Tailoring SnO2, (Mg,Zn)O, and Ga:(Mg,Zn)O Electro-Optical Properties and Stability for Solar Cells

The electron density, mobility, bandgap and band alignment of transparent conducting oxides (TCOs) can be tailored by adjusting composition and stoichiometry, thereby enabling interface engineering for diverse semiconductor applications. For example, solar cell efficiency can change enormously by adjusting TCO properties. At the same time, these TCO properties can shift during the deposition of other layers, anneals and device operation. An ideal TCO should have tunable but stable electro-optical properties. Here, we deposit SnO2, (Mg,Zn)O (MZO), and Ga:(Mg,Zn)O (GMZO) films on glass and measure their electro-optical characteristics before and after reducing, inert, oxidizing and CdCl2 anneals over a range of temperatures. Electron density generally increases in the progression from oxidizing to inert and reducing ambients. SnO2 is relatively stable compared to MZO but has less flexibility for interface engineering. We investigate GMZO as a similar but more stable alternative to MZO. The addition of Ga to MZO has significant effects on electron density and improves electro-optical stability, which can be advantageous for semiconductor applications. Furthermore, we demonstrate that GMZO can be readily incorporated into solar cells.