Examining the transparency of gallium-doped zinc oxide for photovoltaic applications

In this work, we examine the optical properties of gallium-doped ZnO (GZO) thin films grown by pulsed laser deposition with varying oxygen pressures and substrate temperatures. In analyzing the optical properties of the thin films, we use a normalized transparency index that is directed at quantifying the transmission for usage as electrodes in photovoltaic devices. With this, we can clearly show the influence of oxygen on the transmission for different wavelengths. This allows us to clearly dissect the influence of band gap, oxygen pressure and carrier concentration on transparency. We achieved GZO films with a transparency index of 0.84 at room temperature and an improved index of 0.92 (92% of total solar spectrum transmitted) at a substrate temperature of 500 °C. The room temperature films, in particular, showed excellent transparency and conductivity, which are useful for use as electrodes in organic devices.

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► Introduction of a normalized transparency index for electrodes in photovoltaic devices.
► Correlation of transmission with oxygen pressure and temperature.
► Distinguish between effects of band gap, defects and free-carrier absorption in transmission.
► Highly conducting Ga–ZnO films with a transparency index of up to 0.92.