Temperature dependence of potential fluctuations in chalcopyrites

Several studies have shown that Cu-poor Cu(In, Ga)Se₂ shows potential fluctuations at low temperatures which dramatically reduce the mobility and thus the diffusion length in solar cells. It is however often assumed that the fluctuations persist at room temperature. In order to characterize the properties of these fluctuations and their temperature dependence epitaxial CuInSe₂ and CuGaSe₂ absorbers are examined by temperature and intensity dependent photoluminescence. The results indicate that the potential fluctuations flatten for temperatures higher than 150 K. In slightly Cu-poor material the fluctuations totally disappear at room temperature. In samples with a larger Cu-deficiency ([Cu]/[III]<;0.95) the fluctuations remain even at room temperature, but the magnitude of the fluctuations is reduced to a few meV. Thus, potential fluctuations in Cu-poor chalcopyrite cannot be expected to reduce the efficiency of solar cells.