Stange, H.; Brunken, S.; Hempel, H.; Rodriguez Alvarez, H.; Schäfer, N.; Greiner, D.; Scheu, A.; Lauche, J.; Kaufmann, C.A.; Unold, T.; Abou-Ras, D.; Mainz, R.: Effect of Na presence during CuInSe2 growth on stacking fault annihilation and electronic properties. Applied Physics Letters 107 (2015), p. 152103/1-5
While Na presence is essential for the performance of high-efficiency Cu(In,Ga)Se2 thin film solar cells, the reasons why Na addition by post-deposition treatment is superior to pre-deposition Na supply - particularly at low growth temperatures - are not yet fully understood. Here we show by X-ray diffraction and electron microscopy that Na impedes annihilation of stacking faults during the Cu-poor/Cu-rich transition of low temperature 3-stage co-evaporation and prevents Cu homogeneity on a microscopic level. Lower charge carrier mobilities are found by optical pump terahertz probe spectroscopy for samples with remaining high stacking fault density, indicating a detrimental eect on electronic properties if Na is present during growth.