Optical band gap energy and urbach tail of CdS:Pb2+ thin films

M. Chávez^a, H. Juárez^a, M. Pacio^a, X. Mathew^c, R. Gutiérrez^b L. Chaltel^b, M. Zamora^b and O. Portillo^b,*

^a Centro de Investigación en Dispositivos Semiconductores, del Instituto de Ciencias de la Universidad Autónoma de Puebla, Av. 14 Sur Col Jardines de San Manuel, Ciudad Universitaria, Puebla, Pue., México.

^b Lab. Mat. Sci. Facultad de Ciencias Químicas, Universidad Autónoma de Puebla. Puebla, Pue., P.O. Box 1067,72001 México. * Tel. (01 222) 2-29-55-00 Ext. 7519. e-mail: osporti@yahoo.mx

^c Instituto de Energía Renovables, Universidad Nacional Autónoma de México, Temixco, Morelos, México.

Received 14 May 2015;
accepted 27 November 2015

Abstract

PbS-doped CdS nanomaterials were successfully synthetized using chemical bath. Transmittance measurements were used to estimate the optical band gap energy. Tailing in the band gap was observed and found to obey Urbach rule. The diffraction X-ray (XRD) show that the size of cristallites is in the ~33 nm to 12 nm range. The peaks belonging to primary phase are identified at 20 = 26.5° and 20 = 26.00° corresponding to CdS and PbS respectively. Thus, a shift in maximum intensity peak from 20 = 26.4° to 28.2° is clear indication of possible transformation of cubic to hexagonal phase. Also peaks at 20 = 13.57°, 15.9° correspond to lead perchlorate thiourea. The effects on films thickness and substrate doping on the band gap energy and the width on tail were investigated. Increasing doping give rise to a shift in optical absorption edge ~0.4 eV

Keywords: Cadmium sulfide; thin films; solar cells; optical band gap; urbach tail.

PACS: 81.10.Bk; 81.05.Dz; 81.10.-h; 81.10.Dn; 81.15.-z; 81.15.Rs

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