title: Stoichiometry gradient, cation interdiffusion, and band alignment between a nanosized TiO2 blocking layer and a transparent conductive oxide in dye-sensitized solar cell front contacts.
abstract: An angle-resolved photoemission spectroscopy study allowed us to identify cation interdiffusion and stoichiometry gradients at the interface between a nanosized TiO2 blocking layer and a transparent conductive Cd-Sn oxide substrate. A stoichiometry gradient for the Sn cations is already found in the bare Cd-Sn oxide layer. When TiO2 ultrathin layers are deposited by RF sputtering on the Cd-Sn oxide layer, Ti is found to partially replace Sn, resulting in a Cd-Sn-Ti mixed oxide layer with a thickness ranging from 0.85 to 3.3 nm. The band gap profile across the junction has been reconstructed for three TiO2 layers, resulting in a valence band offset decrease (and a conduction band offset increase) with the blocking layer thickness. The results are related to the cell efficiencies in terms of charge injection and recombination processes.
authors.affiliation: Interdisciplinary Laboratories for Advanced Materials Physics (I-LAMP) and Dipartimento di Matematica e Fisica, Università Cattolica del Sacro Cuore , I-25121 Brescia, Italy.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Salvinelli
authors.forename: Giovanni
authors.initials: G
authors.lastname: Drera
authors.forename: Camilla
authors.initials: C
authors.lastname: Baratto
authors.forename: Antonio
authors.initials: A
authors.lastname: Braga
authors.forename: Luigi
authors.initials: L
authors.lastname: Sangaletti
keywords: DSSC; band alignment; blocking layer; front contact; photoemission; solar cell