CdTe Nanocrystals in Ink-Based Photovoltaics: A Study of Grain Growth and Device Architecture

We present on the use of cadmium telluride (CdTe) nanocrystal colloids as a solution-processable “ink” for large-grain CdTe absorber layers in solar cells. After layer-by-layer processing into thin film devices, the resulting grain structure and solar cell performance are found to depend on the initial nanocrystal size, shape, and crystal structure. Inks composed of predominantly wurtzite tetrapod-shaped nanocrystals exhibit better device performance compared to inks composed of irregular faceted nanocrystals or spherical zincblende nanocrystals despite the fact that the final sintered film has a zincblende crystal structure. Five different working device architectures were investigated. Surprisingly, we find the indium tin oxide/CdTe/zinc oxide structure leads to our best performing device architecture (with efficiency >11%) compared to others including two with a cadmium sulfide (CdS) n-type layer typically used in high efficiency sublimation-grown CdTe solar cells. Moreover, devices without CdS have improved response at short wavelengths.