Doping saturation in dye-sensitized solar cells based on ZnO:Ga nanostructured photoanodes

Author(s)

Goncalves, Agnaldo S. ^{[1, 2]} ; Goes, Marcio S. ^[2] ; Fabregat-Santiago, Francisco ^[3] ; Moehl, Thomas ^[3] ; Davolos, Marian R. ^[2] ; Bisquert, Juan ^[3] ; Yanagida, Shozo ^[4] ; Nogueira, Ana F. ^[1] ; Bueno, Paulo R. ^[2]

Affiliation

^[1] Univ Estadual Campinas, Inst Chem, BR-13083970 Campinas, SP - Brazil

^[2] Univ Estadual Paulista, Dpto Fis Quim, Inst Quim Araraquara, BR-14800900 Araraquara, SP - Brazil

^[3] Univ Jaume 1, Grp Dispositius Fotovota & Optoelect, Dept Fis, Castellon de La Plana 12071 - Spain

^[4] Osaka Univ, Ctr Adv Sci & Innovat, Suita, Osaka 5650871 - Japan

• Document type: Journal article
• Source: Electrochimica Acta; v. 56, n. 18, p. 6503-6509, JUL 15 2011.
• Web of Science Citations: 29

Abstract

The origins of the performance of dye-sensitized solar cells based on ZnO:Ga nanostructured photoelectrodes, compared to analogous ZnO solar cells, were studied by means of impedance spectroscopy under illumination as a function of forward bias voltage. The film capacitance is governed by Ga doping. It can be assumed that the higher donor density of states of ZnO materials and, principally. ZnO:Ga-doped materials pin the Fermi level at a certain shallow energy level so that there is no photovoltage variation as a function of doping level. On the other hand, short circuit current is determined by the increasing roughness factor obtained at the higher doping levels while the lower fill factor values of DSCs based on ZnO:Ga, compared to analogous ZnO, were attributed to the higher ohmic resistive losses associated with the increasing photocurrent densities. In any case, the microstructure and morphological aspects were also considered as a possible origin of the low fill factor values. The estimated donor density level exceeds 10(21) cm(-3), indicating a high doping level in the semiconductor. As a consequence of the synthesis process of ZnO:Ga nanoparticles its size diminishes with the higher Ga contents producing an increase in the overall roughness factor of the films, and then a larger dye upload and short circuit current. (C) 2011 Elsevier Ltd. All rights reserved. (AU)

• FAPESP's process: 09/14713-3 - Electrochemical Impedance Spectroscopy application on nanostructure device of the solar energy conversion and biosensor
• Grantee: Márcio de Sousa Góes
• Support Opportunities: Scholarships in Brazil - Post-Doctoral