The effect of the CdCl2 treatment on CdTe/CdS thin film solar cells studied using deep level transient spectroscopy

Review of the CdCl2 Treatment Used in CdS/CdTe Thin Film Solar Cell Development and New Evidence towards Improved Understanding

“…White CdCl 2 powder is clearly visible on the dark surface of CdTe after this process. Some groups have alternatively deposited a layer of CdCl 2 by methods such as vacuum evaporation and laser ablation for the treatment of both CdS and CdTe layers [12][13][14][15][16][17][18]. In the case of electrodeposition, addition of CdCl 2 into the electrolytic bath is another method of CdCl 2 treatment [19].…”

“…It is important to note that the application of CdCl 2 on CdTe layer and subsequent heat treatment should be carried out in the presence of oxygen in order to achieve highest efficiencies [15]. This can be achieved by using normal atmospheric conditions, exposing to O 2 ambient, or in the case of CdTe growth in a vacuum chamber, inserting halogen containing gas, such as Freon and O 2 gas mixture, to the chamber during the growth.…”

“…The interface states could pin the Fermi level, and fix the potential barrier present, thereby strongly affecting the open circuit voltage and other parameters in thin film solar cells [2,37]. In order to determine the defects in CdCl 2 -treated and untreated device structures, the techniques like PL [13,17], DLTS [15], CL [14,20], and photo-capacitance [24] have been carried out. The CL studies show that there is a formation of defect level just above the valence band (see Figure 2 in Section 3.2), converting the material towards p-type electrical conduction [20].…”

Effect of CdCl2 activation on the impurity distribution in CdTe/CdS solar cell structures

“…These calibration standards were undoped CdTe (Japan Energy) and CdS (Girmet) single crystals implanted at the University of Surrey Ion Beam Centre with 208 Pb, 29 Si, 115 In, 35 Cl, 23 Na, 16 O, 63 Cu, 121 Sb, 64 Zn, 120 Sn, 32 S (in CdTe only) and 128 Te (in CdS only). The implantation energy was 200 keV for all the species and the doses were in the range of 1.6Â10 12 to 5Â10 13 ions/cm 2 .…”

Segregation of Te at the back contact in electrochemically deposited CdTe thin film solar cells

“…Herndon et al [3] further report the preferential diffusion of S along the grain boundaries of polycrystalline CdTe. The effect of CdCl 2 treatment has also been investigated extensively and it is believed to passivate grain boundaries minimising the non-uniformity of S distribution in the interfacial compound [4]. Krishna and Dutta [5] describe the interfacial phase as an eutectic solid solution, which lowers the melting point of CdTe, promoting grain growth and reducing defect density.…”