Investigation of interface morphology and composition mixing in CdTe/CdS heterojunction photovoltaic materials using synchrotron radiation

Abstract

The interface microstructure in thin film photovoltaic materials is an important problem which can severely affect the light-conversion efficiency and stability of heterojunction solar cells. This is a long-standing fundamental problem, but has not been studied in the past by effective probing methods. In the present experiment, the interfacial roughness, correlation lengths of interface height fluctuations, effects of heat treatment, and diffusion of Te atoms across the heterojunction interface have been investigated by means of grazing incidence x-ray scattering and angular dependence of x-ray fluorescence using synchrotron radiation. We thus demonstrate that these x-ray techniques can provide a powerful tool for nondestructive characterization of the interfacial roughness and intermixing of selected atomic species in heterojunction photovoltaic materials.

Migration of constituent atoms and interface morphology in a heterojunction between CdS and CuInSe2 single crystals

“…Detailed experimental procedures have been reported elsewhere. 5,6 The generic features of the ADXRF output are illustrated with the results of a model calculation assuming uniform depth distribution of constituent atoms as shown in Fig. 1.…”

Properties of Te-rich cadmium telluride thin films fabricated by closed space sublimation technique

“…As a result of recent advances in the efficiency of Cadmium telluride (CdTe)-based solar cells [1][2][3], interest in this material for thin film terrestrial photovoltaic applications [4][5][6] temperature, which is optimum for single junction solar cell efficiency [3]. CdTe can exhibit both types of conductivity, n and p, which makes diode technology [7] and field effect transistors [8] possible, and it can exhibit a semi-conducting state as well [9].…”

Migration of Te atoms and structural changes in CdS/CdTe heterojuctions studied by x-ray scattering and fluorescence

“…It is generally believed that such an efficiency change could originate from either the structural or compositional variations in the annealed junctions due to intermixing of Te or S across the junction interface. The heat treatment gives rise to the formation of ternary alloys CdS x Te 1Ϫx [3][4][5][6][7][8] and thus leads to an improvement of the transport properties of the CdS/CdTe heterojunction through a bowing-effect 8 and a reduction of the 10% lattice mismatch between the two constituent materials. 9,10 Nevertheless, the degree of interdiffusion is such a limiting factor for solar cell performance that an excess of intermixing could result in a depletion of the n-type material of the p-n junction and a blurred interface, thereby degrading the electrical properties.…”

“…These two techniques are uniquely suited for investigating elemental composition and interface morphology on a nanometer scale as already demonstrated in our earlier work studying the roughness and intermixing of elements across various interfaces. 5,16 In the present experiments, these x-ray methods are applied to a quantitative study of the changes in interface morphology and atomic distribution when the CdS/CdTe heterojunction is subjected to thermal annealing at various temperatures.…”