First-principles study of carbon impurities in CuIn$_{1-x}$Ga$_x$Se$_{2}$, present in nonvacuum synthesis methods

摘要

A first-principles study of the structural and electronic properies of carbonimpurities in CuIn$_{1-x}$Ga$_x$Se$_{2}$ is presented. Carbon is present inorganic molecules in the precursor solutions used in nonvacuum growth methods,making more efficient use of material, time and energy than traditional vacuummethods. The formation energies of several carbon impurities are calculatedusing the hybrid HSE06 functional. C$_{\mathrm{Cu}}$ acts as a shallow donor,C$_{\mathrm{In}}$ and interstitial C yield deep donor levels in CuInSe$_{2}$,while in CuGaSe$_{2}$ C$_{\mathrm{Ga}}$ and interstitial C act as deepamphoteric defects. So, if present, these defects reduce the majority carrier(hole) concentration by compensating the acceptor levels and become trap statesfor the photogenerated minority carriers (electrons). However, the formationenergies of the calculated carbon impurities are high, even under C-rich growthconditions. Therefore, these impurities are not likely to form and willprobably be expelled to the intergranular region and out of the absorber layer.