Influence of Cl and H2O in spray-ILGAR® solutions on the voltage gain of Cu(In,Ga)(S,Se)2 solar cells with In2S3 buffer

Abstract In 2 S 3 thin layers can be prepared by Spray-ILGAR ® (Ion Layer Gas Reaction) from indium trichloride or from indium triacetylacetonate solutions. In the first case, the film contains a controllable amount of Cl. The concentration of H 2 O or Cl was varied systematically in the precursor solutions that were used for the deposition of In 2 S 3 buffer layers on commercially available Cu(Ga,In)(S,Se) 2 absorbers. The layers were characterized by ultraviolet photo electron spectroscopy, optical spectroscopy, modulated surface photovoltage spectroscopy and X-ray photoelectron spectroscopy, combined with a sequential etching procedure. The latter allowed to estimate an element-specific depth profile. Experimental findings were correlated with the performance of the corresponding solar cells. The presence of H 2 O or Cl in the precursor solutions has a strong influence on the diffusion of Cu + and Na + cations from the absorber into the buffer layer. The open circuit voltage of solar cells with In 2 S 3 buffer layers prepared from Cl-free, H 2 O-containing precursor solutions was higher by up to 100 mV than those from Cl-containing, but H 2 O-free solutions. For this reason, the average solar energy conversion efficiency of cells of the first buffer type was higher (14.7%) than for solar cells of the second type (12.1%).