6 research outputs found

    Lead Free CH3NH3SNI3 Perovskite Thin-Film with P-type Semiconducting Nature and Metal-like Conductivity

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    CH3NH3SnI3 and CH3NH3PbI3 have become very promising light absorbing materials for photovoltaic devices over the last several years. CH3NH3PbI3 based perovskite solar cells have reached a solar-to-electricity conversion efficiency of ~ 22%. Nevertheless, CH3NH3PbI3 perovskite solar cells contain lead, which has serious consequences for the environment and human health. In this work, the lead was replaced with less toxic tin. Lead free CH3NH3SnI3 perovskite thin film was prepared by two low temperature solution processing methods and characterized using various tools such as Xray Diffraction (XRD) and absorption spectroscopy (UV-VIS). The distinctive p-type semiconducting nature and metal like conductivity of CH3NH3SnI3 were confirmed by the measurements of electrical and optical properties. Crystal structures and uniform film formation of CH3NH3SnI3 layer were analyzed by XRD and scanning electron microscopy (SEM). The CH3NH3SnI3 film morphology, uniformity, light absorption and electrical properties strongly depend on the preparation methods and precursor solutions. The CH3NH3SnI3 perovskites fabricated using dimethylformamide (DMF) exhibited higher crystallinity and stronger light harvesting capability than those fabricated using a blend solvent of dimethyl sulfoxide (DMSO) and gamma-butyrolactone (GBL). The local nanoscale photocurrent mapping confirmed that CH3NH3SnI3 can be used as an active layer and has a potential to fabricate lead free photovoltaic devices. The CH3NH3SnI3 film also showed a strong absorption in visible and near infrared spectrum with an absorption onset of 1.3 eV

    Transparent Platinum Counter Electrode for Building Integrated Dye-sensitized Solar Cells

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    A new method for fabrication of highly transparent Pt counter electrodes (CE) has been developed based on spray deposition of Pt nanoparticles (Pt-NPs) on hot substrates. The platinum consumption hence the cost of the counter electrode was reduced over 86%, compared to conventional Pt counter electrode prepared by sputter deposition method. The prepared Pt-NP film led to 89% transparency and 80% transparency when integrated with indium tin oxide/glass substrate. Scanning electron microscope (SEM) and atomic force microscope (AFM) images showed a large surface area for the nanoporous Pt nanoclusters. DSSCs with Pt-NP counter electrode had 6.17% power conversion efficiency, comparable to the 6.46% efficiency of the corresponding reference opaque DSSC with sputtered Pt counter electrode

    Interconnected ZrO2 doped ZnO/TiO2 network photoanode for dye-sensitized solar cells

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    In this study, ZrO2 surface modified ZnO/TiO2 composite film is adapted as photoanode in dye sensitized solar cells (DSSCs) and compared with un-passivated ZnO/TiO2 DSSC performance. The performance is investigated by dark and photocurrent density–voltage ( J–V) characteristics, quantum efficiency and electrochemical impedance spectroscopy. The J–V characteristics shows that DSSCs with ZrO2surface passivation produces significantly high open-circuit voltage of 0.87 V, short-circuit current density of 13.6 mA cm−2, fill factor of 0.65 and a power conversion efficiency of ∼6.97% under simulated AM1.5 solar irradiation. The higher onset potential in the dark, larger open-circuit potential under illumination, and an enhancement in power conversion efficiency strongly suggests an efficient suppression of back electron transfer from the conduction band of the hetero-phase junctions to the oxidized species in the electrolyte as established by dark and illuminated J–V characteristics. Thus, the oxidized dye molecules are readily regenerated by a redox couple dissolved in an electrolyte, allowing more photon excitation by dye molecules. The electrochemical impedance data extracts further provide additional evidence of the enhancement in photocurrent and lower charge carrier resistances observed in ZrO2/ZnO/TiO2/dye photoelectrode. With the ZrO2 surface modification, main loss mechanism in the device is suppressed and backward recombination reaction is minimized. Keywords: ZrO2 passivated ZnO/TiO2 hetero-phase composite, Mesoporous films dye-sensitized solar cells, Dark current, Equivalent circuit mode

    Transparent Platinum Counter Electrode for Efficient Semi-transparent Dye-sensitized Solar Cells

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    A method for fabrication of highly transparent platinum counter electrodes (CEs) has been developed based on spray coating of Pt nanoparticles (NPs) on hot substrates. This method leads to 86% reduction in Pt consumption reducing the Pt cost per peak watt of counter electrode from 0.79/Wpdownto0.79/Wp down to 0.11/Wp compared to the conventional Pt counter electrodes made by sputter deposition. The simplicity and low cost of this method provide a basis for an up-scalable fabrication process. The Pt NP layer is over 88% transparent, leading to overall transparency of 80% when incorporated with indium tin oxide/glass substrates for functional counter electrodes. This counter electrode exhibits a large surface area and high catalytic activity, comparable to that of the conventional opaque CEs. Semi-transparent dye-sensitized solar cells fabricated based on this counter electrode showed 6.17% power conversion efficiency

    Efficient Perovskite Solar Cells by Temperature Control in Single and Mixed Halide Precursor Solutions and Films

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    Thermal annealing and precursor composition play critical roles in crystallinity control and morphology formation of perovskite thin films for achieving higher photovoltaic performance. In this study we have systematically studied the role of annealing temperature on the crystallinity of perovskite (CHNH<sub>3</sub>PbI<sub>3</sub>) thin films cast from single (without PbCl<sub>2</sub>) and mixed (with PbCl<sub>2</sub>) halide precursors. Higher annealing temperature leads to agglomeration of perovskite crystals. The effects of annealing temperature on the performance of perovskite solar cells are different in single and mixed halide processed films. It is observed that the perovskite crystallinity and film formation can be altered with the addition of lead chloride in the precursor solution. We report that single halide perovskite solar cells show no change in morphology and crystal size with increase in annealing temperature, which was confirmed by UV–vis absorption spectroscopy, X-ray diffraction (XRD), and atomic force microscopy (AFM). However, mixed halide perovskite (CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3–<i>x</i></sub>Cl<sub><i>x</i></sub>) solar cells show significant change in crystal formation in the active layer when increasing annealing temperature. In addition, heating perovskite precursor solutions at 150 °C can lead to enhancement in solar cell efficiency for both single and mixed halide systems. Perovskite solar cells fabricated using heated precursor solutions form dense film morphology and thus significantly improved fill factor up to 80% with power conversion efficiency exceeding 13% under AM 1.5 condition

    Interfacial Study To Suppress Charge Carrier Recombination for High Efficiency Perovskite Solar Cells

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    We report effects of an interface between TiO<sub>2</sub>–perovskite and grain–grain boundaries of perovskite films prepared by single step and sequential deposited technique using different annealing times at optimum temperature. Nanoscale kelvin probe force microscopy (KPFM) measurement shows that charge transport in a perovskite solar cell critically depends upon the annealing conditions. The KPFM results of single step and sequential deposited films show that the increase in potential barrier suppresses the back-recombination between electrons in TiO<sub>2</sub> and holes in perovskite. Spatial mapping of the surface potential within perovskite film exhibits higher positive potential at grain boundaries compared to the surface of the grains. The average grain boundary potential of 300–400 mV is obtained upon annealing for sequentially deposited films. X-ray diffraction (XRD) spectra indicate the formation of a PbI<sub>2</sub> phase upon annealing which suppresses the recombination. Transient analysis exhibits that the optimum device has higher carrier lifetime and short carrier transport time among all devices. An optimum grain boundary potential and proper band alignment between the TiO<sub>2</sub> electron transport layer (ETL) and the perovskite absorber layer help to increase the overall device performance
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