Interdiffusion of CdS and Zn2SnO4 layers and its application in CdS/CdTe polycrystalline thin-film solar cells

In this work, we found that the interdiffusion of the CdS and Zn2SnO4 (ZTO) layers can occur either at high temperature (550-650 degreesC) in Ar or at lower temperature (400-420 degreesC) in a CdCl2 atmosphere. By integrating a Zn2SnO4 film into a CdS/CdTe solar cell as a buffer layer, this interdif fusion feature can solve several critical issues and improve device perform ance and reproducibility of both SnO2-based and Cd2SnO4-based CdTe cells. I nterdiffusion consumes the CdS film from both the ZTO and CdTe sides during the device fabrication process and improves quantum efficiency at short wa velengths. The ZTO film acts as a Zn source to alloy with the CdS film, whi ch results in increases in the band gap of the window layer and in short-ci rcuit current density J(sc). Interdiffusion can also significantly improve device adhesion after CdCl2 treatment, thus providing much greater process latitude when optimizing the CdCl2 process step. The optimum CdCl2-treated CdTe device has high quantum efficiency at long wavelength, because of its good junction properties and well-passivated CdTe film. We have fabricated a Cd2SnO4/Zn2SnO4/CdS/CdTe cell demonstrating an NREL-confirmed total-area efficiency of 15.8% (V-oc=844.3 mV, J(sc)=25.00 mA/cm(2), and fill factor=7 4.82%). This high-performance cell is one of the best thin-film CdTe solar cells in the world. (C) 2001 American Institute of Physics.