Structural and optical properties of ionic liquid based hybrid perovskitoid: a combined experimental and theoretical investigation

Herein, we report a novel layered lead bromide, (CH3CH2)3N+Br−(CH2)2NH+3)PbBr3, where bulky organic cations, (CH3CH2)3N+Br−(CH2)2NH+3), amino-ethyl triethyl ammonium [aetriea] were not only incorporated between the inorganic layers but also sandwiched within the inorganic [PbBr6]4− octahedral layered structure. The UV-Visible, photoluminescence spectroscopy (PL), X-ray diffraction (XRD) and a field-emission scanning electron microscope (FE-SEM) result show that the new perovskitoid has a microrod shape with an estimated bandgap of ∼3.05 eV. The structural and optoelectronic properties of the [aetriea]PbBr3perovskitoid were further corroborated by first-principles density functional theory (DFT) calculations. Thermogravimetric analysis (TGA) data show good stability of the [aetriea]PbBr3perovskitoid. Time-resolved photoluminescence (TRPL) decays from new [aetriea]PbBr3perovskitoid showing 6 ns average lifetime. These results suggest that doubly charged cation hybrid perovskite materials are potential candidates for optoelectronic applications

A step towards environmental benign Mg/Pb based binary metal mixed halide perovskite material

Today's the best performing perovskite solar cells utilise Pb2+ as a major bivalent cation source, however, the presence of toxic Pb is major issue that put its commercialization in dire straits. In this report, we unveiled the chemical synthesis and characterisation of Mg/Pb binary metal mixed halide perovskite with chemical formula CH3NH3PbxMg1-xI3-yCly using MgCl2 as a compositional gradient with nominal value of x from 0.1 to 0.9. The FESEM images of compositions corresponding to higher proportion of Cl- (or MgCl2) demonstrate improved particle (or grain) size of similar to 8-12 mu m. There is a close resemblance of stoichiometric ratio of Pb:Mg obtained from EDX analysis with that of incorporated stoichiometric ratio of Pb:Mg. Further, Mg and Cl incorporation is strengthened by the characteristic spectral peak for core level electron of Mg(2p) and Cl(2p) other than Pb(4f) and I(3d) in the XPS survey spectrum of composition x = 0.5. These binary Mg/Pb Perovskite with bandgap in the range 1.57-1.59 eV behave as comparatively less toxic potential candidate for the single junction module. The IR studies at room temperature show observable shift in peak positions on comparing two extreme compositions i.e., x = 0.1 and x = 1.0. It is noticeable that both standard CH3NH3PbI3 and binary Mg/Pb Perovskite with nominal value x = 0.7 have comparable thermal stability, however, the composition x = 0.1 have lower thermal stability than x = 0.7. The carrier lifetimes measurements by Microwave Detected Photoconductivity (MDP) showed an improvement of lifetime to 142 mu s for nominal value x = 0.9 compared to 76 mu s in case of MAPbI(3) film. Correspondingly we see a 160 mV improvement in open-circuit voltage (V-OC) in the solar cells fabricated with nominal value x = 0.9 (V-OC = 1.07 V) as compared to standard MAPbI(3) cells (V-OC = 0.90 V). The champion cell with nominal value x = 0.9 shows PCE of 14.2% where as the best PCE of MAPbI(3) cell is 14.50% under a reverse scan

Molecular Engineering and Structure-Related Properties of Squaraine Dyes Based on the Core and Wings Concept

Three new squaraine-based functional π-conjugated molecules were synthesized considering the core and wings concept. The molecules, SQ-DICN, SQ-DIEt-RH, and SQ-DICN-RH, were end-capped with three different wings, such as malononitrile, 2-(3-hexyl-4-oxothiazolidin-2-ylidene)­malononitrile, and 3-ethyl-2-thioxothiazolidin-4-one. Among the three dyes, SQ-DICN-RH showed the highest molar extinction coefficient. The photoluminescence of all the dyes showed an opposite trend to that of the absorption maximum. The electrochemical results showed that the lowest unoccupied molecular orbital level of all the dyes ranged from −3.72 to −3.82 eV, whereas the highest occupied molecular orbital ranged from −4.89 to −4.94 eV. Solvatochromism was carried out to observe the effects of the solvent containing the dyes. The electronic structure of the dyes was examined using ab initio simulations. The dyes were characterized theoretically, and the red-shifted absorption of SQ-DICN-RH was explained and correlated with its biradicaloid character and singlet–triplet energy gap

Selective integration of hierarchical nanostructured energy materials : an effective approach to boost the energy storage performance of flexible hybrid supercapacitors

High energy density, fast charge–discharge capability, high flexibility, and sustained cycle life are the key challenges in the application of flexible supercapacitors (SCs) in modern electronics. These primary requirements could be accomplished by engineering a new class of current collectors consisting of hierarchical combinations of various active materials. This study reports the selective integration of hierarchical Ni(OH)₂ nanoneedle arrays with NiO–NiCo₂O₄ nanosheet arrays (Ni(OH)₂ NNAs@NiO–NiCo₂O₄ NSAs) on flexible fabric for high-performance electrodes. The novel core–shell-like hetero-nanoarchitectures not only enhance the electrochemical activity and specific surface area but also, more importantly, provide superhighways for the ultrafast transport of electrons and ions. As a battery-type material, the core–shell-like Ni(OH)₂ NNAs@NiO–NiCo₂O₄ NSAs display a high specific capacity of 326.7 mA h g⁻¹ at 2 A g⁻¹ in aqueous 3 M KOH; this value is 1.89, 1.23 and 1.14 times those of NiO–NiCo₂O₄, NiO@NiO–NiCo₂O₄ and Co₃O₄@NiO–NiCo₂O₄ electrodes, respectively. Most importantly, a flexible hybrid SC (FHSC, Ni(OH)₂ NNAs@NiO–NiCo₂O₄ NSAs//graphene-ink) demonstrates a superhigh energy density of 97.1 W h kg⁻¹ and a superior long cycling lifespan with 94.7% retention over 5000 cycles. Utilizing these excellent energy storage properties, the fabricated FHSC operated a multifunction electronic display and light up different colored light emitting diodes for real-time applications.This work was supported by BK 21 PLUS, Creative Human Resource Development Program for IT Convergence, Pusan National University, Busan, South Korea

Unveiling the role of carbon black in printable mesoscopic perovskite solar cells

Carbon-based perovskite solar cells (C–PSCs) have attracted significant attention from the scientific community owing to their improved stability, low-cost fabrication, and potential scalability with screen printing technology. In this study, we examine the effect of three most commonly used carbon blacks, i.e. vulcan carbon (VC), meso carbon (MC) and super P (SP), on the properties of the resultant carbon electrode and the effect on photovoltaic performance as well as device stability. It shows that VC based carbon electrode promotes decent wettability to perovskite precursor solution, excellent infiltration and strong adhesion within the device stacks due to its high porosity and high pore volume. Furthermore, counter electrodes consisting of highly conductive VC exhibit sheet resistance of as low as 11.0 Ohm/□ as compared to those of MC (15.3 Ohm/□) and SP (22.0 Ohm/□). C–PSCs fabricated using VC based carbon electrode display champion power conversion efficiency of 12.55% with almost no decrease in efficiency under ambient conditions (~75% relative humidity) for 30 days without encapsulation. This work highlights the importance of carbon paste formulation for developing highly efficient and stable perovskite solar cells.National Research Foundation (NRF)N.M., S.G.M., would like to acknowledge funding from the Singapore National Research Foundation through the Intra-CREATE Collaborative Grant (NRF2018-ITC001-001)

Iodide manipulation using zinc additives for efficient perovskite solar minimodules

Abstract Interstitial iodides are the most critical type of defects in perovskite solar cells that limits efficiency and stability. They can be generated during solution, film, and device processing, further accelerating degradation. Herein, we find that introducing a small amount of a zinc salt- zinc trifluoromethane sulfonate (Zn(OOSCF3)2) in the perovskite solution can control the iodide defects in resultant perovskites ink and films. CF3SOO̶ vigorously suppresses molecular iodine formation in the perovskites by reducing it to iodide. At the same time, zinc cations can precipitate excess iodide by forming a Zn-Amine complex so that the iodide interstitials in the resultant perovskite films can be suppressed. The perovskite films using these additives show improved photoluminescence quantum efficiency and reduce deep trap density, despite zinc cations reducing the perovskite grain size and iodide interstitials. The zinc additives facilitate the formation of more uniform perovskite films on large-area substrates (78-108 cm2) in the blade-coating process. Fabricated minimodules show power conversion efficiencies of 19.60% and 19.21% with aperture areas of 84 and 108 cm2, respectively, as certified by National Renewable Energy Laboratory (NREL), the highest efficiency certified for minimodules of these sizes

Toward efficient and stable perovskite photovoltaics with fluorinated phosphonate salt surface passivation

Surface passivation has been proven as an effective strategy to improve power conversion efficiency and stability of perovskite solar cells. However, the rationale of choosing appropriate passivator is still not clear yet, whether it should form strong or weak interaction with perovskite beneath. Here, we selectively choose two molecules, fluorinated phosphonic acid and its corresponding phosphonate salt, and monitor the extent of interaction between these passivators and perovskite surface. The effect of these passivation on stability and device performance is also conducted. Higher photoluminescence and carrier lifetime were observed in perovskite film treated with phosphonium salt passivation which possesses stronger interaction with perovskite. The corresponded device shows enhancement in conversion efficiency from 18.27% to 19.44%. Furthermore, water contact angle of passivated perovskite film was exceeding 110.9° as compared to the untreated perovskite (74.5°). This super hydrophobic nature enables excellent long term stability of devices, retaining over 90% of their initial efficiency after 90 days stored under ambient condition with 30% relative humidity.Ministry of Education (MOE)Nanyang Technological UniversityNational Research Foundation (NRF)Accepted versionThe authors acknowledge funding from the National Research Foundation, Prime Minister’s Office, Singapore under its Intra-CREATE Collaborative Grant (NRF2018-ITC001-001), Competitive Research Program (CRP Award No. NRF-CRP14-2014-03) and Singapore- Berkeley Research Initiative for Sustainable Energy (SinBeRISE) CREATE Program, Office of Naval Research Global (ONRG-NICOP-N62909-17-1-2155), Nanyang Technological University start-up grants (M4080514 and M4081293); the Ministry of Education Academic Research Fund Tier 1 grants (RG184/14, RG166/16 and RG101/15), and Tier 2 grants (MOE2016-T2-1-100, MOE2014-T2-1-044, and MOE2015-T2-2-015). G. Han would like to acknowledge the support of the Fundamental Research Funds of Shandong University numbered 2019GN002

Effects of all-organic interlayer surface modifiers on the efficiency and stability of perovskite solar cells

Surface imperfections created during fabrication of halide perovskite (HP) films could induce formation of various defect sites that affect device performance and stability. In this work, all-organic surface modifiers consisting of alkylammonium cations and alkanoate anions are introduced on top of the HP layer to passivate interfacial vacancies and improve moisture tolerance. Passivation using alkylammonium alkanoate does not induce formation of low-dimensional perovskites species. Instead, the organic species only passivate the perovskite's surface and grain boundaries, which results in enhanced hydrophobic character of the HP films. In terms of photovoltaic application, passivation with alkylammonium alkanoate allows significant reduction in recombination losses and enhancement of open-circuit voltage. Alongside unchanged short-circuit current density, power conversion efficiencies of more than 18.5 % can be obtained from the treated sample. Furthermore, the unencapsulated device retains 85 % of its initial PCE upon treatment, whereas the standard 3D perovskite device loses 50 % of its original PCE when both are subjected to ambient environment over 1500 h.National Research Foundation (NRF)The authors would like to acknowledge funding from the Singapore National Research Foundation through the Intra-CREATE Collaborative Grant (NRF2018-ITC001-001), Energy Innovation Research Program (NRF2015EWT-EIRP003-004, Solar CRP: S18-1176-SCRP) and the Competitive Research Program (NRF-CRP14-2014-03)

Stabilizing the electroluminescence of halide perovskites with potassium passivation

Halide perovskites are of great interest for light-emitting diodes (PeLEDs) in recent years due to their excellent photo- and electroluminescence properties. However, trap/defects and ion migration of devices under high external driving voltage/current are yet overcome. In this work, it is found that upon potassium (K) addition to a CsPbBr3/Cs4PbBr6 (3D:0D = 0.85:0.15) perovskite, a locally-disordered 0D Cs4-xKxPbBr6 phase is formed with nearly 0.35:0.65 admixture of 0D:3D, along with an unreacted KBr phase potentially passivating the surface and grain boundaries. The formation of CsPbBr3 nanocrystals (~10nm) confined within the Cs4-xKxPbBr6 matrix accompanied by larger CsPbBr3 grains (~50nm) is further confirmed by high-resolution transmission electron microscopy. In addition, the kinetics of ion migration were characterized with Auger electron spectroscopy and double-layer polarization using capacitive-frequency measurements, revealing significantly lower hysteresis, halide ion migration and accumulation for the K-incorporated samples during device operation, resulting in substantial improvements in LED performances and stability.NRF (Natl Research Foundation, S’pore)MOE (Min. of Education, S’pore)Accepted versio