Pulsed-DC magnetron sputtering of intrinsic ZnO film and its application to CIS solar cell

Abstract

To create an intermediate layer in CuInSe2(CIS)-based solar cells, an intrinsic zinc oxide(i-ZnO) thin film was deposited on a glass substrate and a cadmium sulfide(CdS) buffer layer using an in-line pulsed-DC sputtering. In comparison with i-ZnO films sputtered using RF power, i-ZnO films sputtered using pulsed-DC power showed much higher deposition rates and similar structural characteristics, without causing any damage to the CdS buffer layer. During pulsed-DC sputtering, the O2/Ar gas ratio, reverse time, and pulse frequency were changed to optimize the process parameters. From the transmittance and scanning electron microscope(SEM) images, the optimized i-ZnO film was obtained at an O2/Ar gas ratio of 1%, a pulsed frequency of 200 kHz, and a reverse time of 1.3 μs. For showing the feasibility, it was applied to the fabrication of a CIS solar cell which was processed using the two step method by the rapid thermal processing (RTP) annealing of Cu–In stacked layers. It showed a possibility of the pulsed-DC sputtered ZnO as an intermediate layer of a CIS solar cell even though a cell efficiency was shown with a low value of 2.2% due to an early stage of our study in the two step CIS process.