Properties of CdSe1−xSx films by magnetron sputtering and their role in CdTe solar cells

Abstract

CdS/CdSe composite window layer is a better candidate than CdS or CdSe single layer for CdTe solar cells. In order to find the underlying reason, the properties of co-sputtered CdSe 1-x S x thin films with different compositions (0 x 1) were examined. XRD patterns show that all CdSe 1-x S x films (0 x 1) are polycrystalline with hexagonal structures and the prominent peak position shows an increasing trend with the increase of x. This suggests that CdSe 1-x S x window layer with a gradient composition, formed during the hightemperature growth and heat treatment of CdTe films, has the gradient lattice constant, meaning the less defect density. This is beneficial to the device performance. Hall measurements show that CdS 1-x Se x films (x C 0.772) are n-type semiconductors with carrier concentrations ranging from 10 15 cm -3 to 10 16 cm -3 . It reveals that CdS/CdSe bi-layers can form a strong built-in electric field with CdTe layer as CdS does. The electronic band structure of CdSe 1-x S x window layer with a gradient composition suggests that the spikes formed in the conduction band are lower than 0.3 eV, which would not impede the electron transport. The valence band alignment is beneficial for the hole transport. Therefore, an appropriate band alignment can be formed between CdSe 1-x S x and CdTe layers. These results reveal that CdSe 1-x S x film is a good candidate as the window layer for high-efficiency CdTe solar cells considering its structural, optical and electrical properties as well as its electronic structure.

First-principles investigation on the electronic structures of CdSexS1−x and simulation of CdTe solar cell with a CdSexS1−x window layer by SCAPS

“…The CdSe x S 1− x films was fabricated by magnetron sputtering on a silica glass substrate at room temperature which was published in another work. 26 The Se concentration x was measured by X-ray fluorescence spectrometer (XRF) of RIGAKU ZSX Primus model. The transmittance spectra of CdSe x S 1− x film was measured by the Lambda 950 spectrophotometer of PerkinElmer, as shown in Fig.…”