Titanium incorporation to In 2 S 3 thin films for photovoltaic applications
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1165-M05-08
Titanium incorporation to In2S3 thin films for photovoltaic applications Begoña Asenjo*, José Herrero and M. Teresa Gutiérrez Dep. Renewable Energies, CIEMAT. Avda. Complutense, 22. 28040 Madrid SPAIN * Corresponding author. Email address: [email protected]
ABSTRACT Preliminary studies on the properties of undoped and Ti-doped In2S3 thin films grown on soda lime glass by chemical solution deposition under different conditions are presented. Different physical, chemical and morphological properties of the films have been analysed. At the beginning of the deposition of In2S3 films, In2O3 and In(OH)3 deposited by electrolesschemical reaction are dominant. The optical properties observed for Ti-In2S3 films show the partial contribution of the electronic transitions. The study is completed with SEM analysis which shows the influence of the deposition time and the precursor used, in the morphology for incorporation of titanium at the beginning of deposition and X-ray diffraction when is observed the amorphous nature of the films.
INTRODUCTION Currently diverse theoretical studies have been done focused on materials to be used for intermediate band in photovoltaic systems. The transition metal impurities have been known to introduce deep levels in the band gap of semiconductors. Transition metal doped III-V materials based on GaAs or GaP have been the first candidades proposed by us to obtain this intermediate band [1] Titanium was soon known to enter the host lattice substitutionally on a cation. This element could form an intermediate band (IB) between valence band (VB) to the conduction band (CB) with the subsequent production of electric current of chemical reactions. In a recent theoretical work [2] Ti-substituted CuGaS2 is proposed and characterized by the formation of an isolated transition-metal band between the valence band and the conduction band. This material would be able of absorbing photons of energy lower tan the band-gap of the host chalcopyrite. In2S3 is a good candidate to make an IB material through substitution of In by Ti and V as transition metals dopants [3]. In this work, the properties of Ti-doped In2S3 thin films obtained by chemical solution deposition under different conditions are presented.
EXPERIMENTAL DETAILS The indium sulfide films have been grown on soda lime glass substrate. CBD films have been synthesized from an acidic solution of different concentrations of thioacetamide [TA], and InCl3. Other additives necessary to improve the film quality are hydrochloric acid and acetic acid. The TiS2, TiCl4 and TiCl3 have been used as precursors for titanium. The synthesis has been realized in a thermostatised bath at 70 ºC temperature. Different CBD layers have been selected for the present work, obtained at 35 and 45 min deposition times. The composition, structure, morphology and optical characteristics of the synthesized indium sulfide samples have been analyzed as a function of the preparation conditions. Optical measurements were done with unpolarized light at normal
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