Colloidal copper sulfide nanocrystals: Electrochemical, electrical and morphological properties
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Colloidal copper sulfide nanocrystals: Electrochemical, electrical and morphological properties Alejandro Baray-Calderón1, R. Galindo2,3, J. L Maldonado.2, Omar Martínez-Alvarez4, L.S. Acosta-Torres5, José Santos-Cruz6, J. de la Fuente-Hernández5, M.C. Arenas-Arrocena5* 1
Posgrado en Ciencia e Ingeniería de Materiales, Universidad Nacional Autónoma de México, UNAM, México 2 Centro de Investigaciones en Óptica A.C., León Guanajuato, México 3 Cátedra CONACyT, Universidad de Guanajuato 4 Universidad Politécnica de Guanajuato, Guanajuato, México 5 Escuela Nacional de Estudios Superiores, Unidad León, UNAM, León Guanajuato, México. 6 Universidad Autónoma de Querétaro, Querétaro México * Corresponding Author ABSTRACT The highlight of this work is the synthesis of copper sulfide nanocrystals by a simple onepot colloidal process, and the study of its electrochemical, electrical and morphological properties. Nanocrystals of Cu1.8S of about 15-30 nm were obtained at a temperature of 240°C under an argon atmosphere. The colloidal solution of the nanocrystals was analyzed by cyclic voltammetry. Agreeing to the values of EOx and ERed vs. SCE, and the average of three samples the HOMO and LUMO levels are 6.16 and 4.27 eV, respectively, the calculated HOMO – LUMO (Eg) is 1.89 eV. The Eg value, differs of that value obtained from Kubelka-Munk equation (1.7 eV). The photocurrent vs. time results showed that the Cu1.8S/Cu junction is photosensitive and could be used as absorbing material. The morphology and the topography of the film were analyzed by SEM and AFM techniques. Irregular agglomeration of nanocrystals was observed and a roughness of about 194 nm. INTRODUCTION Copper sulfide is a p-type semiconductor that shows different stoichiometries (CuxS, where x=1 to 2). Colloidal chalcocite (Cu2S) and digenite (Cu1.8S) are copper sulfides that have been obtained by one-pot colloidal process in organic solution in the temperature range from 220 to 260ºC [1]. Priscilla et al.[1], found that the digenite is more conductive than the chalcocite due to the deficiency of copper and these crystalline phases presented adequate optical properties (maximum absorbance peak from 440 to 540nm), which could be used as an absorbent material for solar cells. For example, chalcocite nanocrystals have been added in heterojunctions for organic photovoltaic (OPV) applications [2,3]. The incorporation of these nanocrystals improved the performance of the OPV devices [2,3], however the copper sulfide has not been widely exploited and fully studied for hybrid photovoltaic devices. In our previous work [4] is added copper sulfide in active layer of poly(3-hexylthiophene)/titania as a hybrid solar cell for the first time, but the photovoltaic effect was very low. Nowadays the digenite phase copper sulfide is also taking interest for nonlinear optical (NLO) applications [5]. In this work, copper sulfide in a digenite phase has been characterized by electrochemical, electrical and morphology techniques as a hybrid solar cell for the first time.
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