambipolar character. The corresponding photoluminescence quantum efficiency of NSeD reaches 52% in solution and retains 17% in the blend film. The optimized NIR-OLEDs demonstrated a strong emission at 700 nm, a high maximum EQE of 2.1% (vs. the predicted theoretical maximum efficiency of 1.3%) and the EQE remained at around 2% over a wide range of current densities from 18 to 200 mA cm−2, which is amongst the highest performance for NIR-OLEDs based on organic fluorescent materials.

The morphology and crystal structure of perovskite films are critical for achieving high-performance perovskite solar cells; however in most cases, the conventional one-step solution deposition method hardly yields a homogeneous perovskite film over a large area, especially for CH3NH3PbI3. Here, we propose a facile and environmentally friendly hexane-assisted one-step solution approach for dense and uniform CH3NH3PbI3 thin films. According to the phase diagram of immiscible liquids, n-hexane was chosen as the assistant solvent to speed-up the evaporation of the main solvent N,N-dimethylformamide (DMF) during the solution deposition process, thus significantly promoting the nucleation and crystallization process of CH3NH3PbI3 perovskite. The as-prepared CH3NH3PbI3 films demonstrated a uniform and dense morphology, and enhanced light absorption in a long-wavelength range. In particular, such n-hexane treatment could help eliminate the residual DMF and greatly improve the thermal stability of the obtained perovskite films. The full solution-processed CH3NH3PbI3 solar cells using n-hexane treatment exhibited a maximum power conversion efficiency of 11.7% and average efficiencies of 11.3 ± 0.4% under standard AM 1.5 conditions in comparison with 7.0 ± 0.4% of the conventional cells. The recombination resistance of the cells increased nearly 5 times by using n-hexane. These results suggest that this hexane-assisted one-step solution approach is promising for controlling the crystallization process of perovskites to achieve high-performance perovskite solar cells.

Two near-infrared- (NIR-) emitting cationic iridium(III) complexes, [Ir(dpbpa)2(Bphen)]+PF6− (1) and [Ir(dtbpa)2(Bphen)]+PF6− (2), were rationally designed and synthesized, where dpbpa, dtbpa, and Bphen represent 1,4-diphenylbenzo[g]-phthalazine, 1,4-di(thiophen-2-yl)benzo[g]phthalazine and 4,7-dipheny-1,10-phenanthroline, respectively. By using highly conjugated cyclometalated benzo[g]phthalazine ligands, these two complexes exhibited a significantly large red shift in wavelength to the truly NIR region with maximum peaks at 715 nm for 1 and 775 nm for 2. Complex 1 exhibited unexpectedly improved quantum efficiency up to 6.1% in the solid films. Based on these solution-processable phosphors, NIR organic-light-emitting devices (OLEDs) have been fabricated and demonstrated negligible efficiency roll-off with nearly constant external quantum efficiency around 0.5% over a wide range of current density of 1–100 mA cm−2. Density functional theory calculations were performed to discover that the newly cyclometalated benzo[g]phthalazine ligands have several areas of superiority over the previous benzo[g]quinoline ligands in views of stronger Ir–N bonds, smaller chelate congestion, higher electron-accepting ability, thus improving the overall phosphorescence of the corresponding iridium complexes in the NIR region.

Two novel chelated aluminum complexes, bis(2-methyl-8-quinolinato)(2,6-di(pyridin-3-yl)phenolato)Al(III) (BPyAlq) and bis(2-methyl-8-quinolinato)(2,4,6-tri(pyridin-3-yl)phenolato)Al(III) (TPyAlq), have been designed and synthesized by introducing the electron-withdrawing pyridine moieties into the ancillary ligand. Their single-crystal and molecular structures, thermal and photophysical properties, and electron-transporting (ET) capabilities were systematically investigated in comparison with the parent complex bis(2-methyl-8-quinolinato)(4-phenyl-phenolato)Al(III) (BAlq). The introduction of the pyridine moieties helps to not only greatly lower the LUMO and HOMO energy levels but also bring about extra strong intra- and intermolecular interactions, thus significantly improving the electron-injection (EI) and ET capabilities of the involved materials. BPyAlq and TPyAlq exhibited significantly higher glass-transition temperatures (106 and 141 °C) than BAlq (92 °C). The electron-only devices based on BPyAlq or TPyAlq showed more than 2 orders of magnitude higher current density than that of BAlq, indicating much higher ET/EI capabilities. Their excellent ET/EI properties were investigated via the phosphorescent OLEDs using fac-tris(2-phenylpyridine)iridium as the green emitter. The devices with BPyAlq and TPyAlq as an electron-transporting layer (ETL) demonstrated superior performance compared to those using BAlq, remarkably lowering the drive voltage and improving efficiencies. In particular, the green PhOLEDs with BPyAlq as an ETL exhibited the maximum current and external quantum efficiency of 59.8 cd A–1, 17.3% with small efficiency roll-off.

Chemical stability of organic materials on service toward excitons and charge carriers is intrinsically associated with the operational stability and economics of state-of-the-art organic light-emitting devices. Here we conducted comprehensive experiments and theoretical calculations to comparatively investigate the intrinsic chemical stability of organic materials, which contain typical electron-accepting moieties of sulfonyl, phosphine-oxide, and carbonyl group. The materials with a diphenylsulfonyl moiety suffered a fatal chemical instability originating from the cleavage of C–S single bond whether under UV irradiation or in electrical-stressed devices. The material with a dibenzothiophene-S,S-dioxide moiety exhibited significantly improved chemical stability because of effective shielding of the weak C–S single bond in a ring. In contrast, the commercially used carbonyl-containing compound demonstrated the highest chemical stability with negligible degradation under the same condition. Quantum chemical calculations fully supported the experimental results and suggested that the bond strength of the weak chemical bonds of the molecules would determine the intrinsic chemical stability of the organic materials in their excited and charged states, which might be a plausible origin of the limited stability of high-energy blue-emitting materials and devices. Several implications have been drawn for the design of new blue-emitting materials.

The three near-infrared-emitting cationic iridium(III) complexes [Ir(pbq-g)2(N∧N)]+PF6– (pbq-g = phenylbenzo[g]quinoline; N∧N = bipyridine (1), 1,10-phenanthroline (2), 4,7-diphenyl-1,10-phenanthroline (3)) have been demonstrated as phosphorescent dyes in live cell imaging. These complexes with different ancillary ligands show similar near-infrared (NIR) emission with λmax,peak at 698 nm and λmax,shoulder at 760 nm in CH2Cl2 solutions, with a moderate quantum yield of around 3%. However, these complexes behave quite differently as NIR dyes for live cell imaging. Complexes 1 and 2 exhibit exclusive staining in the cytoplasm with good cell membrane permeability under excitation at 488 nm, while 3 gives almost no cell uptake, as further determined by flow cytometry. Although the lipophilicities of these complexes follow the order 1 < 2 < 3, their cytotoxicities are in the reverse order. The exceptionally low cytotoxicity of 3 could be attributed to its poor solubility in aqueous buffer and thus substantially low exposure dose. This comparative study suggested that the ancillary ligands could fine-tune the amphiphilicity and cytotoxicity of the cyclometalated iridium(III) complexes and thus might play a key role in the design of NIR-emitting iridium(III) complexes for practical applications in bioimaging.

For NIR-emitting organic light-emitting devices (OLEDs), platinum complexes have the record maximum external quantum efficiency (EQE), although such devices generally suffer from severe efficiency roll-off with increasing current densities. Here, we report on iridium complexes as a competent alternative for NIR dyes with high EQEs and negligible efficiency roll-off. A simple, charge-neutral iridium complex, iridium(III) bis(2-methyl-3-phenylbenzo[g]quinoxaline-N,C′) acetylacetonate (Ir(mpbqx-g)2acac, 1), has been synthesized and characterized by a strong NIR emission with λmax,peak at 777 nm and λmax,shoulder at 850 nm in CH2Cl2 solutions. The single-crystal and electronic structure as well as photophysical and electrochemical properties were systematically studied in comparison with its cationic counterpart [Ir(mpbqx-g)2(Bphen)]+PF6− (2, Bphen = 4,7-diphenyl-1,10-phenanthroline). Complex 1 has seven times the quantum efficiency of complex 2 because of its much stronger spin–orbit coupling. NIR-emitting OLEDs based on complex 1 have been fabricated with a bipolar gallium complex as the host. The devices achieved a maximum EQE of up to 2.2% (J = 13 mA cm−2) and a maximum radiant emittance (Rmax) of 1.8 mW cm−2. In particular, the EQEs remained around 2% over a wide range of current densities from 3 to 100 mA cm−2.

Two near-infrared- (NIR-) emitting cationic iridium(III) complexes, [Ir(pbq-g)2(Bphen)]+PF6– (1) and [Ir(mpbqx-g)2(Bphen)]+PF6– (2), were synthesized and characterized, where pbq-g, mpbqx-g, and Bphen represent phenylbenzo[g]quinoline, 2-methyl-3-phenylbenzo[g]quinoxaline, and 4,7-diphenyl-1,10-phenanthroline, respectively. By employing sp2-hybridized N opposite the chelating N atom in the cyclometalated ligand, we succeeded in expanding the emission of iridium complexes with simple structures to the truly NIR region of the spectrum. This subtle structural adjustment significantly lowered the LUMOs of the iridium complexes, leading to a 60–80-nm emission red shift of complex 2 relative to complex 1. Based on these solution-processable phosphors, NIR organic light-emitting devices (OLEDs) were fabricated with the emission covering the range 690–850 nm. Compared with common OLEDs, these NIR-emitting electrophosphorescent devices demonstrate exclusive small efficiency roll-off with increasing current density. For complex 1, the external quantum efficiency (EQE) was 0.67% at a current density of 6 mA/cm2, and the value held at 0.61% at a current density of 20 mA/cm2. In particular, the EQEs of devices based on complex 2 remained almost constant even up to 100 mA/cm2. Such unique characteristics are desirable for the practical application of OLEDs in terms of energy savings. They can be ascribed to the bulky aromatic cyclometalated and ancillary ligands, together with the octahedral configuration of Ir(III) complexes, thereby hindering molecular aggregation and triplet–triplet annihilation under high populations of triplet excitons.

For long-living organic light-emitting diodes (OLEDs), the chemical stability of all employed materials is essential. In this work, we take a typical bipolar material, 9-(3,5-bis(diphenylphosphoryl)phenyl)-9H-carbazole (CzPO2), as an example for exploring the intrinsic chemical stability of the hot-spot phosphine oxide (PO) based materials for OLEDs. Compared to the carbazole-only counterparts, PO-based carbazole materials typified by CzPO2 have prominent advantages in terms of electrochemical stability and bipolar character, which are generally required for improving the device stability. However, we discovered that CzPO2 suffers a fatal chemical instability just originating from the PO moieties. Under UV irradiation or electrical stress, the identified degradation products of CzPO2 point to the dissociation of relatively weak C–P bonds as the initiating step. Quantum chemical calculations were carried out to gain further insight into the role of the C–P single bond in the intrinsic degradation mechanism associated with the aging process of OLEDs. The cleavage of vulnerable C–P single bonds may occur not only in excited states, but also more easily in charged states. These findings strongly suggested that the chemically unstable C–P bond of PO derivatives could undermine the stability of the corresponding OLEDs, regardless of the function that the PO materials played in devices. For improving the lifetimes of OLEDs, it is highly suggested to consider the relative bond strengths in charged states or excited states of OLED materials, in addition to the generally required thermal stability.

A novel binuclear aluminum(III) complex with acylpyrazolone derivative as ligands, bis(salicylidene-o-aminophenol)-bis(4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one)-bis-aluminum(III) [Al2(saph)2(PMBP)2] was designed and synthesized. A detailed study was carried out on its thermal stability, photophysical, electrochemical and electroluminescent properties. It was found that the introduction of 4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one (PMBP) ligands improved the thermal stability remarkably. Organic light-emitting diodes (OLEDs) based on this Al complex as the sole emitter and the host for red dopant were fabricated. Bright green-yellow emission was observed from the device using Al2(saph)2(PMBP)2 as the emitter and the electron transporting layer. Pure red emission peaked at 632 nm was obtained from the Al2(saph)2(PMBP)2 doped with DCJTB [4-(dicyanomethylene)-2-tertbutyl-6(1,1,7,7,-tetramethyljulolidyl-9-enyl)-4H-pyran] device with a luminance efficiency of 1.51 cd/A at 200 A/m2. No light from Al2(saph)2(PMBP)2 was found, indicating that the matched energy levels provide an efficient red emission system in Al2(saph)2(PMBP)2 device. Those results demonstrated that Al2(saph)2(PMBP)2 might be a promising material for OLEDs.

An azomethin-zinc complex, bis[salicylidene(4-dimethylamino)aniline]zinc(II) (Zn(sada)2) was synthesized and structurally characterized by single-crystal X-ray crystallography. Crystal data for Zn(C15H15N2O)2 was determined as follows: space group, triclinic, P1¯; a = 10.2791(9) Å, b = 16.5008(14) Å, c = 17.5984(15) Å, α = 114.830(2)°, β = 96.579(2)°, γ = 97.674(2)°, Z = 4. Through thermal analysis characterization and FT-IR spectra, this complex was proved to have good thermal stability. The vapor-deposited films exhibited uniform and environment-stable morphology. The light emission and charge transporting performance of Zn(sada)2 in organic light emitting diodes (OLEDs) were investigated preliminarily, and the results indicated the superior electron transporting property of this complex. Compared with the typical bilayer device of N,N′-diphenyl-N,N′-bis(1-naphthyl)-benzidine (NPB)/tris-(8-hydroxyquinoline)aluminum (Alq3), the device with Zn(sada)2 as the electron transporting layer exhibited a much lower turn-on voltage of 2.5 V (it is usually 3.5 V for an NPB/Alq3 device).An new azomethin-zinc complex, bis[salicylidene(4-dimethylamino)aniline]zinc(II) was structurally characterized as a racemic compound, which shows excellent thermal stability, environment-stable film-forming capability, and good electron transporting property for use in organic light emitting diodes.

Shape memory polymers (SMPs) have been widely used in our daily life (e.g. shrinkable tubes) and are expected to play more important roles in soft robotics, biomedical devices and other high-tech areas. Due to the energy shortage the world is facing now, it would be ideal to convert normal heat-driven SMPs into sunlight-responsive SMPs, so that solar energy could be converted into mechanical work. It is even more desirable to make SMPs flexibly switch between photo-responsiveness and photo-inertness. However, these objectives have not been realised so far. Here, we come up with a straightforward and low-cost method to do so by coating thermal-responsive SMPs with CH3NH3PbI3 perovskite. We find that CH3NH3PbI3 has excellent photo-thermal effect. As it can effectively convert solar energy into heat, the shape change of SMPs can be controlled by sunlight. The CH3NH3PbI3 layer can be easily washed off with water. The coating–erasing can be repeated many times to make the SMPs photo-responsive and photo-inert alternatively. The concept introduced here will not only expand the application of many currently available thermal-responsive SMPs, but also provide a practical method to make good use of solar energy.

For NIR-emitting organic light-emitting devices (OLEDs), platinum complexes have the record maximum external quantum efficiency (EQE), although such devices generally suffer from severe efficiency roll-off with increasing current densities. Here, we report on iridium complexes as a competent alternative for NIR dyes with high EQEs and negligible efficiency roll-off. A simple, charge-neutral iridium complex, iridium(III) bis(2-methyl-3-phenylbenzo[g]quinoxaline-N,C′) acetylacetonate (Ir(mpbqx-g)2acac, 1), has been synthesized and characterized by a strong NIR emission with λmax,peak at 777 nm and λmax,shoulder at 850 nm in CH2Cl2 solutions. The single-crystal and electronic structure as well as photophysical and electrochemical properties were systematically studied in comparison with its cationic counterpart [Ir(mpbqx-g)2(Bphen)]+PF6− (2, Bphen = 4,7-diphenyl-1,10-phenanthroline). Complex 1 has seven times the quantum efficiency of complex 2 because of its much stronger spin–orbit coupling. NIR-emitting OLEDs based on complex 1 have been fabricated with a bipolar gallium complex as the host. The devices achieved a maximum EQE of up to 2.2% (J = 13 mA cm−2) and a maximum radiant emittance (Rmax) of 1.8 mW cm−2. In particular, the EQEs remained around 2% over a wide range of current densities from 3 to 100 mA cm−2.

The morphology and crystal structure of perovskite films are critical for achieving high-performance perovskite solar cells; however in most cases, the conventional one-step solution deposition method hardly yields a homogeneous perovskite film over a large area, especially for CH3NH3PbI3. Here, we propose a facile and environmentally friendly hexane-assisted one-step solution approach for dense and uniform CH3NH3PbI3 thin films. According to the phase diagram of immiscible liquids, n-hexane was chosen as the assistant solvent to speed-up the evaporation of the main solvent N,N-dimethylformamide (DMF) during the solution deposition process, thus significantly promoting the nucleation and crystallization process of CH3NH3PbI3 perovskite. The as-prepared CH3NH3PbI3 films demonstrated a uniform and dense morphology, and enhanced light absorption in a long-wavelength range. In particular, such n-hexane treatment could help eliminate the residual DMF and greatly improve the thermal stability of the obtained perovskite films. The full solution-processed CH3NH3PbI3 solar cells using n-hexane treatment exhibited a maximum power conversion efficiency of 11.7% and average efficiencies of 11.3 ± 0.4% under standard AM 1.5 conditions in comparison with 7.0 ± 0.4% of the conventional cells. The recombination resistance of the cells increased nearly 5 times by using n-hexane. These results suggest that this hexane-assisted one-step solution approach is promising for controlling the crystallization process of perovskites to achieve high-performance perovskite solar cells.

Though urgently needed, high-performance near-infrared organic light-emitting diodes (NIR-OLEDs) are still rare. NIR-OLEDs based on conventional NIR fluorescent materials usually suffer from low external quantum efficiencies (EQEs) because of the intrinsic obstacles according to the spin-statistics limit and energy-gap law. Herein, we realized high-efficiency and low efficiency roll-off fluorescent NIR-OLEDs through efficient triplet fusion of a bipolar host doped with a special naphthoselenadiazole emitter (4,9-bis(4-(2,2-diphenylvinyl)phenyl)-naphtho[2,3-c][1,2,5]selenadiazole, NSeD). Unlike typical NIR organic donor–acceptor (D–A) chromophores, NSeD features a non-D–A structure and a very large HOMO/LUMO overlap and displays a strong deep-red to NIR fluorescence and unique ambipolar character. The corresponding photoluminescence quantum efficiency of NSeD reaches 52% in solution and retains 17% in the blend film. The optimized NIR-OLEDs demonstrated a strong emission at 700 nm, a high maximum EQE of 2.1% (vs. the predicted theoretical maximum efficiency of 1.3%) and the EQE remained at around 2% over a wide range of current densities from 18 to 200 mA cm−2, which is amongst the highest performance for NIR-OLEDs based on organic fluorescent materials.