title: Implications of the negative capacitance observed at forward bias in nanocomposite and polycrystalline solar cells.
abstract: Four different types of solar cells prepared in different laboratories have been characterized by impedance spectroscopy (IS): thin-film CdS/CdTe devices, an extremely thin absorber (eta) solar cell made with microporous TiO2/In(OH)xSy/PbS/PEDOT, an eta-solar cell of nanowire ZnO/CdSe/CuSCN, and a solid-state dye-sensitized solar cell (DSSC) with Spiro-OMeTAD as the transparent hole conductor. A negative capacitance behavior has been observed in all of them at high forward bias, independent of material type (organic and inorganic), configuration, and geometry of the cells studied. The experiments suggest a universality of the underlying phenomenon giving rise to this effect in a broad range of solar cell devices. An equivalent circuit model is suggested to explain the impedance and capacitance spectra, with an inductive recombination pathway that is activated at forward bias. The deleterious effect of negative capacitance on the device performance is discussed, by comparison of the results obtained for a conventional monocrystalline Si solar cell showing the positive chemical capacitance expected in the ideal IS model of a solar cell.
authors.affiliation: Departament de Ciències Experimentals, Universitat Jaume I, E-12080 Castelló, Spain. sero@exp.uji.es
authors.forename: Ivan
authors.initials: I
authors.lastname: Mora-Seró
authors.forename: Juan
authors.initials: J
authors.lastname: Bisquert
authors.forename: Francisco
authors.initials: F
authors.lastname: Fabregat-Santiago
authors.forename: Germà
authors.initials: G
authors.lastname: Garcia-Belmonte
authors.forename: Guillaume
authors.initials: G
authors.lastname: Zoppi
authors.forename: Ken
authors.initials: K
authors.lastname: Durose
authors.forename: Yuri
authors.initials: Y
authors.lastname: Proskuryakov
authors.forename: Ilona
authors.initials: I
authors.lastname: Oja
authors.forename: Abdelhak
authors.initials: A
authors.lastname: Belaidi
authors.forename: Thomas
authors.initials: T
authors.lastname: Dittrich
authors.forename: Ramón
authors.initials: R
authors.lastname: Tena-Zaera
authors.forename: Abou
authors.initials: A
authors.lastname: Katty
authors.forename: Claude
authors.initials: C
authors.lastname: Lévy-Clément
authors.forename: Vincent
authors.initials: V
authors.lastname: Barrioz
authors.forename: Stuart J C
authors.initials: SJ
authors.lastname: Irvine
mesh_terms: D019187:Cadmium Compounds / Q000737:chemistry* / Q000528:radiation effects; D003198:Computer Simulation; D003460:Crystallization / Q000379:methods; D025802:Electric Capacitance; D011211:Electric Power Supplies; D004563:Electrochemistry / Q000295:instrumentation* / Q000379:methods; D004867:Equipment Design; D019544:Equipment Failure Analysis; D008027:Light; D008422:Materials Testing; D008956:Models, Chemical; D049329:Nanostructures / Q000032:analysis / Q000737:chemistry* / Q000528:radiation effects; D012993:Solar Energy; D013440:Sulfides / Q000737:chemistry* / Q000528:radiation effects; D013691:Tellurium / Q000737:chemistry* / Q000528:radiation effects
chemical_list: D019187:Cadmium Compounds; D013440:Sulfides; C034939:cadmium sulfide; D013691:Tellurium; C028337:cadmium telluride