Engineered Cu(InGa)Se-2 thin films through CaF2 post-deposition treatment for enhancing solar cell performance

摘要

It is considered that alkaline elements (such as Na, K, Rb) introduced through post-deposition treatment are able to modify the near-surface region of Cu(InGa)Se-2 thin films. However, research on the effects of Ca element on properties of Cu(InGa)Se-2 thin films is hardly reported. In this paper, Cu(InGa)Se-2 thin films were prepared on quartz glass by e-beam evaporation via two-step process. Study of structural property showed that a certain amount of CaF2 through post-deposition treatment was beneficial to the uniform composition distribution of Cu(InGa)Se-2 thin films. Near-surface region of Cu(InGa)Se-2 thin films was more Cu-depleted by increasing introduced amount of Ca element. It was inferred that Ca diffused into the Cu(InGa)Se-2 thin films substituted the In sites as Ca-In so as to increase the carrier concentration. By calculation, the spike barrier of CdS/Cu(InGa)Se-2 heterojunction was shown to decrease with increased thickness of CaF2 layers. As a result, Cu(InGa)Se-2 solar cell subjected to 20 nm CaF2 postdeposition treatment, which possessed higher fill factor, open circuit voltage and short circuit current density, achieved the optimal power conversion efficiency. An efficiency of Cu(InGa)Se-2 solar cell was enhanced by 2.9% after 20 nm CaF2 post-deposition treatment. (c) 2018 Elsevier B.V. All rights reserved.