LAUSR

Abstract A doping process of potassium-ion was adopted as an alternative to the toxic KCN etching used for the removal of Cu 2-x Se compounds. The effects of potassium-ion doping on the phase formation and photovoltaic characteristics of the solution-coated Cu(In,Ga)Se 2 films was investigated. As the incorporation of potassium ions was increased from 0 mol% to 1.0 mol%, the coexistent Cu 2-x Se compounds were gradually reduced and the monophasic Cu(In,Ga)Se 2 films were obtained. The potassium-ion doped Cu(In,Ga)Se 2 films with dense and smooth morphology improved the coverage of CdS buffer layer and suppressed the additional shunt paths. Hence, the conversion efficiency of the solar cells fabricated without KCN treatment was significantly improved from 4.70%to 11.02%. Additionally, the diode factor (A) and the saturated current (J 0 ) were reduced due to the suppression of carrier recombination and leakage current. Further increasing the content of potassium ions to 5.0 mol%, the oversupplied potassium ions reduced the grain size and induced the carrier recombination in the obtained films, thereby resulting in the deterioration of the cell performance. This investigation demonstrates that the incorporation of potassium ions into Cu(In,Ga)Se 2 films with appropriated amounts can effectively diminish the formation of Cu 2-x Se compounds, thereby improving the photovoltaic performance of the fabricated Cu(In,Ga)Se 2 solar cells.