Author: ISAAC ZARAZUA MACIAS

CONVERSIÓN FOTOVOLTÁICA EN NANOCRISTALES DE TiO2 SENSIBILIZADOS CON P3OT Y DECORADOS CON NANOCRISTALES DE Au Y CdSe

ISAAC ZARAZUA MACIAS (2009)

"En los últimos años ha habido un incremento en la actividad de investigación sobre celdas solares. Esto se debe a la creciente problemática energético-ambiental que nos hace ir en busca de fuentes de energía mas eficientes y limpias. Por otra parte, con la llegada de los nanomateriales, en los cuales se controla la morfología y tamaño se han mostrado resultados importantes y un incremento en la eficiencia de conversión fotovoltáica. En términos económicos, el desarrollo de celdas solares representa un área de oportunidad enorme, no sólo el ahorro de energía sino también una fuente inagotable que además reducirá los problemas de contaminación asociados a los métodos de producción actual. En el presente trabajo se presenta un estudio de celdas solares nanoestructuradas basadas en TiO2 sensibilizado con P3OT y decoradas con nanocristales de CdSe y Au. Desarrollando desde la técnica de síntesis de los materiales hasta las técnicas de caracterización."

Master thesis

CELDAS SOLARES, ENERGÍA, MEDIO AMBIENTE, NANOCRISTALES, NANOPARTÍCULAS CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA ÓPTICA

STUDY OF THE PHOTOCONVERSION EFFICIENCY ON NANOSTRUCTURED SOLAR CELLS BASED ON TIO2 FILMS SENSITIZED WITH QDS AND DECORATED WITH AU NANOPARTICLES AND P3OT

ISAAC ZARAZUA MACIAS (2013)

"Novel composite titanium dioxide (TiO2) films of 10 µm thickness have been prepared and characterized with emphasis on evaluating their photovoltaic properties. The films contain TiO2 nanocrystals (NCs) with anatase crystalline phase deposited on a substrate with a thin conductor oxide film, composited with CdSe quantum dots (QDs), Au nanoparticles (NPs), and poly(3-octylthiophene) (P3OT) in different configurations. In the case of single sensitized films, Au NPs considerably increases the FF of titania films, indicating that such NPs help to the charge carriers transport. P3OT slightly increases the photocurrent and FF of the TiO2 films, indicating that the polymer may acts as a photogenerator and as a hole conductor giving a relatively good cell performance. However, CdSe QDs sensitized films exhibited the largest photocurrent (237 µA/cm2) giving a photoconversion efficiency of 0.149%, overcoming the efficiency of the other two materials and giving a four-fold efficiency increase of not sensitized TiO2 (0.034%).

These results are attributed to the ability of QDs to photogenerate charge carriers efficiently giving a great amount of electrons to increase the photocurrent. With the introduction of Au NPs or P3OT into the TiO2/QDs films, the photocurrent increases up to ~85% and ~150% while the photoconversion efficiency increases by ~167% and ~177%, respectively. An interesting synergistic effect was observed when Au NPs and P3OT were used in conjunction. The configuration of TiO2/Au/QDs/P3OT film exhibits a photocurrent of 906 !A (an enhancement of ~285%) and the photoconversion efficiency of 0.661% (an enhancement of ~600%) compared to that of TiO2/QDs films. Such significant enhancement is attributed to the ability of Au NPs to facilitate charge separation and improve electron injection as well as P3OT’s ability to inject electrons and enhance hole transport avoiding electron recombination. Such ability when combined with the QD’s strong photoabsorption in the visible, lead to the overall increase in photocurrent generation, fill factor, and consequently photoconversion efficiency."

Doctoral thesis

ORGANIC SOLAR CELLS, IMPEDANCE MODELING, SPECTROSCOPY, PHOTOCONVERSION EFFICIENCY, PHOTOVOLTAIC APPLICATIONS CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA FÍSICA FÍSICA DE ALTAS ENERGÍAS FÍSICA TEÓRICA ALTAS ENERGÍAS

PANCHROMATIC SOLAR-TO‑H2 CONVERSION BY A HYBRID QUANTUM DOTS−DYE DUAL ABSORBER TANDEM DEVICE

ISAAC ZARAZUA MACIAS ELDER DE LA ROSA CRUZ Sixto Gimenez (2013)

Solution-processed mesoscopic oxide semiconductor-based materials offer potentially low-cost and high stability

alternative for next generation of water to hydrogen conversion photoelectrochemical cells (PEC). In the present study, we

demonstrate the effective unassisted H2 generation by a tandem device based on a quantum dot (QD)−dye dual absorber

system. These systems are constituted by a TiO2 mesoscopic photoanode sensitized with CdS QDs and a dye sensitized solar cell

(DSSC), based on ruthenium dye, connected in series. This solar cell supplies the needed photovoltage to induce photodriven

hydrogen production. Opto-electrochemical characterization of the single components allows the prediction of the operational

photocurrents and a reliable estimation of the theoretical power conversion efficiencies of tandem systems. Evolved hydrogen

under simulated solar illumination was collected, and solar to hydrogen conversion efficiencies (STH) were obtained. The

tandem devices have demonstrated high stability in aqueous medium and solar-to-hydrogen conversion efficiency of (0.78 ±

0.04)%, near tripling the efficiency of single QD based photoanodes. These results highlight the importance of the design of

hybrid photoanodes combining the effect of different light absorbers working in parallel tandem devices for the development of

efficient H2 generation QD-based photoelectrochemical cells

Article

CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA

Panchromatic Solar-to-H2 Conversion by a Hybrid Quantum Dots–Dye Dual Absorber Tandem Device

ISAAC ZARAZUA MACIAS ELDER DE LA ROSA CRUZ Sixto Gimenez (2014)

Solution-processed mesoscopic oxide semiconductor-based materials offer potentially low-cost and high stability alternative for next generation of water to hydrogen conversion photoelectrochemical cells (PEC). In the present study, we demonstrate the effective unassisted H2 generation by a tandem device based on a quantum dot (QD)–dye dual absorber system. These systems are constituted by a TiO2 mesoscopic photoanode sensitized with CdS QDs and a dye sensitized solar cell (DSSC), based on ruthenium dye, connected in series. This solar cell supplies the needed photovoltage to induce photodriven hydrogen production. Opto-electrochemical characterization of the single components allows the prediction of the operational photocurrents and a reliable estimation of the theoretical power conversion efficiencies of tandem systems. Evolved hydrogen under simulated solar illumination was collected, and solar to hydrogen conversion efficiencies (STH) were obtained. The tandem devices have demonstrated high stability in aqueous medium and solar-to-hydrogen conversion efficiency of (0.78 ± 0.04)%, near tripling the efficiency of single QD based photoanodes. These results highlight the importance of the design of hybrid photoanodes combining the effect of different light absorbers working in parallel tandem devices for the development of efficient H2 generation QD-based photoelectrochemical cells.

Article

CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA

Impedance Analysis of CdSe Quantum Dot-Sensitized TiO2 Solar Cells Decorated with Au Nanoparticles and P3OT

ISAAC ZARAZUA MACIAS TZARARA LOPEZ LUKE ALEJANDRO TORRES CASTRO ELDER DE LA ROSA CRUZ (2014)

Electrochemical impedance spectroscopy was used to analyze 10 mu m thickness TiO2 films containing 250 nm TiO2 nanoparticles (NPs) with anatase crystalline phase deposited on FTO substrates. The TiO2 films were sensitized with CdSe quantum dots (QDs) (4.5 nm) and decorated with Au nanoparticles (NPs) (7 urn) and poly-3-octylthiophene (P3OT) in three different configurations, namely TiO2/QDs, TiO2/Au/QDs, and TiO2/Au/QDs/P3OT. The characteristic absorption bands for each component, TiO2, P3OT, CdSe QDs, and Au NPs, are centered at 338 nm (3.67 eV), 459 nm (2.7 eV), 552 nm (2.24 eV), and 517 nm (2.40 eV), respectively. The UV-Vis spectrum of the composite film TiO2/Au/QDs/P3OT shows clear absorption peaks from 338 to 700 nm. Equivalent circuits were proposed for the different configuration interfaces to fit experimental impedances. The results suggest that the introduction of Au NPs into the TiO2/Au/QDs films strongly reduces resistance to the electron flux from QDs to TiO2 and increases the overall charge transport. Meanwhile, P3OT in the TiO2/Au/QD/P3OT films promotes hole transport and increases the capacitance with the electrolyte, reducing the electron leakage and improving the fill-factor and the final light energy conversion efficiency.

Article

CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA