Alloys in cadmium telluride solar cells

Alloys formed intentionally or unintentionally during the fabrication of CdTe/CdS solar cells were investigated. The primary focuses were (1) characterizing thin films of {dollar}rm CdTesb{lcub}1-x{rcub}Ssb{lcub}x{rcub}{dollar} since these alloys appear to be present in all high-efficiency CdTe/CdS solar cells, and (2) investigating how these alloys affect solar cell performance.; Thin films of {dollar}rm CdTesb{lcub}1-x{rcub}Ssb{lcub}x{rcub}{dollar} were fabricated and subjected to heat treatments under conditions identical to those used for making CdTe/CdS solar cells. The films were characterized by X-Ray Diffraction, Energy Dispersive Spectroscopy, Scanning Electron Microscopy, and optical measurements. The as-deposited {dollar}rm CdTesb{lcub}1-x{rcub}Ssb{lcub}x{rcub}{dollar} films were generally single-phase even when x was well within the miscibility gap shown on CdTe-CdS pseudo-binary phase diagrams. Heat treatments at {dollar}415spcirc{dollar}C in the presence of {dollar}rm CdClsb2{dollar} promoted phase segregation. From diffraction analysis of the phase-segregated films, the solubility limits at {dollar}415spcirc{dollar}C of CdS in CdTe, and of CdTe in CdS were found to be {dollar}5.8pm 0.2%{dollar} and {dollar}3pm 1%,{dollar} respectively.; Conventional CdTe/CdS solar cells and novel solar cells made by depositing {dollar}rm CdTesb{lcub}1-x{rcub}Ssb{lcub}x{rcub},{dollar} in place of CdTe were fabricated, tested, characterized, and compared. For the conventional solar cells, diffusion of CdS into the CdTe layer during the fabrication process converted the CdTe to {dollar}rm CdTesb{lcub}1-x{rcub}Ssb{lcub}x{rcub}{dollar} with x ranging from the 5.8% solubility limit near the junction to {dollar}{lcub}<{rcub}1%{dollar} near the back contact. Similarly, the CdS layer was converted to {dollar}rm CdSsb{lcub}1-y{rcub}Tesb{lcub}y{rcub}{dollar} with y near the 3% solubility limit, in some cases, and {dollar}{lcub}<{rcub}1%{dollar} in cases where the CdS film was annealed with {dollar}rm CdClsb2{dollar} prior to depositing CdTe. The performance of {dollar}rm CdTesb{lcub}1-x{rcub}Ssb{lcub}x{rcub}{dollar}/CdS cells made with x = 0.05-0.06 throughout the absorber layer was nearly identical to the CdTe/CdS cells. This indicates that the operation of conventional devices is largely controlled by the alloys formed by interdiffusion. For the {dollar}rm CdTesb{lcub}1-x{rcub}Ssb{lcub}x{rcub}{dollar}/CdS devices, less CdS was consumed by the interdiffusion process than for the conventional CdTe/CdS devices suggesting that devices can be made using thinner CdS layers than before possible without pinholes forming in the CdS.