Shyam S. Pandey

CH3NH3SnxPb(1–x)I3 Perovskite Solar Cells Covering up to 1060 nm

We report photovoltaic performances of all-solid state Sn/Pb halide-based perovskite solar cells. The cell has the following composition: F-doped SnO2 layered glass/compact titania layer/porous titania layer/CH3NH3SnxPb(1-x)I3/regioregular poly(3-hexylthiophene-2,5-diyl). Sn halide perovskite itself did not show photovoltaic properties. Photovoltaic properties were observed when PbI2 was added in SnI2. The best performance was obtained by using CH3NH3Sn0.5Pb0.5I3 perovskite. 4.18% efficiency with open circuit voltage 0.42 V, fill factor 0.50, and short circuit current 20.04 mA/cm(2) are reported. The edge of the incident photon to current efficiency curve reached 1060 nm, which was 260 nm red-shifted compared with that of CH3NH3PbI3 perovskite solar cells.

Control of charge dynamics through a charge-separation interface for all-solid perovskite-sensitized solar cells.

The relationship between the structure of the charge-separation interface and the photovoltaic performance of all-solid dye-sensitized solar cells is reported. This cell is composed of porous a TiO2/perovskite (CH3NH3PbI(x)Cl(3-x))/p-type organic conductor. The porous titania layer was passivated with Al2O3 or Y2O3 to remove surface traps of the porous titania layer. Both passivations were effective in increasing the efficiency of the solar cell. Especially, the effect of Y2O3 passivation was remarkable. After passivation, the efficiency increased from 6.59 to 7.5%. The increase in the efficiency was discussed in terms of the electron lifetime in TiO2, the thermally stimulated current, the measurement of the microwave refractive carrier lifetime, and transition absorption spectroscopy. It was proven that surface passivation resulted in retardation of charge recombination between the electrons in the porous titania layers and the holes in the p-type organic conductors.

Regioregularity vs Regiorandomness: Effect on Photocarrier Transport in Poly(3-hexylthiophene)

The time-of-flight technique has been used to study transports of photocarriers in regioregular and regiorandom poly(3-hexylthiophene) (P3HT) films by fabricating indium-tin-oxide/P3HT/Al sandwich cell. It has been found that regularity in the coupling of monomers, head-to-tail (HT) has a marked effect on electrical properties and photocarrier transport in P3HT. Both regular and random P3HT films exhibit a dispersive photocurrent response with the positive sign of photocarrier (hole). The room temperature hole mobility of regioregular P3HT is estimated to be 1.21 ×10-3 cm2/Vs and is one order of magnitude larger than that of the random one. The mobility in regioregular P3HT is almost independent of the applied field while that of random P3HT shows a positive field dependence at the field larger than 1.0 ×105 V/cm.

Cyclic step-voltammetric analysis of cation-driven and anion-driven actuation in polypyrrole films

Cation-driven and anion-driven electrochemomechanical deformations (ECMD) in electrodeposited polypyrrole (PPy) films have been investigated by means of cyclic voltammetry and cyclic step-voltammetry (CSV). The film deposited from hydrochloric acid (PPyCl) expanded upon anodic reaction (anodic expansion) while that deposited from dodecyl-benzene sulfonic acid (PPyDBS) exhibited cathodic expansion. In the case of the film deposited from p-phenol sulfonic acid (PPyPPS), it was found to show the anodic expansion at 600 mV (vs Ag wire as a reference electrode) along with the cathodic contraction at -800 mV in CSV. The film obtained from the same lot, however, showed cathodic contraction and anodic expansion only by changing the oxidative potential from 600 mV to -100 mV. This phase inversion indicates that not only the polymerization electrolyte but also the redox potential determines the (de)insertion of ions in the PPyPPS film. Contractive electrochemical creeping was only observed in PPyPPS film in chloride salt electrolytes, indicating that the cation insertion induces the deinsertion of initial-dopant anion from the film.

Transparent conductive oxide layer-less dye-sensitized solar cells consisting of floating electrode with gradient TiOx blocking layer

A transparent conductive oxide less dye-sensitized solar cell (TCO-less DSC) consisting of a glass/a floating electrode (FE)/a stained nanoporous titania layer/a gel electrolyte sheet/a Pt layer/a Ti sheet is reported. The FE is composed of a stainless mesh sheet covered with a gradient TiOx layer, which suppressed back-electron transfers from the stainless to electrolytes. The efficiency increased from 2.87% to 4.68% by replacing a conventional dense TiO2 blocking layer with the gradient TiOx layer. The cell in this architecture gave the efficiency of 5.56% after optimization.

Cyclic voltammetric and electrochemomechanical characteristics of freestanding polypyrrole films in diluted media

Cyclic voltammograms and electrochemomechanical deformations (ECMD) in freestanding polypyrrole (PPy) films have been investigated as a function of electrolyte concentration. It was found that both the oxidative and reductive peaks shifted towards lower potential with the dilution of the electrolyte in PPy films deposited from dodecylbenzene sulfonic acid. In the case of PPy films deposited from p-phenol sulfonic acid, the oxidation and reduction peaks tend to shift towards higher and lower potentials, respectively. These results indicate that the ion contributing to the redox reaction determines the polarity of the potential shift according to the Nernst equation. The ECMD magnitudes were also changed with electrolyte concentration. However, the efficiency of the deformation per degree of doping did not change much over 0.01 M. This indicates that the decrease in ECMD magnitude is not attributed to degradation of the ECMD behavior, but that a decrease in doping quantity for the film essentially effects the decrease in deformation magnitude in diluted media.

Immobilization of glucose oxidase onto Langmuir–Blodgett films of poly-3-hexylthiophene

Abstract Monolayers of poly(3-hexyl thiophene) (P3HT) were obtained by dispensing a solution of P3HT with stearic acid (SA) in chloroform at air-water interface using Joyce–Loebl LB trough. These films were transferred onto indium-tin-oxide coated glass plate by vertical dipping method. Enzyme glucose oxidase (GOX) was immobilized on the films using LB technique. These films were characterized by X-ray diffraction and atomic force microscopic techniques. Photometric response of these P3HT/SA/GOX films was obtained as a function of glucose concentration. These P3HT/SA/GOX LB films show a linearity from 100 to 500 mg/dl of glucose concentration.

Photocarrier Mobility in Regioregular Poly(3-hexylthiophene) Studied by the Time of Flight Method

The carrier mobility in the regioregular poly(3-hexylthiophene)(PHT) film has been studied by means of the time of flight (TOF) method using a sandwich-type cell of indium tin oxide(ITO)/PHT (cast film)/Al. The response of the photocurrent exhibits a dispersive character; however, the clear kink associated with the transit time of the carrier is observed. The drift mobility of holes is determined to be 4 ×10-4 cm2/Vs and almost independent of the field > 105 V/cm at room temperature. This is the largest TOF mobility in poly(3-alkylthiophene) reported to date. It is also found that the activation energy of the mobility is 88 meV and almost independent of the field. The results are discussed taking various transport models into consideration.

Mechanism of Photocarrier Generation and Transport in Poly(3-Alkylthiophene) Films

Carrier mobilities in poly(3-alkylthiophene) (PAT) films (alkyl = 6, 12 and 18), synthesized by chemical oxidation of 3-alkylthiophenes with FeCl3, have been studied using the time of flight (TOF) method. The response of photocurrents indicates the hole as the carrier sign and the highly dispersive transport particularly in the films substituted with long alkyl chains. Using regioregular poly(3-dodecylthiophene) (PAT12) and indium tin oxide (ITO) in the ITO/PAT12/Al sandwich cell, the depletion layer width at the Al/PAT12 interface was estimated to be 60 nm. It has been proposed that photocarriers are effectively generated at the interface and the high internal field helps in the separation of photocarriers. The drift mobilities in PAT12 and PAT18 are 8 ×10-6 cm2/V.s and 3 ×10-6 cm2/V.s, respectively, at the bias field, E = 1.0 MV/cm. They depend on the field as exp (βE1/2/kT), indicating the Poole-Frenkel mechanism for the carrier transport. On the other hand, the mobility of PAT6 is 1.1 ×10-4 cm2/V.s at E = 0.1 MV/cm, shows very weak positive field dependence. The mechanisms of photocarrier generation and transport are discussed taking the polymer structure into consideration and are compared with the results of regioregular PAT films.

Tandem Dye-Sensitized Solar Cells Fabricated on Glass Rod without Transparent Conductive Layers

A tandem dye-sensitized solar cell was fabricated on a glass rod without a transparent conductive oxide layer (TCO-less GR-DSSC). Two model dyes having λmax = 429 nm (Dye II) and λmax = 646 nm (Dye I) respectively were used to examine the potential of the cell. The incident photon to current conversion efficiency (IPCE) curve of the TCO-less GR-DSSC had two peaks at around 490 and 600–650 nm. Open circuit voltage (Voc) of the TCO-less GR-DSSC was 1.13 V which was the sum of the Voc (0.57 V) of each single cell. The results strongly demonstrate that the cell has a tandem character.