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Recombination rates in optoelectronic semiconductors are typically recorded using time-intensive and expensive measurements. Here we present a method to extract decay rate ratios in a facile and rapid manner using only photoluminescence quantum efficiency measurements, which we demonstrate on halide perovskite thin-film samples. We combine these ratios with time-resolved photoluminescence data to extract absolute recombination rates, with excellent agreement when our approach is benchmarked against the more time- and infrastructure-intensive technique of transient absorption spectroscopy. This approach also enables direct quantification of the ratio between total second-order and radiative second-order recombination rates. We demonstrate that radiative recombination is only a fraction of total second-order recombination in the range of halide perovskite samples relevant for photovoltaics. We showcase the implications of rapid extraction of decay rates by extracting decay rate ratios on a microscale and by calculating the expected maximum efficiency of a solar cell fabricated from a measured perovskite film. We show that reducing first-order losses will significantly improve solar cell efficiency for our samples until time-resolved photoluminescence lifetimes are longer than approximately 1 µs (at low excitation pulse intensity), at which point second-order nonradiative recombination limits the efficiency of perovskite solar cells. This work presents a framework for rapidly screening optoelectronic semiconductors with techniques widely accessible to many research groups, identifies decay processes that would otherwise be missed, and directly relates the extracted values to predicted device performance metrics.

Electrochemical energy storage devices that can harvest energy from the environment and store it are increasingly important to address energy poverty in developing parts of the world as well as pow...

Hybrid-perovskite-based optoelectronic devices are demonstrating unprecedented growth in performance, and defect passivation approaches are highly promising routes to further improve properties. Here, the effect of the molecular ion BF4 - , introduced via methylammonium tetrafluoroborate (MABF4 ) in a surface treatment for MAPbI3 perovskite, is reported. Optical spectroscopy characterization shows that the introduction of tetrafluoroborate leads to reduced non-radiative charge-carrier recombination with a reduction in first-order recombination rate from 6.5 × 106 to 2.5 × 105 s-1 in BF4 - -treated samples, and a consequent increase in photoluminescence quantum yield by an order of magnitude (from 0.5 to 10.4%). 19 F, 11 B, and 14 N solid-state NMR is used to elucidate the atomic-level mechanism of the BF4 - additive-induced improvements, revealing that the BF4 - acts as a scavenger of excess MAI by forming MAI-MABF4 cocrystals. This shifts the equilibrium of iodide concentration in the perovskite phase, thereby reducing the concentration of interstitial iodide defects that act as deep traps and non-radiative recombination centers. These collective results allow us to elucidate the microscopic mechanism of action of BF4 - .

Understanding the nanoscopic chemical and structural changes that drive instabilities in emerging energy materials is essential for mitigating device degradation. The power conversion efficiency of halide perovskite photovoltaic devices has reached 25.7 per cent in single-junction and 29.8 per cent in tandem perovskite/silicon cells

Electroluminescence efficiencies of metal halide perovskite nanocrystals (PNCs) are limited by a lack of material strategies that can both suppress the formation of defects and enhance the charge carrier confinement. Here we report a one-dopant alloying strategy that generates smaller, monodisperse colloidal particles (confining electrons and holes, and boosting radiative recombination) with fewer surface defects (reducing non-radiative recombination). Doping of guanidinium into formamidinium lead bromide PNCs yields limited bulk solubility while creating an entropy-stabilized phase in the PNCs and leading to smaller PNCs with more carrier confinement. The extra guanidinium segregates to the surface and stabilizes the undercoordinated sites. Furthermore, a surface-stabilizing 1,3,5-tris(bromomethyl)-2,4,6-triethylbenzene was applied as a bromide vacancy healing agent. The result is highly efficient PNC-based light-emitting diodes that have current efficiency of 108 cd A−1 (external quantum efficiency of 23.4%), which rises to 205 cd A−1 (external quantum efficiency of 45.5%) with a hemispherical lens. Guanidinium doping is shown to enhance the operation of perovskite nanocrystal light-emitting diodes.

Perovskite light-emitting diodes (PeLEDs) based on three-dimensional (3D) polycrystalline perovskites suffer from ion migration, which causes overshoot of luminance over time during operation and reduces its operational lifetime. Here, we demonstrate 3D/2D hybrid PeLEDs with extremely reduced luminance overshoot and 21 times longer operational lifetime than 3D PeLEDs. The luminance overshoot ratio of 3D/2D hybrid PeLED is only 7.4% which is greatly lower than that of 3D PeLED (150.4%). The 3D/2D hybrid perovskite is obtained by adding a small amount of neutral benzylamine to methylammonium lead bromide, which induces a proton transfer from methylammonium to benzylamine and enables crystallization of 2D perovskite without destroying the 3D phase. Benzylammonium in the perovskite lattice suppresses formation of deep-trap states and ion migration, thereby enhances both operating stability and luminous efficiency based on its retardation effect in reorientation., Ion migration can induce overshoot of luminance in normal 3D perovskite light-emitting diode devices and results in reduced lifetime. Here Kim et al. show that the ion migration and overshoot can be suppressed in 3D/2D hybrid perovskites, leading to 21 times longer operational lifetime.

Solar cells and optoelectronics based on lead halide perovskites are generating considerable interest but face challenges with the use of toxic lead. In this study, we fabricate and characterize lead-free perovskites based on germanium and tin solid solutions, CH3NH3Sn(1-x)GexI3 (0 ≤ x ≤ 1). We show that these perovskite compounds possess band gaps from 1.3 to 2.0 eV, which are suitable for a range of optoelectronic applications, from single junction devices and top cells for tandems to light-emitting layers. Their thermodynamic stability and electronic properties are calculated for all compositions and agree well with our experimental measurements. Our findings demonstrate an attractive family of lead-free perovskite semiconductors with a favorable band-gap range for efficient single-junction solar cells.

Over the past few years the organic-inorganic hybrid perovskite systems have emerged as a promising class of materials for photovoltaic and electroluminescent thin-film device applications, in view of their unique set of tunable optoelectronic properties. Importantly, these materials can be easily solution-processed at low temperatures and as such are amenable to facile molecular engineering. Thus, a variety of low-dimensional forms and quantum structures of these materials can be obtained through strategic synthetic manipulations through small molecule incorporation or molecular ion doping. In this Minireview, we specifically focus on these approaches and outline the possibilities of utilizing these for enhanced functionalities and newer application domains.

State-of-the-art Li (or Na) ion batteries work by insertion/extraction of the alkali metal ions into a porous electrode material, where the overall capacity is strongly dependent on the accessibility of the host material interior to the ions. On the other hand, the performance stability depends on various factors governed by the specific constitution of the electrode. Here we show that molecularly engineered low-dimensional hybrid perovskites can work as excellent anode materials for alkali-ion batteries. We measure a high reversible capacity of 646 mA h g−1 at 100 mA g−1 with good stability tested up to 250 cycles for the benzidine mediated lead iodide based 1D system. An ex situ analysis of the electrodes reveals that the storage primarily occurs via the Lix(or Nax)Pb alloying/de-alloying process. We anticipate that these results open a new direction for the use of low-dimensional hybrid perovskites for energy storage applications.

We report the synthesis of fully molecular ion (BF4–)-based organic–inorganic hybrid perovskite CH3NH3Pb(BF4)3, which is a wide band gap semiconductor, and the same can be easily tuned toward the visible by the incorporation of bromide or iodide ions in the crystal framework simply by changing lead precursors. We have also successfully transformed the distorted 3D molecular-ion-induced perovskite to 2D (C4H9NH3)2Pb(BF4)4, (C4H9NH3)2PbBr(4–x)(BF4)x, and (C4H9NH3)2PbI(4–x)(BF4)x perovskites that exhibit the optical absorption over the UV to visible region. The thin films of molecular-ion-containing 2D perovskites with Br– and I– anions show blue and green luminescence, respectively, under UV illumination.

We report facile, one step synthesis of disordered graphitic carbon by high temperature (1000 °C) pyrolysis of indanthrone dye (ID). The pyrolysed carbon is disordered in nature and the same is clearly evidenced by various analytical techniques like X-ray diffraction, Raman spectroscopy and high resolution transmission electron microscopy. Na-insertion properties of such indanthrone dye derived disordered graphitic carbon (IDDGC) is evaluated in half-cell assembly (Na/IDDGC). The test cell delivered a reversible capacity of ∼160 mAh g −1 at current density of 25 mA g −1 . In addition, excellent cycling profiles are noted for such IDDGC, which retains ∼67% of initial reversible capacity after 500 cycles. The present study clearly highlights the importance of disorder in the graphitic carbon for efficient Na-ion storage.

We report the synthesis of fully molecular ion (BF

Three new D-A-π-A metal-free organic dyes viz. (E)-2-cyano-3-(10-dodecyl-7-(7-(10-dodecyl-10H-phenothiazin-3-yl)benzo[c][1,2,5]thiadiazol-4-yl)-10H-phenothiazin-3-yl)acrylic acid (AI-1), (E)-2-cyano-3-(10-dodecyl-7-(7-(10-dodecyl-10H-phenothiazin-3-yl)-2-octyl-2H-benzo[d][1,2,3]triazol-4-yl)-10H-phenothiazin-3-yl)acrylic acid (AI-2) and (E)-2-cyano-3-(10-dodecyl-7-(6-(10-dodecyl-10H-phenothiazin-3-yl)pyridin-2-yl)-10H-phenothiazin-3-yl)acrylic acid (AI-3) based on phenothiazine as donor and non-conjugated π-spacer were designed and synthesized. The incorporation of different 'internal acceptors' (electron traps) such as benzothiadiazole (BTD), benzotriazole (BTA) and pyridine were shown to allow systematic tuning of the energy levels and the photo-physical properties. AI-1 dye showed lower electronic disorder as compared to the other two dyes. The efficiencies achieved with AI-1, AI-2 and AI-3 dyes were 8.5 % (Jsc = 15.42 mA/cm2, Voc = 0.78 V, FF = 68 %), 7% (Jsc = 12.8 mA/cm2, Voc = 0.78 V, FF = 68 %), and 6.7 % (Jsc = 11.57 mA/cm2, Voc = 0.82 V, FF = 68.26 %), respectively. The incorporation of non- conjugated phenothiazine as a π-spacer in D-A-π-A dyes showed remarkable enhancement in photovoltaic performance of DSSC devices. The sealed DSSC devices with iodide/tri-iodide (I-/I3-) based liquid electrolyte showed promising stability under ambient condition.

Two novel metal-free organic donor–π–acceptor dyes were synthesized using electron-rich 10-butyl-(2-methylthio)-10H-phenothiazine as a donor and cyanoacrylic acid as an acceptor. The spectral response of the dye was tuned by introducing a vinylene thiophene π-bridge. Obtained optical and electrochemical properties of the dyes seemed to be promising in terms of employing them as light harvesters in dye-sensitized solar cells (DSCs). The efficiencies of the devices under standard AM 1.5G (100 mW cm−2) conditions reached 7.3% with volatile electrolyte. The differences in the photovoltaic parameters of these DSCs were explained by comparing the results of electrochemical impedance spectroscopy (EIS) measurements and transient photovoltage and photocurrent decay experiments.

Perovskites based on organometal lead halides have attracted great deal of scientific attention recently in the context of solar cells and optoelectronic devices due to their unique and tunable electronic and optical properties. Herein, we show that the use of electrospray technique in conjunction with the antisolvent–solvent extraction leads to novel low-dimensional quantum structures (especially 2-D nanosheets) of CH3NH3PbI3- and CH3NH3PbBr3-based layered perovskites with unusual luminescence properties. We also show that the optical bandgaps and emission characteristics of these colloidal nanomaterials can be tuned over a broad range of visible spectral region by compositional tailoring of mixed-halide (I- and Br-based) perovskites.

A molecular ion (BF4(-)) substituted hybrid perovskite CH3NH3PbI(3-x)(BF4)x is synthesized. The substituted perovskite shows significant enhancement in electrical conductivity at low frequencies and improved photoresponse under AM1.5 illumination as compared to the perovskite (CH3NH3PbI3).

A molecular ion (BF4−) substituted hybrid perovskite CH3NH3PbI(3−x)(BF4)x is synthesized. The substituted perovskite shows significant enhancement in electrical conductivity at low frequencies and improved photoresponse under AM1.5 illumination as compared to the perovskite (CH3NH3PbI3).

We report realization of strong green fluorescence in a fully biocompatible highly spherical mesoscale molecular assembly of sophorolipid created by pulsed UV laser processing of a water-based dispersion of sophorolipid. Remarkably, the said fluorescence is totally absent in the original molecule of sophorolipid and is thus the property of the pulsed laser induced modifications in the molecule and the assembly. We have separately examined the consequences of laser irradiation for glucose and oleic acid components which form the sophorolipid. This fluorescence character appears to be driven by the oleic acid component while the assembly process is assisted by the glucose component. Importantly the laser synthesized mesostructures can be easily redispersed in an aqueous medium after being dried and can also be loaded with magnetic nanoparticles (magnetite) for inducing the hyperthermia effect.

A simple two step strategy was developed to introduce carboxyl groups via Vilsmeier–Haack formylation on the commercially available conjugated polymer BEHP-co-MEH PPV followed by Knoevenagel condensation. Adsorption of the carboxyl-modified polymer onto TiO2 film and J–V curves were studied for the dye sensitized solar cell and compared with the base polymer BEHP-co-MEH PPV. Carboxyl-modification of BEHP-co-MEH PPV resulted in significant enhancement in the efficiency (3%), compared to the base polymer which showed an efficiency of only 0.3%. The details of the synthetic procedure, characterization and the photovoltaic property measurements are presented and discussed.