Effect of the Sintering Procedure on the Photoelectrochemical Performances of Nanostructured Mixed Oxides as Photocathodes of p and Tandem Dye-Sensitized Solar Cells with Superior Conversion Properties
Matteo Bonomo a b, Emmanuel Ekoi c, Claudia Barolo a, Denis Dowling c, Danilo Dini b, Aldo Di Carlo d
a University of Turin, Department of Chemistry and NIS Interdepartmental Center, Via Pietro Giuria, 7, Torino, 10125, Italy
b Department of Chemistry Chemistry, University of Rome La Sapienza, Piazzale Aldo Moro 5, 00185, Rome
c School of Mechanical and Materials Engineering, University College Dublin (UCD), Belfield, Dublin 4, Dublin, Ireland
d CHOSE - Centre for Hybrid and Organic Solar Energy, Department of Electronic Engineering, University of Rome Tor Vergata, Via del Politecnico, 1, Roma, Italy
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV19)
Roma, Italy, 2019 May 12th - 15th
Organizers: Prashant Kamat, Filippo De Angelis and Aldo Di Carlo
Oral, Matteo Bonomo, presentation 155
Publication date: 11th February 2019

 

P-type dye sensitized solar cells (p-DSCs) suffer low performances compared to the n-type counterpart[1]. One of the main causes of this is the fast recombination reaction occurring between the photoinjected holes in the valence band of the p-type semiconductor (usually NiO) and the reduced form of the redox shuttle (typically I-). As a matter of fact, recombination phenomena at the NiO/electrolyte interface heavily limit both photovoltage and photocurrent. Different approaches have been adopted to minimize such an unwanted process: these range  from the pretreatment of the electrode surface with NaOH[2] to the employment of passivating organic molecules (e.g. CDCA) in the sensitizing solution and/or in the electrolyte solution.[3]

 

The present contribution describes the implementation of metal oxide (MOx in which M is Al, Zr, Y or Ce) nanoparticles (NPs) as anti-recombination agent in NiO-based photocathodes for p-DSCs. MOx NPs (diameter, Ø = 20 nm) and NiO nanoparticles (Ø < 50 nm) were dispersed together in a methanol solution and spray-deposited onto FTO. Different MOx/NiO molar ratio (ranging from 1 to 20%) were considered. The as deposited films were annealed at 450 °C in a conventional oven or by Microwave-assisted Rapid Discharge Sintering (RDS). The latter method was proved to be more effective by assuring the formation of a more porous, able to load more sensitizer (i.e. P1) molecules, and electroactive film. Scanning Electron Microscopy (SEM) was used to check the morphology of the electrodes and the effective dispersion of MOx NPs. It was proved that the nature and the electrochemical and optical properties of MOx deeply influence the photoelectrochemical behavior of photocathodes. Indeed, the optimal MOx/NiO ratio is strongly dependent on the nature of the metal oxide but all tend to form aggregates and macrostructures if their relative concentration exceeds 10%.

 

Among the investigated MOx NPs, Zirconium Oxide (ZrO2) was found to be the most performing additive: an 80% enhancement of the photoconversion compared to unmodified photocathode was obtained following on from the minimization of recombination reactions at the electrode/electrolyte interface as proved by Electrochemical Impedance Spectroscopy. Very interestingly, the addition of Y2O3 (ratio 0.02%) has a positive effect on the open circuit voltage (i.e. > 0.145 mV) of the device whereas Al2O3 (ratio = 0.10%) allows to boost the photocurrent powered (i.e. > 3.5 mA*cm-2) by the cell.

 

The most performing cell (i.e. ZrO2/NiO-based electrode sintering by RDS and sensitized with P1) produced a JSC up to 3.6 mA*cm-2, a VOC of 129 mV leading to an overall efficiency of 0.164%. Furthermore, this photocathode was coupled with a VG10-sensitized TiO2-based photoanode to produce a tandem DSC with an overall efficiency close to 2% (JSC = 4.2 mA*cm-2, a VOC = 678 mV and FF = 0.66%).

  

   

The authors acknowledge the financial support from MIUR which funded the research project PRIN 2010–2011 with protocol no. 20104XET32. DD acknowledges the financial support from the University of Rome “LA SAPIENZA” through the program Ateneo 2012 (Protocol No. C26A124AXX). MB thanks University of Rome “LA SAPIENZA” through the program "Bando per progetti mobilità di studenti di dottorato di ricerca 2017".2017                                         “Bando per progetti di mobilità di studenti di dottorato di ricerca

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