Highly efficient copper-rich chalcopyrite solar cells from DMF molecular solution

Theoretical calculation suggests Cu-rich chalcopyrite absorbers contain less defects and have potential to achieve better performance than Cu-poor absorbers. However, this has not been demonstrated due to the detrimental Cu_2-xSe impurity remaining in the absorber. Here, we report highly efficient Cu-rich chalcopyrite solar cells by selenizing dimethylformamide molecular precursor solution processed precursor films under high Ar pressure. Characterizations using XRD, Raman, SEM, TEM, c-AFM, PL, and glow discharge optical emission spectroscopy (GDOES) show high pressure selenization enables high quality Cu-rich chalcopyrite absorber materials with stoichiometric composition, smooth surface, high conductivity, and Cu_2-xSe free grain boundaries, leading to efficient CuIn(S,Se)₂ and Cu(In,Ga)(S,Se)₂ devices with power conversion efficiency of 14.5% and 15.2%, both are the best performing chalcopyrite solar cells from non-hydrazine solutions. Our results demonstrate high Ar pressure selenization is a new strategy to fabricate high quality Cu-rich absorber which has great potential to further improve chalcopyrite solar cell efficiency.