Flexible and light-weight solar cells are important because they not only supply power to wearable and portable devices, but also reduce the transportation and installation cost of solar panels. High-efficiency organometal halide perovskite solar cells can be fabricated by a low-temperature solution process, and hence are promising for flexible-solar-cell applications. Here, the development of perovskite solar cells is briefly discussed, followed by the merits of organometal halide perovskites as promising candidates as high-efficiency, flexible, and light-weight photovoltaic materials. Afterward, recent developments of flexible solar cells based on perovskites are reviewed.

While most luminescent organic dyes display intense Stokes fluorescence, some of them exhibit unique single-photon frequency upconversion luminescence (FUCL). Compared to conventional anti-Stokes luminescence of lanthanides and two-photon excitation, FUCL materials display adjustable spectrum area and require a much lower excitation power. Although this is very beneficial for biological applications in the perspective of reducing photodamage to biological samples and photobleaching of the dyes, the utilization of FUCL for biosensing and bioimaging in vivo has not been reported. In this study, we developed a near-infrared (NIR) rhodamine derivative (FUC-1) as a chemodosimeter, which displays weak luminescence but undergoes thiolactone ring-open process leading to luminescence turn-on in response to mercury(II) cation or methylmercury with good selectivity and high sensitivity in aqueous solution. Interestingly, FUC-1 displays particular FUCL, excitation at 808 nm leads to luminescence at 745 nm. Compared to Stokes luminescence resulted from excitation at 630 nm, the use of FUCL lowers the detection limit of Hg²⁺ to be 0.207 nM. FUC-1 has been used for FUCL bioimaging of methylmercury in live cells and mice. To the best of our knowledge, this is the first example of FUCL biosensing and bioimaging in vivo using visible and NIR fluorescence of small-molecular dyes.

Temperature plays a crucial role in many biological processes. Accurate temperature determination is important for diagnosis and treatment of diseases. Autofluorescence is an unavoidable interference in luminescent bioimaging. Hence, a large amount of research works has been devoted to reducing background autofluorescence and improving signal-to-noise ratio (SNR) in biodetection. Herein, a dual-emissive phosphorescent polymeric thermometer has been developed by incorporating two long-lived phosphorescent iridium(III) complexes into an acrylamide-based thermosensitive polymer. Upon increasing temperature, this polymer undergoes coil-globule transition, which leads to a decrease in polarity of the microenvironment surrounding the iridium(III) complexes and hence brings about emission enhancement of both complexes. Owing to their different sensitivity to surrounding environment, the emission intensity ratio of the two complexes is correlated to the temperature. Thus, the polymer has been used for temperature determination in vitro and in vivo via ratiometric luminescence imaging. More importantly, by using the long-lived phosphorescence of the polymer, temperature mapping in zebrafish has been demonstrated successfully with minimized autofluorescence interference and improved SNR via time-resolved luminescence imaging. To the best of our knowledge, this is the first example to use photoluminescent thermometer for in vivo temperature sensing.

Highly efficient lepidine-based phosphorescent iridium(III) complexes with pentane-2,4-dione or triazolpyridine as ancillary ligands have been designed and prepared by a newly developed facile synthetic route. Fluorine atoms and trifluoromethyl groups have been introduced into the different positions of ligand, and their influence on the photophysical properties of complexes has been investigated in detail. All the triazolpyridine-based complexes display the blueshifted dual-peak emission compared to the pentane-2,4-dione-based ones with a broad single-peak emission. The complexes show emission with broad full width at half maximum (FWHM) over 100 nm, and the emissions are ranges from greenish–yellow to orange region with the absolute quantum efficiency (Φ_PL) of 0.21–0.92 in solution, i.e., Φ_PL = 0.92 (18), which is the highest value among the reported neutral yellow iridium(III) complexes. Furthermore, high-performance yellow and complementary-color-based white organic light-emitting diodes (OLEDs) have been fabricated. The FWHMs of the yellow, greenish–yellow OLEDs are in the range of 94–102 nm, which are among the highest values of the reported yellow or greenish–yellow-emitting devices without excimer emission. The maximum external quantum efficiency of monochrome OLEDs can reach 24.1%, which is also the highest value among the reported yellow or greenish–yellow devices. The color rendering indexes of blue and complementary yellow-based white OLED is as high as 78.

Molecular oxygen (O₂) plays a key role in many physiological processes, and becomes a toxicant to kill cells when excited to ¹O₂. Intracellular O₂ levels, or the degree of hypoxia, are always viewed as an indicator of cancers. Due to the highly efficient cancer therapy ability and low side effect, photodynamic therapy (PDT) becomes one of the most promising treatments for cancers. Herein, an early-stage diagnosis and therapy system is reported based on the phosphorescent conjugated polymer dots (Pdots) containing Pt(II) porphyrin as an oxygen-responsive phosphorescent group and ¹O₂ photosensitizer. Intracellular hypoxia detection has been investigated. Results show that cells treated with Pdots display longer lifetimes under hypoxic conditions, and time-resolved luminescence images exhibit a higher signal-to-noise ratio after gating off the short-lived background fluorescence. Quantification of O₂ is realized by the ratiometric emission intensity of phosphorescence/fluorescence and the lifetime of phosphorescence. Additionally, the PDT efficiency of Pdots is estimated by flow cytometry, MTT cell viability assay, and in situ imaging of PDT induced cell death. Interestingly, Pdots exhibit a high PDT efficiency and would be promising in clinical applications.

Three kinds of charged star-shaped conjugated macroelectrolytes, named as PhNBr, TPANBr, and TrNBr, are synthesized as electron-collecting interlayers for inverted polymer solar cells (i-PSCs). Based on these well-defined structured interlayer materials, the light soaking (LS) effect observed in i-PSCs was studied systematically and accurately. The general character of the LS effect is further verified by studying additional i-PSC devices functionalized with other common interlayers. The key-role of UV photons was confirmed by electrochemical impedance spectroscopy and electron-only devices. In addition, the ultraviolet photoelectron spectroscopy measurements indicate that the work function of the indium tin oxide (ITO)/interlayer cathode is significantly reduced after UV treatment. In these i-PSC devices the LS effect originates from the adsorbed oxygen on the ITO substrates when oxygen plasma is used; however, even a small amount of oxygen from the ambient is also enough for triggering the LS effect, albeit with a weaker intensity. Our results suggest that the effect of adsorbed oxygen on ITO needs to be considered with attention while preparing i-PSCs. This is an important finding that can aid the large-scale manufacturing of organic solar cells via printing technologies, which do not always ensure the full protection of the device electrode substrates from oxygen.

In this report, the BF₃·Et₂O catalyzed Friedel–Crafts polymerization of cyclopentadithiophene monomers for branched conjugation-interrupted polymer electrets with the potential application in OFET memories were demonstrated. Branched polycyclopentadithiophenes with controlled molecular weights (M_n) of approximately 8800 g/mol and narrow polydispersity index (PDI = 1.08–1.49) were obtained through the optimized polymerization temperature and time, and monomer addition strategy. OFET memories by using the synthesized polymers as the electret layers were fabricated and exhibited multilevel flash memory behaviors, wide memory windows, high on/off ratios, and long retention lifetime. Impressively, due to the strong hydrophobic, extended pi-conjugation and electron-donating properties, the branched polycyclopentadithiophene based OFET memory exhibited much lower programming voltage than other branched polymer electrets based devices. It is expected that the branched polycyclopentadithiophenes probably have potential application in other organic electronic devices. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3140–3150

Flexible and stretchable electronics represent today's cutting-edge electronic technologies. As the most-fundamental component of electronics, the thin-film electrode remains the research frontier due to its key role in the successful development of flexible and stretchable electronic devices. Stretchability, however, is generally more challenging to achieve than flexibility. Stretchable electronic devices demand, above all else, that the thin-film electrodes have the capacity to absorb a large level of strain (>>1%) without obvious changes in their electrical performance. This article reviews the progress in strategies for obtaining highly stretchable thin-film electrodes. Applications of stretchable thin-film electrodes fabricated via these strategies are described. Some perspectives and challenges in this field are also put forward.

A family of trigonal starburst conjugated molecules (TrFPy, TrFPy, and TrF2Py) composed of a truxene core and pyrene cappers with various bridge lengths is synthesized and characterized. The incorporation of pyrene cappers successfully depress the crystallization tendency, resulting in enhanced glassy temperature and improved morphological stability of the thin films. The high photoluminescence yield in neat films and excellent thermal stability render these pyrene-capped starbursts promising lasing optical gain media. Low amplified spontaneous emission (ASE) thresholds (E_th^ASE) of 180 nJ pulse^-1 and 101 nJ pulse^–1 were recorded for TrFPy and TrF2Py, respectively. One dimensional distributed feedback (1D DFB) lasers demonstrated lasing threshold of 9.3 kW/cm² and 7.3 kW/cm² for TrFPy (at 457 nm) and TrF2Py lasers (at 451 nm), respectively. The ASE performance of TrFPy and TrF2Py in an ambient condition was recorded with various annealing temperature (from 80 to 250 °C, 10 min). Surprisingly, TrFPy exhibited excellent ASE stability in an ambient condition, which is still detectable even after annealing at 250 °C for 10 min. The results suggest the pyrene-capped molecular design strategy is positive on improving the optical gain stability and meanwhile maintaining excellent lasing properties.

Hybridbio/-synthetic sensory conjugated polymer nanoparticles (CPNs) are developed for selective label-free detection of target ssDNA in serum. Carboxylic acid-functionalized anionic polyfluorene nanoparticles are rationally designed as signal amplifying unit to bioconjugate with amine functionalized single stranded oligonucleotides as a receptor. The covalent DNA coating can significantly improve the photostability of the DNA-bioconjugated CPNs over a wide range of buffer conditions. Better ssDNA discrimination for the DNA-bioconjugated CPNs sensor is achieved owing to increased interchain interactions and more efficient exciton transport in nanoparticles. The distinguishable fluorescent color for DNA-bioconjugated CPNs in the presence of target ssDNA allows naked-eye detection of ssDNA under UV irradiation.

Oxygen plays a crucial role in many biological processes. Accurate monitoring of oxygen level is important for diagnosis and treatment of diseases. Autofluorescence is an unavoidable interference in luminescent bioimaging, so that an amount of research work has been devoted to reducing background autofluorescence. Herein, a phosphorescent iridium(III) complex-modified nanoprobe is developed, which can monitor oxygen concentration and also reduce autofluorescence under both downconversion and upconversion channels. The nanoprobe is designed based on the mesoporous silica coated lanthanide-doped upconversion nanoparticles, which contains oxygen-sensitive iridium(III) complex in the outer silica shell. To image intracellular hypoxia without the interferences of autofluorescence, time-resolved luminescent imaging technology and near-infrared light excitation, both of which can reduce autofluorescence effectively, are adopted in this work. Moreover, gradient O₂ concentration can be detected clearly through confocal microscopy luminescence intensity imaging, phosphorescence lifetime imaging microscopy, and time-gated imaging, which is meaningful to oxygen sensing in tissues with nonuniform oxygen distribution.

Electrical stimuli-induced change in absorption spectra, or electrochromism, has been well studied due to its promising applications in displays, sensors, smart windows, memory chips, and electronic papers, etc. However, electrochromic luminescent materials are rather scarce. In view of their advantages including easy tuning of luminescence color, short response time, and relatively high contrast, an electrochromic phosphorescent Ir(III) complex (IrOH) with an OH moiety in the N^N ligand is designed. This complex displays long-lived phosphorescence, whose wavelength and lifetime are very sensitive to complex concentration, pH value, and electric field. Based on the interesting electrochromic phosphorescence of complex IrOH, a quasi-solid information recording and storage device has been designed. A short-lived fluorescent dye has been selected to encrypt the recorded information. In view of the much longer lifetime of IrOH compared with that of the fluorescent dye, decryption has been accomplished by using time-resolved imaging techniques. Hence, it is believed that electrochromic phosphorescence will open up a new and efficient avenue for applications in information encryption and decryption.

A nanoprobe with highly efficient lanthanide luminescence sensitized by transition metal complex has been developed for luminescence imaging in living cells. In this work, Ir(III) complex as the sensitizer and Eu(III) complex as the energy acceptor have been chosen. Both the sensitizer and the energy acceptor have been embedded into the silica nanoparticles through covalent attachment. By optimizing the ligand structures and triplet energy levels of Ir(III) complex, efficient energy transfer from Ir(III) moiety to Eu(III) complex occurred in nanoparticles, which leads to the stable and intense red emission from Eu(III) complex in aqueous solution under the visible excitation of up to 488 nm. This nanoprobe exhibits multiple advantages, including long excitation wavelength, high quantum efficiency, long emission lifetime, narrow emission bands, high photostability, excellent water dispersibility, and good biocompatibility, all of which are very beneficial for applications in bioimaging. The successful application of nanoprobe in bioimaging with visible excitation has been demonstrated. Thus, the design strategy will be a versatile and convenient way to realize excellent lanthanide(III) complex-based bioprobes for practical biomedical applications.

A series of semiconducting polymer dots (Pdots) composed of phosphorescent Ir(III) complexes and polyfluorene units in the main polymer chains are designed, synthesized, and applied in ratiometric oxygen sensing and photodynamic cancer therapy. The ultrasmall Pdots with particle size less than 10 nm are fabricated in aqueous solution on account of amphiphilic nature of the polymers. The Pdots possess fine photostability, biocompatibility, and efficient energy transfer from the polymer main chain to the Ir(III) complex. By utilizing the excited-state energy transfer from phosphorescent Pdots to the ground state molecular oxygen, these Pdots are applied in the optical sensing of oxygen with ratiometric and naked-eye detection as well as high sensitivity in aqueous solution. The Pdots also show low cytotoxicity and can pass across the cell membrane to enter into the cytoplasm. The singlet oxygen photo-generated from the Pdots under irradiation at 488 nm can effectively induce the apoptosis and death of tumor cells for photodynamic cancer therapy in vitro.