The Influence of CuCl Treatment on the PL Spectra of CdTe Thin Film, Component of CdS/CdTe Heterojunctions
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1165-M08-16
The Influence of CuCl Treatment on the PL Spectra of CdTe Thin Film, Component of CdS/CdTe Heterojunctions Sergiu A. Vatavu1, Hehong Zhao2, Iuliana M. Caraman3, Petru A. Gasin1, Don L. Morel2 and Chris S. Ferekides2 1
Faculty of Physics, Moldova State University, 60 A. Mateevici str., Chisinau, MD 2009, Republic of Moldova 2 Electrical Engineering Department, University of South Florida, 4202 East Fowler Ave., Tampa, FL 33620, U.S.A. 3 Engineering Department, University of Bacau, 157 Calea Marasesti, Bacau, 600115, Romania ABSTRACT Technology variations involving Cu and Cl impurities are among the major performance influencing factors for CdS/CdTe thin film solar cells. CuCl and CdCl2 influence on the energetic diagram of impurity levels with respect to variation of deposition parameters has been investigated. A comparative analysis has been carried out using low temperature photoluminescence (PL) studies (17-98K) of CdTe thin films in the device configuration (from CdS/CdTe inteface and CdTe sides). To study the effect of the CuCl influence, as-deposited and annealed heterojunctions, with CuCl treatment of CdS have been investigated. INTRODUCTION The importance of the knowledge of levels energetic distribution in the band gap of CdTe is crucial for obtaining high performance devices. One of the methods on elucidating the structure of the levels in the band gap is low temperature photoluminescence (PL) analysis. Recent studies showed the necessity of finding new ways of improving the quality and properties of CdTe thin film solar cells, which are currently at 16.5% efficiency [1]. Copper and Cl play an important role in the state of the art CdTe solar cells. Copper will additionally p dope CdTe, increasing its conductivity, but can also cause device degradation over a period of time; chlorine may passivate the grain boundaries and introduce complex defects in the CdTe films. Both of these can influence device performance. There have been several studies on understanding Cu introduced at the CdTe/CdS interface [2] and at the back contact [3, 4]. The main aim of this work is the study of the changes in the radiative states diagram due to Cu influence at the interface of the HJ by means of low temperature PL investigated from CdS/CdTe interface and CdTe surface. EXPERIMENT CdTe thin films and solar cell structures (i.e. CdS/CdTe heterojunctions without the back contact) were prepared on SnO2 coated 7059 glass using processes described elsewhere [5]. Tin oxide bi-layers deposited by MOCVD have been used as front contacts. The close-spaced sublimation (CSS) process was used for the preparation of CdS and CdTe films [5]. The CdTe deposition was followed by CdCl2 annealing [5]. The PL measurements were carried out using
an Ar-Ion Laser with maximum output power 488 nm, the wavelength used for these measurements. A grating-based monocromator and a Ge detector were used for signal detection. The samples were cooled using a RMC Cryosystems closed-loop cryostat with a CTI-Cryogenics (Helix Technology Corporatio
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