Photovoltaic characteristics and computational simulation of samarium-ion doped Cu(In, Ga)Se2 thin films prepared via a non-vacuum coating process

Abstract

The effects of samarium ions on the photovoltaic performance of Cu(In, Ga)Se2 (CIGS) films were investigated through experiments and computational simulation. Compared with pristine CIGS films, the conversion efficiency of the prepared solar cells increased by 26.6% (from 8.62% to 10.91%) when 0.5 mol% samarium ions were doped into CIGS films. The incorporation of 0.5 mol% samarium ions facilitated the formation of the Cu2−xSe phase during the selenization reaction. The Cu2−xSe phase as the flux agent melted at high temperatures and thus promoted the growth of CIGS grains and reduced the number of surface pores on CIGS films. The smooth morphology of 0.5 mol% samarium-ion doped CIGS films improved the coverage of the buffer layers and suppressed the formation of additional shunt paths, thereby decreasing defect density in the CIGS/cadmium sulfide (CdS) interface and the absorber layer. The simulated results revealed the incorporation of 0.5 mol% samarium ions reduced the defect density from 1 × 1011 cm−3 to 1 × 109 cm−3 in the CIGS/CdS interface and from 3 × 1017 cm−3 to 4 × 1016 cm−3 in the absorber layers. The shunt conductance and saturation current of the prepared solar cells also decreased, from 4.38 mS/cm2 to 2.60 mS/cm2 and from 7.25 × 10−3 mA/cm2 to 1.31 × 10−3 mA/cm2, respectively. Excess doping of samarium ions caused a residual Cu2−xSe phase in CIGS films and resulted in the formation of additional shunt paths to deteriorate the performance of CIGS solar cells. The incorporation of appropriate concentrations of samarium ions into CIGS films was an effective approach to improve the photovoltaic properties of CIGS solar cells.